Anisotropic thermal expansion coefficient of multilayer graphene reinforced copper matrix composites

Highlights: • Multilayer graphene (MLG) dispersed in copper matrix with a preferred orientation. • The thermal properties of Cu-MLG composites are of significant anisotropy. • The microstructure anisotropy is the main reason for the thermal property anisotropy. • The variation of MLG bond length is consistent with the thermal expansion behavior. Multilayer graphene reinforced copper matrix (Cu-MLG) composites were fabricated via molecular-level mixing combined with vacuum hot-pressing (VHP). The MLG displayed a preferred orientation in the copper matrix, with the in-plane surface perpendicular to the hot-pressing direction, resulting in significant anisotropy in the thermal properties of Cu-MLG composites. Theoretical predictions were made using four models (Schapery, Kerner, Turner and mixture rule) to investigate the effect of the preferential orientation of MLG on the CTE anisotropy of Cu-MLG composites. The CTE anisotropy was further analyzed by carrying out molecular dynamics (MD) simulations to determine the variation in bond lengths for copper and MLG in different directions in the interface regions. The MLG bond length increased gradually with increasing temperatures in the in-plane direction, while in the out-plane directions, it increased significantly at first and then decreased at higher temperatures. The variations of bond lengths for MLG are consistent with the CTE anisotropy of the Cu-MLG composites in the same direction.