Intermittent 'self-locking' of grain growth in fine-grained materials

The vacancy generation accompanying grain growth in fine-grained materials has a strong inhibiting effect on the grain growth. A simple thermodynamic argument shows that for sufficiently small grain sizes, `self-locking' of grain growth when vacancy generation arrests grain boundary motion and intermittent `stop and go' cycles occur repetitively. As a result of intermittent `self-locking', the jerky motion of the grain boundaries during grain growth is expected. The kinetics of grain growth for t*<τ when `self-locking' occurs are determined by bulk self-diffusion. In nanocrystalline materials, a linear time dependence of the grain size follows the corresponding grain growth rate and the critical radius.