Effects of sintering additives on microstructure and mechanical properties of TiB2–WC ceramic–metal composite tool materials

Abstract TiB 2 –WC ceramic–metal composite tool materials were fabricated using Co, Ni and (Ni, Mo) as sintering additives by vacuum hot-pressing technique. The microstructure and mechanical properties of the composite were investigated. The composite was analyzed by the observations of scanning electron microscope (SEM), X-ray diffraction (XRD) and energy dispersive spectrometry (EDS). The microstructure of TiB 2 –WC ceramic–metal composites consisted of the fine WC grains and uniform TiB 2 grains. The brittle phase of Ni 3 B 4 and a few pores were found in TiB 2 –WC–Ni ceramic–metal composite. A lot of pores and brittle phases such as W 2 CoB 2 and Co 2 B were formed in TiB 2 –WC–Co ceramic–metal composite. The liquid phase of Co was consumed by the reaction which led to the formation of the pores and the coarse grains of TiB 2 . The pores, brittle phases and coarse grains of TiB 2 were harmful to the improvement of the mechanical properties of the composite. The sintering additive of (Ni, Mo) had a significant effect on the density and the mechanical properties of TiB 2 –WC ceramic–metal composite. The formation of intermetallic compound of MoNi 4 inhibited the consumption of liquid phase of (Ni, Mo). The liquid phase of (Ni, Mo) not only inhibited the formation of the pores and the coarse grains of TiB 2 but also strengthened the interface energy between WC and TiB 2 grains. The grain size was fine and the average relative density of TiB 2 –WC–(Ni, Mo) ceramic–metal composite reached 99.1%. The flexural strength, fracture toughness and Vickers hardness of TiB 2 –WC–(Ni, Mo) ceramic–metal composite were 1307.0 ± 121.4 MPa, 8.19 ± 0.29 MPa m 1/2 and 22.71 ± 0.82 GPa, respectively.