Manufacturing Processes Multiple Choice Questions on “Annealing – 10”.
1. Temperature dependence of the grain-growth can be explained by ______
a) recrystallization theory
b) planks theory
c) assuming that grain boundaries brake due to thermal vibrations
d) strain energy theory
Answer: c
Clarification: The temperature dependence of the grain-growth exponent can be explained by assuming that the grain-boundary solute atmospheres are broken up by thermal vibrations at high temperatures. Those elements that distort the lattice structure the most have the largest effect on the rate of grain growth.
2. The presence of foreign particles _____
a) increases recrystallization temperature
b) improves surface hardness of the specimen
c) retards the grain boundary motion
d) softens the specimen
Answer: c
Clarification: Solute atoms in solid solution can form grain boundary atmospheres, the presence of which retards the normal surface-tension induced boundary motion. In order for the boundary to move, it must carry its atmosphere along with it.
3. _____ lowers the retarding effect of the solute/foreign atoms.
a) Increase in temperature
b) Decrease in temperature
c) Increase in amount of solute atoms
d) Decrease in size of solute atoms
Answer: a
Clarification: An increase in temperature lowers the retarding effect of the solute atoms and grain growth occurs under conditions more closely resembling the growth of soap cells.
4. At the high temperatures normally associated with annealing, _____
a) grooves may form on the surface
b) irregularity in surface roughness may occur
c) unwanted bump may form
d) decrease in yield strength may occur
Answer: a
Clarification: At the high temperatures normally associated with annealing, grooves may form on the surfaces where grain boundaries intersect the specimen surface.
5. Grain-boundary grooves are important in grain growth because of _____
a) they can counter the unwanted surface irregularities
b) they improve surface finish
c) they tend to fix the ends of grain boundaries
d) they are the result of perfect recrystallization process
Answer: c
Clarification: Grain-boundary grooves are important in grain growth because they tend to anchor the ends of the grain boundaries (where they meet the surface), especially if the boundaries are nearly normal to the surface.
6. Thermal grooving has little effect on the overall rate of growth when ______
a) average grain size of the specimen is very small as compared to the size of the specimen
b) average grain size of the specimen is larger as compared to the size of the specimen
c) temperature of the specimen is lower than recrystallization temperature
d) specimen has a high thermal conductivity
Answer: a
Clarification: When the average grain size of a metal specimen is very small compared to the dimensions of the specimen, thermal grooving, or the lack of curvature in the surface grains, has little effect on the overall rate of growth. However, when the grain size approaches the dimensions of the thickness of the specimen, it can be expected that grain-growth rates will be decreased.
7. During normal grain growth, the moving boundaries will be attached to the particles, so that _____
a) the particles exert a pulling force on the boundary
b) the particles exert a pushing force on the boundary
c) grain growth occurs at higher rate
d) surface structure does not get disturbed