A scaling analysis of recovery creep

Here we propose that recovery is a general dislocation-level coarsening process whereby the length scale, lambda, is refined by dislocation generation by plastic deformation and is increased concurrently by coarsening processes. Coarsening relations generally take the form: dlambda(m) = K (.) M(T) (.) dt where, lambda, is a length scale, M(T) is a temperature dependent mobility, K is a free constant, dt is a time increment and m, is the coarsening exponent. Arguments are presented that m(c) should be in the range of 3-4 for dislocation coarsening. This is coupled with standard arguments for modeling plastic deformation. Combining these we can easily justify the form of the empirically derived Dorn creep equation: (gamma)over dot(ss) = C (.) M(T) (.) (tau/mu)(n) where the mobility of the recovering feature, M(T) should typically scale with self-diffusivity and the value of the steady state creep exponent, n is m(c)+2 (.) (1-c) where c is a constant related to dislocation generation that should be in the range of 0 to 0.5. Hence this approach predicts creep as being controlled by self-diffusion and that the steady-state stress exponent should be on the order of 4-6. One can also use this approach to make rough predictions of absolute creep rates in simple materials.