Enhancement of fracture toughness in nanostructured diamond–SiC composites

We synthesized diamond–SiC nanocomposites with superhardness and greatly enhanced fracture toughness through a synthetic approach based on high-energy ball milling to form amorphous Si precursors followed by rapid reactive sintering at high pressure (P) and high temperature (T). We show how the simultaneous P–T application allows for better control of the reactive sintering of a nanocrystalline SiC matrix in which diamond crystals are embedded. The measured fracture toughness KIC of the synthesized composites has been enhanced greatly, as much as 50% from 8.2 to 12.0 MPa m1/2, as the crystal size of the SiC matrix decreases from 10 μm to 20 nm. Our result contradicts a commonly held belief of an inverse correlation between hardness and fracture toughness. We demonstrate the importance of nanostructure for the enhancement of mechanical properties of the composite materials.