THE EFFECT OF ELASTIC-ANISOTROPY ON THE MIGRATION OF INTERGRANULAR LIQUID-FILMS AND THE PRECIPITATION OF A LIQUID-PHASE IN A CO-CU ALLOY

Abstract

When a Co-20Cu (wt%) alloy prepared by liquid phase sintering at 1300-degrees-C is heat-treated at 1150-degrees-C, the intergranular liquid films and grain boundaries migrate, leaving behind a new solid solution with reduced Cu content. The phenomenon is identical to that observed previously in Mo-Ni. The calculated driving force for the migration is almost equal to the coherency strain energy in the solute diffusion zone ahead of the migrating boundaries. The migrating liquid films show faceting with curved planes and edges. Their shape closely resembles the growth shapes predicted on the basis of the coherency strain energy with anisotropic elastic constants. During the heat-treatment, liquid precipitates form within grains and at grain boundaries, and they also show faceting, which is consistent with orientation dependent coherency strain energy in the diffusion zone around the precipitates.