Microstructure and thermal properties of Al/W-coated diamond composites prepared by powder metallurgy

Highlights: • A tungsten coating improves the interfacial bonding between diamond and matrix. • Thermal conductivity of Al/35–50% W-coated is about 90% of the theoretical values. • Thermal conductivity increases first and then decreases with the diamond fraction. • Thermal expansion of Al matrix is more effectively suppressed with W-coated diamond. Al/(35–60) vol.% diamond composites are prepared by hot pressing, and the microstructures, thermal conductivity, and coefficient of thermal expansion (CTE) are characterized considering the tungsten coating and the volume fraction of diamond. The results show that diamond particles distribute quite uniform in Al matrix without formation of Al₄C₃ phase at the interface. Although the tungsten coating effectively improves the interface bonding between the diamond and matrix, relative densities decrease with increasing diamond fraction. The thermal conductivity of W-coated specimens containing 35–50 vol.% of diamond are about 90% of the theoretical values, but it decreases with further increasing diamond fraction due to the existence of higher porosity. However, most of the thermal conductivity of uncoated specimens are less than 90% of the calculated ones. CTE of the composites is found to decrease as the diamond fraction increases, and the W-coated specimens are more effectively to suppress the thermal expansion of Al matrix.