High thermal conductivity composite of diamond particles with tungsten coating in a copper matrix for heat sink application

Abstract A composite material from particles of synthetic or natural diamond in a copper matrix, having a thermal conductivity (TC) of 500–900 W m−1 K−1, is obtained by capillary infiltration. A tungsten coating of 100–500 nm thickness is first applied to the diamond powder. The carbidization of the coating during annealing and melt infiltration is studied by X-ray diffraction. Measurements of TC λ, using the stationary heat flux method, and of thermal diffusivity a, using the flash method, agree. A longitudinal speed of sound of 8–9 km/s, an ultimate tensile strength of 150 MPa and a coefficient of thermal expansion (CTE) of ∼6 ppm/K at 25 °C are also measured for the composite. Model calculations of the composite’s CTE are carried out using the rule of mixtures and the Kerner and Turner equations. The composite’s specific electric resistance is 5–8 μΩ cm, according to calculations by the rule of mixtures, the Maxwell equation and the differential effective medium model. In comparison with other diamond–metal composites and materials with high TC intended for heat sinks, the composite developed is characterized by a combination of good thermal and mechanical properties, manufacturability and a relatively low cost.