1
MAE 20 1Chapter 5: Diffusion in Solids
Rate process
ln(ra
te)
1/T
MAE 20 2Chapter 5: Diffusion in Solids
Diffusion Mechanisms
increasing elapsed time
2
MAE 20 3Chapter 5: Diffusion in Solids
Diffusion Mechanisms
• Interstitial diffusion
MAE 20 4Chapter 5: Diffusion in Solids
Vacancy and interstitial diffusion
3
MAE 20 5Chapter 5: Diffusion in Solids
Steady state diffusion
MAE 20 6Chapter 5: Diffusion in Solids
Steady-State Diffusion
C1
C2
x
C1
C2
x1 x2
4
MAE 20 7Chapter 5: Diffusion in Solids
Diffusion and Temperature
1000 K/T
D (m2/s) C in α-Fe
C in γ-Fe
Al in Al
Fe in α-Fe
Fe in γ-Fe
0.5 1.0 1.510-20
10-14
10-8T(°C)
1500
1000
600
300
MAE 20 8Chapter 5: Diffusion in Solids
Non-steady state diffusion
Concentrationprofile after atime, t
x
C
Constant gas pressure of aspecies that dissolves in bar
Cs
5
MAE 20 9Chapter 5: Diffusion in Solids
Non-steady state diffusion
CS
Co
C(x,t)
MAE 20 10Chapter 5: Diffusion in Solids
The Error Function
6
MAE 20 11Chapter 5: Diffusion in Solids
Factors that affect diffusion
• Crystal structure
1000 K/T
D (m2/s) C in α-Fe
C in γ-Fe
Al in Al
Fe in α-Fe
Fe in γ-Fe
0.5 1.0 1.510-20
10-14
10-8
T(°C)15
00
1000
600
300
MAE 20 12Chapter 5: Diffusion in Solids
Factors that affect diffusion
• Type of defect
7
MAE 20 13Chapter 5: Diffusion in Solids
Solution
MAE 20 14Chapter 5: Diffusion in Solids
Interpolation method