Effects of TiC content and melt phase on microstructure and mechanical properties of ternary TiB2-based ceramic cutting tool materials

Ternary TiB2-WC-TiC ceramic composites were fabricated by hot-pressed sintering at 1650 degrees C. Sintering additives such as WC, TiC, Mo, Ni and Co were used to create a liquid phase and promote densification. The effect of TIC content, (Mo,Ni) and Co on microstructure and mechanical properties of the ternary TiB2-WC-TiC ceramic composites was presented. Flaw structures such as pores and microcracks reduced as the TiC content increased. Wettability of (Mo,Ni) and Co to TiB2 had a significant influence on the microstructure. The microstructure of these composites showed a typical core/rim structure. The core was TiB2 and the rim was mainly composed of TIC. The relative density, microhardness, flexural strength and fracture toughness of these composites increased as the TiC content increased. Results indicated that ternary TiB2-WC-30 wt.% TiC-(Mo,Ni) ceramic composite provided the optimal combination of dense microstructure and mechanical properties, including the relative density of (99.3 +/- 0.3)%, the microhardness of 24.8 +/- 0.3 GPa, the flexural strength of 946.9 +/- 24.9 MPa, and the fracture toughness of 7.4 +/- 0.2 MPa . m(1/2). The high fracture toughness of ternary TiB2-WC-30 wt.% TiC-(Mo,Ni) ceramic composite was due to an intensive coupled mechanism of the near-full density, the typical core/rim structure, crack deflection, crack bridging, crack branching and pull-out by a large number of fine WC grains. (C) 2014 Elsevier B.V. All rights reserved.