Effect of Al content on high-temperature oxidation behavior and mechanism of AlxCoCrFeNi1.5Ti0.1 high-entropy alloy coatings by laser cladding

Abstract

In this study, the oxidation behavior and mechanism of Al_xCoCrFeNi_1.5Ti_0.1 (x = 0, 0.25, 0.5, 0.75, 1.0) high-entropy alloy (HEA) coatings at high temperatures ranging from 700 °C to 900 °C were investigated. The microstructure and oxidation products of the HEA coatings were characterized with scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD). In order to elucidate the effect of Al content on the oxidation behavior of HEA coatings, a novel oxidation kinetic model modified by Al content was developed. The results indicate that the oxidation weight gain of the HEA coatings generally follows a parabolic law. With the increase of Al content, the microstructure of HEA coatings transforms into a dual-phase structure (FCC and BCC) containing new BCC phases. When the HEA coatings are composed of the dual-phase structure (FCC and BCC), the oxidation process of the coatings is primarily inhibited by the diffusion of Al and Cr within the oxide layer, and the oxidation rate of the coatings is significantly reduced. The oxide layer of HEA coatings mainly comprises an inner Al₂O₃ layer and an outer Cr₂O₃ layer.