Interface formation evolution of the hot-forged copper-(Cr)diamond composite and its thermal conductivity

Abstract

Due to the distinction of (111) and (100) faces on the diamond particle, the preferential formation of interface layers on the diamond particle is discovered when adding metal additives like titanium, chromium, aluminum in copper/diamond composites. The formed interface would affect the thermal conductivity of the copper/diamond composites. In this study, copper-55 vol%(Cr-coated) diamond composites were successfully produced by hot forging under 800 ℃, 900 ℃ and 1050 ℃. Heat treatment of Cr-coated diamond powders was conducted under a series of temperatures for studying the evolution of the carbide interface formation on surfaces of diamond particles. It was found that the average grain size of the Cr7C3 on diamond (111) faces was larger than that on (100) faces when the temperature is below 850 ℃, and the opposite trend was observed when the heat treatment temperature is above 850 ℃. The Cr layer was fully transformed into Cr7C3 when the temperature was above 950 ℃. Unlike the results obtained after heat treatment, the interface layers was directly transformed into Cr3C2 due to the non-equilibrium phase transformation after hot forging. The Cr3C2 interface layers were preferentially kept on (100) diamond faces, and exfoliated on (111) faces after hot forging. The grain size of the formed Cr3C2 on diamond (100) faces was increased with raising the hot forging temperature. The 1050 ℃-hot-forged sample showed the highest thermal conductivity, attributed to large grain sizes of the Cr3C2 interface layer. This study elaborates the mechanisms of the evolution of the interface layer formed under different temperatures on the diamond surfaces in copper-(Cr-coated) diamond composites, and the phenomenon of preferential formation of the interface layers is verified.