Creep deformation of materials in light water reactors (LWRs) - Materials' Ageing and Degradation in Light Water Reactors - page 34

3.11 Deformation microstructure in Nb-modifi ed Zr-alloy crept in the
three power-law regime. 61

were summarized by Murty. 60 Some of the different alloys that exhibit three
power-law creep behavior are Al-Zn, Al-Ag, and Ni-Fe alloys.

Microstructural features

Since the n = 3 region is dislocation glide-controlled, recovery based pro-
cesses (such as climb) are considered to be less important. The deformation
microstructures are found to consist of a large number of dislocations as
shown in Fig. 3.11. In comparison to class-M alloys, the deformation micro-
structures of class-A alloys are devoid of subgrains. 61

￿ ￿ ￿ ￿ ￿ ￿

3.3.4 The n = 4-7 creep regime: fi ve power-law creep

The fi ve power-law creep regime is observed at higher stresses and lower
temperatures. This creep regime is generally controlled by dislocation climb
but describing it as dislocation climb-controlled creep is not appropriate.
This is because some of the other creep regimes such as GBS could also be
dislocation climb-controlled.
The fi ve power-law creep regime is commonly displayed by class-M alloys
and can be described by

⎛
⎜

⎞

Q
RT

47

−

exp ε A

−

⎛
⎝

σ

[3.27 ]

,