ON THE KINETIC-BEHAVIOR AND DRIVING-FORCE OF DIFFUSION-INDUCED GRAIN-BOUNDARY MIGRATION

The diffusion induced grain boundary migration (DIGM) has been studied in the Ni(Cu) system over the temperature range 723-1023 K using ligh t microscopy, scanning electron microscopy and electron probe microana lysis (EPMA). Four different stages of the grain boundary (GB) migrati on during DIGM were found, involving nucleation, initial, stationary a nd mixed stages. During the mixed stage the DIGM process occurs simult aneously with the diffusion induced recrystallization, and it is impos sible to separate the two phenomena. The EPMA measurements reveal that the Cu concentration in the DIGM zone does not remain constant, but i ncreases with increasing annealing time. The highest Cu concentration which does not depend on annealing conditions is situated in the middl e of the DIGM zones. Based on the measured Cu distribution in the DIGM zones, the coherency strain driving force for GB migration is calcula ted. In some cases the calculated values are lower than the energy dif ference across the GB due to its curvature. It is concluded that some other driving force should be involved. The nucleation and initial sta ges of the DIGM process can be explained by a model based on the diffu sion induced GB stresses. The Arrhenius parameters of the diffusion al ong and across the GB in Ni-rich Ni-Cu alloys have been determined.