The early stages of oxidation of ion-implanted nickel at high temperature

Abstract

The early stages of oxidation of nickel implanted with nickel, chromium, or lithium ions in oxygen at 1100°C have been studied using various electron-optical techniques. The unimplanted metal develops initially a fine-grained, convoluted scale having a ridged, cellular structure. Subsequently, the oxide grains increase in size significantly and oxidation becomes predominantly controlled by diffusion of Ni2+ions across a compact, columnar scale. Implantation of the surface with nickel ions has no significant effect on the initial oxidation behavior. However, after implantation with chromium or lithium ions, the development of the NiO scale is, in the early stages of oxidation, suppressed by formation of NiCr2O4 or LiO2nodules, respectively. Subsequently, the implanted species are incorporated into the steady-state NiO scale where they dope the oxide and thus influence the diffusion rate of Ni2+ions through it. As would be predicted, the steady-state oxidation rate of chromium-implanted nickel is increased while that of lithium-implanted nickel is decreased compared with that of the unimplanted metal.