Influence of Cr content on high-temperature oxidation behaviour of arc sprayed Ni–Cr coatings

In this study, the high-temperature oxidation behaviour of arc-sprayed Ni-Cr coatings with high Cr contents of 30, 45 and 50 at.% was investigated in comparison with reference AISI 1020 steel. X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy were utilised to characterise the oxide scales. The oxidation resistance of the steel substrates was found to be enhanced after the application of the Ni-Cr coatings since the oxidation kinetics followed the parabolic law. In addition, the oxidation rate of Ni-50Cr coating was 56.5% lower than that of Ni-30Cr coating, indicating that the oxidation performance of coatings was improved with increasing Cr content. The oxide layers of Ni-Cr coating were found to be a double layer structure protecting the substrate from severely oxidation, which composed of a top layer of NiO and a basal layer of Cr2O3 and NiCr2O4. The surface of Ni-30Cr coating contained lots of multi-angle NiO crystals, while the surface of Ni-50Cr coating contained a dense Cr2O3 structure, suggesting that the growth of NiO crystals was limited due to the large amount of Cr-rich oxides.