Effect of High-Energy Mechanical Alloying Duration and Boron Content on the Structural and Phase Evolution of W–B Powder Mixtures

Tungsten borides are promising superhard materials, but their mechanochemical synthesis requires prolonged processing, leaving the early and intermediate stages of mechanical alloying (MA) and the role of boron content largely unexplored. This study investigated the effect of boron content and high-energy MA duration (2–10 h) on the morphology, particle size distribution, and structural and phase evolution of W–B powder mixtures, comparing a near-stoichiometric W90B10 composition with a boron-excess W80B20 composition. Scanning electron microscopy, laser diffraction, X-ray diffraction, and TEM-EDS were used for characterization. The average particle size of W90B10 initially increased to 3.48 μm after 6 h and then decreased to 1.28 μm after 10 h, whereas W80B20 exhibited non-monotonic behavior, stabilizing at approximately 4.3 μm. With increasing MA duration, bcc-tungsten reflections broadened and weakened, indicating a highly disordered nanocrystalline state. Reflections of hexagonal WB2 (crystallite size 12.5 nm) appeared in W90B10 after 8 h, whereas no crystalline boride phases were detected in W80B20 up to 10 h. TEM–EDS and SAED analyses revealed local compositional inhomogeneity and provided additional crystallographic support for the formation of nanocrystalline WB2. These results show that boron content determines the kinetics of boride phase formation and the morphology evolution pathway during MA, identifying W90B10 as the more favorable composition for rapid nanocrystalline WB2 synthesis.