This set of Powder Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Structure and Property Changes during Sintering”.
1. Densification cannot be treated as equal to the amount of porosity removed.
a) True
b) False
View Answer
Answer: a
Explanation: Densification is proportional to the shrinkage or the number of pores removed in the case of single component systems (e.g. metals). In the case of multicomponent systems such as premixed powders, during sintering solid solutions may form resulting in an expansion rather than shrinkage. Expansion of the compact may also take place due to the entrapped gases. Thus, densification cannot be treated as equal to the amount of porosity removed.
Explanation: Densification is proportional to the shrinkage or the number of pores removed in the case of single component systems (e.g. metals). In the case of multicomponent systems such as premixed powders, during sintering solid solutions may form resulting in an expansion rather than shrinkage. Expansion of the compact may also take place due to the entrapped gases. Thus, densification cannot be treated as equal to the amount of porosity removed.
2. Sintering results in ________
a) Change in structure of compact
b) Structural change, recrystallization, and grain shrinkage
c) Structural change, reduction of surface oxides, and grain growth
d) Pore growth
View Answer
Answer: c
Explanation: Densification during sintering usually results in a change in the structure of grains as well those of pores present in the initial compact. Reduction of surface oxides may occur during sintering in a reducing atmosphere. In case of powder mixes, containing metals with lower melting point, evaporation of these metals can occur. Other changes occurring during sintering include recrystallization and grain growth. Pore growth also occurs if sintering is carried out for longer times at high temperatures.
Explanation: Densification during sintering usually results in a change in the structure of grains as well those of pores present in the initial compact. Reduction of surface oxides may occur during sintering in a reducing atmosphere. In case of powder mixes, containing metals with lower melting point, evaporation of these metals can occur. Other changes occurring during sintering include recrystallization and grain growth. Pore growth also occurs if sintering is carried out for longer times at high temperatures.
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