dislocation and strengthening mechanisms plastic deformation through dislocation: slip ideal shear...
TRANSCRIPT
Dislocation And Strengthening Mechanisms
Plastic deformation through dislocation: SlipPlastic deformation through dislocation: Slip
Ideal shear stress
da
~ G d/a ~ G d/a ~ 106 psi (calc.)
~ 10~103 psi (measured !)
FCC
This is due to other mechanisms ~ dislocation movement or fracture propagation
Dislocation Movement
Take much less energy !
Lattice strains in dislocation
Slip systems
Slip direction : closest distance or highest linear atomic density
Slip plane : planes with a highest atomic density
Easier deformation(higher ductility)
Brittle !
Slip systemsSlip systems
Slip distance
Slip planeSlip plane
Slip distance
FCC
HCP
A combination of close-packed planes and close-packed directions on those planes where slip occurs.
A combination of close-packed planes and close-packed directions on those planes where slip occurs.
Burgers vectors and slip systems in FCCBurgers vectors and slip systems in FCC
]101)[2/( 0
ab ]101)[2/( 0
ab
Slip in ionic materialsSlip in ionic materialsNiO
V3 is favorable, sinceit is the shortest vector connecting crystallographically equivalent potions
(Lowest-energy Burgers vector)(Lowest-energy Burgers vector)
Critical Resolve Shear Stress (CRSS)
max)coscos((max) RCrss max)coscos((max) RCrss
max)coscos( Crss
y max)coscos(
Crssy Or
Yield strength
coscosR coscosR
Znsinglecrystal
CRSS: min stress required for slip
PolycrystallineCu
PolycrystallineCu
Plastic Deformation Of Polycrystalline Materials
After deformationEquiaxed
Before deformation
Slip band
Deformation By Twining
BCC and HCP
BCC: (112) [111] for twining
Strengthening Mechanisms
Grain size reduction GB阻斷 Slip movement
Solid solution hardening
2/10
dk yy 2/10
dk yy Hall-Petch Eq:
Strain Hardening
100%0
0
A
AACW d
Cold work
Recovery, Recrystallization, Grain Growth
Recovery: The stored energy is relieved by dislocation motion at the elevated temperature. Some physcail properties, such as electrical conductivity, are improved.
Recrystalliztaion: After recovery, the residual strain is further reduced by the formation of strain-free ann equiaxed grains.
Tensile strength
Ductility
Grain sizeGrain size
Annealing temperature
RecoveryRecrystallization
Grain growth
Grain growth: Grain growth to reduce the interfacial energy
Ktdd nn 0Ktdd nn 0