Manufacturing Processes Multiple Choice Questions on “Annealing – 1”.
1. The metal is said to be cold worked if it is plastically deformed at temperatures lower than _____
a) sublimation point
b) critical point
c) melting point
d) saturation point
Answer: c
Clarification: When a metal is plastically deformed at temperatures that are low relative to its melting point, it is said to be cold worked. A rough rule-of-thumb is to assume that plastic deformation corresponds to cold working if it is carried out at temperatures lower than one-half of the melting point measured on an absolute scale.
2. The fraction of total energy stored in the material _____ with increasing deformation.
a) increases
b) decreases
c) first increases and then decreases
d) remains constant
Answer: b
Clarification: Most of the energy expended in cold work appears in the form of heat, but a finite fraction is stored in the metal as strain energy associated with various lattice defects created by the deformation. The stored energy increases with increasing deformation, but at a decreasing rate, so that the fraction of the total energy stored decreases with increasing deformation.
3. The amount of stored energy can be greatly increased by _____
a) lowering the deformation temperature
b) increasing the deformation temperature
c) increasing the purity of the metal
d) reducing the net volume
Answer: a
Clarification: The amount of stored energy can be greatly increased by,
• increasing the severity of the deformation
• lowering the deformation temperature
• changing the pure metal to an alloy.
4. A soft annealed metal can have dislocation densities of the order of _____
a) 105 to 106 m-2
b) 108 to 1010 m-2
c) 1010 to 1012 m-2
d) 1010 to 1015 m-2
Answer: c
Clarification: Cold working is known to increase greatly the number of dislocations in a metal. A soft annealed metal can have dislocation densities of the order of 1010 to 1012 m-2, and heavily cold-worked metals can have approximately 1016.
5. Strain energy of the metal _____ with increasing the dislocation densities.
a) increases
b) decreases
c) does not change
d) first decreases and then remains constant
Answer: a
Clarification: Since each dislocation represents a crystal defect with an associated lattice strain, increasing the dislocation density increases the strain energy of the metal. Cold working is able to increase the number of dislocations in metal by a factor as large as 104to 106.
6. Vacancies in the metal lattice will be formed in greater numbers than interstitial atoms during _____
a) plastic deformation
b) brittle deformation
c) heating over melting temperature
d) non-linear deformation
Answer: a
Clarification: Since the strain energy associated with a vacancy is much smaller than that associated with an interstitial atom, it can be assumed that vacancies will be formed in greater numbers than interstitial atoms during plastic deformation.
7. Which of the following relations is true?
a) ΔG = ΔH – TΔS
b) ΔH = ΔG – TΔS
c) ΔT = ΔH – GΔS
d) ΔG = TΔH – ΔS
Answer: a
Clarification: ΔG = ΔH – T ΔS, this equation is known as Gibb’s free energy equation. While plastic deformation certainly increases the entropy of a metal, the effect is small compared to the increase in internal energy (the retained strain energy). The term T∆S in the free energy equation may be neglected and the free-energy increase equated directly to the stored energy. Where ∆G is the free energy associated with the cold work, ∆H is the enthalpy or stored strain energy, ∆S is the entropy increase due to the cold work, and T is the absolute temperature.
8. Free energy of cold-worked metals is _____ than/as that of annealed metals.
a) greater
b) lower
c) same
d) greater of few metals
Answer: a
Clarification: Since the free energy of cold-worked metals is greater than that of annealed metals, they may soften spontaneously. Heating a deformed metal greatly speeds up its return to the softened state.
9. The anisothermal anneal method, the energy release is determined as a function of temperature.
a) True
b) False
Answer: a
Clarification: The anisothermal anneal method, the cold worked metal is heated continuously from a lower to a higher temperature and the energy release is determined as a function of temperature. One form of the anisothermal anneal measures the difference in the power required to heat two similar specimens at the same rate.
10. The one specimen form above mentioned specimen is cold worked.
a) True
b) False
Answer: a
Clarification: One specimen of the two is cold worked before the heating cycle, while the other serves as a standard and is not deformed. During the heating cycle, the cold-worked specimen undergoes reactions that release heat and lower the power required to heat it in comparison with that required to heat the standard specimen. Measurements of the difference in power give direct evidence of the rate at which heat is released in the cold-worked specimen.
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