The type of dislocation interaction as the factor determining work hardening

Abstract

In this paper we present a critical review of the results of experimental and theoretical investigations of the dependence of the flow stress τ on the dislocation density ϱ in crystals of different lattice types (f.c.c., b.c.c., h.c.p.). It was found that the τ(ϱ) dependence is preferentially described by an equation of the type τ = τ 0 + α Gbϱ 1 2 . The effects of different factors such as deformation, deformation rate, structural state and dislocation distribution type on τ(ϱ) are considered. Analysis of the available experimental data was carried out. It showed that (a) the various dislocation types contribute differently to the flow stress, (b) the value of the contribution is mainly determined by the energy gain value at pairwise dislocation interactions, (c) the value of the contribution is contained in the parameter α (the larger the energy gain at the pairwise dislocation interaction, the larger is the value of α, i.e. α is an interaction constant) and (d) in general the τ(ϱ) dependence should be written τ = τ 0 + Σ i α i G 1b i ϱ i 1 2 The available theoretical models of work hardening are discussed. In most of these models the energy gain factor is not taken into account. This makes the models insensitive to the type of dislocation interaction chosen and leads to identical calculated α values. The theories and models in which the energy gain is taken into account are more realistic as they show good agreement between the calculated and measured α values. The role of forest dislocations in the work hardening of metal crystals and their contribution to the short- and long-range flow stress components are discussed. In h.c.p. metal crystals with similar densities of primary and forest dislocations the contribution from the forest dislocations to flow stress and its long-range component were shown to be of most importance.