It was recalled that, in previous work, diffusion-induced grain boundary migration and recrystallization in B-doped Ni3Al(Cu) systems had been observed for the first time when Ni76Al24-0.22at%B was electroplated with Cu and isothermally annealed within a temperature range where volume diffusion occurred ahead of the migrating grain boundary. Segregation of B to the grain boundary was expected to produce a narrow disordered phase there. Such a disordered layer was often not observed. Diffusion-induced grain boundary migration and recrystallization experiments were performed here on B-free alloys. The results showed that sufficient volume diffusion occurred, ahead of the migrating grain boundary, to cause some coherency strain. However, the coherency strain energy which developed in the Ni3Al(Cu) system was too small to provide the driving force for diffusion-induced grain boundary migration because of the minute lattice parameter difference (0.00015/at%) between Ni3Al and Cu atoms. An experimental result which was contrary to the coherency strain model was that diffusion-induced grain boundary migration and recrystallization occurred during Cu diffusion in polycrystalline Ni-19.4at%Pd; where little or no coherency strain was expected to develop because the lattice parameter of the alloy and of Cu were the same. This suggested that some other force was causing boundary migration. It was possible that an atomic mechanism which involved individual atomic jumps across the migrating boundary was active.

Diffusion Induced Grain Boundary Migration and Recrystallization in Boron-Free Ni3Al Intermetallics. Ma, C.Y.: Scripta Metallurgica et Materialia, 1994, 30[6], 769-74