To the problem of nucleation of the diffusion-induced grain boundary migration

The diffusion-induced grain boundary migration (DIGM) reaction has been studied in the Ni(Cu) system over the temperature range from 723 to 1023 K using light microscopy, scanning electron microscopy and electron probe microanalysis. It is shown that at the initial stages of DIGM the time dependence of the averaged grain boundary displacements is strongly non-linear: there is a nucleation time during which the grain boundaries do not migrate, and afterwards the migration proceeds with a high velocity decreasing with time down to the steady-state value. The temperature dependence of the nucleation time is shown to obey an Arrhenius law with an activation energy close to the activation energy for Cu tracer bulk diffusion in Ni. A model of DIGM based on the diffusion-induced grain boundary stresses is shown to describe the initial stage of the DIGM process satisfactorily.