This set of Powder Metallurgy Multiple Choice Questions & Answers (MCQs) 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
View Answer
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
View Answer
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
View Answer
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
View Answer
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
View Answer
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
View Answer
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
View Answer
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
View Answer
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
View Answer
Explanation: Rotating disk atomization process falls under the category of Rapid Solidification Process (RSP) techniques, where, because of high cooling rates involved, the solidification time is reduced. The other advantages include: (1) reduced tendency for chemical segregation, (2) very fine microstructural features like grain size, (3) increased solid solubility od alloying elements, and (4) 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
View Answer
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
View Answer
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.
Sanfoundry Global Education & Learning Series – Powder Metallurgy.
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