Fabrication and evaluation of mechanical properties of polycrystalline diamond reinforced with carbon-nanotubes by HPHT sintering

In this study, carbon nanotubes (CNTs) have been employed as reinforcements for polycrystalline diamond (PCD) to fabricate CNTs/PCD composites at high-pressure and high-temperature (HPHT, 5.5 GPa and 1550 degrees C) conditions. The microstructure, phase composition, elemental distribution, and the effect of CNTs on mechanical properties of CNTs/PCD composites were systematically investigated. Vickers hardness of the sample with 1.5 wt % CNTs reached to 58.3 GPa, while flexural strength was improved to 650.8 MPa. Fracture toughness was enhanced from 5.4 MPa m(1/2) to 9.1 MPa m(1/2), which was 68.5% higher compared with that of the monolithic PCD composites. Furthermore, the toughening mechanism was explored, the increase of fracture toughness is attributed to the pull-out and bridging of CNTs during crack deflection. Additionally, it was concluded that sintering time for 90 s in HPHT can effectively ensure the integrity of CNTs and guarantee their toughening effects.