metals Flashcards
name the 4 different crystalline defects
Point defects
line defects
planar defects
volume defects
name the type of point defects
substitution
vacancy
atom out of place (self interstitial)
interstitial impurity
name the type of line defects
edge, screw and mixed dislocation
name the type of planar defects
stacking fault, grain boundaries and twin boundaries
name the volume defects
precipitates
inclusions
voids
what is a phase
a physically distinct homogenous region of an assembly atoms defined by a set of thermodynamic parameters like density
phase transformation
rearrangement of atoms of molecules to a new configuration of lower free energy
out of ferromagnetic and paramagnetic which on retains its magnetism when the magnetic field is removed
ferromagnetic
unlimited solubility is
1 solid phase regardless of the amount of solute of solvent
limited solubility
describes the extent to which one phase can tolerate the addition of a new solute
what is solid solution strengthening
the addition of atoms (a solute) from one element to a phase (solvent) giving rise to a solid solution
causes distortions In the lattice which leads to localised stress fields that interact with dislocations strengthening it
effects of solid solution strengthening
increases: hardness, strength, creep resistance and resistivity
decreases ductility
what is the solidus
defines a temp below which is 100% solid for a given composition
whats the formuls for % of a phase
opposite lever arm/ full length *100
what are nucleations
the first step of either a new thermodynamic phase or a new structure via self assembly
when does non equilibrium cooling occur
when something cools too quick for atoms to diffuse produces segregation
describe the process of solidification, starting at 52% Ni
Ni atoms diffuse away from solid
remaining liquid becomes enriched in carbon
Process continues to solidus is reached
do atoms diffuse quicker in a solid or liquid?
liquid
explain micro segregation and how its reduced
- occurs over short distances
- cools too quick for atoms to diffuse (so the solids are high in Ni)
- reduced by homogenisation heat treatment
whats macro segregation and how is it reduced
occurs over large distances
- reduced during processing- rolling
when does precipitation strengthening occur and whats the effects
- occurs in a system of limited solubility
- occurs when solubility of one material is exceeded by the addition of too much of a given alloy element
- gives rise to an interface boundary
- which interferes with the movement of dislocations» strengthening it
explain the steps in precipitation strengthening
1- solution treatment: heat to temp above solvus temp
2-quench- to RT
3-Age- hold at a temp range between RT and solvus temp
after a long enough time precipitation of equilibrium theta phase
eutectic phases- fast cooling has what effect
- less time for diffusion
- results in small intermellor spacing
- more boundaries
- higher strength
the 4 classes of alloys in a eutectoid system
1- solid solution alloys
2-alloys that exceed solubility limit
3-eutectoid alloys
4-off eutectoid alloys
