GRAIN GROWTH AND PHASE MORPHOLOGY IN ION BEAM MIXED, TWO PHASE Ni-AI AND Ni-Cr-Al ALLOYS

Multilayers of Ni-2lAl and Ni-ZOCr-1OAl were subjected to ion beam mixing using 350 keV Ni+ ions and/or thermal annealing at 440 o C to study the development of grain growth and phase morphology. Two film thicknesses of Ni-21 Al (60 and 120 nm) were investigated. Both thermal annealing and irradiation resulted in grain growth in the Ni-21Al samples. Grain size increased by a factor of 7 after irradiation and only 3-4 after annealing. Annealing produced a two phase y + y ’ structure and nonuniform grain sizes while the irradiation produced a supersaturated solid solution with more uniform grain size. Annealing subsequent to irradiation produced a structure consisting of y + y’ and an HCP phase. There was no difference in grain growth behavior as a function of film thickness. The Ni-Cr-Al film exhibited no grain growth during annealing and only a factor of 6 increase during irradiation. Irradiation alone or post-irradiation annealing produced nearly identical structures of y and the HCP phase. The y’ phase was never observed in the Ni-Cr-Al film. All irradiated samples showed a more uniform grain size compared to that following annealing. Considerable texture was observed in all irradiated samples in which the gamma grains in the film were aligned with the Ni grains in the substrate.