Phase Transformation

Question 1

Categories of phase transformation

Answer 1

Diffusion dependent with no change in composition/number of phase, diffusion dependent with change in composition/number of phase, diffusion-independent

Question 2

Examples of diffusion dependent phase transformation with no change in composition/number of phases

Answer 2

Melting, solidification, recrystallization, congruent phase transformations

Question 3

Examples of diffusion dependent phase transformation with changes in composition or number of phases

Answer 3

eutectic, peritectic, eutectoid, peritectoid, precipitation

Question 4

Example of diffusion independent phase transformation

Answer 4

martensitic

Question 5

Eutectic

Answer 5

Liquid transforms into two solids

Question 6

Peritectic

Answer 6

Liquid plus solid transforms into a different solid phase

Question 7

Eutectoid

Answer 7

Solid transforms into two solids

Question 8

Peritectoid

Answer 8

Two solids transform into one different solid

Question 9

Factors that affect phase transformation

Answer 9

Composition at interface, kinetics of reaction, diffusion vs. nucleation driven, heat flow

Question 10

What is the controlling parameter of the phase transformation

Answer 10

Slowest of affecting factors

Question 11

Why is slowest factor controlling

Answer 11

Uses more of available driving force, leaving less for other processes

Question 12

Rate of phase transformation

Answer 12

1/(t_0.5)

Question 13

Percent of material transformed vs. log time

Answer 13

S-shaped curve

Question 14

If there is a positive relation between temperature and rate

Answer 14

The phase transformation is diffusion driven

Question 15

If there is a negative relation between temperature and rate

Answer 15

Phase transformation is nucleation driven

Question 16

Avrami equation

Answer 16

y = 1 - exp(-kt^n)

Question 17

What are k and n in Avrami

Answer 17

time independent constants

Question 18

What is y in Avrami

Answer 18

Sigmoidal time-dependent transformation fraction

Question 19

What is n in Avrami specifically

Answer 19

Order of phase transformation

Question 20

Why do rates not have constant relation with temperature IRL

Answer 20

Mechanism can switch from nucleation to diffusion dominated

Question 21

Martensitic transformation

Answer 21

Crystal lattice displacement decreases free energy

Question 22

Martensitic transformation

Answer 22

Crystal lattice displacement decreases free energy

Question 23

Bainitic transformation

Answer 23

Both diffusional and martensitic transformations occur together

Question 24

What controls kinetics of martensitic transformation

Answer 24

Elastic strain energy

Question 25

Elastic strain energy

Answer 25

0.5v(\sigma^2)/E

Question 26

v in elastic strain energy

Answer 26

Volume

Question 27

Coherent conjugation

Answer 27

Aligned planes

Question 28

Why martensitic transformations only occur under high driving force conditions

Answer 28

High kinetic barrier

Question 29

Result of martensitic reformation of atoms/lattices

Answer 29

Doesn’t complete at starting temp; must decrease temp as transformation progresses

Question 30

Martensitic hysteresis

Answer 30

Reverse transformation finishes at a higher temperature than Ms

Question 31

Speed of martensitic transformation after start

Answer 31

Very fast

Question 32

Speed of martensitic transformation in general

Answer 32

Speed of sound in material