The manufacture and characterization of WC-(Al)CoCrCuFeNi cemented carbides with nominally high entropy alloy binders

Abstract

Recently, there has been increasing interest in cemented tungsten carbide hardmetals and titanium carbonitride cermets with binders of multi-component alloys (≥4 elements) or high entropy alloys (≥5 principal elements in equimolar ratios). Property improvements have been reported, such as increased ambient and elevated temperature hardness, as well as greater oxidation resistance.This study has thoroughly investigated model cemented carbides manufactured using coarse WC with a binder content of 20 wt% (32–37 vol%) from three different (Al)CoCrCuFeNi high entropy alloys (HEAs) and at different carbon levels (low, medium and high).Binder alloys were manufactured by both planetary ball milling of elemental powder mixtures and gas atomizing. Sintering was performed in vacuum for 2 h at different temperatures between 1200 °C and 1500 °C. Post-HIP treatments were also applied in some cases as all systems were difficult to densify without residual porosity.Detailed analyses were performed on the as-manufactured binder alloys, sintered binder alloys (without WC) and the actual sintered cemented carbides (WC + HEA). Various analysis methods were used to examine the materials. These included thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC) to determine the melting behaviour; X-Ray Diffraction (XRD), Electron Backscatter Diffraction (EBSD) and Energy-Dispersive X-Ray Spectroscopy (EDS) to identify the type, crystal structure and exact composition of the phases present; and light optical microscopy (LOM) and scanning electron microscopy (SEM) for microstructural characterization. Additionally, the hardness and Palmqvist indentation toughness of each composition were also measured.2-Phase WC-HEA microstructures could not be obtained using the investigated high entropy alloys. Several solid solution binder alloys and numerous carbide phases were present after sintering, formed by segregation and reaction. The type and quantity of the phases depend on the carbon balance. For the compositions containing aluminium, it was found that aluminium forms oxides and intermetallic phases during sintering. The paper presents these findings in detail.