Differences in growth mechanisms of oxide scales formed on ODS and conventional wrought alloys

Abstract

The oxidation behavior in air of two ODS alloys, MA 754, a chromia former, and MA 956 an alumina-scale former, has been compared with that of conventional wrought model alloys with similar compositions. The main effects on scale properties of both oxide types due to oxide dispersions were found to be improved adherence, decreased growth rates, and enhanced selective oxidation. In addition to metallography, X-ray diffraction, energy dispersive X-ray analysis of the scales, and studies of scale morphology, the detailed growth mechanisms of the oxide layers were studied using an18O tracer technique. The results show that the oxides on the conventional alloys grow by both metal and oxygen transport, and that the addition of oxide dispersions suppresses the outward scale growth. This change in growth mechanism is a possible explanation for the observed improved scale adherence, decreased growth, and enhanced selective oxidation in the yttria-containing alloys.