EFFECT OF CRYSTAL ORIENTATION ON GRAIN-BOUNDARY MIGRATION AND RADIATION-INDUCED SEGREGATION

Fe-Cr-Ni, Ni-Al and Ni-Si alloys were electron-irradiated using a high voltage electron microscope (1 MeV), and in situ observations of the structural evolution and micro-chemical analysis were carried out. Dur ing the irradiation, the grain boundaries in the irradiated region mig rated, while no grain boundary migration occurred in the unirradiated area. The occurrence of boundary migration depended on the orientation relationship of the boundary interfaces. Grain boundary migration too k place in Fe-Cr-Ni and Ni-Si alloys with large crystal orientation di fference between the two grains across a grain boundary. In Ni-Al, how ever, the grain boundary migration did not occur. The solute segregati on was caused at grain boundary under irradiation and this segregation behavior was closely related to solute size, namely the concentration s of undersized Ni and oversized Cr elements in Fe-Cr-Ni alloy increas ed and reduced at grain boundary, respectively. The same dependence of segregation on the solute size was derived in Ni-Si and Ni-Al alloys, in which Si and Al solutes are undersized and oversized elements, res pectively. Therefore, Si solute enriched and Al solute depleted at gra in boundary From the present segregation behavior, it is suggested tha t the flow of point defects into the boundary is the cause of grain bo undary migration.