Manufacturing Processes Multiple Choice Questions on “Annealing – 2”.
1. In _____ annealing, the energy is measured while the specimen is maintained at a constant temperature.
a) isothermal
b) adiabatic
c) anisothermal
d) isentropic
Answer: a
Clarification: The other method of studying energy release involves isothermal annealing. Here the energy is measured while the specimen is maintained at a constant temperature. The large energy releases appear simultaneously with the growth of an entirely new set of essentially strain-free grains, which grow at the expense of the original badly deformed grains.
2. Which of the following is not a microstructural change occurring in the metal while is plastic deformation?
a) change in grain size
b) strain hardening
c) formation of metallic bonds
d) change in dislocation density
Answer: c
Clarification: Plastic deforming a polycrystalline metal specimen at temperatures that are low relative to its absolute melting temperature produces microstructural and property changes that include (1) a change in grain size, (2) strain hardening, and (3) an increase in dislocation density.
3. Properties such as _____ may be modified as a consequence of plastic deformation.
a) electrical conductivity
b) tensile strength
c) malleability
d) weldability
Answer: a
Clarification: Properties such as electrical conductivity and corrosion resistance may be modified as a consequence of plastic deformation. These properties and structures may revert back to the precold-worked states by an annealing treatment. Such restoration results from two different processes that occur at elevated temperatures: recovery and recrystallization, which may be followed by grain growth.
4. During recovery, some of the stored internal strain energy is relieved by virtue of _____
a) increased grain size
b) molten metal
c) dislocation movements
d) high temperature
Answer: c
Clarification: During recovery, some of the stored internal strain energy is relieved by virtue of dislocation motion, as a result of enhanced atomic diffusion at the elevated temperature.
5. During recovery, there is some reduction in the ______
a) number of grains
b) number of dislocations
c) tensile strength of the metal
d) strain energy
Answer: b
Clarification: There is some reduction in the number of dislocations, and dislocation configuration are produced having low strain energies. Physical properties such as electrical and thermal conductivities and the like are recovered to their precold worked states. However, even after recovery is complete, the grains are still in a relatively high strain energy state.
6. The driving force to produce new grain structure is the difference ______ between the strained and unstrained material.
a) entropy
b) temperature
c) internal energy
d) conductivity
Answer: c
Clarification: The driving force to produce new grain structure is the difference in internal energy between the strained and unstrained material. The new grains form as very small nuclei and grow until they completely consume the parent material, processes that involve short-range diffusion.
7. During recrystallization, the metal becomes _____
a) harder
b) soft
c) brittle
d) malleable
Answer: b
Clarification: During recrystallization, the metal becomes softer, weaker, yet more ductile. Recrystallization of cold-worked metals may be used to refine the grain structure.
8. The degree of recrystallization increases with _____
a) temperature
b) softness
c) time
d) strain energy
Answer: c
Clarification: Recrystallization is a process the extent of which depends on both time and temperature. The degree of recrystallization increases with time. Metal becomes soft due to recrystallization but they are not dependent on each other.
9. Recrystallization is the formation of a new strain-free grain.
a) True
b) False
Answer: a
Clarification: Recrystallization is the formation of a new set of strain-free and equiaxed grains that have low dislocation densities and are characteristic of the precold-worked condition.
10. Recrystallization temperature is the temperature at which molten metal starts solidifying.
a) True
b) False
Answer: b
Clarification: Recrystallization temperature is the temperature at which recrystallization just reaches completion in 1 hr. Typically it is between one-third and one-half of the absolute melting temperature of a metal or alloy and depends on several factors, including the amount of prior cold work and the purity of the alloy.