SIMS Investigations of the Transpor Phenomena in Chromia and Alumina Scales on Ods Alloys

The oxidation behaviour of the ODS alloys MA 754, a chromia former and MA 956, an alumina former, was investigated at 1000 and 1100°C. Main emphasis was placed on the studies of scale growth mechanisms using SIMS analysis of oxide scales grown during a two-stage oxidation where an ¹⁸O-enriched gas was used in the second stage. It was found that the oxide scales on both materials grow mainly by oxygen transport, but a significant amount of outward scale growth occurs, especially for the chromia former. Indications have been found that not only differences in the oxidation behaviour of various heats of one material but even differences between the chromia and alumina forming alloys can be attributed to differences in the amount of outward scale growth.