DIFFUSION INDUCED GRAIN-BOUNDARY MIGRATION IN A RAPIDLY SOLIDIFIED, OXIDIZED NI-CU ALLOY

Diffusion induced grain boundary migration (DIGM) has been observed to date in over 20 binary alloy systems. This phenomenon, which can be ascribed to the diffusion of solute atoms along grain boundaries, involves grain boundry migration which leaves in its wake an alloyed or dealloyed zone. The authors have previously observed what appeared to be diffusion-induced recrystallization (DIR) during a study of annealing twin formation in cast and annealed specimens of several binary Cu-base alloys. The work reported began with the aim of determining whether or not DIGM and DIR occur during homogenization annealing of castings. The results found that concentration gradients produced by preferential oxidation during annealing of one of the components (Ni) in the Ni-Cu binary alloy lead to pronounced DIGM. This is believed to be the first report of DIGM occurring as a result of oxidation.