The effects of heat treatment and implantation of aluminium on the oxidation resistance of Fe Cr Al Y alloys

The oxidation resistance of FeCrAlY alloys is known to be due to the rapid formation of a protective film containing ?-Al2O3. The near-surface concentration of Al has been increased by ion implantation, and for a dose of 1017 Al+ ions cm-2 (equivalent to 4.5 ? cm-3 the parabolic oxidation rate constant has been reduced by a factor of 140 in tests at 1100°C. Heat treatment prior to oxidation also proved beneficial for reasons which are discussed. These relate to the diffusivity of Cr and other spinel-forming elements within the metal. Analysis of Al+-implanted steels after oxidation, using ESCA and EDS techniques, confirmed the high concentration of Al2O3 within the oxide, and SEM examination showed that the scale is much more compact than in the unimplanted case. Suggestions are made for enhancing still further the efficacy of Al+ implantation as a means of improving oxidation resistance and for optimizing the synergistic effect of yttrium and aluminium.