Oxidation behaviours of electron beam physical vapour deposition fabricated microcrystalline Ni–23·5Cr–2·66Co–1·44Al superalloy sheet at 1000°C

Abstract

Isothermal oxidation of as-deposited microcrystalline Ni–23·5Cr–2·66Co–1·44Al (wt-%) alloy sheet fabricated by electron beam physical vapour deposition exposed at 1000°C in air up to 100 hours was investigated. Surfaces and cross-sections of the oxidised specimens were studied by scanning electron microscopy. Phase identification of the oxide scale was performed by glancing angle X-ray diffraction. The results indicated that the oxidation kinetics of the alloy sheet obeyed an approximate cubical power law at the early stage of exposure and approximate fourth power law for long oxidation terms. It was found that the oxide scales consisted mainly of an outer Cr2O3 oxide layer, and an inner NiO and NiCr2O4 mixed oxides layers. An Al2O3 layer was formed at the scale/substrate interface after a long-time oxidation. This showed that the outward diffusion rate of Cr atoms was higher than that of Ni atoms and Al atoms.