ELEVATED-TEMPERATURE MICROSTRUCTURAL STABILITY OF AL+-ION IMPLANTED NICKEL

Composition profiles were measured following 180 keV Al** plus -ion implantation of nickel at temperatures up to 600 degree C and following 600 degree C annealing of nickel implanted at 25 degree C. The phases present are compared to those found on the Ni-Al phase diagram. TEM examination shows the defect-enriched region beyond 3000 Angstrom recrystallizes at elevated temperatures and enhances diffusion via the high diffusivity paths provided by the grain boundaries. Phases found in elevated temperature specimens often differ from those in 25 degree C implanted specimens. Ni//3Al replaces the extended portion of the Al in Ni f. c. c. solution, Ni//3Al and NiAl replace an h. c. p. phase peculiar to lower temperatures, and phases richer than 50% Al are replaced by Ni//3Al due to compositional instabilities. Phase prediction based on local chemical composition and the phase diagram is valid but can proceed only when compositional instabilities are taken into account.