Exam 2 Flashcards
Peierls stress/energy
point of max energy/shear stress
slip plane
shear plane where dislocation formation and motion is possible
slip plane
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slip direction
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elastic stress
main reason for higher energy when a dislocation happens
activation energy, highest/lowest for?
highest: bcc systems
lowest: fcc systems
Schmid factor (slip system)
slip system aligned with this factor: first one to activate when stress increases
Gibbs free energy G
G = H - T . S
enthalpy
H, sum of all energies in a system
entropy
S, number of possibilities of a structure
self-diffusion
atoms of a pure element jump around when T > 0 K
impurity-diffusion
diffusion speed of the impurity is independent of the concentration
inter diffusion
the mixing of elements in solid state
interstitial-diffusion
smaller atoms jumping in between lattice sites, is very fast
when does nuclei grow into crystals?
at melting temp Tm
what does a finer grain structure increase?
increases yield strength, which increases toughness, but decreases ductility
non-random grain structure
crystallographic texture
climbing
dislocations moving up and down
recovery
- dislocations climb towards each other
- annihilate with their partner
- left over dislocations align to minimise strain energy
forming small-angle grain boundaries
polygonisation
recrystallisation
nucleation of new crystals
cold-hardening
lowers toughness and fatigue resistance
latent heat
energy absorbed/released during a phase change (no change in temperature)
a-phase
solid phase
tie line
horizontal line between two phase boundaries
how to remove coring?
anneal the alloy at high temperature for diffusion mixing/annealing
precipitates
b-particles within a-matrix
solution annealing
reverting to pure phase by heating
intermediate phases
little to no correclation to the pure element
strictly stoichiometric
no existence range, horizontal line
eutectic reaction
L <> a + b
eutectoid reaction
d <> y + e
peritectic reaction
d + L <> e
congruent phase transformation
L <> y
Gibbs phase rule
P + F = C + N
at what temperature does iron change into an fcc lattice?
912 degrees
austenite with slow cooling
pearlite + a-proeutectoid phase
austenite with moderate cooling
bainite
austenite with rapid cooling
martensite
reheated martensite
tempered martensite
pearlite forming
y <> a + Fe3C
proeutectoid ferrite forming
a + y
proeutectoid cementite forming
y + Fe3C
iron phases
ferrite a, bcc
austenite y, fcc
delta ferrite d, bcc
precipitation
forming b-phase in solidified a
how does precipitation work?
- heating the a-phase to high temperature
- cooling it rapidly
- reheating it to a normal temperature, where precipitates form in the a-matrix
cementite
Fe3C
