10. Recrytallization and Grain Growth Flashcards
define homologous temperature
the ratio of the deformation temperature to melting temperature (in Kelvin)
Why is the homologous temperature higher for alloys than for pure metals
Solutes induce strain –> Strain impedes dislocation motion–>more energy is required to relieve higher strain
As the strength increases the ductility _____ (decreases/increases)
decreases
As the yield stress increases the strength ____ (decreases/increases)
increases
As the strength increases strength increases the %elongation ____ (decreases/increases)
decreases
work hardening _____ (decreases/increases) the internal energy within a material
increases
What does annealing heat treatment do?
reverse the effects of work hardening
Stored energy during work hardening is the driving force for _____
recrystallization
A plastically deformed material is thermodynamically ____, and wants to return to a ____ energy state
unstable
lower
Work hardening involves ____ in dislocation density and dislocation-dislocation interaction
increase
Define recovery
release of stored energy by dislocation motion (without applied stress), due to enhanced atomic diffusion at elevated temperature
What 2 things happen during recovery?
- Restoration of physical properties (electrical and thermal conductivities) to pre-cold worked state begins
- Dislocations reconfigure to have lower strain energy
Define equiaxed grains
grains having approximately equal dimensions in all directions
define recrystallization
formation of new strain-free and equiaxed grains with low dislocation densities
What is the driving force for recrystallization?
The stored internal enery
define recrystallization temperature
the temperature at which recrystallization is complete in one hour
Recrystallization temperature
_____ (decreases/increases) with increasing cold
work
decreases
define critical deformation
the % cold work below which crystallization cannot occur
Which does recrystallization occur in more rapidly alloys or pure metals?
Pure Metals
Why does recystallization occur more rapidly in pure metals than alloys
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
Grain boundaries are regions of ____ (low/high) atomic disorder, and therefore _____ (low/high) energy
high
high
After recrystallization, grains grow to ____ (decrease/increase) grain boundaries and energy within material
decrease
