Material Selection Quiz 8

At ___ temperatures you start to see time-dependent deformation

high

“High” temperature for metals is T/Tm > _____ and ____ for ceramics

0.3-0.4, 0.4-0.5

There are three main stages of creep:

1. Primary creep - strain rate _____ over time

2. Secondary creep - strain rate is ____ over time

3. Tertiary creep - strain rate _____ rapidly before rupture

decreases, constant, increases

Creep reflects a balance between strain ____ (dislocation tangling) and thermal _____ + physical damage

hardening, softening

Time-dependent plastic deformation: Dislocation motion, which can be described by dislocation ___ (thermal glide) and ___ (climb)

slip, creep

Time-dependent plastic deformation: Vacancy diffusion, which can be described by Nabarro-herring (____ ______) and Coble (____ _______)

bulk lattice, grain boundary

Dislocation slip is driven by high stress that’s ____ YS at ___ temperatures

above, low

Dislocation (Power Law) creep is driven by ___ temperatures at ___ stresses. The added energy allows dislocations to climb over/around ________.

high, low, pinned dislocations

Nabarro-herring diffusional creep occurs at _____ temperatures, involved vacancies diffusing ___. Steady state creep rate is inversely proportional to d^__

highest, grain, squared

Coble diffusional creep occurs at _____ temperatures over grain ______. Steady state creep rate is inversely proportional to d^___

mid-high, boundaries, slower, 3

In Coble creep, ____ grains improve creep resistance.

larger

What type of creep dominates at low stress?

diffusional

The Larson-Miller Parameter can be used to translate creep results at high stress low temp to high temp low stress, when does it breakdown?

if mechanism or microstructure changes between test and service