Electrical Transport, Mechanical and Tribological Properties of Composites Produced by Sintering Shock-Synthesized Nanopolycrystalline Diamond Particles

Electrically conductive carbon nanomaterials possessing high mechanical and tribological properties are in high demand for a wide range of applications. In the context of the potential usage, functional characteristics of composite materials produced by HPHT sintering of shock-synthesized nanopolycrystalline diamond powders have been investigated for the first time. Nanodiamonds powders with narrow and polydisperse granulometric distributions were sintered both without a binder and after infiltration with copper and silicon at pressures of 8–9 GPa and temperatures up to 1600°C. The binder-less sintered nanodiamond compacts are characterized by a hardness up to 33 GPa, electrical conductivity of ~6600 Sm^–1, and a friction coefficient on hardened steel as small as 0.07. Silicon infiltration leads to somewhat smaller conductivity (~190 Sm^–1), but produces compacts with hardness increased up to 48 GPa, improved mechanical properties and a low friction coefficient (~0.04). Copper infiltration sintering generally replicates functional properties of the compacts without a binder. However, in contrast to composites with copper, the compacts obtained without a binder and infiltrated with silicon demonstrate semiconductor-type conductivity, favorable for high-temperature applications. The sintering parameters are readily accessible with modern instrumentation, thus opening opportunities for broad use of compacts based on shock-synthesized polycrystalline nanodiamonds, for example, in miniature sliding bearings and electrical contacts working in severe conditions.