Enhanced Strength of Nano-polycrystalline Diamond by Introducing Boron Carbide Interlayers at the Grain Boundaries

The polycrystalline diamond with high mechanical properties and excellent thermal stability are playing important role in industry and material science. However, the increased inherent brittle strength with the increasing of hardness has severely limited their further widespread application. In this work, we produced well-sintered nano-polycrystalline (np) diamond by directly sintering fine diamond powders with boron carbide (B4C) additive at high pressure and high temperatures. The highest hardness value up to ~ 90 GPa was observed in the np-diamond by adding 5 wt.% B4C at 18 GPa and 2237 K (consisting of fine grains in size of 16 nm). Moreover, our results reveal that the produced samples have shown noticeably enhanced strength and toughness (18.37 MPa m0.5) with the assistance of the soft phase at the grain boundaries, higher than that of the hardest known nano-twined diamond by ~ 24 % and a little greater than the toughest CVD diamond (18 MPa m0.5). This study offers a novel functional approach in improving and controlling the hardness and stiffness of polycrystalline diamond.