Effect of copper powder morphology and graphite flakes content on the graphite flakes orientation and thermal conductivity of Cu/GF composites

With the increasing demand for efficient thermal management in modern electronic devices, the development of advanced heat dissipation materials has become increasingly crucial. Copper/Graphite Flakes (Cu/GF) composites have emerged as a promising class of two-dimensional thermal management materials. However, their thermophysical and mechanical properties are significantly influenced by the orientation distribution of graphite flakes. This study systematically investigated the roles of Cu powder morphology and GF volume fraction in regulating microstructural orientation, interfacial integrity, and anisotropic thermal conductivity of hot-pressed Cu/GFs composites. Two distinct Cu powder morphologies—irregular blocky (IB-Cu) and dendritic (D-Cu)—were used to fabricate composites with GF volume fraction ranging from 20 to 70 vol%. Microstructural analysis revealed that dendritic Cu powder remarkably enhances the alignment of graphite flake parallel to the hot-pressing plane, which is attributed to mechanical interlocking and deformation-driven restructuring effects. This optimized orientation, combined with reduced interfacial defects, enabled the D-Cu/30GF composite to achieve an exceptional in-plane thermal conductivity of 581 W/mK, which is 28.3% higher than that of IB-Cu/30GF composite (453 W/mK). Increasing the GF volume fraction improved in-plane thermal conductivity, but concurrently exacerbated anisotropy, graphite agglomeration, and porosity within the composites. Notably, high-temperature thermal conductivity tests conducted over the range of 25–300 °C further confirmed the superior thermal stability of the D-Cu/30GF composite, which maintained a thermal conductivity exceeding 580 W/mK even after 50 thermal cycles. Theoretical modeling based on the Effective Medium Approximation (EMA) corroborated experimental trends, highlighting the orientation of graphite flakes as critical performance limiters. These findings provide actionable strategies for designing high-thermal-conductivity composites for next-generation electronic thermal management.