Enhanced hardness in tungsten–substituted molybdenum diboride solid solutions by local symmetry reduction

MoB 2 , with a layered structure, is a potential functional material that is expected to be used as catalysts and conductors. However, the lower hardness limits its application in extreme environment. Solid-solution hardening is a suitable way to enhance hardness and keep structure, but it is complicated in transition metal borides (TMBs) solid solutions . Up to now, uncovering the intrinsic factors of solid-solution hardening is still a challenge. In this work, the structural, electronic and hardness properties of Mo 1-x W x B 2 ( x  = 0.01~0.20) is studied to explore the potential factors. It is found that sharp increase in hardness of Mo 1-x W x B 2 at low W doping level (≤5 at%), and highest Vickers hardness of 26.7 ± 1.2 GPa (applied 0.49 N load) was obtained by Mo 0.95 W 0.05 B 2 . The high hardness reason is ascribed to the lattice distortions lead to internal stress at the nanoscale , which created local symmetry reduction by affected local electron distribution of B–B bond and the lattice position of Mo atoms. Moreover, at higher W doping level, TM-B bond is strengthened by increasing electron transfer from the tungsten atoms to the boron atoms , which resulting in the hardness increasing of Mo 1-x W x B 2 . This provides guidance for designing TMBs solid solutions with better mechanical properties.