Interphase layer characteristics and thermal conductivity of hot-forged Cu-B/diamond composites

Abstract

Copper/diamond composites are regarded as the next-generation heat sink materials and have great potential to be used for future high-power electronic devices. The interphase layer characteristics between the copper matrix and the diamond have a significant influence on the composite’s thermophysical properties. In this work, a cost-effective hot forging process is used to fabricate diamond particles (about 70 μm diameter) reinforced Cu-xB matrix (x = 0.3, 0.5 and 1.0 wt.%) composites. The results show that B4C particles are easier to nucleate on the diamond (100) facet than on diamond (111) facet during the hot forging. The morphology of the newly formed B4C interphase layer on the diamond (100) facet evolved from a fine dispersed particle (Cu-0.3B/diamond) to a continuous dense structure (Cu-1B/diamond). On the diamond (111) facet, the B4C nucleation is difficult due to relative stronger carbon bonds formed on the diamond (111) facet (three bonds) than on the diamond (100) facet (two bonds), the growth of previously nucleated B4C become predominated, resulting in forming a B4C interphase layer with large particle size and low density on the diamond (111) facet. The Cu-0.5B/diamond has the highest thermal conductivity among the three fabricated composites (440 W/mK), and a low coefficient of thermal expansion (6.57 × 10–6 /K) at 313 K is obtained. With increasing the diamond particle size to 200 μm, the hot-forged Cu-0.5B/diamond had an increased thermal conductivity (495 W/mK). It demonstrates that hot forging is a feasible method to fabricate Cu/diamond composites with acceptable thermal conductivity from powder mixture.