Processing and properties of monolithic TiB2 based materials

Titanium diboride (TiB2) based materials have received wide attention because of their high hardness and elastic modulus, good abrasion resistance, and superior thermal and electrical conductivity. Potential applications include high temperature structural materials, cutting tools, armour, electrodes in metal smelting and wear parts. Despite its useful properties, the application of monolithic TiB2 is limited by poor sinterability, exaggerated grain growth at high temperature and poor oxidation resistance above 1000 degrees C. Pure TiB2 can be densified only at high temperatures (similar to 2000 degrees C), with an applied pressure generally being necessary during sintering. However, these high sintering temperatures cause abnormal grain growth and microcracks, which are detrimental to the mechanical properties. Various sinter additives are commonly added to obtain dense TiB2 with optimised mechanical properties at lower sintering temperature. The present review surveys the current state of knowledge on development of bulk TiB2 based materials, with particular emphasis on consolidation microstructure property relationships. Three major issues are addressed: the preparation of bulk titanium boride with metallic and non-metallic sinter additives (up to 20 wt-%), tribological properties and thermal stability of the borides. In conclusion, a perspective for future development of boride materials is provided.