Selective interfacial bonding in Al(Si)–diamond composites and its effect on thermal conductivity

With the aim of obtaining materials with high thermal conductivities for solid state thermal management applications, metal-matrix composites were produced by reinforcing aluminum and aluminum–silicon with diamond single crystals via two different liquid metal infiltration techniques – gas pressure infiltration and mechanically assisted infiltration (squeeze casting). The obtained composites exhibited thermal conductivities as high as 670 W/mK, but also as low as 130 W/mK. The large variation in the thermal conductivities can be related to the microstructural characteristics of the interface between diamond and the metal-matrix. On fracture surfaces of the composites, it was found that preferential adhesion between aluminum and diamond occurs on the {1 0 0} faces of diamond. Chemical and electrochemical etching treatments of the composites along with TEM observations of interfacial cross-sections suggest that this adhesion may be attributed to the local formation of aluminum carbide at the diamond surface. The contact time between melt and diamond during processing and also the addition of silicon to the matrix material were found to significantly affect the thermal conductivity of the composites by modification of the interface.