Boron carbide is a strategic material, finding applications in nuclear industry, armour for personnel and vehicle safety, rocket propellant, etc. Its high hardness makes it suitable for grinding and cutting tools, ceramic bearing, wire drawing dies, etc. Boron carbide is commercially produced either by carbothermic reduction of boric acid in electric furnaces or by magnesiothermy in presence of carbon. Since many specialty applications of boron carbide require dense bodies, its densification is of great importance. Hot pressing and hot isostatic pressing are the main processes employed for densification. In the recent past, various researchers have made attempts to improve the existing methods and also invent new processes for synthesis and consolidation of boron carbide. All the techniques on synthesis and consolidation of boron carbide are discussed in detail and critically reviewed.

Titanium diboride (TiB 2 ) 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 TiB 2 is limited by poor sinterability, exaggerated grain growth at high temperature and poor oxidation resistance above 1000uC. Pure TiB 2 can be densified only at high temperatures (y2000uC), 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 TiB 2 with optimised mechanical properties at lower sintering temperature. The present review surveys the current state of knowledge on development of bulk TiB 2 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.

Zirconium diboride is a strategic material, finding applications as thermal protection system in reentry vehicles, high temperature electrode, thermowell tubes, etc. Solid state reactions require high temperature and thus result in coarse powders which are difficult to sinter. Densification of ZrB 2 is extremely difficult due to its refractory nature. Sinter additives help in densification but deteriorate the high temperature properties. In the recent past, various researchers have made attempts to improve the existing methods and also invented new processes for synthesis of pure and fine powders as well as for densification of ZrB 2 . All the techniques on synthesis and consolidation of ZrB 2 are discussed in detail and critically reviewed in this article.

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