10. Recrytallization and Grain Growth

Question 1

define homologous temperature

Answer 1

the ratio of the deformation temperature to melting temperature (in Kelvin)

Question 2

Why is the homologous temperature higher for alloys than for pure metals

Answer 2

Solutes induce strain –> Strain impedes dislocation motion–>more energy is required to relieve higher strain

Question 3

As the strength increases the ductility _____ (decreases/increases)

Answer 3

decreases

Question 4

As the yield stress increases the strength ____ (decreases/increases)

Answer 4

increases

Question 5

As the strength increases strength increases the %elongation ____ (decreases/increases)

Answer 5

decreases

Question 6

work hardening _____ (decreases/increases) the internal energy within a material

Answer 6

increases

Question 7

What does annealing heat treatment do?

Answer 7

reverse the effects of work hardening

Question 8

Stored energy during work hardening is the driving force for _____

Answer 8

recrystallization

Question 9

A plastically deformed material is thermodynamically ____, and wants to return to a ____ energy state

Answer 9

unstable

lower

Question 10

Work hardening involves ____ in dislocation density and dislocation-dislocation interaction

Answer 10

increase

Question 11

Define recovery

Answer 11

release of stored energy by dislocation motion (without applied stress), due to enhanced atomic diffusion at elevated temperature

Question 12

What 2 things happen during recovery?

Answer 12

1. Restoration of physical properties (electrical and thermal conductivities) to pre-cold worked state begins
2. Dislocations reconfigure to have lower strain energy

Question 13

Define equiaxed grains

Answer 13

grains having approximately equal dimensions in all directions

Question 14

define recrystallization

Answer 14

formation of new strain-free and equiaxed grains with low dislocation densities

Question 15

What is the driving force for recrystallization?

Answer 15

The stored internal enery

Question 16

define recrystallization temperature

Answer 16

the temperature at which recrystallization is complete in one hour

Question 17

Recrystallization temperature
_____ (decreases/increases) with increasing cold
work

Answer 17

decreases

Question 18

define critical deformation

Answer 18

the % cold work below which crystallization cannot occur

Question 19

Which does recrystallization occur in more rapidly alloys or pure metals?

Answer 19

Pure Metals

Question 20

Why does recystallization occur more rapidly in pure metals than alloys

Answer 20

impurities/solutes interact with grain boundaries which reduces the mobility of grain boundaries –> recrystallization involves the motion of grain boundaries –> therefore solutes reduce recrystallization rates and increases recrystallization temperatures

Question 21

Grain boundaries are regions of ____ (low/high) atomic disorder, and therefore _____ (low/high) energy

Answer 21

high

high

Question 22

After recrystallization, grains grow to ____ (decrease/increase) grain boundaries and energy within material

Answer 22

decrease