Design of a comprehensive experiment on fabrication of carbon/copper composite structures via magnetron sputtering and hot-press diffusion bonding

By effectively connecting carbon materials with copper and constructing graphite/copper hetero-composite components, the performance and processing advantages of both materials can be fully exploited, opening up broad application prospects in the field of heat dissipation. However, a typical nonmetallic–metallic connection exists between carbon materials and copper. Direct connection between the two presents problems such as poor interface wetting, low bonding strength, and poor heat conduction capability.

To address these issues, this study fabricated a carbon/copper composite structure with high thermal conductivity and excellent processing performance by combining magnetron sputtering of a titanium transition layer with vacuum hot-pressing diffusion bonding. Initially, an active metal titanium layer was deposited on the surface of the carbon material (diamond or graphite) by magnetron sputtering. Then, a copper layer was deposited on top to protect the titanium layer and improve the interfacial wettability. Subsequently, the titanium-coated graphite is subjected to vacuum hot-press diffusion bonding with the metallic copper at 900 ℃and 10 MPa for 30 min. After sintering was completed, the graphite obtained from magnetron sputtering and the components combining graphite and copper are vertically cut along their interface. Cross-sectional samples were prepared through mechanical polishing to obtain a smooth and undamaged surface, which facilitates microscopic observation. The morphology of the magnetron-sputtered coating, as well as the interface morphology and microstructure characteristics of graphite/copper, were examined using energy dispersive scanning electron microscopy. The integrity of the interface, the thickness of the reaction layer, and the elemental diffusion behavior at the interface were analyzed using scanning and transmission electron microscopy. The mechanical bonding performance of the graphite/copper interface was evaluated through shear strength tests. These tests were conducted using an electronic universal material testing machine at room temperature and at a constant loading rate. The shear strength of the interface was calculated based on the maximum shear load recorded during the test.

The results show that (1) the deposited layer prepared by magnetron sputtering has good film formation quality, is continuous, and does not leave the substrate obviously exposed. (2) After vacuum hot-pressing sintering, the titanium diffuses on both sides of the graphite/copper interface, forming a composite connection structure that is jointly composed of the interfacial reaction bonding and the mechanical interlocking effect. (3) On the basis of the results of high-resolution transmission electron microscopy and selected area electron diffraction (SAED), a distinct reaction layer is observed to have formed at the interface region. Typical TiC phases and Cu—Ti intermetallic compounds can be identified in this layer. This finding indicates that during vacuum hot-press sintering, the titanium interlayer reacted with graphite and copper at the interface, and various reaction products were formed on both sides of the interface. (4) The results of the interface shear test show that the shear strength of the graphite/copper composite structure reaches 20 MPa, and the fracture occurs within the graphite matrix, indicating that the constructed interface has a higher bonding strength than the graphite matrix itself.

The connection effect is stable and reliable, and the heat transfer mechanism at the interface was analyzed. The proposed method successfully enhanced the interface bonding strength and promoted efficient heat transfer across the carbon/copper interface, demonstrating its effectiveness in overcoming the limitations of direct bonding.