Theoretical and experimental investigation of the W-Al-B and Mo-Al-B systems to approach bulk WAlB synthesis

Abstract MAB phases are a family of ternary transition metal borides with a layered crystal structure, that provides them with properties likely to be suitable for applications within extreme environments. Here, we report a computational and experimental examination of the W-Al-B system compared to the isostructural Mo-Al-B system. Utilising DFT calculations, WAlB and MoAlB were found to be thermodynamically favourable compared to their most stable competing phases, with respective total energy differences of -0.15 eV and -0.28 eV at 0 K. Partial substitution of W on the Mo-site of MoAlB was observed for certain solid solution compositions. The experimental results indicate that synthesis of (Mo,W)AlB compounds is driven by in-situ formation of metal boride solid solutions, (Mo,W)B, which further react with Al, Mo-Al, W-Al or (Mo,W)-Al compounds to obtain the MAB phase structure. Finally, reactive hot-pressing was shown to be a promising avenue for the production of dense engineering (Mo,W)AlB-containing components.