Ultrahard Metallic Conductive Composite with Nickel Foam Embedded Polycrystalline Diamonds

Abstract Multi‐functionalization of diamond‐based materials is significant for applications under extreme conditions, especially possessing ultrahard (HV > 80 GPa) and conductivity (10 5 S·m −1 ) simultaneously. However, overcoming the trade‐off between superhard properties and conductivity is challenged by constructing conductive channels in diamond‐based materials. Here, a metallic conductive diamond composite with nano‐sized channels of nickel skeleton (Ni‐NPD) has been prepared at high pressure and high temperature (HPHT). Ni‐NPD shows the ultrahard Vickers hardness of 80.0 GPa, electrical conductivity of 5.0 × 10 5 S·m −1 , and fracture toughness of 14.3 m Pa·m 0.5 , simultaneously. Nano‐sized nickel skeleton serves as a stress concentrator to reinforce itself, can trigger dislocation multiplication, and even can transfer dislocations to diamond via coherent phase boundaries (cPBs), which obtain remarkable hardness and fracture toughness. These initiate finite deformation around the phase boundary (PB), effectively prevent cracking along the phase boundary and maintain the ultrahard properties. The excellent conductivity stems from the homogeneous distribution of the nickel skeleton, which provides the electronic channel. So, in addition to serving as an electronic channel, the nano‐sized nickel skeleton balances the deformation ability and stiffness in the composite, ultimately enables the realization of ultrahard materials with conductivity. This work presents a novel strategy for endowing diamond composites with conductive functionality.