Engineering Questions with Answers - Multiple Choice Questions
Manufacturing Processes – Annealing – 2
1 - Question
In _____ annealing, the energy is measured while the specimen is maintained at a constant temperature.
Explanation: 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 - Question
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
Explanation: 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 - Question
Properties such as _____ may be modified as a consequence of plastic deformation.
a) electrical conductivity
b) tensile strength
Explanation: 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 - Question
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
Explanation: 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 - Question
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
Explanation: 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 - Question
The driving force to produce new grain structure is the difference ______ between the strained and unstrained material.
c) internal energy
Explanation: 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 - Question
During recrystallization, the metal becomes _____
Explanation: During recrystallization, the metal becomes softer, weaker, yet more ductile. Recrystallization of cold-worked metals may be used to refine the grain structure.
8 - Question
The degree of recrystallization increases with _____
d) strain energy
Explanation: 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 - Question
Recrystallization is the formation of a new strain-free grain.
Explanation: 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 - Question
Recrystallization temperature is the temperature at which molten metal starts solidifying.
Explanation: 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.