This set of Powder Metallurgy Multiple Choice Questions & Answers (MCQs) 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
View Answer
Explanation: In the sintering of multicomponent systems, the material transport mechanisms involve interdiffusion of the components into one another (due to concentration gradient) 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
View Answer
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
View Answer
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
View Answer
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
View Answer
Explanation: For liquid phase sintering to occur there are three main considerations: (1) Presence of an appreciable amount of liquid phase, (2) Appreciable solubility of solid in liquid, and (3) 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
View Answer
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
View Answer
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=\(\frac{\gamma_{GS}-\gamma_{SL}}{\gamma_{LG}}\)
b) sinθ=\(\frac{\gamma_{GS}-\gamma_{SL}}{\gamma_{LG}}\)
c) cosθ=\(\frac{\gamma_{SL}-\gamma_{GS}}{\gamma_{LG}}\)
d) cosθ=\(\frac{\gamma_{LG}-\gamma_{SL}}{\gamma_{GS}}\)
View Answer
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,γGS, γSL, and γLG are the surface energies or tensions of the solid-gas interface, solid-liquid interface and liquid-gas interface respectively.
Sanfoundry Global Education & Learning Series – Powder Metallurgy.
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