MSE 503 EXAM 5 QUESTIONS AND VERIFIED
ANSWERS
If a solid nucleus is formed within a liquid, there is a solid liquid interface between the
nucleus and the surrounding liquid. Does this interface have a higher energy or a lower
energy than that of the interface of the bulk solid with air? - Answers - Lower
How can a nucleus with a radius less than r* decrease its free energy? - Answers - by
dissolving into the liquid
At high temperatures, are there many nuclei formed or a few? - Answers - Fewer nuclei
Solidification is a transformation between what two states of a metal? - Answers -
crystallographic and non crystallographic
Solidification and melting transformations are basic to which of the following
technological applications? - Answers - ingot casting, semiconductor single crystal
growth, directionally solidified composite alloys
Which of the following parameters affect the process of solidification? - Answers -
cooling rate, temperature distribution , alloying
A liquid metal has a single solid sphere within it. What are the free energy terms? -
Answers - Solid, liquid, liquid-solid interface
What is the relationship between the drop in free-energy and the melting point of a
metal? - Answers - inversely proportional
What is the relationship between the drop in free energy per unit volume and the latent
heat of fusion of the metal? - Answers - directly proportional.
The critical radius of a solid particle is ___ proportional to the interfacial energy of the
solid to liquid interface. - Answers - directly
The critical radius of a solid particle is ___ proportional to the difference in free energy
between the liquid and solid phases. - Answers - inversely
If the melting point of a metal increases the critical radius of a metal particle ___. -
Answers - increases
Why is large undercooling not typically observed in liquid metals that are cooled? -
Answers - Walls of the container and impurities catalyze nucleation of solid from the
liquid.
, Solid particles with a radius equal to the critical radius are in ___ equilibrium with the
adjacent liquid. - Answers - unstable
If the solid-to-liquid interfacial-energy of a metal particle increases, the critical radius of
the metal solid particle ___. - Answers - increase
what does heterogeneous nucleation do to enhance solidification? - Answers - reduces
the interfacial energy term
what does heterogeneous nucleation do to the DeltaG compared to homogenous
nucleation? - Answers - reduces it
What does an inoculant do to enhance heterogeneous nucleation in a liquid? It ___ this
acts as a nucleation site. - Answers - forms a solid compound with one of the
components of the melt.
An iron-Carbon alloy of 0.76 wt% carbon is heated to 750C, rapidly cooled to 450C,
held for 10 seconds, then rapidly cooled to room temperature. What is the resulting
microstructure? - Answers - mostly pearlite and a little bit of proeutectoid ferrite.
What is the microstructure we obtain after tempering plain carbon steel? - Answers -
martensite
What are the four solid phases in the Fe-Fe3C phase diagram? - Answers - alpha-
ferrite, austenite, cementite, delta ferrite
What is the solid solution of carbon in alpha-iron called? - Answers - Alpha ferrite
What is austenite? Solid solution of ___ in ___. - Answers - Carbon, gamma-iron
What is cementite? - Answers - Fe3C compound
What is delta ferrite? solid solution of ___ in ___. - Answers - carbon, delta iron
What is the peritectic reaction in the Fe-Fe3C phase diagram? - Answers - liquid+delta
ferrite--> Gamma austenite
What is the eutectic reaction in the Fe-Fe3C phase diagram? - Answers - Liquid ->
gamma austenite+ Fe3C
What is the eutectoid reaction in the Fe-Fe3C phase diagram? - Answers - Gamma
austenite --> alpha ferrite+ Fe3C
ANSWERS
If a solid nucleus is formed within a liquid, there is a solid liquid interface between the
nucleus and the surrounding liquid. Does this interface have a higher energy or a lower
energy than that of the interface of the bulk solid with air? - Answers - Lower
How can a nucleus with a radius less than r* decrease its free energy? - Answers - by
dissolving into the liquid
At high temperatures, are there many nuclei formed or a few? - Answers - Fewer nuclei
Solidification is a transformation between what two states of a metal? - Answers -
crystallographic and non crystallographic
Solidification and melting transformations are basic to which of the following
technological applications? - Answers - ingot casting, semiconductor single crystal
growth, directionally solidified composite alloys
Which of the following parameters affect the process of solidification? - Answers -
cooling rate, temperature distribution , alloying
A liquid metal has a single solid sphere within it. What are the free energy terms? -
Answers - Solid, liquid, liquid-solid interface
What is the relationship between the drop in free-energy and the melting point of a
metal? - Answers - inversely proportional
What is the relationship between the drop in free energy per unit volume and the latent
heat of fusion of the metal? - Answers - directly proportional.
The critical radius of a solid particle is ___ proportional to the interfacial energy of the
solid to liquid interface. - Answers - directly
The critical radius of a solid particle is ___ proportional to the difference in free energy
between the liquid and solid phases. - Answers - inversely
If the melting point of a metal increases the critical radius of a metal particle ___. -
Answers - increases
Why is large undercooling not typically observed in liquid metals that are cooled? -
Answers - Walls of the container and impurities catalyze nucleation of solid from the
liquid.
, Solid particles with a radius equal to the critical radius are in ___ equilibrium with the
adjacent liquid. - Answers - unstable
If the solid-to-liquid interfacial-energy of a metal particle increases, the critical radius of
the metal solid particle ___. - Answers - increase
what does heterogeneous nucleation do to enhance solidification? - Answers - reduces
the interfacial energy term
what does heterogeneous nucleation do to the DeltaG compared to homogenous
nucleation? - Answers - reduces it
What does an inoculant do to enhance heterogeneous nucleation in a liquid? It ___ this
acts as a nucleation site. - Answers - forms a solid compound with one of the
components of the melt.
An iron-Carbon alloy of 0.76 wt% carbon is heated to 750C, rapidly cooled to 450C,
held for 10 seconds, then rapidly cooled to room temperature. What is the resulting
microstructure? - Answers - mostly pearlite and a little bit of proeutectoid ferrite.
What is the microstructure we obtain after tempering plain carbon steel? - Answers -
martensite
What are the four solid phases in the Fe-Fe3C phase diagram? - Answers - alpha-
ferrite, austenite, cementite, delta ferrite
What is the solid solution of carbon in alpha-iron called? - Answers - Alpha ferrite
What is austenite? Solid solution of ___ in ___. - Answers - Carbon, gamma-iron
What is cementite? - Answers - Fe3C compound
What is delta ferrite? solid solution of ___ in ___. - Answers - carbon, delta iron
What is the peritectic reaction in the Fe-Fe3C phase diagram? - Answers - liquid+delta
ferrite--> Gamma austenite
What is the eutectic reaction in the Fe-Fe3C phase diagram? - Answers - Liquid ->
gamma austenite+ Fe3C
What is the eutectoid reaction in the Fe-Fe3C phase diagram? - Answers - Gamma
austenite --> alpha ferrite+ Fe3C
