For the creep map below briefly explain the mechanisms of cr

For the creep map below, briefly explain the mechanisms of creep in different regions of creep map (see lecture notes).

Solution

Here the size of the Nabarro-Herring creep field expands, and also of the dislocation creep field.. Now this occurs due to the larger grain size inhibits diffusional flow, but inhibits the Coble creep variety of diffusional flow more effectively than the Nabarro-Herring variety because of its more rapid grain size dependence.

Note that the application of a strengtheneing mechanism for diffusional flow (the change of grain size) has side effects as it expands the dislocation creep fields downwards.

An elongated grain structure(which inhibits diffusional flow) is due to doping stabilization and, independently, it lowers slowly the dislocation creep.