Synthesis and Evaluation of Titanium Boride Powder Prepared by Solid State Reaction from an Activated Boride Precursor

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Titanium diboride (TiB_2) has high melting point, hardness and chemical stability as well as an appreciable electrical conductivity. The TiB_2 sintered compact is desired to be applied to wear-resistant material, electrode material or corrosion- resistant crucible. The heat of formation of TiB_2 is so high that the reaction control of TiB_2 formation is required so as to prepare a sinterable TiB_2 fine powder by means of solid state reaction. In the present paper, an appropriate selection of starting powder and the formation of boride precursor by an ambient pretreatment resulted in the controlled formation reaction of TiB_2 in the subsequent heat treatment. The sinterability of TiB_2 was evaluated by hot-pressing of the synthesized powder.1. Synthesis of TiB_2 powder from titanium metal and amorphous boron: Low crystalline TiB_2 precursor was formed by the pretreatment of titanium metal and amorphous boron in an argon atmosphere at 600ﾟC for 60 min. TiB_2 powder with 15-20 mum diamete … More r was prepared by the subsequent heat treatment in an argon atmosphere at 900-1500ﾟC. This powder was not suited for sintering because of the presence of hollows in the TiB_2 particles.2. Synthesis of TiB_2 powder from titanium hydride and amorphous boron: A reformed titanium metal with hydrogen diffused lattice was formed after the ambient treatment of TiH_2 powder in argon at 700-800ﾟC. In the following heat treatment at 1000ﾟC for 360 min, hollow-free TiB_2 powder was obtained.3. Synthesis and evaluation of TiB_2 powder from titanium nitride and amorphous boron. TiB_2 formation reaction was appropriately controlled by the heat treatment of TiN powder (grain size: 0.5-3 mum) and amorphous boron in an argon atmosphere at 1400ﾟC for 360 min. Fine-grained and active synthesized TiB_2 powder (composition: TiB_2 + 0.2B) with added 10 mol% titanium metal was sintered at 20 MPa and 1800ﾟC for 30 min. A single phase sintered compact of TiB_2 had a relative density of 98% and a Vickers microhardness of 2850 kg/mm^2. Less