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

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 solutio n with reduced Cu content. The phenomenon is identical to that observe d 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 sh ow faceting with curved planes and edges. Their shape closely resemble s the growth shapes predicted on the basis of the coherency strain ene rgy with anisotropic elastic constants. During the heat-treatment, liq uid precipitates form within grains and at grain boundaries, and they also show faceting, which is consistent with orientation dependent coh erency strain energy in the diffusion zone around the precipitates.