THE EFFECT OF ION-IMPLANTED YTTRIUM ON THE OXIDATION OF AUSTENITIC STAINLESS-STEEL

The effect of ion-implanted yttrium on the oxidation of austenitic stainless steel is studied by combining ion backscattering (RBS) and SIMS characterizations of implanted and unimplanted specimens. Elemental depth distributions are measured after oxidation in <114> single crystals (17Cr-13Ni) and type-304 polycrystalline samples (18Cr-10Ni). Implantation of 5 x 10(15) and 2 x 10(16) Y/cm2 (200 keV) reduces the extent of oxidation (10 min at 800-degrees-C) by approximately 20%. In addition, the 2 x 10(16) Y/cm2 implantation changes the oxidation mechanism from being iron out-diffusion to be predominantly oxygen in-diffusion. This effect is believed to be beneficial for preventing spallation. While the single crystal oxidizes more than a micron for 10 min at 800-degrees-C, type 304 oxidizes less than 100 nm. At 1000-degrees-C the oxidation of 304 steel amounts to less than 200 nm. Yttrium implantation reduces the oxidation rate, but both in the implanted and unimplanted case, the oxidation mechanism appears to be chromium out-diffusion.