High-temperature oxidation behavior of low-energy high-flux nitrided Ni and Ni-20% Cr substrates

Nitridation at low-energy, high-flux implantation-diffusion has been performed on pure Ni and Ni-20at.% Cr substrates in order to study their high-temperature oxidation behavior at 700 and 800 degreesC in synthetic air. The nitridation treatment leads to significant sputtering on pure Ni, but no implanted nitrogen has been detected. However, the Ni-20at.% Cr substrates are able to incorporate nitrogen, with a very different surface state. Porosity is found on both substrates after the nitridation treatment. No particular difference is found in the oxidation kinetics of Ni specimens, but in their scales morphology. In contrast, in Ni-20at.% Cr specimens, oxidation is enhanced mainly upon the first exposure times owing to trapping of chromium by the implanted nitrogen. Furthermore, the expanded austenite gamma(N) layer formed on the nitrided Ni-20at.% Cr samples is stable up to 700 degreesC for 24 h, where after nitride precipitation sets in. (C) 2003 Elsevier Science B.V. All rights reserved.