Delicate control of graphite flakes alignment in the copper matrices via powder selections and filling processes

Due to the anisotropy properties of graphite flakes (Gf), the control of their orientation inside copper (Cu) matrice is strictly correlated with the final properties of such metal matrix composite (MMC). In this study, MMCs are fabricated by powder metallurgy process using three types of Cu powder particles (flake, dendritic, and spherical) as well as different powder filling methods. By using Cu flake powder with a relatively lower apparent density as compared to the two other Cu powder types (dendritic and spherical), high aligned Gf could be easily obtained, after uniaxial hot pressing, in a one-step powder filling approach. For the other two types of powders, a comparable orientation degree of Gf could be achieved only via several steps of delicate powder pressing. In-plane thermal conductivities of Cu/Gf composites were enhanced by improving the orientation degree of Gf, agreeing with effective medium approximation predictions (Maximum TC up to 540 W mK-1). A modeling, based on the apparent density of Cu powders, was discussed to show the effect of the alignment process on the final thermal property of such MMCs. This model supplies a basic guideline to obtain highly orientated Gf.