Oxidation behaviour of an ODS NiAl-based intermetallic alloy

Abstract

The oxidation behaviour of an oxide dispersion-strengthened (ODS) NiAl intermetallic, microalloyed with Ti and Mo and strengthened by a fine dispersion of Y2O3, is investigated in the temperature range of 900-1200°C for up to 200h exposure. The results have shown that a nearly pure alumina scale is formed irrespective of the exposure time, which is consistent with previous results on oxidation of NiAl or doped NiAl alloys. From the analysis of the kinetics results and the surface scale morphology it follows that below 1100°C metastable alumina control the oxidation kinetics, even after long exposure times. The presence of yttria seems to account for this increase in the transient oxidation period. Preoxidation of the alloy (1200°C/3 h) leads to a substantial reduction of the oxidation rate and precludes void formation at the scale/gas interface. Furthermore, formation of uniform scale, which would diminish the probability of failure of the scale due to thermal stresses, is favoured. © 1998 Elsevier Science Ltd. All rights reserved.