4. Strengthening Mechanisms Flashcards
Strengthening mechanisms for both pure metal and alloys?
Work-hardening and grain size reduction
Strengthening mechanisms for alloys only.
Solid solution strengthening
multiphase strengthening
dispersion strengthening/age-hardening/precipitation hardening
Describe the mechanism of solid solution strengthening
inserting substitutional or interstitial atoms will distort the slip planes making dislocations harder to move
Age-hardening heat treatment steps
heat treatment - heated above solvus line
quenching - rapid cooling
ageing - heating (to a temperature below solvus line) to allow atoms to diffuse
What is special about BCT, body centered tetragonal?
it has no slip systems
Describe the mechanism of dispersion strengthening
distorts the lattice making it harder for dislocations to move (more than the solid solution strengthening)
Describe the optimal dispersion strengthening method
using many small precipitates of a HARD phase in a ductile parent phase.
Four requirements for precipitation hardening alloy
phase diagram must show decreasing solid solubility of the strengthening phase with decreasing temperature
parent mix should be soft, strengthening phase should be hard and brittle
precipitates should be coherent with parent matrix (so it distorts it instead of just cutting it)
alloy should be able to survive quenching (no cracking)
structure of martensite
BCT, body centered tetragonal
When do you get coarse pearlite and fine pearlite?
coarse pearlite = high temp, fine pearlite = low temp
describe the process of spherodising of steels
heating pearlite to about 700 degrees and holding for several hours, forming spheres of fe3c in alpha
what is the driving force of spherodising?
thermodynamic: pearlite has large surface area while spheres of Fe3C have less, this means that spherodising is at a lower energy level.
