Atomic Substitution to Balance Hardness, Ductility, and Sustainability in Molybdenum Tungsten Borocarbide

Mo2–xWxBC is suggested to be one of the only exceptionally high hardness, transition-metal-rich materials that also shows moderate ductility and compositional sustainability. This is demonstrated here through the synthesis of the Mo2–xWxBC (x = 1.1, 0.75, 0.5, 0.25, 0) solid solution and structural characterization using X-ray diffraction, electron microscopy, and density functional theory. All compounds crystallize in the orthorhombic space group, Cmcm, and follow Vegard’s law. Vickers microindentations show a decrease in hardness as tungsten is substituted by molybdenum owing to changes in the crystal chemistry and the loss of electron density. Calculating Pugh’s ratio based on the values derived from density functional perturbation theory reveals that these materials are surprisingly ductile throughout the solid solution, providing the potential to manipulate the hardness and ductility. Controlling this relationship is of great technological interest as most hard materials suffer from brittleness. Moreover, evaluating the elemental scarcity and economic indicators such as the Herfindahl–Hirschman index demonstrates the sustainability of the solid solution relative to other high-hardness, transition-metal-rich materials. The ability to fine-tune the mechanical properties for any application by varying the ratio of the transition metals while optimizing their sustainability is undoubtedly of significant industrial interest.