EMA3010 FINAL LATEST EXAM
QUESTIONS AND CORRECT VERIFIED
ANSWERS
Q: transformation rate
Ans: The reciprocal of the time necessary for a reaction to
proceed halfway to its completion.
Quiz: 3 types of phase transformations
,Ans: 1. simple diffusion-dependent transformations - no
change in either the number or composition of the phases
present (solidification of a pure metal, allotropic
transformations, and recrystallization and grain growth).
2. diffusion dependent transforamtion #2 - some alteration in
phase compositions and often in the number of phases present;
the final microstructure typically consists of two phases.
3. diffusionless transformation - metastable phase is produced.
Quiz: stages of phase transformation
,Ans: 1. nucleation - evidenced by the formation of small
particles (nuclei) of the new phase that are capable of growing.
2. growth - nuclei increase in size, which results in the
disappearance of some (or all) of the parent phase.
Quiz: Types of Nucleation
Ans: 1. homogeneous - nuclei of the new phase form
uniformly throughout the parent phase. nuclei form in the bulk
of liquid metal. requires considerable supercooling
2. heterogeneous - nuclei form preferentially at structural
inhomogeneities, such as container surfaces, insoluble
impurities, grain boundaries, and dislocations. much easier since
stable "nucleating surface" is already present — e.g., mold wall,
impurities in liquid phase. only very slight supercooling.
, Quiz: A transformation occurs spontaneously only when
Ans: ΔG has a negative value
Quiz: 2 contributions to the total free energy change that accompany a
solidification transformation.
Ans: 1. free energy difference between the solid and liquid
phases, or the volume free energy, ΔGv. Negative if the
temperature is below the equilibrium solidification temperature.
2. Results from the formation of the solid-liquid phase boundary
during the solidification transformation. Associated with this
boundary is a surface free energy, γ which is positive
Quiz: as a solid particle begins to form as atoms in the liquid cluster
together, its free energy first increases. If this cluster reaches a size
corresponding to the critical radius r*, then growth will continue with
the accompaniment of a decrease in free energy. However, a cluster of
QUESTIONS AND CORRECT VERIFIED
ANSWERS
Q: transformation rate
Ans: The reciprocal of the time necessary for a reaction to
proceed halfway to its completion.
Quiz: 3 types of phase transformations
,Ans: 1. simple diffusion-dependent transformations - no
change in either the number or composition of the phases
present (solidification of a pure metal, allotropic
transformations, and recrystallization and grain growth).
2. diffusion dependent transforamtion #2 - some alteration in
phase compositions and often in the number of phases present;
the final microstructure typically consists of two phases.
3. diffusionless transformation - metastable phase is produced.
Quiz: stages of phase transformation
,Ans: 1. nucleation - evidenced by the formation of small
particles (nuclei) of the new phase that are capable of growing.
2. growth - nuclei increase in size, which results in the
disappearance of some (or all) of the parent phase.
Quiz: Types of Nucleation
Ans: 1. homogeneous - nuclei of the new phase form
uniformly throughout the parent phase. nuclei form in the bulk
of liquid metal. requires considerable supercooling
2. heterogeneous - nuclei form preferentially at structural
inhomogeneities, such as container surfaces, insoluble
impurities, grain boundaries, and dislocations. much easier since
stable "nucleating surface" is already present — e.g., mold wall,
impurities in liquid phase. only very slight supercooling.
, Quiz: A transformation occurs spontaneously only when
Ans: ΔG has a negative value
Quiz: 2 contributions to the total free energy change that accompany a
solidification transformation.
Ans: 1. free energy difference between the solid and liquid
phases, or the volume free energy, ΔGv. Negative if the
temperature is below the equilibrium solidification temperature.
2. Results from the formation of the solid-liquid phase boundary
during the solidification transformation. Associated with this
boundary is a surface free energy, γ which is positive
Quiz: as a solid particle begins to form as atoms in the liquid cluster
together, its free energy first increases. If this cluster reaches a size
corresponding to the critical radius r*, then growth will continue with
the accompaniment of a decrease in free energy. However, a cluster of
