Synthesis and sintering of tungsten tetraboride and tantalum-bearing tungsten tetraboride under ultra high temperature and high pressure

As a highly controversial candidate superhard material, tungsten tetraboride (WB4) has attracted widespread attention due to its desirable mechanical properties. Here, single phase WB4 ceramics and WB4-based materials containing tantalum (Ta) have been successfully synthesized by a high-pressure reaction at 5.0 GPa and 1400 °C - 3000 °C. We systematically investigated the effect of processing temperature on the phase stability of WB4 and doping with different amounts of Ta on mechanical properties and thermal stability. The results confirm that increasing treatment temperature is beneficial to the synthesis of the WB4 phase, and high pressure can effectively inhibit the decomposition of WB4. Additionally, the hardness value of the WB4-based ceramic is found to decrease with the increase of the doped tantalum content. However, the hardness of WB4 is less than W0.9Ta0.1B4 (10 at. % Ta), indicating that a small amount of Ta doping is positive for the mechanical properties of WB4. The results show that the W0.9Ta0.1B4 ceramic synthesized at a temperature of 2800 °C and 5.0 GPa has excellent overall properties. Its Vickers hardness is 42 GPa (0.49 N), and its oxidation resistance temperature is 542 °C, which is much higher than the hardness and thermal stability of tungsten carbide (WC). This work can provide practical guide for the design of new transition metal boride superhard materials, and point out the visual direction for exploring the next generation of superhard materials.