Investigation of the matrix and interface of Cu–B/diamond composite by atom probe tomography

Metal matrix alloying is an effective modification strategy to introducing an interfacial carbide at the Cu/diamond interface for improving thermal conductivity of Cu/diamond composite. However, the distribution and diffusion of C and alloying elements in Cu/diamond composite are still unclear. Here, transmission electron microscopy was utilized to characterize the microstructure of Cu/diamond interface and an atom probe tomography nanotip of the Cu–B/diamond composite was successfully prepared. For the first time, we give a clear distribution of C and alloying elements in a Cu–B/diamond composite. The formation of B4C is the consequence of C and B atoms diffusing to the Cu/diamond interface. The solubility of B in Cu is confirmed to be 0.06 at.% at room temperature. The extremely low solubility (<4.8 ppm) of C in Cu limits the reaction between C and B, and thus a B-rich and C-free area is formed between Cu and B4C. The residual C and B atoms are accumulated at the Cu boundaries, forming carbides after the Cu matrix solidifies. The presence of solid-solution atoms and carbides at the Cu boundaries decreases the thermal conductivity of the Cu matrix and further the Cu–B/diamond composite. The findings provide insights into the formation of interfacial carbide and the regulation of thermal conductivity in Cu/diamond composite modified by metal matrix alloying methods.