The effect of ion-implanted yttrium on the oxidation of nickel

Abstract

Yttrium ions with 150 keV energy were implanted to their steady state concentration into nickel and the nickel was then annealed in a vacuum of 5 × 10 −7 Torr for 1 h at selected temperatures. Yttrium diffused to the surface of nickel to form randomly oriented grains of Y 2O 3 at temperatures between 600 and 1000°C. The oxidation kinetics of nickel and yttrium-implanted nickel were measured at 990°C in air at 1 atm, and the oxidation rate was found to be less in the implanted nickel than in the unimplanted nickel. The kinetic behavior was parabolic in the latter case but non-parabolic in the former case. The surface microstructures of implanted and unimplanted specimens were studied as a function of time at 900°C in air; the yttrium-implanted specimens yielded very uniform surface microstructures which reflected a lack of an orientation relationship between the oxide and the nickel substrate. For short oxidation times (12 h and less), the oxide layer was adherent to the nickel substrate. However, after oxidation for 24 h, the oxide layer was non-adherent.