The effects of yttrium ion implantation on the oxidation of nickel-chromium alloys. 1. The microstructures of yttrium implanted nickel-chromium alloys

Yttrium ions of 150 keV energy were implanted into the alloys Ni-20Cr, Ni-4Cr, and into nickel. The microstructures were then characterized using transmission electron microscopy, selected area channeling patterns and backscattered electron images. Low yttrium fluences did not alter the microstructures of No-20Cr. However, fluences of 1 x 1016, 5 x 1016, and 7.5 x 1016 caused the crystalline structures of the alloy to be replaced by an amorphous phase. Fluences of 7.5 x 1016 Y+/cm2 also rendered Ni-4Cr and nickel amorphous. Self-ion implantation experiments on Ni-20Cr did not cause the amorphous phase to form. The depth distribution of elements Ni-20Cr following yttrium ion implantation was determined by Auger electron spectroscopy. This showed in addition to the added yttrium a surface depletion in nickel concentration and a simultaneous enrichment in chromium concentration. At approximately 500 angstrom, the chromium concentration is approximately 32 at.%. This depletion/enrichment zone extends throughout the implanted layer. Annealing the Ni-20Cr in vacuum for one hour at 600C resulted in the recrystallization of Ni-Cr solid solution and the formation of very fine grains of Y2O3. Annealing at 800C for 5 minutes showed recrystallized Ni-Cr, Y2O3, and an additional phase or phases