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

• Published in: Materials chemistry and physics 2020-09, Vol.251, p.123188, Article 123188
• Main Authors: Zhao, Feng, Tao, Qiang, You, Cun, Ye, Meiyan, Li, Li, Han, Yang, Dong, Shushan, Wang, Xin, Cui, Tian, Zhu, Pinwen
• Format: Article
• Language: English
• Subjects: Borides; Boron; Conductors; Diamond pyramid hardness; Doping; Electron distribution; Electron transfer; Extreme environments; Functional materials; Hardening; Hardness; Mechanical properties; Molybdenum; Residual stress; Solid solution; Solid solutions; Solution strengthening; Symmetry; Symmetry reduction; Transition metal borides; Transition metals; Tungsten
• ISSN: 0254-0584; 1879-3312
• DOI: 10.1016/j.matchemphys.2020.123188

MoB2, 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 Mo1-xWxB2 (x = 0.01~0.20) is studied to explore the potential factors. It is found that sharp increase in hardness of Mo1-xWxB2 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 Mo0.95W0.05B2. 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 Mo1-xWxB2. This provides guidance for designing TMBs solid solutions with better mechanical properties. •Mo1-xWxB2 (x = 0.01–0.20) solid solutions have been successfully synthesized.•Mo0.95W0.05B2 obtains high hardness of 26.7 GPa by solid-solution hardening.•Local symmetry reduction is a factor for hardness enhancement in solid solution.