Microstructure and thermal properties of copper matrix composites reinforced by chromium-coated discontinuous graphite fibers

• Discontinuous graphite fiber/Cu composites for heat sink applications are developed.
• The Cr element is pre-coated on graphite fiber to improve interfacial bonding.
• The formed Cr3C2 layer helps to enhance thermal conductivity and reduce CTE.
• The composites have high thermal conductivity, low CTE and good machinability.

Discontinuous mesophase pitch-based graphite fibers were coated with chromium via chemical vapor deposition technique and Cr-coated graphite fiber/Cu composites were fabricated by hot-pressing sintering. Their microstructure and thermal properties, including thermal conductivity and coefficient of thermal expansion (CTE), were investigated. Results show that the fabrication process led to the fibers with a 2-D random arrangement in Cu matrix, resulting in anisotropic thermal properties of the composites. The Cr coating reacted with graphite fiber and formed a thin and continuous Cr3C2 layer. This Cr3C2 layer established a good metallurgical interfacial bonding between the fiber and Cu matrix, which helps to enhance the thermal properties and to reduce the CTEs of the composites. The composites with 35–50 vol% content of fibers achieved the relative densities of >98%, the in-plane thermal conductivities of 380–412 W/mK and the in-plane CTEs of 6.1–9.4 × 10−6/K. Due to the high thermal conductivity, low CTE and good machinability, the composites are promising materials for heat sink applications.

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