A dislocation network model of recovery-controlled creep

Abstract

A new model of recovery-controlled creep deformation, based on the jerky glide motion of dislocations between obstacles, is proposed. A three-dimensional distribution of dislocation links is visualized such that only links which attain a certain threshold size,λ _a, through recovery can glide rapidly until they are again arrested at the next obstacle. The rate of mobilization of arrested dislocations is shown to be directly proportional to the annihilation rate, ϱ_a. The strain rate, γ, during transient creep is related to the annihilation rate, the obstacle spacingL and the Burgers vectorb of the dislocations according to the expression

$$\gamma = \alpha _1 \psi (t)\dot \varrho bL$$

where α₁ is a geometrical constant and ψ(t) is a time-dependent parameter whose value is determined by the instantaneous (free) dislocation density as well as some salient features of the dislocation distribution. At steady state, ψ(t) translates into a constant which is stress and temperature independent. The average effective dislocation velocity is also shown to be directly proportional to the annihilation rate. The model is used to rationalize the familiar creep transients which are usually observed when the stress is altered abruptly during recovery creep.