The effects of pre-oxidation and thin Y2O3 coating on the selective oxidation of Cr18-Ni9-Ti steel

Pre-oxidation at 400degreesC and thin Y2O3 film deposition were applied to a Cr18-Ni9-Ti stainless steel. The effects of these treatments on the selective oxidation behavior at 900degreesC have been studied. Both treatments were found to improve the oxidation resistance of the alloy significantly. Scanning electron microscopy (SEM), EDS and XRD analyses show that a Fe-rich oxide scale preferentially formed on the surface of the alloy during the pre-oxidation treatment, resulting in an oxide-alloy interface with increased Cr content and decreased oxygen pressure. Thus, after the pre-oxidation, the selective oxidation of Cr at the oxide-alloy interface was promoted during oxidation at 900degreesC. Surface applied Y2O3 film, on the other hand, can change the growth mechanism of the scales and decrease their growth rate, also promoting the selective oxidation of Cr. These experimental results can be explained by a modified Wagner's theory on selective oxidation of alloys. (C) 2003 Elsevier B.V. All rights reserved.