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 back-scattered electron images. Low yttrium fluences between 1 X 10(14) and 5 x 10(15) Y+/cm2 did not alter the microstructures of Ni-20Cr. However, fluences of 1 X 10(16), 5 x 10(16), and 7.5 X 10(16) caused the crystalline structures of the alloy to be replaced by an amorphous phase. Fluences of 7.5 x 10(16) 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 in Ni-20Cr following yttrium ion implantation (7.5 x 10(16) Y+/cm2) 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 implanted with 7.5 x 10(16) Y+/cm2 in vacuum for one hour at 600-degrees-C resulted in the recrystallization of Ni-Cr solid solution and the formation of very fine grains of Y2O3. Annealing at 800-degrees-C for 5 minutes showed recrystallized Ni-Cr, Y2O3, and an additional phase or phases.