Tailoring interfacial bonding states of highly thermal performance diamond/Al composites: Spark plasma sintering vs. vacuum hot pressing

Interfacial configurations of the diamond/Al composites fabricated by vacuum hot pressing (VHP) and spark plasma sintering (SPS) have been investigated to evaluate feasibility of both techniques for tailoring interfacial bonding states, namely non-bonded, diffusion-bonded, partially and fully reaction-bonded interfaces. Multiscale interfacial characterization reveals that the unique diffusion-bonded interface at the micrometer scale, being very favorable for enhancing global thermal conductivity (TC), has been achieved by conventional VHP technique due to its large processing window and homogenous thermal field. Comparatively, micrometer-scale and, even macroscopic (radial and axial) thermal gradients can be inevitably generated during the SPS process in rapid heating-cooling mode. As a result, the mixed interfacial bonding states have always been introduced in the SPSed samples which reduce the effectiveness of TC enhancement. The formation mechanisms of nanoscale interfacial Al2O3 and Al4C3 at the diamond/Al interface are also discussed.