The influence of surface ion implantation upon the oxidation behaviour of a 20% Cr-25% Ni, niobium stabilized austenitic stainless steel, in carbon dioxide, at 825°C

Abstract A study has been made of the influence of the surface ion implantation of platinum, silicon, aluminium with and without yttrium and cerium upon the oxidation behaviour of a 20% Cr-25% Ni-Nb stabilized stainless steel. The oxidation tests were in carbon dioxide (1 atm pressure), at 825°C, for periods up to 5900 h. Platinum, silicon and aluminium implantation had no significant influence upon either the extent of kinetics of oxidation or of spallation. An additional implantation of yttrium into a surface layer containing implanted aluminium improved the oxidation resistance slightly but had no effect on oxide adherence. Cerium implantation exerted the greatest influence on the oxidation behaviour of the steel. It reduced by at least a factor of two the attack of the steel throughout the exposure period and also improved oxide adherence. It was combined, probably with chromium, as a mixed oxide. The improvement in oxidation resistance with the incorporation of cerium in the protective barrier film derived from a more effective restriction to cation movement than with the film formed on the steel alone. The mechanical properties of the outer layer were also improved by the incorporation of cerium to account for the improved oxide adherence.