Engineering Questions with Answers - Multiple Choice Questions

# Manufacturing Processes – Annealing – 6

1 - Question

The rate at which a metal recrystallizes depends on the rate of ______
a) cooling
b) polygonization
c) nuclei formation
d) grain growth
Explanation: The rate at which a metal recrystallizes depends on the rate at which nuclei form, and also on the rate at which they grow. These two rates also determine the final grain size of a recrystallized metal.

2 - Question

The grain size will be smaller when ______
a) nuclei form rapidly and grow slowly
b) nuclei form slowly and grow rapidly
c) recrystallization temperature is high
d) activation energy is low
Explanation: If nuclei form rapidly and grow slowly, many crystals will form before their mutual impingement completes the recrystallization process. In this case, the final grain size is small. On the other hand, it will be larger if the rate of nucleation is small compared to the rate of growth.

3 - Question

The number of nuclei that form per second is called as _____
a) recrystallization frequency
b) nucleation frequency
c) nuclei growth frequency
d) grain growth frequency
Explanation: It is customary to define the nucleation frequency, N, as the number of nuclei that form per second in a cubic centimetre of unrecrystallized matrix. The grain size is dependent on the rate of formation and growth of nuclei.

4 - Question

The time rate of change of the diameter of a recrystallized grain is known as_____
a) diameter rate
b) linear growth rate
c) growth rate
d) nucleation rate
Explanation: The linear rate of growth, G, is defined as the time rate of change of the diameter of a recrystallized grain. In practice, G is measured by annealing for different lengths of time a number of identical specimens at a chosen isothermal temperature.

5 - Question

The variation of this diameter with isothermal annealing time gives the _____
a) nucleation rate
b) linear rate of growth
c) grain size change rate
d) diametrical growth rate
Explanation: The variation of this diameter with isothermal annealing time gives the rate of growth, G. The diameter of the largest grain in each specimen is measured after the specimens are cooled to room temperature and prepared metallographically.

6 - Question

The rate of nucleation can be defined as______
a) number of grains per unit area
b) number of grains per unit volume
c) number of nuclei formed per unit area per unit time
d) number of grains formed per nuclei
Explanation: The rate of nucleation can be determined from the same metallographic specimens by counting the number of grains per unit area on the surface of each.

7 - Question

For ______ nucleation will take place preferentially at highly energetic sites.
a) pure metals
b) alloys
c) polycrystalline
d) brittle
Explanation: For polycrystalline materials, nucleation will take place preferentially at highly energetic sites, such as grain-boundary triple points, original grain boundaries, and boundaries between deformation bands.

8 - Question

The nuclei may form by ______
a) grain growth
b) sub-grain growth
c) nuclei boundary growth
d) combining multiple grains
Explanation: The nuclei may form by subgrain growth and/or grain boundary migration. As a result of polygonization, it might be possible to produce a subgrain capable of growing out into the surrounding polygonized matrix.

9 - Question

In recrystallization, an entirely new set of grains is formed.
a) True
b) False