1

1Chapter 7 Dislocations and strengthening mechanisms

Dislocations and materials classes

+ + + +

+++

+ + + +

- - -

----

- - -

++

++

++++++++ + + + + +

+++++++

2Chapter 7 Dislocations and strengthening mechanisms

Dislocation Motion

2

3Chapter 7 Dislocations and strengthening mechanisms

Stress around dislocations

⊥ ⊥

⊥ ⊥

4Chapter 7 Dislocations and strengthening mechanisms

Slip systems in FCC

3

5Chapter 7 Dislocations and strengthening mechanisms

Slip system in FCC

6Chapter 7 Dislocations and strengthening mechanisms

Slip in HCP

4

7Chapter 7 Dislocations and strengthening mechanisms

Slip in single crystals

Ao

P

slipdirection

slip plane normal

slip planeAslip

8Chapter 7 Dislocations and strengthening mechanisms

Critical Resolved Shear Stress

σ σ σ

5

9Chapter 7 Dislocations and strengthening mechanisms

Deformation of single crystal

10Chapter 7 Dislocations and strengthening mechanisms

1. Reduction in grain size

6

11Chapter 7 Dislocations and strengthening mechanisms

2. Solid solution strengthening

A

B

C

D

r = 0.143 nm

r = 0.155 nm

r = 0.133 nm

12Chapter 7 Dislocations and strengthening mechanisms

Strengthening

7

13Chapter 7 Dislocations and strengthening mechanisms

Solid solution strengthening in Cu

Tens

ile s

treng

th (M

Pa)

wt.% Ni, (Concentration C)

200

300

400

0 10 20 30 40 50 Yiel

d st

reng

th (M

Pa)

60

120

180

0 10 20 30 40 50

wt.%Ni, (Concentration C)El

onga

tion

(%)

14Chapter 7 Dislocations and strengthening mechanisms

3. Precipitation strengthening

Side View

precipitate

Top View

Slipped part of slip plane

Unslipped part of slip plane

S

8

15Chapter 7 Dislocations and strengthening mechanisms

• Internal wing structure on Boeing 767

• Aluminum is strengthened with precipitates formed by alloying.

1.5µm

3. Precipitation strengthening

16Chapter 7 Dislocations and strengthening mechanisms

Effect of heating after cold work

tens

ile s

treng

th (M

Pa)

duct

ility

(%EL

)tensile strength

ductility

600

300

400

500

60

50

40

30

20

annealing temperature (ºC)200100 300 400 500 600 700

9

17Chapter 7 Dislocations and strengthening mechanisms

Recovery

τR

Grain growth

18Chapter 7 Dislocations and strengthening mechanisms

TR

º

º

10

19Chapter 7 Dislocations and strengthening mechanisms

20Chapter 7 Dislocations and strengthening mechanisms