Creep failure

Diffusion creep

•

bulk crystaldiffusion

d

grain boundarydiffusion

d

Dislocation creep

glide

glide

climb

Diffusion assisted climb important:

climb

1. Annihilation:

poof !

2. By passing obstacles:

Dislocation Climb:

Stress Relaxation

total = el + pl = 0 so el = - pl

el = / E and pl = c = A n (@ cont. T)

-n d = - A E dt

1-n | =- A E t |0

. .

. .

. .

time

time

p

el

o

t

Tertiary creep :

c

time

tertiary creep

Creep damage starts

Creep Failure

Design against creep (metals)

• Minimize T / Tmelting

to slow diffusion, climb, and creep.

• Arrange for large grain sizes to slowdiffusion.

• Use precipitates (oxide particles) and solid solutions to slow dislocations.