Thermodynamic effects on the kinetics of vacancy-generating processes

The inhibiting effect of vacancies on the very process in which they are generated is considered from a thermodynamic viewpoint. Examples of such processes treated here in some detail are grain growth and pore dissolution. It is shown that these processes are inhibited due to vacancy generation. A particular scenario discussed implies intermittent "locking". After a period of uninhibited kinetics the process comes to a halt due to a thermodynamic back force "locking" it. It can only re-start once the vacancies produced are removed by diffusion. This repetitive cycle leads to an overall reduction in the rate of the kinetic process in question. Specific predictions with regard to grain growth in fine-grained (particularly nanocrystalline) materials and void dissolution kinetics in sintering an made. A third example considered is vacancy drag on a moving individual grain boundary. The magnitude of the drag is re-assessed by taking into account the Gibbs free energy of the vacancies generated. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.