Interfacial layers in high‐temperature‐oxidized NiCrAl

The oxide and diffusion layers produced in a Ni–14Cr–24Al alloy by oxidation in air at 1180 °C for 25 h have been studied using scanning Auger microscopy and ball cratering for depth profiling. During cooling, following oxidation, the oxide layers formed by this alloy spalled profusely. The remaining oxide was very thin (<100 A) and was primarily Cr2O3 with a trace of Ni (although other oxides are possible). The underlaying metal substrate exhibited γ/γ′ (Ni/Ni3Al) and β (NiAl) phases; however, there was metallic interfacial layer at the surface. This layer was similar to the bulk γ/γ′ phase, but slightly enriched in Cr and Al. These data are compared to electron microprobe results from a nominally identical alloy. The diffusion layer thickness is modeled with a simple mass balance equation and compared to recent results on the diffusion process in NiCrAl alloys.