Simultaneous synthesis and sintering of TiB2-TiN composite at moderate pressures and Temperatures

Titanium nitride and titanium diboride are materials with high melting points, hardness and low density and are suitable for wear resistant and cutting tool applications. The TiB2-TiN composites has been reported to be produced by hot pressing of TiN and TiB2 powders (2473K) and reactive hot pressing of TiH2 and BN (2123K). The addition of nickel was found to improve the density and fracture toughness of the composite. We report the synthesis and sintering of the TiB2 (40%)-TiN composite by reactive hot pressing of titanium and boron nitride with 1% (wt) nickel. The composite compacts were produced by hot pressing at 7-40 MPa, the cold pressed powder mixtures under argon atmosphere in two steps: step I at 1223K for 2 h followed by step II at 1873K for 2h. The composite was 98% dense, with a hardness of 25  2.6 GPa, fracture toughness 6.18  0.7 MPam and coefficient of thermal expansion 10.7 x 10-6K-1. These are in good agreement with those reported in literature for samples prepared by reactive hot pressing of TiH2 and BN and better than those prepared with fine powders. The results of the x-ray diffraction and electron microscopic studies, hardness and fracture toughness measurements are presented in this paper