Enhancing the fracture toughness of polycrystalline diamond by adjusting the transgranular fracture and intergranular fracture modes

Enhancing the fracture toughness of polycrystalline diamond (PCD) is challenging because of its inherent brittleness and the absence of a toughness mechanism. Elucidating the transgranular fracture (TF) and intergranular fracture (IF) modes in PCD is urgent for fabricating robust PCDs. In this study, the toughness of PCD was optimised by adjusting the IF and TF modes. The high pressure and high temperature method (HPHT) was used to fabricate PCDs with different grain sizes (nano- to micro-scale) to modulate the IF and TF modes. The results indicate that a mixture of the IF and TF modes yields an optimum toughness in PCD compared to the single fracture mode, which yielded a high hardness (114.6 GPa) and high toughness (13.0 MPa∙m0.5). The toughness was approximately three times that of single-crystal diamonds (SCDs) and comparable to that of pure nanotwinned diamonds (NtDs). The mixed modes induce a toughening mechanism of high frequency large crack deflection, crack bridging, pull-out, and crack branching, which increases the toughness of the PCD. This work provides new insights into optimising the toughness of PCD, which is significant for fabricating robust PCDs for future applications.