Effects of sintering additives on microstructure and mechanical properties of TiB 2–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 3B 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 2CoB 2 and Co 2B 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.