On the enhanced grain growth in ultrafine grained metals

The static grain growth has been investigated in ultrafine grained copper with an initial grain size of 160 nm. It has been revealed that its kinetics follows to normal grain growth behaviour, but a grain growth starts at a relatively low temperature (0.32 T_m). Good fits with experimental data for several ultrafine grained metals have been obtained if the activation energy for grain boundary diffusion is assumed to be lower than for coarse grained materials, but increases during grain growth. It is suggested that this unusual behaviour of the activation energy is caused by the presence of non-equilibrium grain boundaries in ultrafine grained materials and their recovery during heating.