Low-Temperature Densification of TiN-TiB₂ Composites through reactive hot pressing with excess Ti additions

Abstract

Reactive hot pressing of Ti and BN powder mixtures is used to produce dense TiN_x-TiB₂ composites. The effect of excess Ti along with a small addition, ~1 wt% Ni, on the reaction and densification of the composite was investigated. A composite of ~99.9% relative density (RD) was produced at 1200°C at 40 MPa for 30 min with 1 wt% Ni, whereas composites produced without Ni are porous and contain residual reactants. The microstructural studies on composite samples with excess Ti produced at short durations indicate the presence of a transient (Ni-Ti) phase from which Ti is finally removed to form substoichiometric TiN_x. The hardness of the dense TiN_x-TiB₂ composite is ~22 GPa. The densification mechanism in this system is contrasted with the role of nonstoichiometry in the Zr-B₄C system.