材料期刊网

The transient oxidation behavior of beta-NiAl and NiAl-0.5Ag in 1 atm O-2 at 1273K was studied by thermogravimetry, giving special emphasis to the evolution of the morphology of the oxide scale, especially for what concerns the transformation of transient aluminas into the stable alpha-Al2O3 form. The oxidation kinetics can be described as being composed of three different parabolic stages for NiAl-0.5Ag and of two stages for beta-NiAl. Three different oxide morphologies are observed for the two alloys at different oxidation times. The SEM and XRD results show that the transient oxidation can be divided into two main stages, including the initial formation of gamma-Al2O3, which transforms quickly into theta-Al2O3, and the subsequent transformation of theta-Al2O3 into alpha-Al2O3. A combination of the results by XRD, EDAX and SEM shows that silver promotes the transformation of theta-Al2O3 into alpha-Al2O3, which is faster on NiAl-0.5Ag than on beta-NiAl.