Reaction behavior during Spark Plasma Sintering of cBN-TiCN-Ni powders

Polycrystalline cubic boron nitride (PcBN) is the designation given to composites constituted by cBN hard particles within a ceramic/metallic matrix. These composites are normally processed in severe pressure and temperature conditions to achieve full densification and prevent hexagonal BN formation, which would decrease the composite hardness. In this work, the Spark Plasma Sintering (SPS) technique was investigated as an alternative to sinter cBN-TiCN based composites, with and without addition of metallic Ni. The initial compositions were selected according with calculated phase diagrams, using the Thermo-calc software. The thermal behavior during SPS was studied up to 2000°C, namely the densification, reactivity and phase transformations. A larger densification was achieved with Ni addition, but full removal of open porosity was only possible at 1700 °C, where the cBN phase transformation to hBN completely occurred. In agreement with the thermodynamic calculations, other matrix phases, as TiB2 and Ni3B, were formed during sintering.