Two step hot pressing sintering of dense fine grained WC–Al2O3 composites

WC–40 vol% Al2O3 composites were prepared by high energy ball milling and the following two step hot pressing sintering (TSS). The tungsten carbide (WC) and commercial alumina (Al2O3) powders composed of amorphous Al2O3, boehmite (AlOOH) and χ-Al2O3 were used as the starting materials. The feasibility of two step sintering (TSS) method to WC–40 vol% Al2O3 composites was demonstrated, optimum TSS regime was discussed and phase transformation during TSS process was investigated. The results showed that both the pre-sintering at a proper first step temperature (T1) to obtain a critical initial density and isothermal hot pressing at an appropriate second step temperature (T2) to inhibit grain boundary migration (GBM) were of significant importance. When the as milled WC–40 vol% Al2O3 powders were hot pressed under TSS4 regime, a relative density of 99% and a grain size of 2.38 μm were obtained, an excellent Vickers hardness of 19.71 GPa was achieved, combining a fracture toughness of 12 MPa m1/2 with a flexural strength of 1285 MPa. Compared with the near full dense samples consolidated under CS1 regime (1540 °C for 90 min), the grain size decreased, the Vickers hardness, fracture toughness and flexural strength were all improved due to the refined microstructure and the transgranular fracture mode. The amorphous Al2O3, AlOOH and χ-Al2O3 were transformed to α-Al2O3 completely during the sintering process.