Enhancing the hardness of diamond through twin refinement and interlocked twins

Abstract

Nanostructuring strategies are widely recognized for their ability to substantially enhance the mechanical properties of materials. Among them, nanotwinning stands out for its effectiveness in enhancing the mechanical attributes of diamond by impeding dislocation movement at twin boundaries. However, the precise mechanisms that control nanotwinning and the distinct strengthening effects of various twin configurations remain inadequately understood. Here bulk diamonds were synthesized from onion-like carbon nanoparticles of different sizes, graphite nanopowder and diamond nanopowder under high-pressure and high-temperature conditions. Smaller onion-like carbon particles facilitated the formation of finer diamond grains with thinner twins, leading to a substantial increase in hardness. This approach yielded a hardness of 276 GPa for diamond with an average twin thickness of 2.3 nm. By contrast, diamonds sintered from diamond nanopowder or synthesized from graphite nanopowder exhibited minimal nanotwinning and consequently lower hardness values. Microstructure analyses revealed two predominant twin configurations: interlocked and penetrating twins. The updated diamond model that incorporates both twin configurations revealed a strong correlation between the predicted and experimental hardness values, especially when the model microstructure closely matched that of synthesized diamonds. This research explains the mechanisms of twin-induced hardness enhancement in diamond and suggests strategies for tailoring the microstructure of diamond to achieve precisely controlled properties. Nanotwinning strategies are widely recognized for their ability to substantially enhance the mechanical properties of materials. Here diamond with both penetrating and interlocked twins was synthesized, yielding a hardness of 276 GPa, which can be explained by diamond models that feature diverse twin configurations and dimensions.