Binderless sub-micron WC consolidated by hot pressing and treated by hot isostatic pressing

Abstract

Highly dense binderless WC was obtained by hot press sintering (HP) and then treated by hot isostatic pressing (HIP). Compositional and phase analyses of the products were carried out using field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). The mechanical properties were evaluated, and the location of the inhibitors was studied by transmission electron microscopy (TEM). The sub-micron (0.53 µm) powders of WC (doped with 0.33 wt % VC and 0.54 wt % Cr₃C₂) were HP sintered at 1800, 1900, and 2000°C. WC with a relative density of 97.9% and a grain size of approximately 0.73 µm was obtained after sintering at 2000°C for 30 min under a pressure of 28 MPa. The Vickers hardness and fracture toughness were 24.15 ± 0.33 GPa and 4.40 ± 0.10 MPa·m^1/2, respectively. After treatment by HIP at 1750°C for 120 min under a pressure of 150 MPa, the relative density of the samples was increased to 99.4%, the hardness was over 26.00 GPa, and the grain size was 0.75–0.81 µm. The grain growth inhibitors were also characterised by TEM and energy dispersive X-ray spectroscopy (EDX); the results show that the grain growth was effectively suppressed by the inhibitors of VC and Cr₃C₂ as a result of the segregation of the inhibitors at the grain boundaries.