Evolution of size distribution of shearable ordered precipitates under homogeneous deformation: Application to an Al-Li-alloy

Based on the model of the ''pseudo Portevin-Le Chatelier effect'' by Brechet and Estrin, a quantitative description is developed for the homogeneous precipitation of small, coherent and hence shearable ordered second-phase particles when small and homogeneous plastic deformation of constant strain rate is exerted. A modified Gibbs-Thompson equation is derived for the re-dissolution of a sheared particle. The growth on shrinkage of the sheared particle is described phenomenologically. By means of a modified Kampmann-Wagner numerical model, the evolution of the precipitate structure, i.e. the size distribution under plastic deformation, is simulated for the example of an aged AI-Li alloy. Three regimes of the precipitation process, i.e. nucleation, growth and coarsening are treated to be ''concomitant'' instead of being ''consecutive'' The hardening stress owing to precipitation is calculated. It is demonstrated that the strain-rate sensitivity of the hardening stress turns negative under certain conditions. This is of relevance for the Portevin-Le Chatelier effect. (C) 1997 Acta Metallurgica Inc.