Oxidation behavior of ultrafine WC-based cemented carbides with AlxCoCrCuFeNi high-entropy alloy binders

Abstract

The isothermal oxidation behavior of WC-based cemented carbides with AlxCoCrCuFeNi (x = 0, 0.5, 1.0, 1.5) high-entropy alloy (HEA) binders at 600–800 °C in air was studied by a thermogravimetric method, as well as WC-Co for comparison. The oxidation of the WC-HEA cemented carbides accompanies swelling and follows a linear law that is controlled by reaction at the oxide layer/matrix interface. The WC-HEA cemented carbides show better oxidation resistance than WC-Co, even though WC-Co has a denser microstructure and coarser WC grain size. With increase of Al content in the HEA binder, the oxidation rate of WC-HEA decreases, and the specific mass gains of the samples with HEA binder containing Al are at least 20% smaller than that of WC-Co after isothermal oxidation at 800 °C for 2 h. Moreover, as the HEA content increases from 5 to 20 wt%, the specific mass gain reduces from 61.89 to 24.55 mg/cm2. Selective oxidation of the HEA binder occurs, and the excellent anti-oxidation property of the HEA binder impedes inward diffusion of oxygen to the oxide layer/matrix interface, which suppresses oxidation of the matrix and enhances oxidation resistance of the WC-HEA. The results also indicate that the improved oxidation resistance of the WC-HEA system should not be attributed mainly to the formation of a dense oxide layer with high tungstate content during oxidation.