Tungsten diboride (${\mathrm{WB}}_{2+x}$) has been predicted to be a superhard material. It, however, has yet to be practically realized, because of its intrinsically low toughness, without involving favorable dislocation slip systems. Here, we report a viable strategy to effectively strengthen both the toughness and hardness of ${\mathrm{WB}}_{2+x}$ by introducing ordered atomic vacancies to increase dislocation mobility along certain directions. By doping with rhenium atoms, the ordered metal-vacancy pairs are revealed to occur extensively in the optimally doped sample with a composition of ${({\mathrm{W}}_{0.9}{\mathrm{Re}}_{0.1})}_{1-\delta }{\mathrm{B}}_{2+x}$ synthesized under high pressure. Such vacancy pairs are found to mainly reside in the $\{210\}$ and $\{102\}$ planes, along which the long-range dislocations are kinetically favored for improving its toughness and plasticity to achieve a load-invariant superhardness of $\sim 40\mathrm{GPa}$. In addition, its thermal stability is drastically promoted and rivals that of cubic boron nitride ($c\mathrm{BN}$). These discoveries not only experimentally identify a superhard material but also provide powerful insights into how the mechanical properties of transition-metal diborides can be improved by tailoring atomic deficiencies.

Close

PrevNext

View figure in article

• Doping effects
• Fracture
• Hardness
• Plasticity
• Single crystal materials
• Scanning electron microscopy
• Transmission electron microscopy
• X-ray diffraction