New oxidation features in NiCrAl-Zr revealed by an Auger microprobe

A NiCrAl‐0.5 (wt. %) Zr alloy, oxidized in air for 1 h at 1180 °C was studied using a 30‐nm resolution Auger microprobe. Depth analysis was achieved using crater edge profiling. This first application of AES to these alloys enabled several new observations of the chemical composition of microstructural features in the corrosion layer. The external oxide was rough, about 2–3 μm thick, and contained Ni, Cr, Al, and O. It was discovered that stoichiometric Al2O3 was restricted to a homogeneous layer about 300‐nm thick between the oxide and the base metal. The metal immediately beneath this Al2O3 layer was found to be depleted in Al and roughly ten times richer in Zr than the bulk alloy. These observations are compared with the predictions of current models of the oxidation of MCrAl alloys.