Defects in Solids

1
Defects in Solids

• 0-D or point defects
• vacancies, interstitials, etc.
• control mass diffusion
• 1-D or linear defects
• dislocations
• control deformation processes
• 2-D or planar defects
• grain boundaries, surfaces, interfaces
• 3-D or volume defects
• voids, secondary components (phases)

concentrations ?
2
Diffusional Processes
diffusion coefficient
concentration gradient
Pd
flux
H2
response ? driving force
CO
CO2
Ficks first law (similar to Ohms
law) phenomenological
H
Applies under steady state conditions c(x) ? f(t)
x
hydrogen separation membrane
3
Diffusional Processes
Steady-state c(x) ? f(t)
Non steady-state c(x) f(t)
Continuity requirements
Ficks second law
if D ? f(x)
4
Defects in Solids

• 0-D or point defects
• vacancies, interstitials, etc.
• control mass diffusion
• 1-D or linear defects
• dislocations
• control deformation processes
• 2-D or planar defects
• grain boundaries, surfaces, interfaces
• 3-D or volume defects
• voids, secondary components (phases)

concentrations ?
5
Linear (line) defects
Dislocations intimately tied to mechanical
properties

• small stress
• ? elastic deformation
• recoverable
• large stress
• ? plastic deformation
• permanent

s F/A stress
huge energy penalty, yet happens easily in metals
answer slip, dislocation glide
6
Dislocation Motion Deformation
dislocation
slip plane
7
Dislocations
vector between finish and start
Burgers vector
Edge
b ? dislocation line
8
(No Transcript)
9
Dislocations
Screw
b dislocation line
10
Dislocations Mixed
Burgers vector is constant
11
Dislocation Loops
12
Dislocation Loops
13
Dislocation Loops
14
Dislocation Loops
in projection
15
Dislocation Loops
16
Dislocation Loops
Dislocation lines cannot simply terminate. They
either form complete loops or terminate at
crystal edge