Powder Metallurgy Pune University MCQs
Powder Metallurgy Pune University MCQs
This set of Powder Metallurgy Multiple Choice Questions & Answers focuses on “Types of Sintering”.
1. The _______ defines sintering as, “the thermal treatment of a powder or compact at a temperature below the melting point of the main constituent, for the purpose of increasing its strength by bonding together of the particles”.
a) ASME
b) ASTM
c) ISO
d) BIS
Answer: c
Explanation: The International Standards Organization defines sintering as, “the thermal treatment of a powder or compact at a temperature below the melting point of the main constituent, for the purpose of increasing its strength by bonding together of the particles”. The ASME, ASTM, and BIS are organization which provides us with specific standards for various materials.
2. ________ transforms compacted mechanical bonds between powder particles into metallurgical bonds.
a) Sintering
b) SHP
c) Mechanical alloying
d) Metal Injection Molding
Answer: a
Explanation: Sintering is defined as the heating of loose or compacted aggregate of metal powders below the melting point of base metal to transform it to a denser material by interparticle bonding and thus, sintering transforms compacted mechanical bonds between powder particles into metallurgical bonds.
3. In _________, the densification is a result of atomic diffusion in solid-state.
a) Reaction sintering
b) Solid-state sintering
c) Activated sintering
d) Liquid phase sintering
Answer: b
Explanation: In solid-state sintering, the densification is a result of atomic diffusion in the solid-state. Solid-state sintering is a very common process of agglomeration for most of the metals and alloys.
4. _________ refers to those processes where solid and liquid coexist during the entire or part of the sintering process.
a) Spark plasma sintering
b) SHS
c) Activated sintering
d) Liquid phase sintering
Answer: d
Explanation: Liquid phase sintering, refers to those processes where solid and liquid coexist during the entire or part of the sintering process. It is one of the most common method of achieving rapid densification in the powder compact. This has proved valuable in the production of W-Cu, W-Ag, cemented carbide type, and cermet materials.
5. Doping of Ni in tungsten compacts is an example of _________
a) Activated sintering
b) Reaction sintering
c) Microwave sintering
d) Gas plasma sintering
Answer: a
Explanation: The doping of Ni in tungsten compacts is an example of activated sintering. In activated sintering, the addition of a small amount of an alloying element called ‘doping’ increases the rate of densification to a great extent compared to the undoped compacts.
6. Which of the following characteristic the ‘doping’ additive should not possess?
a) Segregate at the grain boundary
b) Formation of low melting point phase
c) High atomic weight
d) High solubility
Answer: c
Explanation: To promote activated sintering, any additive must form a low-melting phase during sintering and also must segregate at the grain boundaries. The additive must also have a very high solubility for the base metal to promote the rapid diffusion of base metal through the additive phase.
7. The presence of nickel at grain boundaries greatly increases the grain boundary lattice-diffusion of tungsten.
a) True
b) False
Answer: b
Explanation: Nickel, which is added as a solution of its salts, gets reduced during sintering and forms a coating of a few monolayer on the surface of the W particles. By diffusing over the W particles, Ni accumulates at the necks of the particles from where the nickel penetrates the grain boundaries. This presence of nickel at the grain boundaries greatly increases the grain boundaryself-diffusion of tungsten. Thus, the segregation of the additive at the interparticle boundary creates a short circuit diffusion path for the rapid diffusion of the base metal resulting in enhanced densification.
8. _______ takes place when two or more components chemically react during the sintering process to form the final product.
a) Rate controlled sintering
b) Reaction sintering
c) Microwave sintering
d) Spark plasma sintering
Answer: b
Explanation: Reaction sintering takes place when two or more components chemically react during the sintering process to form the final product. It is a special form of rapid sintering technique to process high-temperature materials, resulting from the chemical reaction between the individual constituents, giving very good bonding.
9. SiN is prepared by _______
a) Reaction sintering
b) Hot forging
c) Solid-state sintering
d) Liquid phase sintering
Answer: a
Explanation: Reaction sintering may also involve heating in a gas atmosphere, which reacts with the powder compact resulting in the formation of the desired compound. A typical example is the production of reaction bonded SiN made by sintering green compact of Si powders in N 2 atmosphere at 1,523 to 1,673 K for time up-to 70 hours.
10. _________ has the advantage of producing a finer grain size compared to pressureless sintering.
a) Solid-state sintering
b) Microwave sintering
c) Liquid phase sintering
d) Reaction sintering
Answer: b
Explanation: We can obtain a finer grain size in microwave sintering compared to the pressureless sintering because of faster heating rate and shorter dwell time at the selected temperature.
11. _______ is an exothermic combustion process that uses the heat generated during a reaction to sinter the material.
a) SHS
b) Gas plasma sintering
c) Spark plasma sintering
d) Rate controlled sintering
Answer: a
Explanation: Self-propagating High-Temperature Synthesis is an exothermic combustion process that uses the heat generated during a reaction to sinter the material. The process, although is very fast and economical, needs an additional densification step to make useful shapes and hence adds to cost and time.
12. _______ is a process similar to the hot uniaxial pressing.
a) Solid-state sintering
b) SHS
c) SPS
d) Activated sintering
Answer: c
Explanation: Spark Plasma Sintering is a process similar to hot uniaxial pressing in which a momentary DC pulse is generated in addition to joule heating, by producing a ‘spark’ between the powder particles. The temperature can reach up-to 5,000°C to 10,000°C, but only momentarily so that no melting is allowed to take place.
This set of Powder Metallurgy Multiple Choice Questions & Answers focuses on “Sintering Theory – 1”.
1. Sintering involves _____ types of system.
a) Unary
b) Binary
c) Single component andmulticomponent
d) Ternary
Answer: c
Explanation: Sintering may involve single component system, wherein shrinkage is a major factor or multi-component system, involving more than one phase, where several processes like solid solution formation and liquid phase formation may also occur in addition to densification.
2. _______ is the major material transport mechanism in sintering of the single component system.
a) Inter-diffusion
b) Self-diffusion
c) Lattice-diffusion
d) Volume-diffusion
Answer: b
Explanation: Self-diffusion is the major material transport mechanism in sintering of single component system and the driving force resulting from a chemical potential gradient due to surface tension and capillary forces between particles.
3. Which of the following are the stages of sintering, according to Sauerwald theory?
a) Adhesion, recrystallization
b) Adhesion, crystallization
c) Adhesion
d) Adhesion, bonding
Answer: a
Explanation: According to Sauerwald theory, there are two stages in sintering- adhesion which occurs during heating due to atomic attraction, and recrystallization consists of diffusion of atoms between adjacent grains.
4. Which of the following changes do not occur on during recrystallization?
a) Pore shrinkage
b) Phase changes
c) Grain shrinkage
d) Precipitation
Answer: c
Explanation: Recrystallization includes changes in the microstructure, phase changes, grain growth, precipitation and pore shrinkage.
5. _______ requires mass transport.
a) Pore expansion
b) Grain shrinkage
c) Densification
d) Adhesion
Answer: c
Explanation: Densification requires mass transport and hence sintering is carried out at temperatures where material transport due to diffusion is appreciable so that the purpose of sintering is achieved.
6. The process of sintering will stop when _______
a) dE=γ SS dA SS +γ SV dA SV =0
b) dE=γ SS dA SS +γ SV dA SV >0
c) dE=γ SS dA SS +γ SV dA SV <0
d) dE=γ SS dA SV +γ SV dA SS =0
Answer: a
Explanation: The process of sintering will stop when the overall change in the free energy of the system becomes zero i.e. dE=γ SS dA SS +γ SV dA SV =0 where γ SS and γ SV are the surface energies of the solid-solid interfaces and solid-vapor interfaces respectively, dA SS and dA SV are the interfacial area of solid-solid and solid-vapor interfaces .
7. The driving force for sintering is reduction in ________
a) Internal energy
b) Surface tension
c) Surface energy
d) Entropy
Answer: c
Explanation: In sintering, the driving force is the overall decrease in the surface free energy of the compacts. This occurs by replacing the high-energy solid-vapor (of free energy γ SV ) interfaces with the low energy solid-solid interfaces (of free energy γ SS ). This surface energy reduction results in the densification of the compact.
8. The initial free energy of the compact before sintering must be _______
a) Positive
b) Negative
c) Zero
d) Infinite
Answer: b
Explanation: Initially, the free energy of the system must be negative, that is, the free energy of solid-solid interfaces must have lower free energy than the solid-vapor interface. Thus, during sintering, the newly formed solid-solid interfaces replace the existing solid-vapor interfaces, thereby lowering the free energy of the system.
9. To achieve densification during sintering without grain growth, the γ SS must be _____, while the γ SV must be _____
a) Zero, maximized
b) Maximized, zero
c) Zero, minimized
d) Maximized, minimized
Answer: b
Explanation: To achieve densification during sintering without grain growth , the γ SS must be maximized, while the γ SV must be zero . Such conditions can be achieved by altering the conditions of sintering by doping or by the use of a suitable sintering environment to maximize the surface free energy.
10. It is desirable that sintering stops when ______
a) \
\
γ SS >> γ SV
d) \(\frac{-dA_{SV}}{dA_{SS}}\)is close to zero
Answer: d
Explanation: In sintering, the major objective is to eliminate the porosity and obtain a dense compact. It is, thus desirable that the sintering stops when the values of \(\frac{-dA_{SV}}{dA_{SS}}\) is close to zero, (or γ SS << γ SV ).
11. Sintering can be considered as an irreversible thermodynamic process.
a) True
b) False
Answer: a
Explanation: Sintering is an irreversible thermodynamic process because the change in surface free energy during sintering is irreversible.
This set of Powder Metallurgy Questions and Answers for Experienced people focuses on “Sintering Theory – 2”.
1. Solid-state sintering can be broadly divided into _____ stages.
a) Adhesion, and Densification
b) Adhesion, Densification, and spheroidization of isolated pores
c) Adhesion, and grain growth
d) Initial bonding, and spheroidization of isolated pores
Answer: b
Explanation: Solid-state sintering is a complex process, which may be broadly divided into three stages, Adhesion without shrinkage, Densification and grain growth stage, and Elimination of the last isolated and rounded pores.
2. In final stage of solid-state sintering, _____ become isolated and are no longer _______
a) Grains, connected
b) Grains, interconnected
c) Pores, open
d) Pores, interconnected
Answer: d
Explanation: In the final stage of solid-state sintering, pore channel closure occurs and the pores become isolated and are no longer interconnected. The residual individual pores are located either at the grain boundaries or within the grains. Porosity decreases more quickly in the vicinity of the grain boundary and densification proceeds at a very slow rate.
3. The first stage of solid-state sintering, includes _______ of vacancies and ________ between surface regions with different radii of curvature.
a) Surface diffusion, volume diffusion
b) Volume diffusion, surface diffusion
c) Lattice diffusion, surface diffusion
d) Plastic flow, surface diffusion
Answer: b
Explanation: The first stage of sintering includes volume diffusion of vacancies from the neck region to the convex portion of the system remote from the neck and surface diffusion between surface regions with different radii of curvature.
4. In which stage of solid-state sintering the pores are interconnected and pore shape is irregular?
a) 1 st
b) 2 nd
c) 3 rd
d) 4 th
Answer: a
Explanation: During the first stage of solid-state sintering, rapid neck formation and neck growth take place in the powder compact. This effect a greater extent of bonding within the sintered mass and thus during this stage the pores are interconnected and the pore shape is irregular.
5. In the second stage of sintering, with sufficient neck growth, the pore channels become more _______ in nature.
a) Spherical
b) Cylindrical
c) Cubical
d) Linear
Answer: b
Explanation: In the second stage of sintering, with sufficient neck growth, the pore channels become more cylindrical in nature. During this stage, pore rounding may also occur, without any shrinkage. With continued sintering, these cylindrical pore channels become unstable, gradually pinch off and close.
6. The ________ gradient is high for small neck size leading to faster sintering.
a) Curvature
b) Linear
c) Volume
d) Velocity
Answer: a
Explanation: The interfacial energy is the driving force for the 2 nd stage of solid-state sintering. The curvature gradients near the necks are responsible for the mass flow during this stage. The curvature gradient is high for small neck size leading to faster sintering. With sufficient time at the sintering temperature, the pore eventually becomes rounded. As the neck grows, the curvature gradient decreases and the sintering rate also decreases.
7. The driving force for the various stages of solid-state sintering are ________ and ________
a) Lattice diffusion and capillary force
b) Surface tension forces and diffusional flow
c) Surface tension forces and plastic flow
d) Lattice diffusion and surface tension force
Answer: b
Explanation: The driving force for the various stages of solid-state sintering are surface tension forces and diffusional flow. In the first stage, necks are formed at the contact points between the particles, which continue to grow. During the second stage of sintering, pore channel closure, as well as shrinkage, occurs and in the final stage, the formation of isolated pores occurs.
8. ________ is the mechanism by which bulk transportation can take place in solid-state sintering.
a) Surface diffusion
b) Plastic flow
c) Adhesion
d) Evaporation-condensation
Answer: b
Explanation: Material transport during sintering can occur through the gas phase, liquid phase or solid phase. Plastic flow, viscous flow, grain boundary, and volume diffusion are the mechanisms by which bulk transportation can take place in solid-state sintering.
9. Which of the following is not a mechanism of by which surface transportation occur during solid-state sintering?
a) Plastic flow
b) Volume diffusion
c) Viscous flow
d) Surface diffusion
Answer: d
Explanation: In solid-state sintering, mass transportation can take place either by surface transportation, grain boundaries or bulk transportation. Surface transportation can occur through diffusion, adhesion or evaporation-condensation or by surface diffusion.
10. The following diagram represents the sintering on a microscopic scale.
a) True
b) False
Answer: a
Explanation: The above diagram depicts sintering on a microscopic scale. particle bonding is initiated at contact points. contact points grow into necks. pores between particles are reduced in size. grain boundary develops between particles in place of necked regions.
This set of Powder Metallurgy Multiple Choice Questions & Answers focuses on “Sintering Mechanism – 1”.
1. Which of the following are the main types of material transport mechanisms proposed to be operating during sintering?
a) Evaporation
b) Dislocation movement
c) Evaporation-condensation, viscous flow, plastic flow and diffusion
d) Viscous flow, metal flow
Answer: c
Explanation: A number of material transport mechanisms have been proposed to be operating during sintering. These are, Evaporation and condensation, Viscous flow, Plastic flow, and Diffusion .
2. _______ is the ‘liquid-like’ movement of individual atoms under stress while _______ is the slip of entire planes of atoms.
a) Plastic flow, viscous flow
b) Volume diffusion, plastic flow
c) Viscous flow, volume diffusion
d) Viscous flow, plastic flow
Answer: d
Explanation: Viscous flow is the ‘liquid-like’ movement of individual atoms under stress while the plastic flow is the dislocation movement or the slip of entire planes of atoms.
3. ________ mechanism operates in a system having materials with a high vapor pressure at sintering temperature.
a) Viscous flow
b) Volume diffusion
c) Evaporation and condensation
d) Plastic flow
Answer: c
Explanation: Evaporation and condensation is a simple mechanism, which operates in a system having materials with a high vapor pressure at the sintering temperatures. Evaporation-condensation is driven by pressure differences created by surface curvature and changes the shape of the particles and pores.
4. The driving force for evaporation-condensation mechanism is given by ________
a) μ-μ 0 =Misplaced &/r 1 =RT ln\
μ-μ 0 =Misplaced &/r 1 =RT ln\
μ 0 -μ=Misplaced &/r 1 =RT ln\
μ-μ 0 =Misplaced &/r 1 =RT ln\(\frac{p}{p_0}\)
Answer: b
Explanation: Based on the Gibbs-Thomson equation, the driving force for the evaporation-condensation mechanism is given by μ-μ 0 =Misplaced &/r 1 =RT ln\(\frac{p}{p_0}\) where μ 0 and μ are chemical potentials of initial and final surfaces, R is the universal gas constant, T is the temperature in Kelvin and p and p 0 are the partial pressures over the curved surface and flat surface respectively, γ is the surface energy and Ω is the atomic volume.
5. The mass transport during evaporation-condensation mechanism occurs from _______ particle surface to the ______ necks.
a) Concave, convex
b) Convex, bi-concave
c) Convex, concave
d) Bi-convex, concave
Answer: c
Explanation: The mass transport during the evaporation-condensation mechanism occurs from the flat surface to the stressed region from the convex particle surface to the concave necks. The rate of transfer of materials depends on the vapor pressure gradient between the two surfaces as well as the rate of evaporation.
6. The equilibrium vapor pressure over the neck _____ particle surface.
a) <
b) >
c) =
d) >>
Answer: a
Explanation: The equilibrium vapor pressure over a concave surface is lower compared to that of a convex surface , resulting in mass transport along the vapor pressure gradient, from the convex surfaces to the concave necks and the driving force for this mechanism is the surface tension force, which gives rise to stresses in the green compact.
7. Diffusion occurs as a result of _______ gradient.
a) Velocity
b) Vacancy concentration
c) Pressure
d) Momentum
Answer: b
Explanation: The vacancy concentration gradient is the reason for the diffusion process to occur. This vacancy concentration depends on temperature and chemical potential gradient which occurs due to stress acting on the metal surface.
8. Vacancy concentration causes _______
a) The outflow of vacancies from the curved surface towards the flat region
b) The outflow of vacancies from the flat surface towards the curved region
c) The outflow of atoms from the curved surface towards the flat region
d) The influx of vacancies from the curved surface towards the flat region
Answer: a
Explanation: Vacancy concentration gradient (C-C 0 ) is given by the equation-
(C- C 0 )=γΩC 0 /r
Vacancy concentration gradient (C-C 0 ) causes an outflow of vacancies from the curved surface towards the flat surface and an influx of atoms in the opposite direction.
9. The vacancy concentration is given by D vac = ______
a) D.C 0
b) D.C
c) d.C
d) D.c
Answer: a
Explanation: If the volume of the material is D and the vacancy concentration is D vac in the material are known, then D vac =D.C 0 . The vacancy concentration C 0 causes movement of vacancies from the neck region leading to neck growth.
10. What is the empirical relationship for the rate of neck growth when a sphere is in contact with a flat surface?
a) Rate of neck growth ∝ \
Rate of neck growth ∝ \
Rate of neck growth ∝ \
Rate of neck growth ∝ \(t^{\frac{1}{8}}\)
Answer: b
Explanation: The empirical relationship for the rate of neck growth when a sphere is in contact with a flat surface is given by- Rate of neck growth ∝ \
.
11. What is the empirical relationship for the rate of neck growth when two spheres are in contact with one another?
a) \
\
\
\(\frac{x^5}{a^3}=\frac{40\gamma \Omega D.t}{RT}\)
Answer: c
Explanation: When two spheres are in contact with one another, the rate of neck growth between the two spheres is given by the equation- \
, a=radius of the sphere , t is time , γ is the surface energy, D is the diffusivity of the material and Ω is the atomic or molecular volume.
This set of Powder Metallurgy Interview Questions and Answers for freshers focuses on “Sintering Mechanism – 2”.
1. Which of the following transport mechanisms can occur for two spheres in contact with one another during sintering?
a) Evaporation-condensation, surface diffusion and volume diffusion
b) Evaporation-condensation, surface diffusion, volume diffusion, volume diffusion of vacancies, and grain boundary diffusion
c) Surface diffusion
d) Volume diffusion
Answer: b
Explanation: For two spheres in contact with one another during sintering following transport mechanisms can occur. Evaporation and condensation, Material transport from the flat surface to the neck through surface diffusion, Volume diffusion from flat surface to the neck, and Volume diffusion of vacancies from neck to the neck through the grain boundaries which are under compressive stress and vacancy flow through grain boundaries to the neck region by grain boundary diffusion.
2. Neck growth rate due to surface diffusion from the surface source is R 1 = _______
a) 2D s δ s \
2D s δ s \
2D s \
2D s δ s \(FK_{1}^4\)
Answer: a
Explanation: Neck growth rate due to surface diffusion from the surface source is R 1 =2D s δ s \(FK_{1}^3\) where, R 1 =rate of neck growth for surface diffusion, F=\(\frac{\Omega \gamma_s}{kT}\), K 1 =curvature difference, which drives the diffusive fluxes, D s =surface diffusion coefficient, δ s =effective surface thickness, γ s =surface free energy, Ω=atomic or molecular volume, and k=Boltzmann constant.
3. Neck growth rate due to lattice diffusion from the surface source is R 2 = _______
a) 2D s \
2D s \
2D v \
2D v \(FK_{1}^2\)
Answer: d
Explanation: Neck growth rate due to lattice diffusion from the surface source is R 2 =2D v \(FK_{1}^2\), where D v =lattice diffusion coefficient, , F=\(\frac{\Omega \gamma_s}{kT}\), K 1 =curvature difference, γ s =surface free energy, Ω=atomic or molecular volume, and k=Boltzmann constant.
4. The empirical relationship for neck growth rate due to vapor transport from the surface source is R 3 = _______
a) P v FK 1 \
P v FK 1 \
P v FK 1 \
P v FK 1 \(\sqrt{\frac{\Omega T}{2\pi \rho_{0}k}}\)
Answer: a
Explanation: The empirical relationship for neck growth rate due to vapor transport from the surface source is R 3 =P v FK 1 \(\sqrt{\frac{\Omega}{2\pi \rho_{0}kT}}\) where, P v =vapor pressure, ρ 0 =theoretical density, F=\(\frac{\Omega \gamma_s}{kT}\), K 1 =curvature difference, γ s =surface free energy, Ω=atomic or molecular volume, and k=Boltzmann constant.
5. The empirical relationship for neck growth rate due to grain boundary transport from sources on the grain boundary is R 4 = _______
a) 4D B δ B \
4D B δ B \(FK_{2}^1\)/x 2
c) 4D B δ B \
4D B δ B \(FK_{2}^2\)/x
Answer: d
Explanation: The empirical relationship for neck growth rate due to grain boundary transport from sources on the grain boundary is R 4 =4D B δ B \(FK_{2}^2\)/x, where D B =grain boundary diffusion coefficient, δ B =effective grain boundary thickness, F=\(\frac{\Omega \gamma_s}{kT}\), γ s =surface free energy, Ω=atomic or molecular volume, x=neck radius, and k=Boltzmann constant.
6. Neck growth rate due to lattice diffusion from sources on the grain boundary is R 5 = _______
a) 2D v \
2D v \
4D v \
4D v \(FK_{2}^2\)
Answer: d
Explanation: The empirical relationship for neck growth rate due to lattice diffusion from sources on the grain boundary is R 5 =4D v \(FK_{2}^2\) where, D v =lattice diffusion coefficient, F=\(\frac{\Omega \gamma_s}{kT}\), γ s =surface free energy, Ω=atomic or molecular volume, and k=Boltzmann constant.
7. The empirical relationship for neck growth rate due to lattice diffusion from dislocation sources is R 6 = _______,
a) \Missing or unrecognized delimiter for \Big\)K 2 Nx 2 D v F(K 2 –\
\)
b) \Missing or unrecognized delimiter for \Big\)Nx 2 D v F(K 2 –\
\)
c) \Missing or unrecognized delimiter for \Big\)K 2 Nx 2 D v F(K 2 –\
\)
d) \Missing or unrecognized delimiter for \Big\)K 2 Nx 2 D v (K 2 –\
\)
Answer: c
Explanation: The empirical relationship for neck growth rate due to lattice diffusion from dislocation sources is R 6 =\Missing or unrecognized delimiter for \BigK_2Nx^2D_vF
\) where, N=dislocation density, ε=shear modulus, F=\(\frac{\Omega \gamma_s}{kT}\), γ s =surface free energy, Ω=atomic or molecular volume, x=neck radius, a=radius of the sphere, and k=Boltzmann constant.
8. Which of the following mechanism does not lead to shrinkage?
a) Viscous flow
b) Surface diffusion
c) Volume diffusion
d) Grain boundary diffusion
Answer: b
Explanation: Out of the various mechanisms for sintering only viscous flow, plastic flow, volume diffusion, and grain boundary diffusion can lead to shrinkage. Surface diffusion and evaporation-condensation do not lead to shrinkage.
9. ________ mechanism alters the shape of the neck and particle surface.
a) Viscous flow
b) Volume diffusion
c) Evaporation-condensation
d) Plastic flow
Answer: c
Explanation: Evaporation-condensation and surface diffusion do not lead to shrinkage but do alter the shape of the neck and particle surface by redistribution of atoms as they reach the surface of the neck.
10. The expression for the number of vacant site N is given by ________
a) N=N 0 \
N=N 0 \
N=N 0 \
N=N 0 \(e^{\frac{Q}{RT}}\)
Answer: a
Explanation: Sintering involves the movement of atoms and hence a large number of high energized atoms along with a sufficient number of vacant sites must be available for sintering to take place. This is represented by Arrhenius relation, N=N 0 \(e^{\frac{-Q}{RT}}\) where, N 0 is the total number of lattice sites, R is the universal gas constant, and Q is the activation energy for transport.
11. According to ______, there are six stages of sintering.
a) Schroter
b) Nabarro and Herring
c) Kuczynsky
d) Hutteg
Answer: d
Explanation: According to Hutteg, there are six stages of sintering for different increasing temperature regions that correspond to the dominance of different mechanisms such as adhesion along with particle rearrangement, surface diffusion, grain growth, lattice diffusion, recrystallization, and excessive grain growth respectively.
This set of Powder Metallurgy Questions and Answers for Campus interviews focuses on “Sintering Mechanism – 3”.
1. Nabarro and Herring supported ________ as the dominant mechanism in sintering.
a) Evaporation-condensation
b) Viscous flow
c) Diffusion
d) Recrystallization
Answer: c
Explanation: According to Nabarro and Herring diffusion is the dominant mechanism in sintering because surface stresses change the concentration of the vacancies near the surface and create vacancy gradients that favor diffusion.
2. ___________ are structural arrangement of dislocations and are not perfect sinks.
a) Pores
b) Grain boundaries
c) Vacancies
d) Necks
Answer: b
Explanation: Originally grain boundaries were thought to be pipes that allowed vacancies to reach the surface. Later the concept that the grain boundaries were perfect sinks for vacancies was developed which showed that the diffusion path was dependent on the distance between the pore and grain boundary and not the size. However, it is now considered that grain boundaries are structural arrangement of dislocations and are not perfect sinks. The effectiveness of grain boundaries as a source of atoms or sinks for vacancies is dependent on the mobility of dislocations.
3. The expression for viscous flow mechanism proposed by Frenkel is given by ________
a) \
\
\
\(\frac{x^2}{a}=\frac{3\gamma t}{2\eta}\)
Answer: d
Explanation: The expression for viscous flow mechanism proposed by Frenkel is important in the sintering of glass and it is given by \(\frac{x^2}{a}=\frac{3\gamma t}{2\eta}\) where, x=neck radius, a=radius of particle, γ=surface tension, η=glass viscosity and t=sintering time.
4. Which of the following mechanisms operate during sintering, according to Bal’shin theory?
a) Particle re-arrangement, particle shape change, and grain shrinkage
b) Particle shape change, particle size change, and grain growth
c) Particle re-arrangement, particle shape change, and grain growth
d) Particle re-arrangement and grain growth
Answer: c
Explanation: Bal’shin proposed that following mechanisms are occurring during sintering- Particle re-arrangement, Particle shape change, and Grain growth. According to Bal’shin, although several forces are acting during sintering plastic deformation is the major mechanism leading to densification.
5. The equation for coefficient of viscosity as proposed by Frenkel, is given by ________
a) η=\
η=\
η=\
η=\(\frac{kT}{Da}\)
Answer: b
Explanation: Frenkel was the first to make use of a two-sphere model to develop rate kinetics for sintering. Thus, the equation for coefficient of viscosity as proposed by Frenkel, is given by η=\(\frac{kT}{D\Omega}\) where k=Boltzmann constant, T=absolute temperature, D=self-diffusion coefficient, and Ω=atomic volume.
6. Bulk flow of material by movement of dislocations is a possible mechanism for densification during sintering only if the two conditions are met.
a) True
b) False
Answer: a
Explanation: Bulk flow of material by movement of dislocations has been proposed as a possible mechanism for densification during sintering. However, the following two conditions must be met- movement of dislocation in the neck region under shear stresses, and generation of new dislocations by surface tension forces.
7. Which of the following is the expression for plastic flow as the driving force for sintering?
a) \
\
\
\(\frac{ds}{dt}=A\sigma^{n}e^{\frac{Q_c}{RT}}\)
Answer: d
Explanation: Lenel and Ansell supported plastic flow as the driving force for sintering and derived a sintering rate expression \(\frac{ds}{dt}=A\sigma^{n}e^{\frac{Q_c}{RT}}\) where, A=constant, σ=stress, n=stress exponent, Q c =activation energy for creep, R=ideal gas constant, and \(\frac{ds}{dt}\)=creep rate.
8. At equilibrium, the relation between dihedral angle and surface energy is represented by the equation ______
a) cos\
cos\
cos\
cos\(\frac{\theta}{2}=-\frac{\gamma_{ss}}{\gamma_{sv}}\)
Answer: c
Explanation: The dihedral angle θ is a measure of surface and pore geometry and at equilibrium is related to surface energy by the equation cos\(\frac{\theta}{2}=\frac{\gamma_{ss}}{\gamma_{sv}}\) where, γ ss and γ sv are the surface energies of the solid-solid and solid-vapor interfaces respectively. If the dihedral angle is less than the equilibrium dihedral angle, sintering may continue.
9. Entrapment of gas within the pores is an important reason for not achieving theoretical density in practice during sintering.
a) True
b) False
Answer: a
Explanation: Gas entrapment with in the pores does not allow us to achieve theoretical density in practice during sintering, this is because, during the final stage of sintering, pores become isolated and any gas remaining becomes trapped and thus shrinkage will be opposed by the presence of the gas in the pore. The other reasons for not achieving theoretical density in practice are presence of agglomeration, poor packing, and non-uniform particle size.
10. The equilibrium pore pressure is given by P p = ________
a) P atm -2γ sv /r
b) P atm +2γ sv /r
c) P atm +2γ ss /r
d) P atm +2γ sv /x
Answer: b
Explanation: The equilibrium pore pressure is given by P p for an isolated spherical pore is given by P atm +2γ sv /r where, P atm is the atmospheric pressure, r is the pore radius, and γ sv is the surface energy of solid-vapor interface. Thus, on increasing P atm will decrease the pore radius.
11. The above diagram represents criteria for pore removal during sintering.
a) True
b) False
Answer: a
Explanation: There is a critical pore coordination number N p , that is the number of particles surrounding which is related to \(\frac{\gamma_{ss}}{\gamma_{sv}}\) above which the pore is stable while below which the pore is unstable and disappears.
12. Coble developed rate equations for three stage sintering assuming the compact to be made of packed spheres and in the final stage form interlocking ___________
a) Tetrakaioctahedrons
b) Tetrakaidecahedrons
c) Tetracontagons
d) Tetrakaitetrahedrons
Answer: b
Explanation: Coble developed rate equations for three stage sintering assuming the compact to be made of packed spheres and in the final stage form interlocking tetrakaidecahedrons. According to Coble, the necks form in the initial stage of sintering but the distance between the particle centers remain constant. During the intermediate stage, necks grow, shrinkage may occur and grain growth may occur. During the third stage, the pores become isolated, the pores being considered as spheres at the grain boundaries.
This set of Powder Metallurgy Multiple Choice Questions & Answers focuses on “Structure and Property Changes during Sintering”.
1. Densification cannot be treated as equal to the amount of porosity removed.
a) True
b) False
Answer: a
Explanation: Densification is proportional to the shrinkage or the number of pores removed in the case of single component systems . In the case of multicomponent systems such as premixed powders, during sintering solid solutions may form resulting in an expansion rather than shrinkage. Expansion of the compact may also take place due to the entrapped gases. Thus, densification cannot be treated as equal to the amount of porosity removed.
2. Sintering results in ________
a) Change in structure of compact
b) Structural change, recrystallization, and grain shrinkage
c) Structural change, reduction of surface oxides, and grain growth
d) Pore growth
Answer: c
Explanation: Densification during sintering usually results in a change in the structure of grains as well those of pores present in the initial compact. Reduction of surface oxides may occur during sintering in a reducing atmosphere. In case of powder mixes, containing metals with lower melting point, evaporation of these metals can occur. Other changes occurring during sintering include recrystallization and grain growth. Pore growth also occurs if sintering is carried out for longer times at high temperatures.
This set of Powder Metallurgy Multiple Choice Questions & Answers focuses on “Sintering of Multicomponent System – 1”.
1. In sintering of multicomponent systems, the material transport mechanisms involve ______
a) Self-diffusion
b) Self-diffusion and inter-diffusion
c) Inter-diffusion
d) Intra-diffusion and self-diffusion
Answer: b
Explanation: In the sintering of multicomponent systems, the material transport mechanisms involve interdiffusion of the components into one another through vacancy movement, in addition to the self-diffusion caused by capillary forces.
2. Enhanced volume diffusion is the reason for adding Ni for activated sintering of refractory metals.
a) True
b) False
Answer: b
Explanation: In many multicomponent systems, the dopant is added intentionally to increase the densification rates by about 100 times. This is called activated sintering and is found to occur in refractory metals like W, Mo, Ta, Hf, and rhenium with Ni or Pd as the activators. The improvement in sintering characteristics in the presence of dopants is due to the enhanced grain boundary diffusion caused by the presence of dopants at the grain boundary of these refractory metals.
3. The __________ is the motion of the interface that occurs due to the difference in diffusion rates of the metal atoms.
a) Darkens effect
b) Schroter effect
c) Kirkendall effect
d) Harmer effect
Answer: c
Explanation: The Kirkendall effect is the motion of the interface that occurs as a consequence of the difference in diffusion rates of the metal atoms. The occurrence of Kirkendall effect during sintering may lead to excess vacancy concentration, which may cause pores to appear and grow, in turn causing the growth of the component.
4. _________ is an example of multicomponent sintering.
a) Liquid phase sintering
b) Solid-state sintering
c) Microwave sintering
d) Reaction sintering
Answer: a
Explanation: Liquid phase sintering is an example of multicomponent sintering in which a liquid phase formed during sintering aids in the densification of the compacts. This technique employs a small amount of second constituent having a relatively lowmelting point. During sintering, the temperature is maintained above the melting point of this low-melting constituent, so that it is present either throughout or for a part of the sintering process, as a liquid.
5. Which of the is the must consideration for liquid phase sintering to occur?
a) Incomplete wetting of liquid in solid
b) Appreciable insolubility of solid in liquid
c) Presence of a limited amount of liquid phase
d) Appreciable solubility of solid in liquid
Answer: d
Explanation: For liquid phase sintering to occur there are three main considerations: Presence of an appreciable amount of liquid phase, Appreciable solubility of solid in liquid, and Complete wetting of the solid by liquid.
6. ______ is the form of liquid phase sintering where liquid formed is temporary in nature.
a) Transient liquid phase sintering
b) Persistent liquid phase sintering
c) Transistor liquid phase sintering
d) Progressive liquid phase sintering
Answer: a
Explanation: Transient liquid phase sintering is the form of liquid phase sintering where liquid formed is temporary in nature. In this case, the liquid continues to take the solid into the solution until it reaches a point when the solidus boundary is reached and the liquid resolidifies.
7. Which of the following is the correct sequence for liquid phase sintering?
a) Liquid flow stage → Precipitation stage → Solid-state sintering stage
b) Liquid flow stage → Condensation stage → Liquid-state sintering stage
c) Liquid flow stage → Solution and reprecipitation stage → Liquid-state sintering stage
d) Liquid flow stage → Solution and reprecipitation stage → Solid-state sintering stage
Answer: d
Explanation: Stages in the liquid phase sintering are- Liquid flow stage → Solution and reprecipitation stage → Solid-state sintering stage. The first stage involves melting and liquid flow involving the rearrangement of solid particles. In the intermediate stage, smaller particles redissolve and precipitate on larger particles. The final stage involves the coalescence of solid particles involving slow densification.
8. When a liquid drop is in contact with a solid surface, the contact angle at equilibrium is given by ______
a) cosθ=\
sinθ=\
cosθ=\
cosθ=\(\frac{\gamma_{LG}-\gamma_{SL}}{\gamma_{GS}}\)
Answer: a
Explanation: When a liquid drop is in contact with a solid surface, the contact angle at equilibrium is given by cosθ=\(\frac{\gamma GS-\gamma SL}{\gamma LG}\) where θ is the contact angle,γ GS , γ SL , and γ LG are the surface energies or tensions of the solid-gas interface, solid-liquid interface and liquid-gas interface respectively.
This set of Powder Metallurgy Quiz focuses on “Sintering of Multicomponent System – 2”.
1. Which of the following condition should be satisfied for complete penetration of liquid into the grain boundaries?
a) γ GS < 0.5γ GB
b) γ LG < 0.5γ GB
c) γ GB < 0.5γ LS
d) γ LS < 0.5γ GB
Answer: d
Explanation: A measure of penetration by the liquid between the two grains is given by the dihedral angle. Complete penetration into grain boundary takes place when the liquid-solid interfacial energy is less than one half of the grain boundary energy i.e. γ LS < 0.5γ GB .
2. For liquid phase to sinter successfully, the contact angle should be _______
a) more than 90°
b) less than 90°
c) equal to 90°
d) equal to 0°
Answer: b
Explanation: For the liquid phase to sinter successfully, the contact angle should be less than 90°. When the contact angle is 0°, the liquid phase completely wets the solid particles. In the case of the non-wetting liquid phase , partial exudations from the compact will occur in the form of droplets during sintering.
3. Initial particle size must be small for liquid phase sintering.
a) True
b) False
Answer: a
Explanation: For liquid phase sintering to be effective, the initial particle size must be small for liquid phase sintering. Small particles have higher surface energy/unit volume and so the driving force for sintering is large because liquid phase sintering involves transport of materials from surfaces of higher energy to surfaces of lower energy.
4. ______ dihedral angle, will hinder further densification.
a) Negative
b) Zero
c) Positive
d) Infinite
Answer: c
Explanation: If the dihedral angle is positive, then grain boundaries may appear between the particles and an aggregate of two or more grains will be established. This situation will lead to the formation of a rigid skeleton, which we hinder further densification.
5. In liquid phase sintering, ______ stresses are developed at the contact point of two particles when the dihedral angle is zero.
a) Bending
b) Shear
c) Tensile
d) Compressive
Answer: d
Explanation: When the dihedral angle is zero, a negative pressure gradient is developed because of the small negative radius of curvature of the liquid droplet. At the contact point, compressive stresses are developed. This stress leads to increased dissolution of the material at the contact points and their movement away from contact points cause the center of the particles to come together giving rise to densification.
6. ______ amount of liquid phase must be present to penetrate the adjoining grains.
a) Minimum
b) Sufficient
c) Maximum
d) Unlimited
Answer: b
Explanation: Sufficient amount of liquid phase must be present to penetrate the adjoining grains. However, the amount of liquid phase must be kept as minimum as possible, to avoid deformation of the compact.
7. Liquid phase sintering is advantageous over solid phase sintering due to ______
a) Temperature
b) Microstructure
c) Kinetics
d) Economy
Answer: c
Explanation: Liquid phase sintering promotes enhanced kinetics because of the presence of the liquid phase. The capillary attraction due to wetting allows rapid densification, reduction in interparticle friction leads to a faster rearrangement of particles, and presence of liquid phase aids in material flow and better packing.
8. The greater the ______ more will be the driving force for the liquid flow stage in the liquid phase sintering.
a) Wetting
b) Temperature
c) Pressure
d) Diffusion
Answer: a
Explanation: The greater the extent of wetting the greater will be the driving force for the liquid flow stage in the liquid phase sintering. Moreover, densification increases with the increasing amount of liquid phase in this process. The extent of wetting can be increased by lowering the liquid-solid interfacial energy by diffusion or absorption method at the interface.
This set of Powder Metallurgy Multiple Choice Questions & Answers focuses on “Types of Variables in Sintering”.
1. Which of following is the correct set of material variables in sintering?
a) Particle structure and sintering atmosphere
b) Particle composition, particle shape, green density and sintering temperature
c) Green density and sintering time
d) Green density and particle size
Answer: d
Explanation: The major variables in sintering include process variables and material variables. The process variables include sintering atmosphere, sintering time and sintering temperature whereas the material variables include particle composition, particle shape, particle size, particle structure, and green density.
2. ________ particle size leads to increased sintering.
a) Finer
b) Coarse
c) Medium
d) Ultra-coarse
Answer: a
Explanation: Finer particle size leads to increased sintering. Similar-sized particles have a greater pore/solid interfacial area producing a greater driving force for sintering. Small grain size promotes grain boundary diffusion and a large interparticle contact area to volume diffusion.
3. A _______ in green density signifies a greater driving force for sintering.
a) Maximum
b) Sufficient
c) Decrease
d) Increase
Answer: c
Explanation: The decrease in green density signifies an increasing amount of internal surface area. Although the % change in density ↑ with decreasing green density, the absolute value of the sintered density remains highest for the higher green density material.
4. Heterogenous nature of powders improve sintering kinetics.
a) True
b) False
Answer: a
Explanation: Heterogenous nature of powders promotes enhanced diffusion and improves sintering kinetics. Dispersed phases within the matrix may promote sintering by inhibiting grain boundary motion.
5. ________ sphericity and ________ macro or micro-surface roughness promote sintering.
a) Decreasing, decreasing
b) Increasing, decreasing
c) Decreasing, increasing
d) Increasing, increasing
Answer: c
Explanation: Any factor that lead to greater and intimate contact between particles and increased internal surface area promote sintering and these factors include decreasing sphericity and increasing macro or micro-surface roughness.
6. The degree of sintering _______ with increasing time, though the effect is small in comparison to the effect of temperature.
a) Unaffected
b) Constant
c) Decreases
d) Increases
Answer: d
Explanation: The degree of sintering increases with increasing time, though the effect is small in comparison to the effect of temperature. The loss of driving force with increasing time at any temperature is one of the reasons why it is so difficult to remove all porosity by sintering. Longer times may also result in grain coarsening, which affects the mechanical properties adversely.
This set of Powder Metallurgy Multiple Choice Questions & Answers focuses on “Sintering Practice and Sintering Furnace – 1”.
1. Which of the following condition is necessary for obtaining consistent and satisfactory sintered components?
a) More labor cost
b) Long sintering time
c) High power consumption
d) Short sintering time
Answer: d
Explanation: For obtaining consistent and satisfactory sintered components, it is essential to make use of furnaces operating at the lowest temperatures for the shortest times using the cheapest possible sintering atmosphere with lowest maintenance and power consumption as well as the least labor costs.
2. On the basis of which of the following factors a sintering furnace is selected?
a) Cost
b) Furnace lining
c) Working temperature range
d) Shape
Answer: c
Explanation: A sintering furnace is selected on the basis of the working temperature range, type and purity of the sintering atmosphere during sintering, desired production rate, operation, and maintenance costs for a given production.
3. Which of the following are the essential parts of a sintering furnace?
a) Burn-on zone, sintering zone, and cooling zone
b) Burn-off zone, sintering zone, and cooling zone
c) Preheat zone and sintering zone
d) Sintering zone and cooling zone
Answer: b
Explanation: The essential parts of a sintering furnace include: a burn-off zone or preheat zone for the removal of lubricants, a controlled high-temperature sintering zone, and a cooling and discharging zone.
4. The compacts entering into the burn-off zone must be heated ________
a) Slowly
b) Moderately
c) Rapidly
d) Any desired rate
Answer: a
Explanation: The burn-off zone, must be capable of working up to a temperature of 400-500°C. The green compacts on entering this zone, are heated slowly so as to avoid rapid heating which may result in the expansion of entrapped air and lubricants. The compact should be free from lubricant when it enters into the sintering zone.
5. Incomplete burnout leads to ________ and discoloration of the components.
a) Pungent smell
b) Reduction
c) Cracking
d) Sooting
Answer: d
Explanation: Polymers used as lubricants decompose into methane, ethane, butane, propane, CO, CO 2 , H 2 0 during heating. The decomposition starts at 150°C and is completed at 500°C. When burnout is incomplete, sooting may occur along with discoloration of the components. Sooting occurs because of the rapid rate of heating without sufficient oxygen or moisture.
6. The sintering zone must be ________ in length in relation to the burn-off zone.
a) Shorter
b) Longer
c) Moderate
d) Equal
Answer: b
Explanation: The second or the high-temperature sintering zone is longer in length than the burn-off zone to provide sufficient time to obtain the desired density and strength in the sintered parts.
7. The cooling zone of a sintering furnace is made up of _______
a) A short-insulated cooling zone
b) A short conductive cooling zone and longer oil jacketed cooling zone
c) A longer water-jacketed cooling zone
d) A short-insulated cooling zone and longer water-jacketed cooling zone
Answer: d
Explanation: The cooling zone of a sintering furnace is made up of two sections. The first is a short-insulated cooling zone, which allows the sintered parts to be cooled slowly in order to avoid thermal stresses, and second is a longer water-jacketed cooling zone to cool the sintered parts without exposure to air to prevent oxidation.
8. ________ type furnaces require large volumes of protective gases.
a) Ram-up
b) Roller hearth
c) Mesh-belt
d) Pulley-lift
Answer: c
Explanation: Mesh belt type furnaces require large volumes of protective gases as the doors are kept open during operation. In the case of roller hearth, the doors are kept closed during operation and consequently, heat losses are minimized.
9. By measuring _________ of effluent gas from the furnace continuously, the completeness of purge can be identified.
a) Dew point
b) Specific gravity
c) Carbon potential
d) Gas content
Answer: b
Explanation: Sintering atmosphere must be carefully controlled and thus it is essential to analyze the gas content, the specific gravity of the gases, moisture content and carbon potential of the sintering atmosphere as well as to control them. The evaluation of specific gravity of effluent gas, the completeness of purge can be identified. Bydew point analysis, the moisture content can be found out. Both dew point or carbon dioxide analysis can be used to measure of the carbon potential of the sintering atmosphere.
10. In _______, the analysis takes place in two phases, the absorption phase, and the burning phase.
a) Ortab type analyzer
b) Orsat type analyzer
c) Infrared type analyzer
d) Orson type analyzer
Answer: b
Explanation: In the Orsat type analyzer, a complete analysis of the gaseous mixture is divided into two phases, namely, the absorption phase and the explosion or burning phase. The constituents of the atmosphere such as carbon dioxide, carbon monoxide, and oxygen are determined by chemical absorption. Portable units available lend themselves to rapid spot analysis.
11. ________ works on the principle that each constituent of the sintering atmosphere absorbs infrared energy at a characteristic wavelength.
a) Infrared analyzer
b) Orsat type analyzer
c) Energy analyzer
d) Wave analyzer
Answer: a
Explanation: Infrared analyzer works on the principle that each constituent of the sintering atmosphere absorbs infrared energy at a characteristic wavelength. Any change in the concentration of the particular constituent results in a change in the total energy of a beam passed through the gas.
This set of Powder Metallurgy MCQs focuses on “Sintering Practice and Sintering Furnace – 2”.
1. The moisture content of the gas is determined using a _______
a) dew Jug
b) dew Cup
c) moisture cup
d) dew meter
Answer: b
Explanation: Dew point analysis is an effective method of determining the moisture content of a gas. This is done using a ‘Dew Cup’. The apparatus consists of a glass thermometer, is kept directly in the path of the gas stream.
2. Which solution is used to fill the dew cup for carrying out moisture analysis?
a) Carboxylic acid
b) Propane
c) Ethyl alcohol
d) Acetone
Answer: d
Explanation: The procedure for moisture content analysis includes- first, the dew cup is filled with acetone and the atmosphere gas is passed against the dew cup. After about 5 minutes, dry ice is added to the cup with stirring. Moisture or dew appears on the surface of the cup and the dew point is read from the thermometer in the dew cup.
3. In a more sophisticated type of indicator for moisture analysis the _________ of the gas is converted to the dew point.
a) pressure ratio
b) heat conductivity ratio
c) volume ratio
d) temperature ratio
Answer: a
Explanation: In a more sophisticated type of indicator for moisture analysis, the sample gas is compressed, and then quickly expanded. In the case the gas got cooled down below its dew point due to its rapid expansion, a fog is noticed in the expansion chamber. The pressure ratio of the gas is converted to the dew point.
4. The dew point measurement of a gas either entering or leaving a furnace gives an excellent indication of ________
a) specific gravity
b) moisture content
c) chemical potential
d) carbon potential
Answer: d
Explanation: The dew point measurement of a gas either entering or leaving a furnace gives an excellent indication of carbon potential. Presence of excess moisture can lead to decarburizing of the parts in a non-decarburizing atmosphere.
5. The specific gravity analysis is especially sensitive to changes in _____
a) carbon dioxide
b) carbon Monoxide
c) methane
d) oxygen
Answer: a
Explanation: The specific gravity of gases can be measured with reference to air. This analysis is particularly influenced by the changes in carbon dioxide. Because carbon dioxide is much heavier than the other sintering background components.
6. Carbon potential control is important during sintering of ______
a) tungsten
b) steel
c) silicon carbide
d) molybdenum
Answer: b
Explanation: Carbon potential control of sintering atmosphere is important, particularly during sintering of steels. Equilibrium between the atmosphere and the carbon potential of the steel from getting carburized and decarburized.
7. Which of the following are the important temperature controls used in sintering furnace?
a) Thermocouple
b) Radiation pyrometers
c) On-off controllers
d) On-off controllers and proportional controllers
Answer: d
Explanation: The various important temperature controls used in sintering furnace include: on-off controllers, proportional controllers and transformer controls. Thermocouple and radiation pyrometers are instruments used to measure temperature for low-temperature and high-temperature furnaces respectively.
8. The transformer controls employ a transformer whose AC is connected to______ and DC is connected to _______
a) mains, thermistor
b) thermocouple, mains
c) mains, thermocouple
d) thermistor, mains
Answer: c
Explanation: The transformer control uses a transformer whose AC windings are connected to the mains while a DC winding present in the transformer is connected to the thermocouple. Any changes in the temperature are relayed to the DC windings, which in turn controls the input power to the furnace windings/elements.
9. The sintering furnace can be classified on the basis of _________
a) temperature
b) operation
c) type of heating, and temperature
d) operation, and atmosphere
Answer: d
Explanation: The sintering furnace can be classified n the basis of- Type of heating, such as fuel-fired or electrically-heated furnaces. Type of operation, such as continuous or batch type furnaces. Type of atmosphere used as muffle furnaces, controlled atmosphere furnace or vacuum furnaces.
10. _________ can operate at temperatures of 1350°C.
a) Mesh belt furnace
b) Walking beam furnace
c) Roller hearth furnace
d) Radiant tube furnace
Answer: b
Explanation: In walking beam furnaces, parts are periodically lifted and moved by a lifting mechanism. It can operate at temperatures of 1350°C, because the lifting part is made of refractory baked by alloy steel. Mesh belt and roller hearth furnaces are limited by their service temperature , which in turn is dependent on the belt and roller material.
11. ________ atmosphere can be divided into dry hydrogen, exothermic and endothermic atmosphere.
a) Reducing
b) Oxidizing
c) Inert
d) Vacuum
Answer: a
Explanation: The three types of atmospheres prevalent in sintering furnaces are the reducing, neutral, and oxidizing atmosphere. Reducing atmosphere can be divided into dry hydrogen or dissociated hydrogen, exothermic atmosphere with low or medium carbon potential, and endothermic atmosphere enriched with hydrocarbon gas.
This set of Powder Metallurgy Multiple Choice Questions & Answers focuses on “Sintering – Infiltration”.
1. ______ process involves preparing a porous metallic body and filing its pores with a molten metal having a lower melting point.
a) Liquid phase sintering
b) Infiltration
c) Densification
d) Alloying
Answer: b
Explanation: Infiltration process involves preparing a porous metallic body or skeleton metal with high melting point and subsequently filing its pores with a molten metal having a lower melting point.
2. A continuous network of infiltrant metal is a must.
a) True
b) False
Answer: a
Explanation: A continuous network of a ductile infiltrant metal is must for the process of infiltration to be fruitful because it gives the composite much greater resistance to thermal and mechanical stresses.
3. How many stages occur in the process of infiltration?
a) 5
b) 2
c) 3
d) 4
Answer: b
Explanation: Generally, two stages occur in the process of infiltration: infiltration proper- filling of pores of the skeleton with the molten infiltrant metal by capillary action; structural changes occur during the soaking period.
4. Which of the following is not a characteristic of infiltrant?
a) Melting point lower than the skeleton metal
b) High surface tension
c) Good or perfect wetting
d) Must not alloy or react with the skeleton metal
Answer: b
Explanation: The essential requirements in choosing a suitable infiltrant are: Its melting point must be lower than the skeleton metal; Low surface tension so as to fill small interstices; There should be ‘good or perfect wetting’ of the skeleton by the infiltrant ; and It must not alloy or react with the skeleton metal.
5. For infiltration, the porosity in the skeleton should be ________
a) Closed
b) Interconnected
c) Open
d) Intermittent
Answer: b
Explanation: The porosity in the porous skeleton should be interconnected since the infiltrant cannot penetrate in closed-off pores in the skeleton and the skeleton material should be insoluble in the liquid infiltrant.
6. __________ are among the most important P/M parts produced by infiltration.
a) Electrical contacts
b) Cermet
c) Sintered carbides
d) Porous P/M parts
Answer: a
Explanation: Electrical contacts are among the most important P/M parts produced by infiltration. They are most commonly compound materials with a tungsten skeleton infiltrated with copper, which are also used as resistance welding electrodes. Combinations of W-Ag, Mo-Ag are other examples of infiltrated materials.
7. Which of the following changes does not improve the process of infiltration?
a) Lowering the interfacial tension between skeleton and infiltrant
b) Removing dissolved or adsorbed elements in the skeleton
c) Increasing surface energy of the infiltrant
d) Increasing the interfacial tension between skeleton and infiltrant
Answer: d
Explanation: It has been observed that the process of infiltration can be improved by the addition of properly selected detergents by removing dissolved or adsorbed elements in the skeleton, by increasing the surface energy of the infiltrant and by lowering the interfacial tension between skeleton and infiltrant.
8. A _____ wetting angle promotes infiltration.
a) low
b) 0°
c) 90°
d) large
Answer: a
Explanation: The dihedral angle or wetting angle at the intersection of a boundary of two grains of the solid phase and the liquid phase plays an important role in infiltration. A low wetting angle, therefore, promotes infiltration . With a dihedral angle= 0°, the infiltrant will penetrate along the grain boundaries and thus destroy the skeleton. Moreover, large dihedral angles do not lead to effective wetting.
9. The infiltration process is used to prepare ____ kinds of material.
a) Single phase materials
b) Duplex materials
c) Single phase, and duplex materials
d) Multicomponent materials
Answer: c
Explanation: The process of infiltration is used to prepare two kinds of material. single phase material which are rarely made and Duplex materials, which are of further two types: consists of those metals which exhibit complete insolubility at room temperature and infiltration temperature , and consists of those exhibiting partial solubility of skeleton metal in the infiltrant metal at infiltration temperature .
10. The process of infiltration can be depicted by the following diagram.
a) True
b) False
Answer: a
Explanation: The figure truly represents the process of infiltration, sintered part with an infiltrant slug on top, infiltration in progress, and infiltrated part.
11. Erosion of the contact surfaces of the skeleton metal can be reduced by ______ method.
a) Bridge method
b) Oil method
c) Flyover method
d) Compensation method
Answer: a
Explanation: Erosion of the contact surfaces of the skeleton metal can be reduced by bridge method in which a porous metal part is known as “bridge” is kept between the skeleton and the infiltrant. The infiltrant saturates the skeleton metal after crossing the bridge.
12. Why alloy infiltrant is used for the production of copper-infiltrated ferrous base materials?
a) Cost-saving
b) Reduce erosion of contact surfaces of the skeleton
c) Material saving
d) Variety production
Answer: b
Explanation: In infiltration erosion of contact surfaces of the skeleton metal takes place because of the dissolution of the surface layers of the skeleton metal in molten infiltrant thereby causing an undesirable pitting on the surface of the sintered component. This can be avoided by alloying the infiltrant with one or more elements in which the skeleton metal does not dissolve. Thus, for production of copper-infiltrated ferrous base materials, alloy infiltrant consists of Cu containing 5% Mn and 5%Fe is used.
13. Why infiltrated pump cylinder blocks are popular in use?
a) Mechanical strength
b) Resistance to thermal stress
c) Pressure- tightness
d) Light-weight
Answer: c
Explanation: The infiltrated parts become impermeable due to the absence of interconnected porosity and hence they can be used where pressure tightness is desired. One such example is the infiltrated pump cylinder blocks.
This set of Powder Metallurgy Multiple Choice Questions & Answers focuses on “Postsintering Secondary Operations – Sizing, Coining & Repressing”.
1. _______ involve deformation of the sintered part at room temperature.
a) Sizing and joining
b) Repressing
c) Shot peening
d) Infiltration
Answer: b
Explanation: Sintered P/M parts may need additional processing to impart certain characteristics such as improved corrosion resistance, dimensional tolerances or improved strength. Thus, P/M parts are subjected to a number of secondary operations after sintering. Sizing, repressing, and coining involve deformation of the sintered part at room temperature.
2. _______ is a post sintering operation used to correct the dimensional defects during sintering.
a) Joining
b) Infiltration
c) Sizing
d) Impregnation
Answer: c
Explanation: Sizing is a post sintering operation used to correct size, warping, distortion and other dimensional defects during sintering. It can also be used to improve the surface finish and wear properties of the surface.
3. ______ occurs when an oversize component with hole smaller than core rod is pressed into die.
a) Positive coining
b) Negative sizing
c) Negative coining
d) Positive sizing
Answer: d
Explanation: Positive sizing takes place when a larger component with a smaller hole than core rod is pressed into die. Negative sizing takes place when a small component is put into the sizing die and its hole larger than the core rod.
4. Which of the following treatment is given to a thin-walled bushing which is oversize on both inside and outside diameter?
a) Positive sizing on both inside and outside
b) Positive sizing on inside, and negative sizing on outside
c) Positive sizing on outside, and negative sizing on inside
d) Negative sizing on both inside and outside
Answer: c
Explanation: A thin-walled bushing which is oversize on both inside and outside diameter after sintering can be subjected to positive sizing on outside, and negative sizing on inside.
5. In sizing the amount of deformation is _____ and improvement in density is ______
a) Moderate, constant
b) Small, minimal
c) Minimal, zero
d) Large, significant
Answer: b
Explanation: In sizing, the amount of deformation is small and hence the force required for deformation is less in comparison to the compaction force. The forces involved in sizing are small and, therefore, the improvement in density is minimal.
6. ________ is used for adding surface patterns on to a sintered part.
a) Coining
b) Sizing
c) Plating
d) Resintering
Answer: a
Explanation: Coining is used for adding surface patterns on to a sintered part. The coining operation carried out after sintering achieves the same results as the sizing operation, but there is significant improvement in density, hardness, and strength because of higher pressures used compared to sizing.
7. Hot coining is a useful technique for ______
a) Porous bearings
b) Sintered friction material
c) Cermets
d) Electrical contact
Answer: c
Explanation: Hot coining is a useful technique for cermets. Hot coining consists in the rapid coining of a hot sintered compact directly from the sintering furnace. The bright, clean surfaces within the porous sintered compact are compressed and deformed, producing a sound, highly dense body.
8. _________ is done to reduce dimensional scatter as well as to obtain closure of surface pores.
a) Machining
b) Plating
c) Sizing
d) Repressing
Answer: d
Explanation: The primary aim of repressing is densification of the sintered part to give improved physical and mechanical properties along with dimensional tolerances. Thus, most of the P/M parts are repressed to reduce dimensional scatter as well as to obtain closure of surface pores.
9. External lubrication is not preferred for sizing, coining, and repressing.
a) True
b) False
Answer: b
Explanation: Use of external lubricants is preferred for various post sintering operations like sizing, coining, and repressing and care should be taken to avoid retention of lubricant by the part which may interfere with further operations like plating.
10. For repressing, the tool size is _____ as that of compact.
a) Different
b) Large
c) Small
d) Same
Answer: d
Explanation: For repressing, the compact and tool sizes are the same and material flow is in one direction only. With a repressing treatment, pores near the surface are sealed but internal pores remain mostly unaffected. After repressing, there is slight increase in strength with a reduction in ductility and toughness and fatigue strength improves.
This set of Powder Metallurgy Multiple Choice Questions & Answers focuses on “Postsintering Secondary Operations – Impregnation, Infiltration & Heat Treatment”.
1. Impregnation of sintered component is done using either a _______ or a ________
a) lubricant, resin
b) wax, resin
c) lubricant, aqueous medium
d) oil, wax
Answer: a
Explanation: Impregnation is the process of porosity sealing of sintered components. Impregnation of the sintered component is done using either a lubricant or a resin, the purpose is different in each case.
2. Porous bearings are impregnated with ______
a) resin
b) oil
c) wax
d) metal
Answer: b
Explanation: Porus bearings are generally impregnated with oil. The viscosity of oil prevents corrosion, the additives are used to increase film strength and to prevent oxidation.
3. What is the pressure in the vacuum chamber while carrying out oil impregnation of bearings?
a) ≈ 1mm H 2 O
b) ≈ 1mm Hg
c) ≈ 0.5mm Hg
d) ≈ -1mm Hg
Answer: b
Explanation: During impregnation, the bearings are placed in a vacuum chamber and evacuated to nearly 1mm of Hg pressure. Oil is allowed to enter into the chamber. Air or nitrogen at a pressure of 0.5 MPa is applied for 1 minute to complete the impregnation.
4. Which of the following SAE standards give deatils regarding the impregnation of porous castings and sintered metal components?
a) AMI09_3A
b) AMI05
c) AMS03_1A
d) AMS30_2A
Answer: c
Explanation: The SAE standard AMS03_1A specifies the processes and type of impregnant which can be used when impregnating castings for the following purposes: Eliminating microporosity in castings, for applications requiring pressure tightness. For sealing castings/sinter metal components to improve corrosion resistance and/or to render surface uitable for subsequent surface treatment.
5. _______ is widely practiced for valves, pumps, and compressor parts.
a) Lubricant impregnation
b) Grease impregnation
c) Oil impregnation
d) Resin impregnation
Answer: d
Explanation: Resin impregnation is used for valves, cylinder heads, pistons, pumps, and compressor housing requiring pressure tightness. Gun compnonets are typically resin impregnated to seal the pores.
6. Which of the following is not a benefit of impregnation?
a) Pressure-tightness
b) Dimensional tolerance
c) Porosity elimination
d) Improved machinability
Answer: b
Explanation: The benfits of impregnation include- self lubricating ability, Increase in mechanical properties, Pressure-tightness due to sealing off the porosity, Prevention of the entry of corrosive salts into pores during plating, and Improvement in machinability.
7. Which of the following baths are not used during heat treating P/M steel parts?
a) Oil baths
b) Water baths
c) Cyanide baths
d) Polymer quench
Answer: c
Exxplanation: While heat-treating P/M steel parts, salt baths and cyanide baths are generally not used for austenizing to avoid the possibility of trapping salt in the porous structure.
8. Which of the following quenching medium is used for quenching of P/M parts?
a) Water
b) Brine solution
c) Polymer
d) Oil
Answer: d
Explanation: The typical quenching medium used for P/M parts include plain water, brine solution and oil. However, oil is the preferred medium since it avoids cracking as well as corrosion.
9. Which of the following treatment fives a ferrito-pearlitic structure in P/M steel forgings?
a) Tempering
b) Hardening
c) Annealing
d) Nitrocarburizing
Answer: c
Explanation: The main purpose of annealing heat treatment is to obtain a ferrito-pearlitic structure which gives good machining characteristics. The temperature employed for annealing depends on the carbon content.
10. Which of the following heat treatment for sintered component is carried out in range of 500-570°C?
a) Nitrocarburizing
b) Carbonitriding
c) Carburizing
d) Gas-carburizing
Answer: a
Explanation: Nitrocarburizing treatment is carried out on sintered components at temperature between 500-570°C. Carbonitriding is usually carried out at temperatures of 790°C whereas carburizing and gas- carburizing is carried out at still higher temperature ranges of 800-900°C.
11. Which of the following process gives a case with microstructure consisting of iron carbonitride and iron nitride?
a) Carbonitriding
b) Nitriding
c) Liquid-carburizing
d) Nitrocarburizing
Answer: d
Explanation: In nitrocarburizing, the microstructure of the case consists of a thin layer of iron carbonitride and iron nitride , with a diffused layer of iron nitride, alloy nitrides and nitrogen.
This set of Powder Metallurgy Multiple Choice Questions & Answers focuses on “Postsintering Secondary Operations – Steam Treatment, Machining, Joining & Plating – 1”.
1. Which of the following process consists of heating the P/M part in air at temperature and is not as effective as steam treatment?
a) Low- temperature treatment
b) Hot treatment
c) Blowing
d) Blueing
Answer: d
Explanation: Blueing refers to heating the P/M part in air at a lower temperature to provide a thin magnetite layer that gives some increase in corrosion resistance, but this treatment is not as effective as steam treatment.
2. What is the temperature range for steam treatment process?
a) 600-700°C
b) 350-400°C
c) 500-550°C
d) 400-470°C
Answer: c
Explanation: The steam treatment process is very unique to P/M parts, and it involves exposing the part at a temperature around 500-550°C to high pressure steam. The steam reacts with the outer surface as well as the inner surfaces of the open pores exposed to the steam.
3. ________ layer forms during steam treatment.
a) Oxide
b) Hydride
c) Carbide
d) Nitride
Answer: a
Explanation: Steam treatment of P/M parts leads to the formation of a layer of magnetite on all accessible surfaces. The oxide layer so formed increases the surface hardness and particularly the wear resistance of the part.
4. Steam treatment is not applicable for ________
a) normalized parts
b) hardened and tempered parts
c) annealed parts
d) stress relived parts
Answer: b
Explanation: Seam treatment is not generally applicable to hardened and tempered powder metallurgical parts because the exposure to high temperatures will result in over tempering of the parts.
5. _________ of P/M parts is carried out to add holes, threads, undercuts, grooves.
a) Joining
b) Plating
c) Machining
d) Impregnation
Answer: c
Explanation: Machining of P/M parts is carried out to add holes, threads, undercuts, grooves as well as special features that cannot be incorporated into the die design. When holes at an angle to the direction of pressing or tapped holes are needed, machining is done.
6. Which of the following P/M part exhibit a short cutting tool life?
a) Sintered
b) Porous
c) Dense
d) Very dense
Answer: b
Explanation: The presence of porosity alters the machining characteristics thus porous powder metallurgical part exhibit a low-thermal conductivity and hence the cutting tool life is short due to heat erosion.
7. The stress at the cutting tool tip while machining porous parts is ________
a) cyclic
b) non-cyclic
c) constant
d) linear
Answer: a
Explanation: The stress at the cutting tool tip while machining porous parts is cyclic this is because the tool is stressed while in contact with solid and stress is relieved in contact with a pore.
8. Which type of failure occurs due to cyclic loading?
a) Plastic
b) Creep
c) Fatigue
d) Ductile
Answer: c
Explanation: The stress at the tip of the cutting tool while machining porous parts is cyclic and this cyclic loading leads to fatigue failure of the tool. This fatigue failure becomes more prominent when the pores are open and connected.
This set of Powder Metallurgy Multiple Choice Questions & Answers focuses on “Postsintering Secondary Operations – Steam Treatment, Machining, Joining & Plating – 2”.
1. Which of the following additive is added to improve the tool life of steel parts?
a) Copper
b) Bismuth
c) Lead
d) Sulphur
Answer: d
Explanation: The machinability can be improved by incorporating certain additions in powder mix like lead, copper, graphite, sulphur or a metal sulphide. Sulphur is added to improve the tool life and surface finish of P/M steel parts by mixing it in powder compact.
2. What is added to brass to improve the machining of parts made by brass?
a) Copper
b) Lead
c) Bismuth
d) Tin
Answer: b
Explanation: The addition of lead to brass improves the machining of the parts made by brass. These additions are incorporated to improve machinability, as these additives tend to coat the cutting tool and provide lubrication.
3. Which kind of porosity leads to longer tool life?
a) Very high
b) Very low
c) Either very high or very low
d) Moderate
Answer: c
Explanation: Longer tool life is achieved when the porosity is either very high or very low because the material hardness and residual porosity also affect the tool life. For very low-density parts, tool life may be improved by infiltrating the pores with a low-melting metal before machining.
4. Which of the following tool control systems is now widely used?
a) Multi-axis computer-controlled tool control system
b) Multi-lines computer-controlled tool control system
c) Multi-plane computer-controlled tool control system
d) Multi-surface computer-controlled tool control system
Answer: a
Explanation: The Multi-axis computer-controlled tool control system is now recently used tool control system which enables high-precision fabrication of P/M parts free from cracks and machining of components with the most intricate geometry.
5. Which of the following process is used for removing any ‘rag’ on edges?
a) Derigging
b) Defragging
c) Deluding
d) Deburring
Answer: d
Explanation: Deburring is a process done with sintered parts for removing any ‘rag’ on edges, resulting from the compacting operation or a machining step.
6. Which of the following metal joining process is not applicable for P/M parts?
a) GTAW
b) Extrusion welding
c) Friction welding
d) Laser beam welding
Answer: b
Explanation: The major metal joining processes applicable for P/M parts include resistance projection welding, gas tungsten arc welding , gas metal arc welding, electron beam welding, laser beam welding and friction welding.
7. Electrical resistance welding is preferred over oxyacetylene and arc welding for joining P/M parts.
a) True
b) False
Answer: a
Explanation: Electrical resistance welding is preferred over oxyacetylene and arc welding for joining P/M parts. This is done to avoid the possibility of oxidation of the interiors of the porous P/M parts by oxyacetylene and arc welding processes.
8. Porous parts must be resin impregnated before plating.
a) True
b) False
Answer: a
Explanation: The porous parts must be resin impregnated prior to plating to seal the micro pores to protect from invasion and entrapment. Resin impregnation discards porosity and bleedout.
This set of Powder Metallurgy Multiple Choice Questions & Answers focuses on “Products – Porous Bearings and Types – 1”.
1. What is the pore volume in bearing materials?
a) 14-20%
b) 17-30%
c) 11-50%
d) 28-43%
Answer: b
Explanation: The bearing materials fall under the category of porous components produced by powder metallurgical route. The bearing material contain a pore volume of between 17% and 30%.
2. Which of the following substance is added to iron powder to improve the compressive strength of bearing?
a) Bismuth
b) Zinc
c) Copper
d) Lead
Answer: c
Explanation: Copper is added to the iron powders for improving the compressive strength of the P/M bearings. Iron is used for low-cost bearings, majorly used in automotive applications, farm equipment, and machine tools.
3. Which of the following is not a characteristic of the bearings produced from iron?
a) Good wear resistance
b) High-oil-volume capacity
c) High porosity
d) Low-oil-volume capacity
Answer: d
Explanation: Low-oil-volume capacity is not a characteristic of the bearings produced from iron. The iron material used for production of P/M bearings have a relatively low-limiting value of V in the PV factor, but have high-oil-volume capacity due to the high porosity. They have good wear resistance and are used with hardened and ground steel shafts for heavy and shock loads.
4. Copper is added to iron-copper-graphite powder mix to suppress the formation of ________
a) Cementite
b) Iron oxide
c) Copper oxide
d) Ledeburite
Answer: a
Explanation: The addition of free carbon in iron-copper mix makes it heat-treatable but in case of iron-graphite mix, formation of cementite occurs leading to poor bearing properties. Thus, addition of copper serves to suppress the formation of cementite and makes iron-copper-graphite amenable to heat treatment.
5. What should be added to the iron powder mix to improve the speed capability?
a) Bismuth
b) Lead
c) Vanadium
d) Molybdenum
Answer: b
Explanation: The addition of lead to iron improves the speed capability and even reduces cost. This material so produced for production of P/M bearing is called leaded iron.
6. Which of the following is not a feature of oil-impregnated bearings?
a) Excellent self-lubrication properties
b) Wide range of operating temperature
c) High-thermal expansion
d) Low-thermal expansion
Answer: c
Explanation: The important features of oil-impregnated bearings include: excellent self-lubrication properties, wide range of operating temperature , low-thermal expansion, no water absorption, extended bearing life in severe environments with no need for external manual lubrication, and silent operation.
7. Dry bearing is made up of ______ with metal backing of _______ is available.
a) teflon, aluminum
b) aluminum, teflon
c) leaded bronze, aluminum
d) teflon, bismuth
Answer: a
Explanation: Dry bearings are made from metallic alloys or from fluoropolymer and with metal backing of aluminum and bronze-steel. This bearing material is soft enough to handle interference fits with minimal stick-slip and a low coefficient of friction.
8. Which kind of bearing material is suitable for oscillating and reciprocating motions?
a) Low-graphite content
b) High graphite content
c) High-oil content
d) High porosity
Answer: b
Explanation: A bearing material with low-oil content, with high graphite content and low-porosity is suitable for oscillating and reciprocating motions.
9. What is the property of material for the application of fractional-horsepower motor bearings?
a) Moderate porosity
b) Low porosity
c) Minimum lubricating oil
d) High porosity
Answer: d
Explanation: The material which has high porosity that is which has the more pore volume which also has a maximum amount of lubricating oil is used for fractional-horsepower motor bearings.
10. The porous-metal bearings are used where re-lubrication is difficult.
a) True
b) False
Answer: a
Explanation: Most porous-metal bearings are made of either bronze or iron, with 10 to 35 vol% interconnected voids or porosity. In operation, lubricating oil stored in these pores feed the bearing surface through these interconnected pores, when the temperature increases during operation. Any oil, which is forced from the loaded zone of the bearing, is later reabsorbed by the pores through capillary action. Since these bearings can operate for long periods of time without additional supply of lubricant, they are convenient to be used where re-lubrication is difficult.
11. P/M bearings may be of the type ____________
a) dry type containing aluminum
b) porous type infiltrated with a lubricant
c) dry type containing teflon
d) porous type infiltrated with a lubricant, dry type containing teflon
Answer: d
Explanation: P/M bearing materials are characterized by multiphase structures. These include two-phase alloys, immiscible components like plastics as well as lubricants. P/M bearings may be porous type infiltrated with a lubricant or dry type containing teflon or graphite.
This set of Powder Metallurgy Question Bank focuses on “Products – Porous Bearings and Types – 2”.
1. What is the PV value for thrust bearings?
a) 10,000
b) 50,000
c) 20,000
d) 30,000
Answer: a
Explanation: The performance factor or PV value for thrust bearings is 10,000 whereas in the case of a porous bearing, a PV value of 50,000 is usually specified.
2. The load carrying capacity of bearing is expressed as the _______
a) efficiency factor
b) work factor
c) performance factor
d) capability factor
Answer: c
Explanation: The performance factor is used to express the load carrying capacity of the bearings. The load carrying capacity of porous-metal bearings is usually measured based on the friction/wear criterion, which signifies the heat generated by the bearing.
3. Which of the following is not a characteristic of a P/M bearing material?
a) Ability to withstand both static and impact loads
b) Good wear characteristics
c) Good heat dissipation capacity
d) Short service life
Answer: d
Explanation: The important requirements of a P/M bearing materials are: good lubrication characteristics with minimum maintenance and long service life, adequate mechanical strength, good wear characteristics, good heat dissipation capacity, ability to withstand both static and impact loads, and must not weld/seize with the mating parts during service.
4. ________ type of porosity serves no purpose and must be minimized.
a) Moderate
b) Open
c) Closed
d) Interconnected
Answer: c
Explanation: Closed porosity refers to the amount of isolated or closed pores within the material. These pores do not serve any useful purpose and must be minimized.
5. Which type of porosity is connected to one another and to the external surface?
a) Moderate
b) Open
c) Closed
d) Interconnected
Answer: d
Explanation: Interconnected porosity refers to that fraction, which are connected to one another and to the external surface. The main feature of these bearings is that the presence of interconnected pores enables flow of fluids to flow through these pores.
6. _______ is obtained by subtracting the density of the material from 100.
a) Hardness
b) Porosity
c) Specific gravity
d) Ductility
Answer: b
Explanation: Porosity is usually expressed as a percentage and is obtained by subtracting the density of the material from 100. The pores represent the open volume in a given material and can be classified as closed and interconnected porosity.
7. _________ is possible only with the help of a pump during starting.
a) Hydrostatic lubrication
b) Boundary film lubrication
c) Hydrodynamic lubrication
d) Aerodynamic lubrication
Answer: c
Explanation: Hydrodynamic lubrication is one of the mechanisms through which the lubricant operates. This mechanism is possible only with the help of a pump during starting. It is highly desirable, since the hydrodynamic pressure developed by the relative movement of the bearing and the shaft will enable the bearing to carry the applied load without contact between the bearing and the shaft.
8. Under which of the following mechanisms the bearing performance depends on the ability of the lubricant to maintain a boundary film under load?
a) Hydrostatic lubrication
b) Boundary film lubrication
c) Hydrodynamic lubrication
d) Aerodynamic lubrication
Answer: b
Explanation: The mechanism in which part of the entire load is also carried by the sliding contact between the bearing and the shaft furnaces, which is separated by a thin film of lubricant is known as boundary film lubrication. In this case, the bearing performance depends on the ability of the lubricant to maintain a boundary film under load.
9. The performance factor is given by ______
a) PV
b) VF
c) AV
d) FA
Answer: a
Explanation: The load carrying capacity of the bearing is expressed as the performance factor given by PV. This factor is expressed in lb/in 2 .ft/min, is obtained by multiplying pressure (lb/in 2 ) on the projected area by the peripheral or surface or rubbing speed .
10. Which of the following is not a type of bearing?
a) Steel backed steel
b) Teflon bearing
c) Babbit backed steel
d) Unbacked bearings
Answer: c
Explanation: The various type of bearings available are: Steel backed materials with non-porous sintered lining, Steel backed materials with porous sintered lining, Unbacked porous sintered metallic parts impregnated with oil, Unbacked porous sintered metallic parts containing graphite as a dry lubricant, and Teflon bearing.
This set of Powder Metallurgy Multiple Choice Questions & Answers focuses on “Production of Sintered, Non Porous Bearings and Composition”.
1. For bronze bearings, the amount of shrinkage _______ as the particle size of powder mix decreases.
a) decreases
b) increases
c) constant
d) moderate
Answer: b
Explanation: In the production of bearings by P/M route, powder characteristics like particle size and distribution, and particle shape play an important role. In the bronze bearings, decrease in the particle size of elemental tin or copper powder increases the amount of shrinkage.
2. Which of the following material on addition to the powder mix lowers the strength of the bearing?
a) Oil
b) Lead
c) Bismuth
d) Graphite
Answer: d
Explanation: The addition of graphite improves lubrication but also results in growth and lowers the strength of the bearings. Lubricants used in the mix have significant effect on the apparent density and flow rate but very little influence on the dimensional change.
3. Which of the following bearing doesn’t belong to the class of non-porous bearing with steel backing?
a) Copper-antimony alloy
b) Aluminum based alloy
c) Copper based alloy
d) Babbit
Answer: a
Explanation: The major types of bearings which belong to the class of non-porous bearing with steel backing include: aluminum-based alloy, copper-based alloy, and babbits. Bronzes and aluminum alloys are more common than babbits because of their higher load carrying capacity.
4. Which of the following powder production method is used for the production of non-porous bearing with steel backing?
a) Mechanical alloying
b) Gas atomization
c) Water atomization
d) Electrolysis
Answer: b
Explanation: The pre-alloyed powders for the production of non-porous bearing with steel backing are manufactured by gas atomization. In this process the molten metal stream is disintegrated using high velocity argon, nitrogen or helium gas jets and the atomized powders are collected in a water bath.
5. Lower lead content in copper-lead alloy is undesirable.
a) True
b) False
Answer: a
Explanation: Copper with 30wt% and 40wt% lead is commonly used for production of bearings. Lower lead content gives better strength but poor surface characteristics whereas higher lead contents ensure better lubrication.
6. What should be amount of tin in copper-lead alloy containing 25% lead for production of non-porous bearing?
a) 14 – 20wt%
b) 4 – 10wt%
c) 1 – 5wt%
d) 11 – 15wt%
Answer: b
Explanation: The amount of tin in copper-lead alloy containing copper with up to 25% lead for production of non-porous bearing is 4 – 10wt%. Addition of tin not only improves the strength but also increases the seizure resistance, and oil corrosion is reduced.
This set of Powder Metallurgy Multiple Choice Questions & Answers focuses on “Production of Porous Bearings – 1”.
1. _______ are bearings containing bronze or iron powder mixed with graphite.
a) Hydrocarbon impregnated
b) Oil impregnated
c) Plastic impregnated
d) Metal impregnated
Answer: b
Explanation: The production of porous bearings involves its infiltration with either oil or plastic. Oil impregnated bearings are typically bearings containing bronze or iron powder mixed with graphite.
2. Tin powder is made by _________
a) Atomization
b) Electrolysis
c) Reduction
d) Cold stream process
Answer: a
Explanation: For the production of porous bearings of tin by powder metallurgical route involves production of tin powder by atomization. It consists of mechanically disintegrating a stream of molten metal into the fine particles by means of jet of compressed air, inert gases or water.
3. _______ base bearings, atomized or reduced powders are employed.
a) Bismuth
b) Bronze
c) Iron
d) Tin
Answer: c
Explanation: For iron base bearings, atomized or reduced powders are employed. Powders of bronze base bearings use elemental copper made by electrolytic, atomized or reduction route whereas tin powder is made by atomization.
4. Mixing of elemental powder is essential prior to compaction.
a) True
b) False
Answer: a
Explanation: Mixing of elemental powder is essential prior to compaction. For making bronze bearings, copper powder is mixed with tin and graphite powders and thus it is important to ensure through mixing to avoid segregation of tin particles during sintering resulting in non-uniform sintering.
5. Green density distribution is an important factor for production of porous bearings.
a) True
b) False
Answer: a
Explanation: Green density distribution is an important factor for production of porous bearings because uneven green density distribution may cause non uniform sintering or poor oil impregnation.
6. What is the compaction pressure range used for bronze bearings?
a) 775-1000 MPa
b) 500-800 MPa
c) 275-480 MPa
d) 200-300 MPa
Answer: c
Explanation: The mixed powders are compacted to the required dimensions using automated compaction presses. Pressures used for bronze bearings are in the range of 275 to 480 MPa. For iron parts, higher pressures are employed.
7. The microstructure of sintered copper base self-lubricating bearing consists of ________
a) pores
b) graphite particles
c) alpha phase, graphite particles
d) alpha phase, graphite particles, and pores
Answer: d
Explanation: The copper base self-lubricating bearing consists of copper + tin + graphite powders. Thus, the final microstructure after sintering shows a three-phase structure consisting of homogenous alpha phase with graphite particles and pores distributed uniformly in the matrix.
8. Which of the following atmosphere is used for the sintering of bronze bearings?
a) Reducing
b) Oxidizing
c) Protective
d) Vacuum
Answer: a
Explanation: The sintering of bronze bearings is carried out in continuous mesh-belt furnaces under a reducing atmosphere. During sintering, the lubricants are driven off at a temperature between 400 and 450°C, and the low melting Sn powders melt and diffuse into copper matrix.
9. Iron base bearings are sintered at _______
a) 1500-1800°C
b) 900-1000°C
c) 800-850°C
d) 1100-1125°C
Answer: d
Explanation: The sintering of iron base bearings is carried out in the temperature range of 1100-1125°C for 15 minutes, and bronze bearings are sintered in temperature range of 800-850°C for 5-8 minutes.
10. ______ is carried out after sintering of self-lubricating bearings.
a) Sizing
b) Impregnation
c) Plating
d) Joining
Answer: a
Explanation: All self-lubricating bearings are ‘sized’ after sintering to control the dimensions within the allowed tolerances to enable smooth operation of the porous bearings, which require suitable clearance between shaft and housing.
This set of Powder Metallurgy Questions and Answers for Entrance exams focuses on “Production of Porous Bearings – 2”.
1. Resin impregnation of porous bearings makes them _________
a) heat-treatable
b) non-heat treatable
c) reduces density
d) weak
Answer: b
Explanation: Resin impregnation of porous bearings involves the use of polymers such as Teflon or polyacetal to fill up the interconnected pores. This treatment improves the density of the parts significantly but renders parts non-heat treatable.
2. Oil impregnation of porous bearings is done for _____ minutes.
a) 80
b) 50
c) 30
d) 70
Answer: c
Explanation: After the sizing operation, the bearings are impregnated with the lubricant. Oil impregnation can be done using immersion in hot oil at 80 to 1000C for 30 minutes. Longer impregnation times, oxidation of oil at high temperature are the limitations of this technique.
3. Which of the following is an alternative to the immersion technique for impregnation of porous bearings?
a) Reducing impregnation
b) Grease impregnation
c) Oxidizing impregnation
d) Vacuum impregnation
Answer: d
Explanation: The most widely used technique as an alternative to the immersion technique for impregnation of porous bearings is the vacuum impregnation. In this method, the sintered parts are placed in a basket and subjected to vacuum to remove all the moisture and air trapped within the pores. The oil is then introduced into the chamber and allowed to enter the pores.
4. ________ bearing is used where soft journal is employed.
a) Brass bearings
b) Aluminum bearing
c) Lead bronze
d) Straight tin bronze
Answer: c
Explanation: Lead bronzes have lower strength compared to tin bronzes and thus used where soft journal is employed but their performance in dry and water lubrication is superior.
5. The life of aluminum bearings is ________
a) 35 hours
b) > 200 hours
c) 7 hours
d) < 160 hours
Answer: b
Explanation: The life of aluminum bearings is > 200 hours whereas that of bronze and babbit bearings are 35 and 7 hours respectively.
6. Which of the following conditions are necessary for the development of fluid film in porous bearings?
a) Viscosity
b) High speed
c) Low speed
d) High speed and viscosity
Answer: d
Explanation: For boundary film lubrication, the performance of a bearing depends upon the ability of fluid film to carry load. Thus, for the development of fluid film, higher speed and viscosity are essential in the porous bearings than that in solid sintered bearings.
7. The loss of oil occurs from the _____ in a cylindrical bearing.
a) top
b) cylindrical surface
c) ends
d) bottom
Answer: c
Explanation: The pressure under which lubricant circulates around the shaft leads to expulsion of part of the oil from the free surface. In a cylindrical bearing, the loss of oil usually occurs from the ends.
8. Which of the following factors determine the rate of circulation of oil in oil-impregnated bearings?
a) Permeability of the porous bearing
b) Viscosity of the oil
c) Temperature
d) Permeability of the porous bearing, and viscosity of the oil
Answer: d
Explanation: The rate of circulation of oil in oil-impregnated bearings is measured by the permeability of the porous bearing, and viscosity of the oil. The permeability is determined by the pore size and the quantity of the porosity while the viscosity depends on the choice of the correct oil.
9. The temperature of oil should not be _______ than the proper running temperature.
a) lower
b) higher
c) equal
d) very low
Answer: b
Explanation: When the oil is kept at a proper running temperature, its performance will be optimum. If it is heated to a higher temperature above the normal, then physical and chemical changes will take place which will have an adverse effect on the properties of the oil.
10. The running temperature of the oil affects the ______
a) bearing performance
b) bearing life and performance
c) bearing life
d) bearing dimensions
Answer: b
Explanation: The running temperature of the oil affects the bearing performance and life. The bearing life can be determined by the oil losses and renewing ability considering the oil within the bearing or reservoir.
This set of Powder Metallurgy Multiple Choice Questions & Answers focuses on “Products – Testing and Applications of Bearings”.
1. The radial crushing strength of a bearing is given by _______
a) P=KLT 2 /
b) P=KLT 2 /
c) P=KDT 2 /
d) P=KLT 3 /
Answer: a
Explanation: The radial crushing strength of a bearing is given by P=KLT 2 / where P=radial crushing load , K=strength constant, L=length of the bearing , D=outer diameter of the bearing , and T=wall thickness of the bearing.
2. The ratio of interference to bore closure doesn’t rely on ______
a) density of bearing
b) rigidity of housing
c) density of shaft
d) strength of bearing
Answer: c
Explanation: The ratio of interference to the ‘close in‘ of the bore relies on rigidity of the housing, bearing wall thickness and strength and density of the bearing.
3. ________ clearance for higher PV values are required.
a) Small
b) Large
c) Moderate
d) Nil
Answer: b
Explanation: Proper running clearance for bearing depends to a large extent on the particular application. Thus, large clearance is required for higher PV values, and small clearance is employed for high speed applications of light duty bearings.
4. __________ is used in food industries.
a) P.T.F.E bearing
b) Non-porous bearing
c) Infiltrated bearing
d) Dry-lubricated bearing incorporating graphite
Answer: c
Explanation: The importance of infiltrated bearings or self-lubricating bearings lies in the fact that they are useful where external lubrication is difficult or is to be avoided and thus, they are used in food industries. Other applications include fractional horse power motors used in electric fans, sewing machines, food mixers, and office equipment.
5. _________ are employed in gearboxes.
a) Copper-lead bearings
b) Lead-tin alloy
c) Self-lubricating bearing
d) Infiltrated bearing
Answer: a
Explanation: Copper-lead bearings are employed in automotive applications and for low duty applications in compressor and gearboxes.
6. Overlay layer of lead-tin alloy on copper-lead alloy has reduced fatigue properties.
a) True
b) False
Answer: b
Explanation: The copper-lead bearing alloys having an overlay layer of lead or lead-tin alloy are used for heavy duty applications because this overlay confers excellent fatigue properties to the bearing besides improving anti-seizure characteristics and corrosion resistance to oil.
7. _________ are used in hot water circulating pump.
a) P.T.F.E bearing
b) Non-porous bearing
c) Infiltrated bearing
d) Dry-lubricated bearing incorporating graphite
Answer: d
Explanation: Dry-lubricated bearing incorporating graphite are used in hot water circulating pump. The production of such bearing involves blending the metal powder and fine natural graphite, compacting in mechanical or hydraulic presses, sintering and finally recompacting at higher temperature. Other applications include: in pumps handling styrene for chemical industry, in loom for the textile industry.
8. Which of the following is not a feature related to the P.T.F.E material for bearings?
a) Low coefficient of friction
b) Sintering temperature is 90°C
c) Sintering temperature is 900°C
d) Chemical stability from -200°C up to 300°C
Answer: c
Explanation: P.T.F.E, a plastic, has an extremely low coefficient of friction , apparent density of between 0.51-0.57 g/ml, possess chemical stability from -200°C up to 300°C in the presence of most corrosive agents and is available as a powder which can be compacted, sintered or hot pressed or hot extruded or hot rolled into large piece components. The sintering is done at 90°C in air for about 90 minutes.
9. Which of the following is a drawback of the P.T.F.E material for bearings?
a) High thermal expansion
b) High thermal conductivity
c) High shear strength
d) Non-toxic
Answer: a
Explanation: The major drawbacks of the P.T.F.E material for bearings are- low shear strength which restricts the bearing load, high thermal expansion, low thermal conductivity which results in an inability to dissipate heat developed at the bearing surface, toxicity of inhaled fumes or dust, and the use of solid P.T.F.E bearings is limited to below 200°C.
10. Which of the following are methods for impregnating the metallic matrix with P.T.F.E, according to Blainey?
a) Hot pressing
b) Hot rolling, and aqueous impregnation
c) Hot rolling
d) Hot pressing, and aqueous impregnation
Answer: d
Explanation: According to Blainey, two methods namely hot pressing, and aqueous impregnation can be commonly used for impregnating the metallic matrix with P.T.F.E. The former method consists in placing a P.T.F.E sheet on the porous metal, and extruding the plastic into the pores under the simultaneous action of both heat and pressure.
11. Which of the following is the limitation of aqueous impregnation method?
a) Easy to get a penetration depth > 0.01”
b) Suitable for flat sheets only
c) Suitable for curved sections only
d) No loss of P.T.F.E by extrusion
Answer: b
Explanation: The limitations aqueous impregnation method includes: It is very difficult to get a penetration depth >0.01”. Suitable for flat sheets only. Bulk of P.T.F.E may be lost by extrusion around the porous metal strip.
12. The performance of P.T.F.E /metal bearings largely depends on _________
a) Base material
b) Compacting pressure
c) Journal material
d) Sintering temperature
Answer: c
Explanation: The performance of P.T.F.E/metal bearings is largely dependent on the journal material. The table below shows the effect of sleeve material on the performance of P.T.F.E-impregnated thrust washers which suggests that the bearing life increases with lowering of PV values.
Sleeve Material PV=20,000 PV=40,000
Mild Steel 50 25
Sintered Cu-Pb 10 3
13. DQ and DQ 2 are the two types bearings produced by Glacier Metal Co. Ltd. by dispersing brass and Pb respectively.
a) True
b) False
Answer: b
Explanation: Glacier Metal CQ. Ltd. has produced bearing materials consisting of dispersed metal powder by 20% volume within the P.T.F.E matrix which not only improves the strength and performance but thousand-fold improvement in wear resistance occurs. These are of two types- DQ and DQ 2 .
This set of Powder Metallurgy Multiple Choice Questions & Answers focuses on “Atomization and Types”.
1. Which of the following powder production technique involves the use of high-pressure fluid jets?
a) Electrolysis
b) Reduction
c) Atomization
d) Cold stream process
Answer: c
Explanation: Atomization involves the use of high-pressure fluid jets to break up a molten metal stream into very fine droplets, which then solidify into fine particles. Now, high-quality powders of Al, brass, iron, stainless steel, tool steel and superalloys are produced by commercially by atomization in bulk quantities.
2. ______ is used in atomization of metals.
a) Hydrogen
b) Compressed air
c) Inert gas
d) Water jet
Answer: d
Explanation: Water jets are used in atomization of metals due to their higher viscosity and superior quenching ability. However, this technique is limited to metals or alloys that do not chemically react with water.
3. ________ technique uses high-pressure water jets.
a) Vacuum atomization
b) Water atomization
c) REP process
d) Rotating disk atomization
Answer: b
Explanation: The process which uses high-pressure water jets to bring about the disintegration of molten metal steam is called water atomization. The process is inexpensive and can be used both for small and large-scale production.
4. ________ technique uses high velocity argon, nitrogen or helium gas jets.
a) Centrifugal atomization
b) Gas atomization
c) REP process
d) Rotating disk atomization
Answer: b
Explanation: In gas atomization, the molten metal stream is disintegrated using high velocity argon, nitrogen or helium gas jets and the atomized powder is collected in a water bath. This process is costlier than water atomization.
5. Vacuum atomization is also known as _________
a) RSP
b) Ultrasonic atomization
c) Soluble gas atomization
d) REP
Answer: c
Explanation: Vacuum atomization is also known as soluble gas atomization, uses the principle that when a molten metal supersaturated with a gas under pressure is suddenly exposed to vacuum, the gas coming out of the metal solution expands rapidly, causing atomization of the metal stream.
6. REP is also known as _________
a) Centrifugal atomization
b) RSP
c) Rotating disk atomization
d) Ultrasonic atomization
Answer: a
Explanation: REP i.e. Rotating Electrode Process is also known as centrifugal atomization, this process involves use of centrifugal force to break off molten metal drops from the molten end of a consumable electrode.
7. ______ gas is used for vacuum atomization process.
a) Argon
b) Nitrogen
c) Helium
d) Hydrogen
Answer: d
Explanation: For vacuum atomization process, hydrogen gas is used. Moreover, when hydrogen atoms come out of the solution and recombine, substantial amount of energy is released which not only disperses the metal stream but also increases the temperature at the hydrogen-metal interface thereby producing finer powders.
8. Spherical shaped particles are produced by centrifugal atomization.
a) True
b) False
Answer: a
Explanation: In this process, one end of the metal bar is heated and melted by bringing it in contact with a non-consumable W electrode or a transferred arc plasma torch, while rotating it longitudinally at high speeds. The centrifugal forces cause the metal droplets to be thrown off outwards, which then solidify as spherical-shaped particles inside an evacuated chamber.
9. ________ falls under the category of RSP.
a) Centrifugal atomization
b) REP
c) Rotating disk atomization
d) Ultrasonic atomization
Answer: c
Explanation: Rotating disk atomization process falls under the category of Rapid Solidification Process techniques, where, because of high cooling rates involved, the solidification time is reduced. The other advantages include: reduced tendency for chemical segregation, very fine microstructural features like grain size, increased solid solubility od alloying elements, and formation of novel phases.
10. _______ process involves the use of rapidly spinning disk for powder production.
a) RSP
b) Ultrasonic atomization
c) Rotating disk atomization
d) REP
Answer: c
Explanation: Rotating disk atomization, collide with a stream of molten metal onto the surface of fastly spinning disk. This results in the mechanical atomization of metal stream and results in the droplets to be thrown off the edges of the disk. The particles are generally spherical and their sizes decrease with increasing disk speed.
11. Which of the following process can achieve a solidification rate > 1000°C/s?
a) Ultra-rapid solidification process
b) REP
c) Rotating disk atomization
d) Ultrasonic atomization
Answer: a
Explanation: Ultra-rapid solidification process can achieve a solidification rate of over 1000°C/s, which prevents diffusion of atoms in the material as it is quenched. This results in enhanced chemical homogeneity, formation of metastable crystalline phases, supersaturated phases as well as amorphous materials.
This set of Powder Metallurgy Multiple Choice Questions & Answers focuses on “Atomization Unit Advantages – 1”.
1. Which of the following is not an advantage of atomization process?
a) Cleanliness
b) Processing capability
c) Reduced versatility
d) Productivity
Answer: c
Explanation: The major advantages of atomization process include: processing capability, freedom to alloy, cleanliness, versatility, and productivity.
2. Atomization process is used for production of metal powders of very high melting point.
a) True
b) False
Answer: b
Explanation: Atomization is suitable for producing powders of pure metals and alloys whose melting point is not very high. Very high temperature materials such as W, Mo, and Hf are not usually produced by atomization.
3. Which of the following are major components of atomization set-up?
a) Melting, atomization chamber
b) Melting, atomization chamber, dry collection
c) Melting and superheating facility
d) Melting, atomization chamber, collection tank
Answer: d
Explanation: The major components of a typical atomization set-up include: Melting and superheating facility, Atomization chamber, and Powder collection tank which is further of two types- dry collection and wet collection.
4. Complex alloys are melted by ________
a) Vacuum induction melting
b) Vacuum melting
c) Air melting
d) Inert gas melting
Answer: a
Explanation: Any of the standard furnaces can be used for producing the liquid metal. This is accomplished by air melting, inert gas or vacuum induction melting. Complex alloys which are highly susceptible to contamination are usually melted in vacuum induction furnaces.
5. The atomization chamber consists of _______
a) Nitrogen
b) Tundish
c) Atomizing atmosphere
d) Atomizing nozzle system
Answer: d
Explanation: The atomization chamber consists of an atomizing nozzle system. The nozzle, is usually located at the base of the tundish, controls the shape and size of the metal stream.
6. Which gas is used for purging the atomization chamber?
a) Oxygen
b) Nitrogen
c) Hydrogen
d) Helium
Answer: b
Explanation: The atomization chamber is purged with nitrogen gas to minimize the oxidation of the powder produced by high-velocity atomizing medium issuing out of the nozzle, which breaks the molten stream into very fine droplets, which cool and solidify as they settle at the bottom of the chamber.
7. _______: where particles solidify before the reach the bottom of the tank.
a) Top collection
b) Wet collection
c) Dry collection
d) Bottom collection
Answer: c
Explanation: Dry collection refers to a type of collection where the particles solidify before they reach the bottom of the tank. Thus, the collection tank should have sufficient height to ensure complete solidification of the particles before they fall to the bottom.
8. In ________ the collection of powder is done in a water tank.
a) Hydrated collection
b) Wet collection
c) Water collection
d) Dry collection
Answer: b
Explanation: In wet collection, the powder is collected in a water tank provided at the bottom of the atomization unit. The tank may be cooled externally when large quantities of powders are produced. The powders are then dried to remove the moisture.
This set of Powder Metallurgy Question Paper focuses on “Advantages and Atomization Unit – 2”.
1. The ________ and __________ influence the shape and size of the atomized particles.
a) Cooling conditions, surface energy
b) Cooling conditions, pressure
c) Cooling conditions, surface tension forces
d) Surface tension, volume
Answer: c
Explanation: The prevailing cooling conditions and surface tension forces on the surface of the droplets influence the shape and size of the atomized particles. Thus, fine particles are formed slightly below the point where the fluid jet strikes the liquid.
2. Which of the following factors control the average particle size, for a given nozzle design?
a) Pressure of the atomizing medium
b) Reflex angle between the axes of the gas jets
c) Pressure of the atomizing medium, reflex angle between the axes of the gas jets
d) Pressure of the atomizing medium, apex angle between the axes of the gas jets
Answer: d
Explanation: The average particle size of a nozzle design is controlled by the pressure of the atomizing medium as well as by the apex angle between the axes of the gas jets. Higher apex angles lead to smaller particle sizes.
3. The results of designs used for free fall atomization are difficult to reproduce by _________
a) True
b) False
Answer: a
Explanation: The apex angle for the water atomization is smaller than that for gas atomization. Thus, the results used for free-fall atomization for making spherical and fine powders are difficult to reproduce with water atomization. Moreover, water atomization is also limited to metal or alloys from which the surface oxide can be easily removed by mechanical or chemical method.
4. Which of the following are the types of nozzles used in atomization process?
a) Annular type
b) Discrete jet
c) Annular and discrete jet type
d) Concentric type
Answer: c
Explanation: The nozzles that are used in atomization process are either annular type or discrete jet type. Nozzles are available in ‘free-fall’ or ‘confined’ designs.
5. _______ type of nozzle is used in water atomization.
a) Concentric
b) Free-fall
c) Multiple-jet
d) Annular
Answer: b
Explanation: The free-fall type of nozzle is used in water atomization. In free-fall atomization, the liquid metal issuing from the tundish falls freely under gravity to a certain distance and then comes into contact with the atomization medium and gets disintegrated.
6. ________ type of nozzle design is used frequently in gas atomization.
a) Confined
b) Free-fall
c) Multiple-jet
d) Concentric
Answer: a
Explanation: In confined design used with annular gas jets, atomization occurs at the exit of the tundish nozzle. This design is used in gas atomization systems. Confined atomization has higher efficiency however, ‘freeze-up’ of metal in the nozzle may occur if the design is not proper.
7. ________ gas is produced from fractional distillation of natural gas.
a) Nitrogen
b) Argon
c) Helium
d) Boron
Answer: c
Explanation: The helium gas is produced from fractional distillation of natural gas and it is the most expensive gas too. The nitrogen gas and the argon gas both are produced from the fractional distillation of air.
8. Oil atomization is not suitable for __________
a) bearing steel
b) high speed steel
c) high carbon steel
d) low-carbon steel
Answer: d
Explanation: Oil atomization is suitable for producing powders of high-carbon steel, high-speed steels, bearing steels, and for steels containing high quantities of carbide forming elements such as Cr and Mo. But it is unsuitable for producing powders of low carbon steels. A low temperature heat treatment in a protective atmosphere is necessary to remove the excess oil from the powders.
9. __________ is successfully used as an atomizing medium in place of water and gas.
a) air
b) synthetic oil
c) nitrogen
d) argon
Answer: b
Explanation: Synthetic oils have been successfully used as an atomizing medium in place of water or gas. Use of oil combines the advantages of a high-quenching rate and lower oxygen content as compared to water-atomized particles.
This set of Powder Metallurgy Multiple Choice Questions & Answers focuses on “Mechanism and Process Parameters”.
1. Which force fragments the liquid into ligaments in atomization process?
a) Tensile force
b) Shear force
c) Compressive force
d) Torque
Answer: b
Explanation: The interaction between the jets and the liquid metal stream begins with the creation of small disturbances at liquid surface, which grow into shearing forces that fragment the liquid into ligaments. The energy of the impinging jet is so high that the ligaments further disintegrate into droplets of very fine size.
2. Under which set of conditions is the irregular particle shape obtained?
a) Lower surface tension
b) Lower surface tension and low cooling rates
c) Higher surface tension and low cooling rates
d) Lower surface tension and high cooling rates
Answer: d
Explanation: Lower surface tension of the molten metal and high-cooling rate favor the formation of irregular shaped particles, as in water atomization .
3. Under which set of conditions is the spherical particle shape obtained?
a) Lower surface tension
b) Lower surface tension and low cooling rates
c) Higher surface tension and low cooling rates
d) Lower surface tension and high cooling rates
Answer: c
Explanation: Higher surface tension of the molten metal and low-cooling rate favor the formation of spherically-shaped particles, as in inert gas atomization .
4. The velocity of the liquid metal stream is given by the equation _________
a) v=A\
v=A\
v=A\
v=A\(\sqrt[3]{2g
\rho}\)
Answer: b
Explanation: The liquid metal stream has a velocity v, given by the equation=A\(\sqrt{2g
\rho}\) where A is a geometric constant, g is the acceleration due to gravity, P i is the injection pressure of the liquid metal, P g is the pressure of the atomizing medium, and ρ is the density of the liquid.
5. The shearing forces involved in atomization depends on the ________
a) Reynolds number
b) Temperature
c) Pressure
d) Biot’s number
Answer: a
Explanation: The shearing forces that lead to the formation of ligaments from the liquid metal depends on the Reynolds number, which in turn is related to size and velocity of the stream, density, and viscosity of the liquid metal.
6. Which of the following is a process parameter for atomization process?
a) Orifice volume
b) Pressure of atomizing medium
c) Temperature of atomizing medium
d) Atomizing medium properties
Answer: b
Explanation: The major process parameters for atomization process are- pressure of metal head, pressure of atomizing medium, metal temperature, orifice area, and molten metal properties.
7. The effect of pressure of metal head is given ________
a) r=a+b\ r=a+b\ r=a-b\ r=a-b\(\sqrt{h}\)
Answer: b
Explanation: The effect of the pressure of the metal head on the rate of atomization is given by the relationship r=a+b\(\sqrt{h}\) where r is the rate of atomization, a and b are the constants, and h is the metal head.
8. The fraction of coarse powder will increase as the quantity of metal available for atomization increases.
a) True
b) False
Answer: a
Explanation: Generally, the energy required for atomization depends on the final particle size desired. Since the energy available for disintegration is a constant, any increase in the quantity of the metal available for atomization will result in a decrease in the available energy per unit weight of metal. Thus, the fractions of coarse powders will increase.
9. Which of the following set of conditions leads to maximum fineness?
a) Increase in air pressure and increase in flow of metal
b) Decrease in air pressure and increase in flow of metal
c) Increase in air pressure and decrease in flow of metal
d) Decrease in air pressure and decrease in flow of metal
Answer: a
Explanation: The increase in air pressure increases the fineness, which is possible only when an increase in air pressure and the increase in the flow of metal balance each other, thereby producing maximum fineness.
10. The effect of pressure of atomizing medium is given ________
a) r=a+b\ r=a-b\ r=a-b\ r=a+b\(\sqrt{p}\)
Answer: d
Explanation: The effect of the pressure of the atomizing medium on the rate of atomization is given by the relationship r=a+b\(\sqrt{p}\) where r is the rate of atomization, a and b are the constants, and p is the air pressure.
11. The rate of atomization ______ with increase in temperature.
a) Increases
b) Decreases
c) Zero
d) Constant
Answer: b
Explanation: The rate of atomization declines steadily with increase in temperature. This is because the volume of the metal flowing through the nozzle is important and not the mass of the metal in the case of annular nozzles. Thus, with increase in temperature even though the volume of metal flowing through the nozzle remains constant, the mass of the metal will be less compared to that at lower temperatures.
12. What is the effect of increased temperature on the particle size?
a) Independent
b) Decreases
c) Increases
d) Increases first and then decreases
Answer: c
Explanation: When the temperature of the particle size increases, the surfacetension forces as well as the viscosity decreases. So that the available energy can more methodically break apart the metal stream producing fine particle sizes than at lower temperature.
13. The particle shape of water atomized copper becomes more irregular upon addition of _____
a) Silicon
b) Lithium
c) Tantalum
d) Potassium
Answer: b
Explanation: The additions which lower surface tension of the liquid metal can promote irregular particle shapes. Thus, the particle shape of water-atomized copper powder becomes more irregular by addition of small amounts of elements such as Mg, Ti, Li or Ca.
14. The rate of atomization and orifice area have a _______ relation.
a) Logarithmic
b) Inverse
c) Exponential
d) Linear
Answer: d
Explanation: The rate of atomization varies linearly with the orifice area. The only exception is for low-orifice diameter where wall friction reduces the velocity of liquid flowing through the orifice.
15. Which of the following depicts the stages of molten metal disintegration?
a) Wave formation → ligament formation → powder
b) Wave formation → ligament formation → fine droplets → breakdown to smaller particles → powder
c) Wave formation → ligament formation → fine droplets → breakdown to smaller particles → collision & coalescence of particles
d) Wave formation → ligament formation → fine droplets → collision & coalescence of particles
Answer: c
Explanation: The disintegration of molten metal stream consists of five stages:
i) Wave formation
ii) Ligament formation
iii) Fine droplets
iv) Breakdown to smaller particle
v) Collision & coalescence of particles.
This set of Powder Metallurgy written test Questions & Answers focuses on “Characteristics of Atomized Product”.
1. Which of the following factors affect the particle size of atomized powder?
a) Nozzle configuration
b) Atomizing medium and nozzle configuration
c) Properties of metal, atomizing medium and nozzle configuration
d) Atomizing medium
Answer: c
Explanation: The factors which affect the particle size of atomized powder include- Metal properties . Properties of atomizing medium . Nozzle configurations .
2. The empirical equation for average particle size in μm is ______
a) d=\Missing or unrecognized delimiter for \Big^{0.45}
^{1.5}\)
b) d=\Missing or unrecognized delimiter for \Big^{1.5}
^{0.45}\)
c) d=\Missing or unrecognized delimiter for \Big^{0.45}
^{1.5}\)
d) d=\Missing or unrecognized delimiter for \Big^{0.45}
^{1.5}\)
Answer: a
Explanation: The empirical relationship for calculating the average particle size in μm is given by d=\Missing or unrecognized delimiter for \Big^{0.45}
^{1.5}\) where ρ is the density of the liquid, σ is the surface tension of the liquid, μ is the coefficient of viscosity of liquid, ν is the relative velocity between air and liquid, f 1 is the volumetric flowrate of liquid, f a is the volumetric flowrate of air, and A and B are constants.
3. Weber number is given by ______
a) W=\
W=\
W=\
W=\(\frac{V^2\rho}{\sigma D}\)
Answer: c
Explanation: The Weber number is dependent on the density and surface tension of the liquid metal, the velocity of the atomizing medium, and the melt stream diameter. It is given by the equation W=\(\frac{V^2D}{\sigma \rho}\) where ρ is the density of liquid in g/cm 3 , σ is the surface tension of the liquid in N/m, and V is the velocity of the atomizing medium at the point of impact with the metal stream in m/s.
4. The empirical relation given by Lubanska for particle size is _______
a) d av =D\
)^{0.5}\)
b) d av =kD\
)^{0.5}\)
c) d av =kD\
)^{1.5}\)
d) d av =kD\
)^{0.5}\)
Answer: b
Explanation: The empirical relation developed by Lubanska for particle size is given by d av =kD\
)^{0.5}\) where d av is the mean particle size in mm, k is a constant, D is the diameter of the nozzle in mm, f 1 is the mass flow rate of the metal stream in kg/min, f a is the mass flow rate of the atomizing medium in kg/min, η e is the kinematic viscosity of the metal stream in m 2 /s, η g is the kinematic viscosity of the atomizing medium in m 2 /s, and W is the Weber number of the metal stream.
5. The particle size decreases with _______
a) increasing surface tension of liquid
b) decreasing velocity of atomizing medium
c) decreasing surface tension of liquid
d) constant velocity of atomizing medium
Answer: c
Explanation: The particle size of atomized powder particles decreases with increasing velocity of the atomizing medium, and decreasing surface tension of the liquid metal.
6. ______ apex angles lead to fine particles.
a) 89°
b) 0°
c) Lower
d) Higher
Answer: d
Explanation: For a specific nozzle design, the average particle size is controlled by the pressure of the atomizing medium as well as the apex angle of the gas jets, and thus with higher apex angles we obtain fine particle size.
7. ______ is obtained in water atomization compared to gas atomization.
a) Coarse powder
b) Fine powder
c) Ultra coarse powder
d) Spherical powder
Answer: b
Explanation: Particle shape of powders produced by atomization is influenced by the factor that determine the cooling rate. Thus, the cooling rates are higher in magnitude in the case of water atomization than in gas atomization which results in finer powder in case of water atomization.
8. Gas atomization results in _______
a) dendritic shape powder
b) irregular shape powder
c) spherical shape powder
d) fine powder
Answer: c
Explanation: Gas atomization generally results in spherical particles because of the influence of the surface tension forces. The shape of the powder will be irregular in the case of water atomized powders due to high-cooling rates resulting in smaller dendritic spacing.
This set of Powder Metallurgy Questions & Answers for Exams focuses on “Self Propagating High Temperature Synthesis and Types”.
1. What is the fullform of SHS?
a) Standard pressure High-Temperature Synthesis
b) Standard pressure Heat-Temperature Synthesis
c) Self-propagating Heat-Temperature Synthesis
d) Self-propagating High-Temperature Synthesis
Answer: d
Explanation: Self-propagating High-Temperature Synthesis is a novel material synthesizing technique developed in 1967 by A.G. Merzhanov, I.P. Boroviskaya and V.M. Shkirov at the Research Center of the USSR Academy of Sciences, USSR.
2. In ______, a self-sustaining reaction occurs by local ignition in a reactant mixture.
a) reaction sintering
b) SPS
c) SHS
d) activated sintering
Answer: c
Explanation: In self-propagating high-temperature synthesis , a self-sustaining reaction occurs by local ignition in a reactant mixture. A large number of materials including ceramic powders, including carbides, borides or nitrides as well as their composites in powder or whisker form can be synthesized using this process.
3. Spontaneous formation of product occurs in SHS.
a) True
b) False
Answer: a
Explanation: Spontaneous formation of product occurs in SHS due to the high-exothermic heat of reaction resulting from ignition of the reactants. This process is also called combustion synthesis, gasless combustions, and self-propagating combustion.
4. In SHS, _____ are the different classes of reactions recognized.
a) layer-wise combustion mode
b) propagation mode and simultaneous combustion mode
c) volumetric combustion mode
d) propagation mode and layer-wise combustion mode
Answer: b
Explanation: In SHS, two different classes of reactions have been recognized, those processes in which layer-wise combustion occurs , and those processes wherein volumetric combustion occurs .
5. Conventional combustion processes differ from SHS reactions.
a) True
b) False
Answer: a
Explanation: Conventional combustion processes are generally volumetric and reactions occur in a volume, generating heat and the required products. SHS reaction occurs generally by the propagation of a combustion wave with a definite velocity through a reactant transforming it into products.
This set of Powder Metallurgy Multiple Choice Questions & Answers focuses on “Classes of Reactions and Physicochemical Mechanism ”.
1. ______ different types of reactions are possible in SHS.
a) 6
b) 7
c) 8
d) 5
Answer: a
Explanation: The six different types of reactions possible in SHS are: Synthesis from elements, Redox reaction, Oxidation of metals with complex oxides, Synthesis from compounds, Reaction of the elements with decomposition products and Thermal decomposition.
2. Which of the following equation represents ‘Synthesis from elements’ type of SHS reaction?
a) Ti + C → TiC
b) B 2 O 3 + 3Mg + N 2 → 2BN + 3MgO
c) Nb + Li 2 O 2 + 0.5Ni 2 O 5 → 2LiNbO 3
d) PbO + WO 3 → PbWO 4
Answer: a
Explanation: Ti + C → TiC represents synthesis from elements type of SHS reaction; B 2 O 3 + 3Mg + N 2 → 2BN + 3MgO represents redox reaction; Nb + Li 2 O 2 + 0.5Ni 2 O 5 → 2LiNbO 3 represents oxidation of metals with complex oxides type of SHS reaction while PbO + WO 3 → PbWO 4 represents synthesis from compounds type of SHS reaction.
3. Which of the following equation represents ‘oxidation of metals with complex oxides’ type of SHS reaction?
a) PbO + WO 3 → PbWO 4
b) B 2 O 3 + 3Mg + N 2 → 2BN + 3MgO
c) Ni + Al → NiAl
d) Nb + Li 2 O 2 + 0.5Ni 2 O 5 → 2LiNbO 3
Answer: d
Explanation: Ni + Al → NiAl represents synthesis from elements type of SHS reaction; B 2 O 3 + 3Mg + N 2 → 2BN + 3MgO represents redox reaction; Nb + Li 2 O 2 + 0.5Ni 2 O 5 → 2LiNbO 3 represents oxidation of metals with complex oxides type of SHS reaction while PbO + WO 3 → PbWO 4 represents synthesis from compounds type of SHS reaction.
4. Which of the following equation represents ‘Redox reaction’ type of SHS reaction?
a) Ti + C → TiC
b) B 2 O 3 + 3Mg + N 2 → 2BN + 3MgO
c) Nb + Li 2 O 2 + 0.5Ni 2 O 5 → 2LiNbO 3
d) 2TiH 2 + N 2 → 2TiN + 2H 2
Answer: b
Explanation: Ti + C → TiC represents synthesis from elements type of SHS reaction; B 2 O 3 + 3Mg + N 2 → 2BN + 3MgO represents redox reaction; Nb + Li 2 O 2 + 0.5Ni 2 O 5 → 2LiNbO 3 represents oxidation of metals with complex oxides type of SHS reaction while 2TiH 2 + N 2 → 2TiN + 2H 2 represents reaction of the elements with decomposition products type of SHS reaction.
5. Which of the following equation represents ‘Thermal decomposition’ type of SHS reaction?
a) Nb + Li 2 O 2 + 0.5Ni 2 O 5 → 2LiNbO 3
b) 2TiH 2 + N 2 → 2TiN + 2H 2
c) 2BH 3 N 2 H 4 → 2BN + N 2 + 7H 2
d) B 2 O 3 + 3Mg + N 2 → 2BN + 3MgO
Answer: c
Explanation: 2BH 3 N 2 H 4 → 2BN + N 2 + 7H 2 represents thermal decomposition type of SHS reaction; Nb + Li 2 O 2 + 0.5Ni 2 O 5 → 2LiNbO 3 represents oxidation of metals with complex oxides type of SHS reaction; 2TiH 2 + N 2 → 2TiN + 2H 2 represents reaction of the elements with decomposition products type of SHS reaction while B 2 O 3 + 3Mg + N 2 → 2BN + 3MgO represents redox reaction.
6. Which of the following equation represents ‘Synthesis from compounds’ type of SHS reaction?
a) PbO + WO 3 → PbWO 4
b) B 2 O 3 + 3Mg + N 2 → 2BN + 3MgO
c) Nb + Li 2 O 2 + 0.5Ni 2 O 5 → 2LiNbO 3
d) Ni + Al → NiAl
Answer: a
Explanation: PbO + WO 3 → PbWO 4 represents synthesis from compound type of SHS reaction; B 2 O 3 + 3Mg + N 2 → 2BN + 3MgO represents redox reaction; Nb + Li 2 O 2 +0.5Ni 2 O 5 → 2LiNbO 3 represents oxidation of metals with complex oxides type of SHS reaction while Ni + Al → NiAl represents synthesis from element type of SHS reaction.
7. Which of the following equation represents ‘reaction of the elements with decomposition products’ type of SHS reaction?
a) Ni + Al → NiAl
b) 2TiH 2 + N 2 → 2TiN + 2H 2
c) B 2 O 3 + TiO 2 + 5Mg → TiB 2 + 5MgO
d) 2BH 3 N 2 H 4 → 2BN + N 2 + 7H 2
Answer: b
Explanation: 2TiH 2 + N 2 → 2TiN + 2H 2 represents reaction of the elements with decomposition products type of SHS reaction; Ni + Al → NiAl represents synthesis from element; B 2 O 3 + TiO 2 + 5Mg → TiB 2 + 5MgO represents redox reaction; and 2BH 3 N 2 H 4 → 2BN + N 2 + 7H 2 represents thermal decomposition type of SHS reaction.
8. In SHS reactions, an important parameter is the _________
a) Isothermal temperature
b) Volumetric expansion
c) Adiabatic temperature
d) Heat
Answer: c
Explanation: In SHS reactions, an important parameter is the adiabatic temperature, T ad . This refers to the temperature to which the products are raised under adiabatic conditions due to the heat evolved during the chemical reaction. If this temperature is less than the boiling point of both the constituents, no vapor phase is formed.
9. In the case of TiB 2 , high pressures are needed to make it a gasless combustion.
a) True
b) False
Answer: a
Explanation: In case of TiB 2 , though the adiabatic temperature is less than the boiling point of Ti and B, the vapor pressure of the elements at the adiabatic temperature is high, and hence high pressures are needed to make it a gasless combustion.
10. Solid state combustion leads to _______ combustion velocities.
a) Highest
b) Lowest
c) Lower
d) High
Answer: b
Explanation: Solid state combustion is the combustion process where all components are in a solid state. It occurs entirely when the melting points of the constituents are less than the adiabatic temperature leading to the lowest combustion velocities.
11. For which of the following conditions does the combustion proceeds at the highest velocity (where MP C1 and MP C2 are melting points of component 1 and 2 respectively)?
a) MP C1 < T ad < MP C2
b) T ad > MP C1 and MP C2
c) T ad < MP C1 and MP C2
d) T ad = MP C1 and MP C2
Answer: a
Explanation: If the adiabatic temperature lies in between the melting point of the components, the molten component spreads at a high rate in the compact, and the combustion proceeds at the highest possible speed.
This set of Powder Metallurgy Multiple Choice Questions & Answers focuses on “Tool Materials – Cemented Carbides and its Production – 1”
1. ______ enables us to shape a larger metallic object by removing a part or thin layer of the metal from its surface to the required shape.
a) Electrical contact materials
b) Bearing materials
c) Tool materials
d) Sintered Friction materials
Answer: c
Explanation: Tool material is defined as the one which enables us to shape a larger metallic object by removing a part or thin layer of the metal from its surface to the required shape. Though the various tool materials differ in size and shape, all have a common feature of a wedge shape that is driven asymmetrically into the workpiece material.
2. Cemented carbides are commonly known as ‘Hard Metals’.
a) True
b) False
Answer: a
Explanation: Cemented carbides are commonly known as ‘Hard Metals’, because of their high hardness, abrasion resistance, compressive strength and a considerable amount of toughness.
3. The modern production of hard metal is attributed to ________
a) Kieffer
b) Schroter
c) Schwarzkopf
d) Osram Studiegesellschaft
Answer: b
Explanation: The modern production of hard metal is attributed to Schroter. The technique involves the blending of WC powder with up-to 20% by weight of a metal of the iron group, particularly Co as a binder metal, compaction of the powder mixture and sintering at a temperature close to the melting point of the binder metal.
4. Widia is a trade name of which cemented carbide?
a) WC-Co
b) WC
c) Co-Cr
d) Co-Ni-Cr
Answer: a
Explanation: Cemented WC-Co materials with 4 – 13% cobalt was prepared in the same manner as the WC prepared by Schroter, by Fried Krupp in Essen were marketed under the trade name ‘Widia’.
5. The principle constituents of sintered hard metals are the ______ and _______
a) Metal, reinforcement
b) Metal, carbide powder
c) Non-metal, carbide powder
d) Non-metal, boride powder
Answer: b
Explanation: The principle constituents of sintered hard metals or cemented carbides are the metal and carbide powders. The carbides are produced by either carburization of powdered metals with carbon, or by the reaction of metal oxide with carbon.
6. Recarburization is often necessary for carbide produced by the reaction of metal oxide with carbon.
a) True
b) False
Answer: a
Explanation: In carbide powder production by direct reaction of metal oxide with carbon, accurate control of final carbon content is difficult due to a combination of reduction and carburization reactions in a single operation, thus often necessitating crushing and recarburization.
7. In hard metal industry, the carbide of _____ is produced by the direct metal-carbon reaction.
a) Tantalum
b) Titanium
c) Molybdenum
d) Niobium
Answer: c
Explanation: In hard metal industry, the carbide of molybdenum and tungsten are produced by direct metal-carbon reaction while that of titanium, tantalum, and niobium are produced by metal oxide-carbon reaction since the former technique of production of these metal powders are comparatively expensive.
8. WC is produced by carburization of metallic W powders prepared by the reduction of _______
a) Scheelite
b) Wolframite
c) Tungstic acid
d) Limonite
Answer: c
Explanation: WC is produced by carburization of metallic W powders prepared by the reduction of tungstic acid (H 2 WO 4 ), tungsten trioxide (WO 3 ), ammonium paratungstate. These compounds are produced from either the wolframite or scheelite ores.
9. Which of the following phases occur during sintering in WC powder due to carbon deficiency?
a) α, β, γ phase
b) θ, η, K – phase
c) δ, θ, η phase
d) β, γ, M – phase
Answer: b
Explanation: Carbon deficiency in the tungsten carbide powder results in the formation of brittle carbide phases such as η-phase (Co 3 W 3 C), θ-phase (Co 3 W 6 C 2 ) and K-phase (Co 3 W 10 C 4 ) during sintering. If the material is under-carburized, i.e., the combined carbon content is below about 6.1%, carburization operation is repeated.
10. Why carbide balls are preferred over steel balls in wet milling?
a) Economy purpose
b) Higher iron pick-up
c) Faster production rate
d) Higher carbon pick-up
Answer: b
Explanation: In wet milling, if steel balls are used, results in higher iron pick-up in the charge. Hence, high wear resistant carbide balls made by hot pressing are widely used.
This set of Powder Metallurgy Questions and Answers for Aptitude test focuses on “Tool Materials – Cemented Carbides and its Production – 2”.
1. ______ carbide alloys possess better resistance to diffusion wear under seizure conditions.
a) Medium-grained
b) Ultra-fine grained
c) Coarse-grained
d) Fine-grained
Answer: c
Explanation: Coarse-grained carbide alloys possess better resistance to diffusion wear under seizure conditions while fine-grained carbide alloys having the greater abrasion resistance and high hardness are suited for the resistance to the attrition type of wear in the region of partial contact and to shear stresses in the seizure area.
2. Which of the following is not a characteristic of vibratory mill used for milling of cemented carbide?
a) Shorter milling time
b) Wear of balls and mills is reduced
c) Ratio of powders to balls in mills = 1:3.5 – 1:5.5
d) Ratio of powders to balls in mills = 1:1 – 1:3
Answer: d
Explanation: Vibratory mills are advantageous over rotary mills because of shorter milling time in comparison to longer milling time in rotary mills. Apart from this, wear of balls and mills and hence, the contamination of charge is reduced in the vibratory mill over the rotary mill. However, for rotary mill ratio of powders to balls in mills = 1:1 – 1:3 and for vibratory mill it is 1:3.5 – 1:5.5.
3. In which organic liquid is the lubricant, paraffin wax dissolved?
a) Gasoline
b) Ether
c) Light hydrocarbons
d) Alcohol
Answer: a
Explanation: The addition of lubricant, is done as a solution in an organic liquid such as paraffin wax dissolved in gasoline, camphor in ether or light hydrocarbons and glycol in alcohol and solutions are made in the mixers prior to compacting in order to facilitate pressing and to avoid the formation of defects and cracks in the compacts.
4. The classical method of production of cemented carbide tips is ________
a) Hot pressing
b) Infiltration
c) Double-sintering
d) Liquid phase sintering
Answer: c
Explanation: The classical method of production of cemented carbide tips is double-sintering process, i.e., cold pressing to produce compacts in similar shapes such as round and rectangular blanks and pre-sintering to produce a material which is machined to final shape and sintered.
5. During _______, no liquid phase forms and ________ of only the binder metal occurs.
a) Pre-sintering, liquid phase sintering
b) Liquid phase sintering, pre-sintering
c) Pre-sintering, solid phase sintering
d) Solid phase sintering, pre-sintering
Answer: c
Explanation: During pre-sintering, no liquid phase forms and solid phase sintering of only the binder metal occurs i.e. little or no shrinkage take place. The pre-sintered compacts have a chalky structure and enough strength for further handling and to withstand machining or slicing operations to be carried out.
6. Milled powder mixtures are unsuitable for automatic pressing in comparison to agglomerated carbide-cobalt powder mixtures.
a) True
b) False
Answer: a
Explanation: Milled powder mixtures are unsuitable for automatic pressing due to their very poor flow properties, while the agglomerated carbide-cobalt mixture is required for compaction due to their high apparent density and good flow properties in automatic press. Hence, the powders containing about 2% lubricant are frequently agglomerated by compacting them .
7. _________ is used to produce large carbide balls, bushes and hollow sections with more uniform density.
a) Isostatic pressing
b) Extrusion compaction
c) Rolling
d) Forging
Answer: a
Explanation: Isostatic pressing is used to produce large carbide balls, bushes and hollow sections with more uniform density. The extrusion compaction of powders in the presence of binders and plasticizers is used for the production of fairly simple shapes such as cemented carbide rods, tubes or rectangular, circular or non-symmetrical cross section of greater length.
8. Which of the following is not a characteristic of hot-pressed material?
a) Hard
b) Ductile
c) Wear- resistant
d) Zero residual porosity
Answer: b
Explanation: Hot pressed material is very hard, wear resistant and practically free from residual porosity. In this process, the powder mixture, without the presence of lubricant, is introduced into graphite dies and pressing and sintering operations are carried on simultaneously; the pressure varying from 0.5-2 tsi and the temperature from about 1300-1550°C with direct resistance or induction heating.
9. Which of the following is the correct sequence of grinding cemented carbides?
a) Rough grinding
b) Coarse grinding, polishing, and fine grinding
c) Rough grinding, and final grinding
d) Fine grinding
Answer: c
Explanation: All cemented carbides are ground in two steps. The rough grinding being the first step is usually performed with SiC grinding wheel. The final step is usually done with a metal bonded diamond wheel.
This set of Powder Metallurgy Multiple Choice Questions & Answers focuses on “Tool Materials – Properties and Testing of Cemented Carbides ”.
1. ______ of cemented carbide is the measure of the completeness of sintering operation.
a) Density
b) Volume
c) Strength
d) Ductility
Answer: a
Explanation: Density of cemented carbide is the measure of the completeness of sintering operation owing to the occurrence of contraction or shrinkage on final sintering, depends on the composition. Increasing Co content and TiC addition reduce the density of cemented carbide.
2. Cemented carbide grades can be classified into _____ groups, according to their density by using Hg as a buoyancy medium.
a) 2
b) 3
c) 4
d) 5
Answer: a
Explanation: Cemented carbide grades can be classified into three groups, according to their density by using Hg as a buoyancy medium; WC-Co grades will sink in Hg while WC-TiC-Co and WC-TiC-Ta C-Co grades will float on the surface.
3. _________ of cemented carbide tools is used as a measure of wear performance.
a) Hot hardness
b) Transverse rupture strength
c) Compressive strength
d) Hardness
Answer: d
Explanation: Hardness of cemented carbide tools is used as a measure of wear performance. It is customary to adopt Rockwell as a speed control method. Increasing Co content decreases while increasing TiC addition increases the hardness of cemented carbide.
4. Transverse-Rupture strength of cemented carbide is a measure of _________
a) Hardness
b) Wear resistance
c) Toughness
d) Compressive strength
Answer: c
Explanation: Transverse-Rupture strength of cemented carbide is a measure of toughness. Moreover, lower sintering temperature and over sintering lead to a pronounced decrease in transverse-rupture strength.
5. The oxidation resistance of WC-Co composition is higher than that of the WC-TiC-Co composition.
a) True
b) False
Answer: b
Explanation: The oxidation resistance of WC-Co composition is considerably lower than that of the WC-TiC-Co compositions because of the formation of non-dense and non-adherent oxide layer at elevated temperatures.
6. Lower thermal conductivity of cemented carbides leads to formation of _________
a) Brazing cracks
b) Comb-type cracks
c) Grinding cracks
d) Crumbling
Answer: c
Explanation: Higher thermal conductivity of cutting tools is necessary in order to dissipate larger amount of heat, generated from the cutting action, by conduction through the tool, otherwise overheating of the cutting edges will result in the formation of grinding cracks thereby rapid tool failure.
7. Which of the following property of cemented carbide increases on increase in Co content?
a) Coefficient of thermal expansion
b) Hardness
c) Density
d) Thermal conductivity
Answer: a
Explanation: The addition of Co slightly increases the coefficient of thermal expansion, whereas the other properties like hardness, density, and thermal conductivity of cemented carbide decrease with increase in Co content.
8. The cutting performance of cemented carbide can be plotted as _________
a) T-V curve
b) C-P curve
c) I-V curve
d) M-V curve
Answer: a
Explanation: T-V curves are plotted which are used for comparing the cutting efficiency of cemented carbides of different grade under varying cutting conditions.
9. The microstructure of WC-Co alloy contains ____ phases.
a) 1
b) 2
c) 3
d) 4
Answer: b
Explanation: The microstructure of WC-Co alloy contains only two phases- α phase , and γ phase . The α phase appear as regular shape such as triangles or trapeziums.
10. The microstructure of WC-TiC-Co alloy contains ____ phases.
a) 1
b) 2
c) 3
d) 4
Answer: c
Explanation: In WC-TiC-Co composition, apart from α and γ phase, a second carbide phase, referred to as β phase , usually more rounded than α, forms which is distinguished from α by electrolyte etching in a mixture of hydrofluoric and nitric acids or by heat tinting technique which causes the darkening of β phase.
This set of Powder Metallurgy Multiple Choice Questions & Answers focuses on “Tool Materials – Applications of Cemented Carbides”.
1. ______ is the most important application of cemented carbides.
a) Dies
b) Cutting Tools
c) Drilling Tools
d) Deep drawing Tools
Answer: b
Explanation: The most important application of cemented carbides is in the form of tools for metal cutting and machining of abrasive materials because 70% of cemented carbides produced today are used for cutting tools.
2. Which of the following is not a characteristic of cemented carbide cutting tools?
a) Extremely hard
b) Very brittle
c) High red hardness
d) Low red hardness
Answer: d
Explanation: Cemented carbide cutting tools are Extremely hard, possess High red hardness and are very brittle. The cutting speed with the use of carbide-tipped tools is increased six to eight times over that with the customary high-speed steel tools.
3. Cemented carbide cutting tool is advantageous in mass production.
a) True
b) False
Answer: a
Explanation: Cemented carbide cutting tool is advantageous in mass production owing to their very slow change in shape from wear thereby maintaining close dimensional tolerances with less frequent tool grinding and more rapid removal of workpiece.
4. ________ occurs due to material built-up at the cutting edge.
a) Brazing cracks
b) Comb-type cracks
c) Crumbling
d) Grinding cracks
Answer: c
Explanation: During the cutting of soft and tough materials, the formation of built-up edge takes place, part or entire of which breaks away periodically and some portion of the cutting edge may also be taken away along with the built-up edge, this leads to deterioration of cutting edge by crumbling.
5. Which of the following is not a cause for failure of the cutting tools?
a) Crumbling
b) Hair-type cracks
c) Grinding cracks
d) Thermal shocks
Answer: b
Explanation: The causes for the failure of cutting tools are: edge crumbling, comb-type cracks, grinding cracks, thermal shocks, brazing cracks, incorrect tool geometry, inadequate rigidity of the machine tools, oxidation of the cutting edge and bad handling.
6. The phenomenon of ______ occurs by the combination of considerable pressure, high temperature and longer time of contact only within a certain speed range.
a) Brazing cracks
b) Grinding cracks
c) Crumbling
d) Built-up edge
Answer: d
Explanation: The phenomenon of built-up edge occurs by the combination of considerable pressure, high temperature and longer time of contact only within a certain speed range exceeding which built-up edge tends to become smaller and eventually disappears.
7. The wear due to the indenting action of hot, rough, hard and coiled chips behind the cutting-edge leads to ________
a) Cratering
b) Grinding cracks
c) Crumbling
d) Built-up edge
Answer: a
Explanation: The wear due to the indenting action of hot, rough, hard and coiled chips behind the cutting-edge leads to the formation of grooves or craters. The craters become deeper and deeper as the time of operation is increased and thus the edge of the crater begins to approach the cutting edge more and more. Cratering, due to adhesion or welding, finally leads to edge crumbling thereby interrupting the cutting operation.
8. _______ composition of the carbide cutting tool is suitable for roughing operations.
a) Low-Co
b) High-Co
c) Medium-Co
d) Ultra-high-Co
Answer: b
Explanation: High-Co composition of the carbide cutting tool is suitable for roughing operations, whereas, low-Co compositions are used for light, high-speed machining cuts because of extremely high hardness.
9. High TiC content is used particularly for _________
a) High finish turning and drilling of steel
b) Roughing operation
c) Medium cuts and speeds on steel
d) Rough cuts on Cast iron
Answer: a
Explanation: High TiC content is used particularly for high finish turning and drilling of steel. Cemented TiC grades have also been used for high-speed machining cuts on difficult-to-machine materials.
10. Composite tips, consisting of a thin layer of TiC-Co bonded on a WC-Co grade use is rapidly increasing.
a) True
b) False
Answer: a
Explanation: Composite tips, consisting of a thin layer of TiC-Co bonded on a WC-Co grade use is rapidly increasing, because the surface layer accords good resistance to wear and cratering and considerable improvement in elevated temperature strength while the base renders good strength, toughness, and higher thermal conductivity.
11. Cemented carbide dies replace diamond dies for hole diameters between _______
a) 0.004-0.04 inch
b) 0.04-0.4 inch
c) 0.4-0.9 inch
d) 0.004-0.1 inch
Answer: b
Explanation: For fine drawing diamond dies are superior, but for drawing of larger sections, i.e. for hole diameters between 0.04-0.4-inch, cemented carbide dies replace diamond dies because diamond dies fail due to inadequate compressive strength.
12. High-pressure nozzle made of cemented carbides are used in ________ industry.
a) Chemical
b) Sheet processing
c) Textile
d) Mining
Answer: a
Explanation: High-pressure nozzle made of cemented carbides are used in the chemical industry. Extruding, compacting, and sizing tools made of cemented carbide are used in the sheet processing industry. In the textile industry, thread guides and mattress needled are made of cemented carbide. Drilling tools made of cemented carbide are used in the mining industry.
13. __________ are widely used as projectile cores for armor piercing weapons.
a) Sintered friction material
b) Cermet
c) Cemented carbide
d) Dispersion strengthened material
Answer: c
Explanation: Cemented carbide are widely used as projectile cores forarmor piercing weapons and also find use in high precision measuring instruments such as micrometer calipers, in hardness testers such as cemented carbide balls and pyramid indentors.
This set of Powder Metallurgy Multiple Choice Questions & Answers focuses on “Powder Manufacture – Alloy Powders”.
1. Which of the following metal powder is used as a moderator in the atomic energy field?
a) Uranium carbide
b) Beryllium
c) Zirconium and its alloys
d) Thorium
Answer: b
Explanation: Beryllium is used as a moderator ; uranium carbide as fuel material; zirconium and its alloys as cladding materials; and thorium as fertile material .
2. Beryllium is used as a fuel canning material for nuclear reactors.
a) True
b) False
Answer: a
Explanation: Beryllium is used as a fuel canning material because of its low- thermal neutron- absorption cross-section and good elevated temperature strength.
3. _______ has provided a metal powder designation system, according to which, metal and alloy powders are given a prefix and a four-digit code.
a) ASME
b) ASTM
c) MPIF
d) BIS
Answer: c
Explanation: MPIF has provided a metal powder designation system, according to which, metal and alloy powders are given a prefix and a four-digit code. The prefix will refer to the metals present while the four-digit code will give the % of the alloying elements present. The minimum yield strength is referred to by another two-digit code at the end.
4. Which of the following methods have been developed for the production of complex powders?
a) Atomization and Milling
b) Atomization, Thermal decomposition, Electrolysis, and spray drying
c) Atomization, Thermal decomposition, and Graining
d) Atomization and Electrolysis
Answer: b
Explanation: In recent years, four methods have been developed for production of complex powders: atomization process, combined precipitation in the thermal decomposition of carbonyls, combined precipitation of metals in electrolysis, and spray drying.
5. Complex alloy powders can be produced by electrolytic deposition method by using _____methods.
a) Electrolyte mixture, anode made of cast alloy, and composite anodes
b) Composite cathodes
c) Composite anodes
d) Electrolyte mixture and composite anodes
Answer: a
Explanation: Complex alloy powders can be produced by electrolytic deposition method by using a mixture of electrolytes containing two or more metal salts, cast alloy of required composition as the anodes, or composite anodes of the appropriate metal and alloy component.
6. Spray drying produces a superalloy powder with dispersed _____
a) Thoria
b) Oxalate
c) Nickel
d) Copper
Answer: a
Explanation: Spray drying, consists of contacting a spray with a blast of hot air, calcining the dried mass to convert all the metal compounds to the oxides at 800°C in air and reduction in hydrogen in order to produce a superalloy powder with dispersed thoria.
7. The alloy F-0000-10 refers to pure fluorine powder with anultimate breaking strength of 10 ksi.
a) True
b) False
Answer: b
Explanation: The alloy F-0000-10 refers to pure iron powder with a yield strength or nominal strength of 10 ksi. This designation is given by the MPIF has provided a metal powder designation system, according to which, metal and alloy powders are given a prefix and a four-digit code.
This set of Powder Metallurgy Multiple Choice Questions & Answers focuses on “Powder Manufacture – Electrochemical Method”.
1. In electrodeposition, the final product may be obtained in ____ different forms.
a) 4
b) 3
c) 2
d) 5
Answer: b
Explanation: In electrodeposition, depending on the processing conditions, the final product may be obtained in 3 different forms. The deposit may be: a hard-brittle layer which is later milled to obtain powder; a soft, spongy substance which is loosely adherent and easily removed by scrubbing; a direct powder deposit from the electrolyte which collects at the bottom of the cell.
2. Ta powder is produced commercially by electrolysis of ______ dissolved in a bath of K 2 TaF 7 , KCl, and KF.
a) Tantalum oxide
b) Tantalum sulphate
c) Tantalum chloride
d) Tantalum fluoride
Answer: a
Explanation: Ta powder is produced commercially by electrolysis of tantalum oxide dissolved in a bath of K 2 TaF 7 , KCl, and KF. The addition of tantalum oxide is made continuous during the reaction. Leaching of Ta removes trapped electrolyte but the evolution of H2 at this stage causes embrittlement of the metal thus allowing it to crushed to the required size and finally softened by heat treatment under vacuum.
3. Which of the following factors does not promote powdery deposits?
a) Low temperature
b) High-current-density
c) High-metal concentration
d) High viscosity
Answer: c
Explanation: The factors which promote powdery deposits are: low temperature, high-current density, high-metal concentration, high viscosity, pH of the bath , and circulation of electrolyte to avoid or suppress convection.
4. Which of the following metal powder is generally not prepared by fused salt electrolysis?
a) Copper
b) Tantalum
c) Vanadium
d) Thorium
Answer: a
Explanation: Copper is produced by electro-deposition from the aqueous solution where metals of high purity are precipitated from the aqueous solutions on the cathode of the electrolytic cell. Fused salt electrolysis has been used for the production of tantalum, vanadium and thorium powders.
5. Which of the following is not a characteristic of the electrolytic powder deposit?
a) Low apparent density
b) High apparent density
c) Crystalline
d) Dendritic shape
Answer: b
Explanation: The electrolytic powders deposited are generally crystalline and are characterized by their dendritic or fern-like shape of low apparent density and flow rate, favorable for pressing due to the tendency of the individual particles to readily interlock.
6. _______ particle shape is obtained for powders produced from hard, brittle deposits.
a) Dendritic
b) Acicular
c) Angular
d) Irregular
Answer: c
Explanation: Angular or needle-like shape is obtained in the case of powders produced from hard, brittle deposits, and the particle size is the function of mechanical methods employed for subsequent comminution.
7. _____ is generally added to the iron sulphate or chloride bath to favor high yield of iron powder.
a) NH 4 Cl
b) KCl
c) K 2 SO 4
d) NH 3
Answer: a
Explanation: Iron powder id produced commercially by the electrolysis of sulphate or chloride bath. Addition of NH 4 Cl increases the conductivity and reduces oxidation of the product. Chloride bath has been preferred over the sulphate bath because the latter results in the precipitation of Sulphur in the deposit and tend to cause anode passivity.
8. _____ is used to calculate theoretical weight deposited on the electrode.
a) Faraday’s law
b) Hess law
c) De-Braggs law
d) Stoke’s law
Answer: a
Explanation: Faraday’s law is used to calculate the theoretical weight of powder deposited on the electrode. Faraday’s law is given by W th =I t A/F N c where, I is current in amperes, t is time in seconds, A is atomic weight of metal in grams/mole, F is Faradays constant=96500 C and N c is the valency.
9. Time and current are the two important variables which affect the amount of powder deposited on the electrode during electrodeposition of copper.
a) True
b) False
Answer: a
Explanation: Time and current are the two important variables which affect the amount of powder deposited on the electrode during electrodeposition of copper. As time increases the amount of copper powder deposited on the cathode increases. Similarly, as the current increases, bath conductivity increase and thus the amount of powder deposited also increases.
10. What is the current density when current of 1.5A flows through the electrolytic cell with the cathode plate having an effective length of 46mm, breadth 38mm and negligible thickness?
a) 413.7 A/m 2
b) 377.9 A/m 2
c) 519.3 A/m 2
d) 403.6 A/m 2
Answer: a
Explanation: Current density = current/ effective area of plate ——–
Here, current=1.5A and effective area of plate=2lw+2lt+wt
Given, l=46mm, b=38mm and t=1mm; effective area of plate=36.26x 10 -4 m 2
Substituting the values in equation , we get Current density=1.5 A/36.26 x 10 -4 m 2 =413.7 A/m 2 .
11. What is the current efficiency when actual weight deposited is 0.036g and theoretical weight deposited is 0.049g?
a) 73.46%
b) 136.11%
c) 73.12%
d) 88.88%
Answer: a
Explanation: Current efficiency = x 100——–
Substituting the values in equation , we get
Current efficiency=\(\frac{0.036}{0.049}\) x 100=73.46%.
12. What is the theoretical amount of copper powder deposited on the cathode plate when a current of 1A passes through the electrolytic tank for 5 minutes?
a) 0.098g
b) 0.0016g
c) 0.190g
d) 0.980g
Answer: a
Explanation: Faraday’s law is used to calculate the theoretical weight of powder deposited on the electrode.
Faraday’s law is given by:
W th =I t A/F N c ————
where, I the current in amperes, t is time in seconds, A is atomic weight of metal in grams/mole, F is Faradays constant=96500 C and N c is the valency.
Substituting the values in equation , we get,
W th =\(\frac{1 \times \times 63.5}{96500 \times 2}\)=0.098g.
This set of Powder Metallurgy online test focuses on “Physico-Chemical Methods of Powder Production”.
1. Which process is used for the production of pure reactive metal powder, particularly niobium?
a) Intergranular Corrosion process
b) Oxidation and Decarburization method
c) Gaseous Reduction process
d) Reduction method
Answer: b
Explanation: Oxidation and Decarburization method has been developed for the production of pure reactive metal powder, particularly niobium, by reacting metal carbide with metal oxide in vacuum at an elevated temperature so that both oxygen and carbon are removed as CO.
2. Mannesmann process employed for the production of Fe powders can be regarded as oxidation and decarburization method.
a) True
b) False
Answer: a
Explanation: Mannesmann process employed for the production of Fe powders can be regarded as oxidation and decarburization method since it also involves the elimination of both carbon and oxygen.
3. Which of the following method has the principle that grain boundaries are preferential sites for chemical attack than grains?
a) Gaseous Reduction process
b) Hydrometallurgical process
c) Intergranular Corrosion process
d) Oxidation and Decarburization method
Answer: c
Explanation: Intergranular Corrosion processis based on the fact that grain boundaries of heat-treated alloys are more susceptible to chemical attack than the grains, thus freeing particles of bulk material.
4. Intergranular Corrosion process was used extensively for the production of which of the following powder?
a) Stainless steel
b) Copper
c) Niobium
d) Brass
Answer: a
Explanation: Intergranular Corrosion process was used extensively for the production of stainless-steel powders. This consists of carburizing SS scrap at a temperature of about 500-750°C for a definite time in order to precipitate chromium carbide at the grain boundaries and corroding the boundary by a boiling aqueous solution of 11% CuSO 4 and 10% H 2 SO 4 so as to cause disintegration of the SS into powder.
5. Which process is depicted in the above diagram?
a) Intergranular Corrosion process
b) Precipitation from fused salts method
c) Gaseous Reduction process
d) Precipitation from aqueous solution method
Answer: b
Explanation: The process depicted above is precipitation from fused salts, which is generally used for reactive metals. Thus, for the production of Zr powder, the ZrCl 4 salt is mixed with an equal amount of KCl and some Mg. Mg replaces the Zr when heated to 749°C and particles of latter settle at the base of the chamber.
6. Which of the following are physicochemical methods of powder production?
a) Thermal decomposition and graining
b) Condensation method and milling
c) Condensation method, gaseous pyrolysis method, and reduction method;
d) Condensation method, gaseous pyrolysis method, reduction method, and cold stream process
Answer: c
Explanation: There are 9 physicochemical methods of powder production which are as follows: Condensation method; Gaseous pyrolysis method; Reduction method; Electrodeposition; Precipitation from aqueous solution method; Precipitation from fused salts method; Gaseous Reduction process; Intergranular Corrosion process; and Oxidation and Decarburization method, whereas graining, milling, and cold stream process are mechanical methods of powder production.
7. The process used on a commercial scale for the production of Ni, Co and Cu powder by the hydrometallurgical method is called _____
a) gaseous Reduction process
b) precipitation from fused salts method
c) oxidation and Decarburization method
d) condensation method
Answer: a
Explanation: The process used on a commercial scale for the production of Ni, Co and Cu powder by the hydrometallurgical method is called gaseous reduction process where reduction of aqueous solutions or slurries of salts of metals occurs with H 2 gas at moderate temperature and high pressure .
8. Which of the following is a variant of the hydrometallurgical method?
a) Peace River Process
b) Peace Sea Process
c) Peace Extraction Process
d) Peace Reduction Process
Answer: a
Explanation: Peace River Process, has been developed for production of Fe powder with high purity , low H 2 loss, good pressing properties and sinterability. This process produces a powder with a narrow range of particle size distribution, spherical shape, high apparent densities and flow rates. The process consists of leaching ad Fe- bearing material with HCl, crystallizing the resultant liquor to pure FeCl 2 , then reducing it to sponge iron followed by grinding it to produce a powder.
9. The method employing the principle of precipitating a metal from its aqueous solution by addition of less noble metal is called _____
a) condensation method
b) gaseous Reduction process
c) precipitation from aqueous solution method
d) precipitation from fused salts method
Answer: c
Explanation: The method employing the principle of precipitating a metal from its aqueous solution by addition of less noble metal which is higher in electromotive series is called precipitation from aqueous solution method. This method produces a very fine metal powder with low apparent density.
10. Which of the following is added to the SnCl 2 solution to precipitate Sn?
a) Al
b) Zn
c) Cu
d) Fe
Answer: b
Explanation: Tin powder is precipitated by metallic zinc from stannous chloride. Al is used to precipitate Cu/Fe/Ni from their sulphate solution and Cu, Fe is used to precipitate Ag from its nitrate solution.
11. Which of the following is not a characteristic of powder produced by precipitation from an aqueous solution method?
a) Porous in nature
b) High apparent density
c) Low apparent density
d) Difficult to remove the adherent salts
Answer: b
Explanation: The precipitated metal powders are generally porous in nature and have low apparent density. A major drawback of the precipitation method lies in the fact that the adherent or entrained salts are more difficult to remove than in electrolytic powder products.
12. Which of the reducing agent is used for the production of Zn powder by condensation method?
a) CaC 2
b) Charcoal
c) CO 2
d) H 2
Answer: b
Explanation: Zinc dust is produced by first mixing powdered charcoal to zinc oxide and it is then heated until zinc vapour is formed by the reaction of zinc oxide with carbon monoxide. The Zn vapour is then condensed in a cooler extension of the retort, the condensed vapour is then turned to zinc powder. CaC 2 is used for the production of Mg powder.
This set of Powder Metallurgy Multiple Choice Questions & Answers focuses on “Particle Size Measurement Techniques”.
1. Stoke’s law can be represented by which of the following equation?
a) V=(ρ p – ρ f )d 3 g/18η
b) V=(ρ p – ρ f )d 2 g/18η
c) V=(ρ f – ρ p )d 2 g/18η
d) V=(ρ p – ρ f )d 2 /18ηg
Answer: b
Explanation: Stoke’s law which states that the settling velocity of falling spherical particles at low velocity in a quiescent homogenous fluid of infinite extent is proportional to the square of the particle diameter, can be represented by the equation V=(ρ p – ρ f ) d 2 g/18η where, V is the terminal velocity of the particle in cm/sec, ρ f and ρ p are the density of fluid and particle respectively in gm/cc, d is the diameter of particle in cm, g is the gravitational acceleration in cm/sec 2 and η is the viscosity of fluid in poises.
2. Reynold number can be expressed as R=Vdρ f /η.
a) True
b) False
Answer: a
Explanation: Reynold number is used to determine whether the flow is turbulent or laminar where, V is the terminal velocity of the particle in cm/sec, ρ f is the density of fluid in gm/cc, d is the diameter of particle in cm and η is the viscosity of fluid in poises.
3. Which of the following is a fractionation method for sizing by sedimentation method?
a) Hydrometer method
b) Pipette method
c) Sedimentation and decantation method
d) Turbidimetry
Answer: c
Explanation: Sedimentation and decantation method is a fractionation method for sizing by sedimentation method whereas hydrometer method, pipette method and turbidimetry are non-fractionation methods which are used for determining size distribution and estimating specific surface.
4. Which system of sieves is used in Germany?
a) DIN system
b) B.S. system
c) AFNOR system
d) Tyler system
Answer: a
Explanation: Different systems of sieves are used in various countries for the determination of sieve size powders. In Germany usually the DIN system, in U.K mainly the B.S. system, in France the AFNOR system and in America the Tyler system is widely prevalent.
5. ____ particles are smaller than 44-micron but greater than 1-micron aperture.
a) Sieve
b) Sub-sieve
c) Sub-micron
d) Ultra-fine
Answer: b
Explanation: The particles having size > 44-micron fall in the category of sieve class. Sub-sieve particles are smaller than 44-micron but greater than 1-micron aperture, and the sub-micron or ultra-fine powder particle size is smaller than 1-micron.
6. Which of the following are the techniques for particle size measurement?
a) Macroscopic analysis
b) Sieve analysis and Absorption method
c) Sieve analysis, microscopic analysis, sedimentation method, and permeability method
d) Filtration method and Sieve analysis
Answer: c
Explanation: There are 7 particle size measurement technique which are as follows: Sieving analysis, Microscopic analysis, Sedimentation method, Elutriation method, Permeability method, Adsorption method and Electrolytic Resistivity method.
7. The particle size measurement technique based on the settling velocity of particles in stationary fluid medium is called _____
a) Sedimentation Method
b) Microscopic Method
c) Elutriation Method
d) Permeability Method
Answer: a
Explanation: Sedimentation method is based on the settling velocity of particles in stationary fluid medium whereas, elutriation differs from sedimentation in that the fluid is in motion in the upward direction against the falling particles. Microscopic method involves actual counting of particles. The permeability method involves measuring the pressure drop across the bed of packed powder particles contained in a chamber in relation to the fluid flow.
8. _______ is the statistical relation between amount and size.
a) Particle size distribution
b) Cumulative weight retained
c) Particle size
d) Packing density
Answer: a
Explanation: Particle size distribution is the statistical relation between amount and size. It is also of fundamental importance as it affects the pressing and sintering behavior as well as the physical and mechanical properties of the sintered material.
9. _______ establishes the relationship between the settling velocity of falling particles and particle size.
a) Hess law
b) Continuity equation
c) Stoke’s law
d) Bernoulli’s equation
Answer: c
Explanation: Stoke’s law establishes the relationship between the settling velocity of falling particles and particle size which states that the settling velocity of falling spherical particles at low velocity in a quiescent homogenous fluid of infinite extent is proportional to the square of the particle diameter.
10. The laboratory methods for sizing by _________ can be divided into fractionating and non-fractionation groups.
a) Elutriation method
b) Sedimentation method
c) Adsorption method
d) Permeability method
Answer: b
Explanation: The laboratory methods for sizing by sedimentation can be divided into 2 groups: The fractionating methods are employed when it is essential to separate individual size fractions for individual examinations. Non-fractionation methods are used for determining size distribution and estimating specific surface.
11. In Tyler standard screen scale, sieve series having a ratio of ______ is used.
a) \ \ \ \(\sqrt[4]{3}\) : 1
Answer: b
Explanation: In Tyler standard screen scale, the width of each consecutive opening is exactly \(\sqrt{2}\) times the width of the previous sieve and hence the area of openings is doubled from the next finer sieve. If a closer sizing is required, an expanded sieve series having the ratio of \(\sqrt[4]{2}\):1 is used in which each and every sieve is a part of their \(\sqrt{2}\) series.
12. ________ is the particle size through square grid method where magnification of the objective is x10.
a) 0.259 mm
b) 0.282 mm
c) 0.156 mm
d) 2.963 mms
Answer: b
Explanation: In optical microscopy, there are two objective lens and one of them contain a square grid and area of each square is 0.25m 2 . We can calculate the particle size using this square grid where we have to count the number of 100%, 75%, 50% and 25% squares and then using the below formula we obtain the particle size.
d=\(\frac{\sqrt{x}}{\sqrt{\pi \times magnification \, of \, objective}}\) where, x=Number of squares x Area of 1 square and d=particle diameter
Thus, from the above figure: 100% square=6; 75% square=2; 50% square=4 and 25% square=2. Hence, x=10 x 0.25=2.5. Therefore, d=\(\frac{\sqrt{2.5}}{\sqrt{\pi \times 10}}\)=0.282mm.
13.________ is the particle size through linear/ horizontal scale method where magnification of the objective is x10.
a) 0.21mm
b) 2.10mm
c) 0.20mm
d) 0.22mm
Answer: a
Explanation: The formula to calculate particle diameter is given by:
d=\(\frac{number \, of \, division \times L.C}{magnification \, of \, objective}\) where, number of division=last – start point and L.C=least count=0.1mm
Thus, from the above figure: number of division=56-35=21
Hence, d=\(\frac{21 \times 0.1}{10}\)=0.21mm.
14. The below figure represents the relative size distribution graph.
a) True
b) False
Answer: a
Explanation: The above figure represents the relative size distribution graph which is a curve between % weight retained and particle size. This curve represents a narrow particle size distribution because of narrow peak and thus particles have a close size range .
This set of Powder Metallurgy online quiz focuses on “Particle Characterisation, Particle Shape and Specific Area”.
1. Which of the following concepts are used to differentiate and describe particle shapes?
a) Dimensionality of particle
b) Dimensionality and Surface contour
c) Surface contour of particle
d) Dimensionality and atomic mass
Answer: b
Explanation: Two different concepts used to differentiate and describe particle shapes are based on, the dimensionality of the particle , and the surface contour of the particle.
2. Particle shape can be defined as, “the recognized pattern of relationship between points that form the internal surface of the particle.”
a) True
b) False
Answer: b
Explanation: Particle shape can be defined as, “the recognized pattern of relationship between points that form the external surface of the particle.” Particle shape analysis is a fundamental characteristic of powder particles, which influences other parameters like flow rate, apparent density, compressibility, and sinterability.
3. Which of the following criteria can be used for shape characterization?
a) Verbal expression and evaluation of bulk properties
b) Shape factor
c) Verbal expression, shape factor, and evaluation of bulk properties
d) Shape factor, shape generation, verbal expression, and bulk property evaluation
Answer: d
Explanation: Shape characterization falls under 4 different classes. They are, Verbal expression ; Use of dimensionless number ; Shape generation using Fourier analysis, polynomial fitting, matrix mapping; Evaluation of bulk properties.
4. Which method cannot be used to determine the particle shape?
a) Sieve analysis
b) Optical microscopy
c) SEM
d) TEM
Answer: a
Explanation: Particle shape can be determined through various methods like optical microscopy, scanning electron microscope , transmission electron microscope , image analyzer. Sieve analysis is used to evaluate particle size distribution.
5. Which of the following particle shape is not produced by the chemical decomposition process of powder manufacture?
a) Acicular
b) Flaky
c) Rod-like
d) Rounded
Answer: b
Explanation: Acicular , rod-like , rounded particle shapes are produced on chemical decomposition process to manufacture powder. Flaky is possessed by ball-milled aluminum.
6. ______ determines the surface area of powder by measuring the amount of gas adsorbed by a monomolecular layer of the powder.
a) Centrifugal method
b) Gas absorption method
c) Gas adsorption method
d) Permeability method
Answer: c
Explanation: The gas adsorption method determines the surface area of powder by measuring the amount of gas adsorbed by a monomolecular layer of the powder. Nitrogen is the most commonly used gas. This method can also be used to determine the pore volume and size distribution, for pore diameters ranging from 600Ȧ down to 14Ȧ.
7. _____ measures the resistance to fluid flow through a compacted powder bed to calculate the specific surface of the powder.
a) Permeametry
b) Gas adsorption method
c) Elutriation Method
d) Sedimentation method
Answer: a
Explanation: Permeametry or permeability method measures the resistance to fluid flow through a compacted powder bed to calculate the specific surface of the powder. The principle involves measuring the pressure drop across the bed of packed powder particles contained in a chamber in relation to the fluid flow. This information is used to determine related properties of the powder such as specific surface area and average particle size.
8. The unit for measuring the specific surface of the powder is _____
a) cm 2 /gm
b) cm/sec
c) cm 3 /gm
d) cm/gm 2
Answer: a
Explanation: The specific surface of the powder is defined as the total surface area per unit weight (cm 2 /gm). It depends on the size, shape, density and surface conditions of the particle.
9. Carman’s equation is given by S 0 = _____
a) \
\
\
\(\frac{\sqrt{K\gamma \epsilon^3}}{\sqrt{^2}}\)
Answer: a
Explanation: The relation between surface area and permeability for gases and liquid is given by the Carman’s equation which is as follows: S 0 =\(\frac{\sqrt{K\gamma \epsilon^3}}{\sqrt{^2}}\) where S 0 is the specific surface (cm 2 /gm), k a proportionality constant with a value of 5, K the permeability constant , γ the kinematic viscosity of the fluid , ε is the fractional free volume and g the gravitational constant (cm/sec 2 ).
10. The adsorption method used for determining the specific surface makes use of which instrument?
a) Fisher Sub-siever
b) BET apparatus
c) Hall Flowmeter
d) Scott Volumeter
Answer: b
Explanation: The adsorption method used for determining the specific surface makes use of the BET apparatus, named after Brunauer, Emmett, and Teller, who developed this method. The permeability method used for determining the specific surface makes use of the Fisher Sub-siever apparatus and for measuring apparent density we may use either Hall Flowmeter or Scott Volumeter.
11. The shape factor is given by the ratio of surface area to particle size.
a) True
b) False
Answer: a
Explanation: The shape factor is given by the ratio of surface area to particle size or as the ratio of the length of the particle to its breadth. The presence of cracks, fissures, or grain boundaries in the individual particles increases considerably the shape factor.
12. Which of the following characteristics does irregular shaped particles do not possess?
a) Reduced apparent density
b) Good pressing properties
c) Good sintering properties
d) Maximum flow rate
Answer: d
Explanation: Irregularly shaped particles possess reduced apparent density and flow rate but good pressing and sintering properties. Spherical shaped particles possess maximum apparent density and flow rate but reduced pressing and sintering properties.
