Opportunities and challenges for nanostructured superhard materials

Over decades of research and development, nanostructured diamond and cubic boron nitride have been successfully synthesized, and their high hardness and strength fully demonstrate that their nanomechanical enhancement mechanism is an effective way to pre‐ pare superstrong and superhard materials. To date, knowledge of such nanostructured superhard materials is still limited, and there are many mysteries surrounding the effects of pressure and temperature on the grain growth and defect formation (e. g., twins and stacking faults) during the synthesis. Moreover, the nanoeffects on the mechanical properties and the related underlying strengthening mechanisms of nanostructured superhard materials are still under debate. We review the research in related fields in recent years, outline the strategies and principles for designing and finding superhard materials, and describe the influence of typical nanostructures on the mechanical and thermal stability of these materials. The high-temperature and highpressure phase transitions and transformation mechanisms are discussed, and current research progress as well as potential applications are summarized.