Preparation of ultrafine (W,Mo)B, (W,Mo)B2.5 and (Mo,W)AlB solid solution composite powders

In this study, ultrafine borides powders including (W,Mo)B, (W,Mo)B2.5 and (Mo,W)AlB were successfully fabricated via boronizing ultrafine W-Mo solid solution composite powder with B4C as the boron source under the assistance of Ca melt or Al melt. Ultrafine W-Mo solid solution powder was obtained by using a two-stage reduction route to reduce the precursor powder synthesized by spray drying. Meanwhile, the effects of Mo/W ratio on the phase composition, morphological characteristics and particle size distribution of boride solid solution composite powder were thoroughly investigated. The shift of diffraction peak in the XRD spectrum, the linear change of lattice constant and the homogeneous distributions of W, Mo, B and Al in the EDS energy spectrum comprehensively confirmed that the boride solid solution with different Mo/W ratios could be prepared. Due to the essentially insolubilities of W and Mo in Ca melt, the (W, Mo)B grains grew following a template growth mechanism, and inherited the nearly spherical morphology feature of ultrafine W-Mo solid solution composite powder with a particle size of approximately 200 nm. Nonetheless, as a result of the high solubilities of W, Mo, and B in Al melt, the process of dissolution-precipitation led to the formations of flaky (W, Mo)B2.5 and short rod-shaped (Mo, W)AlB.