Exploring the underlying causes of optimizing thermal conductivity of copper/diamond composites by interface thickness

To unravel the underlying causes of the opposite variation tendency in theoretical and experimental thermal conductivity of copper/diamond composites as the increasing thickness of nanoscale interface layer, WC layers with 70–400 nm thickness were prepared by magnetron sputtering W layers on the diamond substrates and following vacuum annealing treatment. The interface structure of the WC coated diamond was studied by TEM, and the density (ρ) of the WC layers was measured by the relative peaking intensity of the coating phase using the X-ray scattering strength method. Nanoindentation and four-point probe experiments were also carried out for indirectly characterizing average phonon velocity (ν) and thermal conductivity (KWC) of the WC layers. Interfacial thermal conductance (ITC) of the composites was calculated by the actual experimental ρ, ν and KWC of the WC nanoscale layers. Meanwhile, corresponding copper/diamond composites were fabricated by pressure-assisted infiltration method. The maximum thermal conductivity (TC) of the composite achieved 943 W·m−1·K−1. The variation trend of the actual TC in the composites was agreed with that of the calculated ones which were calculated by the ITC and differential effective medium (DEM) model. Based on the above quantitative analysis, the thermal boundary conductance of WC/Cu and diamond/WC interface is the main factor that leads to the variation of TC of the composites with the increase of the WC interlayer thickness. Optimizing a higher thermal boundary conductance by regulating the interlayer thickness is a crucial factor for enhancing the TC of the composite.