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

TiB₂-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 TiB₂-WC ceramic-metal composites consisted of the fine WC grains and uniform TiB₂ grains. The brittle phase of Ni₃B₄ and a few pores were found in TiB₂-WC-Ni ceramic-metal composite. A lot of pores and brittle phases such as W₂CoB₂ and Co₂B were formed in TiB₂-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 TiB₂. The pores, brittle phases and coarse grains of TiB₂ 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 TiB₂-WC ceramic-metal composite. The formation of intermetallic compound of MoNi₄ 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 TiB₂ but also strengthened the interface energy between WC and TiB₂ grains. The grain size was fine and the average relative density of TiB₂-WC-(Ni, Mo) ceramic-metal composite reached 99.1%. The flexural strength, fracture toughness and Vickers hardness of TiB₂-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.