Mechanochemical synthesis and annealing of tungsten di‐ and tetra‐boride

Tungsten diboride and tetra‐boride were synthesized by a combination of mechanochemical method and the subsequent heat treatment. To clarify the formation process of tungsten diboride (WB 2 ) and tetra‐boride (WB 4 ) using W‐B mixture system with variable B concentration, the effects of ball‐to‐powder ratio, W to B molar ratio on mechanochemical process were studied, and the relationship between phase composition and annealing temperature was built. The results show that, the synthesis of WB 2 with W:B = 1:5 can be improved by increasing ball‐to‐powder ratio from 4:1 to 6:1, but no WB 4 phase can be directly synthesized by mechanochemical method. WB 2 (AlB 2 ‐WB 2 , P6/mmm) phase can be only synthesized with W to B molar ratio of 1:4 and 1:5. Further increase in B content to W:B = 1:6 or less, W was present as the main phase with high crystallinity (>71%). WB 4 phase was formed as an annealing temperature as low as 1000°C, which was not stable and may decompose to WB 2 (WB 2 ‐WB 2 , P6/mmm) phase with the increase in temperature. The decomposition temperature of WB 4 can be improved by increasing the B content. Compared with the W‐B mixtures (W:B = 1:12) being milled for 1 hour, the powders milled for 40 hours present 20% higher of WB 4 weight fraction after being annealed at 1400°C for 2 hours.