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