Influence of grain size, solute atoms and second-phase particles on creep behavior of polycrystalline solids

Diffusion-controlled-creep processes are used to assess the creep behavior of dispersion and solute hardened materials at coarse and fine grain sizes. It is shown that the creep behavior of a dispersion strengthened (DS) Al–Mg alloy is similar to the creep behavior of pure Al–Mg alloys. Both materials show dislocation climb and dislocation solute-drag contributions to creep. It is shown that the threshold stress for creep for these materials is a function of the mobile dislocation density, of the dislocation velocity and of the concentration of solute atoms in the dislocation core. It is, therefore, appropriate to describe the threshold stress as the threshold strain rate. It is shown that the same value of the diffusion-compensated strain rate for the threshold stress is obtained for slip in DS Al–Mg material as in a fine-grained Al–Mg alloy, where grain-boundary sliding is the principal deformation process. This is evidence that grain boundary sliding is accommodated by dislocation creep.