# Mechanical Metallurgy Questions and Answers – Strengthening Mechanisms – Strain Hardening – 2

This set of Mechanical Metallurgy Interview Questions and Answers for Experienced people focuses on “Strengthening Mechanisms – Strain Hardening – 2”.

1. Increasing temperature will lower the rate of strain hardening.
a) True
b) False

Explanation: On increasing temperature, flow of dislocation becomes easier, so the rate of strain hardening will be reduced.

2. The following curve is the plot of the percentage of cold work in the sample with various properties. Which of the following combination of the properties to their given values is correct?

a) A-Tensile Strength, B- Yield Strength, C-Ductility
b) A-Ductility, B-Yield strength, C-Tensile Strength
c) A-Ductility, B-Tensile Strength, C- Yield Strength
d) A-Tensile Strength, B-Ductility, C-Yield Strength

Explanation: The tensile strength and yield strength of a material increase with the increase in cold work. But the ductility of the material will reduce.

3. The electrical resistivity and chemical reactivity of the material increase with cold working.
a) True
b) False

Explanation: With cold working, the center for electron scattering increase, so the conductivity decrease and resistivity increase for the given material. Due to the increase in internal energy, the chemical reactivity is also increased.

4. If the cold-worked material of 1 cm3 is enlarged in size of an auditorium(50*50*50m), the typical width of dislocation corresponding to this auditorium would be equivalent to _________
a) the size of rope with thickness 1cm
b) a rope width equal to 1m
c) spider web thickness equal to 0.1mm
d) invisible bacteria with width 1 nm

Explanation: The actual size of a dislocation in a material is equivalent spider web network in an auditorium. This is the typical scale to keep in mind.

5. Property which is most affected by recovery process is ___________
a) structure sensitive property
b) point defect sensitive property
c) dislocation sensitive
d) surface sensitive

Explanation: Recovery is the first process in annealing of metal. Here, the lost properties of the metal such as electrical resistivity, stored lattice energy, etc. are recovered. These properties are generally most associated with point defect of the material.
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6. The driving force for recrystallization is _________
a) the stored energy of cold working
b) the decrease in the grain area energy
c) the decrease in the point defect energy
d) the thermal energy of heating

Explanation: The driving force for both the recovery and recrystallization is stored energy inside the lattice during cold working. This energy is released by recovery and recrystallization.

7. The driving force for grain growth is _________
a) the stored energy of cold working
b) the decrease in the grain area energy
c) the decrease in the point defect energy
d) the thermal energy of heating

Explanation: Grain boundaries are an area of high energy. During grain growth, the size of grain increases, which reduces the total grain boundary area of the material.

8. The recrystallization temperature is defined as the temperature at which highly cold-worked alloy can be recrystallized in 1 hr.
a) True
b) False

Explanation: The recrystallization can be carried out at a higher temperature, but the exact definition for this temperature is the temperature at which highly cold-worked alloy can be recrystallized in 1 hr.

9. The Smaller the degree of deformation, the ____________ the required temperature to cause recrystallization.
a) higher
b) lower
c) unaffected
d) cannot comment

Explanation: If the degree of deformation is smaller, the stored lattice strain energy will be lower. This will result in the lower driving force for recrystallization, and hence, higher temperature will be required.

10. If an annealing process is carried completing in 50 min at temperature T and the annealing time is reduced to 25 min, the temperature should be increased by ________
a) 2T
b) 3T
c) T+10° Degree
d) T+100° Degrees

Explanation: This is experimentally observed that on every 10° increase in temperature, the recrystallization time is reduced to half. So, the temperature should be increased by 10°.

11. The recrystallization temperature _______________ with increasing purity of the material.
a) increases
b) decreases
c) remains unaffected
d) no relationship

Explanation: As the purity increase, it becomes easier for the dislocation to move and rearrange. So the recrystallization becomes easier as the temperature decreases.

12. Abnormal grain growth is defined as ________________
a) growth of grain much larger than other nearby grain
b) growth of all grain to a much larger extent
c) growth in an irregular shape
d) growth in a regular shape

Explanation: Certain grain is crystallographically oriented in favorable direction which make them grow much faster than other grains. The driving force is decrease in surface energy.

13. The texture in a material cannot be found by __________
a) Optical microscope
b) XRD
c) SEM
d) FTIR

Explanation: The texture is preferred orientation of grain along a certain direction. This can be detected by XRD most effectively whereas the FTIR is an analysis method to find bonding between atoms.

14. The transformer sheet is an example of texture in material.
a) True
b) False

Explanation: The cube-oriented iron silicon sheet for transformers is produced because the energy loses can be minimized by orientating grain in the easy direction of magnetization.

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