Evolution of oxidation in Ni-Cr-W alloy at 1100°C

The oxidation process of a newly developed Ni-Cr-W alloy in air at 1100°C has been investigated by varying the holding time. The microstructures and compositions of the surface scale as well as the oxide in cross-section were characterized by Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectrum (EDS). The phase identification of the surface scale was carried out using X-ray diffraction (XRD). Results show that in the initial stage of oxidation (<3 h) a single oxidation layer is formed on the alloy. Surface is mainly composed of Cr₂O₃. With prolonging of oxidation (>7 h), a NiCr₂O₄ layer with spinel structure grows out gradually in the outer layer of Cr₂O₃. Once the outer layer of the compact spinel is formed, the double multi-components layer NiCr₂O₄ · Cr₂O₃ will further decelerate the oxidation rate of the alloy. The degradation of the alloy subsurface includes the inner oxidation of grain boundaries and the formation voids and carbides-free area. The high concentration of W in the alloy does not impair the corrosion resistance of the alloy obviously.