Oxidation behaviour of an ODS NiAl-based intermetallic alloy

The oxidation behaviour of an oxide dispersion-strengthened (ODS) NiAl inte rmetallic, microalloyed with Ti and Mo and strengthened by a fine dispersio n of Y2O3, is investigated in the temperature range of 90-1200 degrees C fo r up to 200 h exposure. The results have shown that a nearly pure alumina s cale is formed irrespective of the exposure time, which is consistent with previous results on oxidation of NiAl or doped NiAl alloys. From the analys is of the kinetics results and the surface scale morphology it follows that below 1100 degrees C metastable alumina control the oxidation kinetics, ev en after long exposure times. The presence of yttria seems to account for t his increase in the transient oxidation period. Preoxidation of the alloy ( 1200 degrees C/3 h) leads to a substantial reduction of the oxidation rate and precludes void formation at the scale/gas interface. Furthermore, forma tion of uniform scale, which would diminish the probability of failure of t he scale due to thermal stresses, is favoured. (C) 1998 Elsevier Science Lt d. All rights reserved.