The oxidation behaviour of NiAl-I. Phase transformations in the alumina scale during oxidation of NiAl and NiAl-Cr alloys

The oxide phases formed on NiAl and NiAl-Cr and their oxidation kinetics have been studied in the temperature range 973–1673 K using TGA, XRD, SEM and TEM. The oxidation rate depends on the oxide phase formed on the alloy. γ-Al 2O 3, θ-Al 2O 3, and α-Al 2O 3 have been observed and different κ p values were correlated to their growth. Cr in NiAl accelerates the θ-α transformation and leads to a higher κ p value. Cr 2O 3 formed in the initial stage of oxidation acts as nuclei for the formation of α-Al 2O 3.