Sintering and Tribology of Boride Hard Materials

Abstract

An experimental and analytical studies for obtaining high performance ceramics of TiB₂-and B₄C-based hard materials are inclusively presented in this paper. An improvement of sinterability and mechanical properties of TiB₂ and B₄C hard materials are achieved by using ultra-fine powders and sintering aids. First results obtained showed that the ultra-fine and size-controlled powders of TiB₂ can be produced by magnesium-thermic reduction method. Fabrication processing of TiB₂ using pressureless sintering was also investigated with special emphasis on the effect of doping Ni₇Zr₂, Ni₃B, NiB, and Co. The pore-free sintered compacts can be obtained by the addition of extreme small amount of Ni₇Zr₂. Moreover, sintering behavior and mechanical properties of B₄C-TiB₂ composites were investigated by pressureless sintering up to 2100°C in vacuum, resulting in a maximum density of 99% of the theoretical density. Tailored microstructures may be obtained in composites on the B₄C-TiB₂ system. The importance of microstructural features, resulting from precipitation phases from supersaturated solid solutions, for the improvement of sinterability and mechanical properties, is also addressed. Finally, sliding friction experiments were conducted on hard materials. A friction coefficient of B₄C-TiB₂ as low as 0.1 can be obtained because the oxidation of btmde produces a trapped-lubricating, glassy phase of boron oxide on the sliding surfaces.