Microstructure and Performance of Graphite/Copper Joints by Brazing with Different Interfacial Structures

Graphite/copper joints are prepared by brazing with Cu-50TiH(2) filler. The influence of the interfacial structure on the microstructure and mechanical properties of graphite/copper joints is investigated. Straight and zigzag interfacial configurations are designed. The microstructure and compositions on the brazing interface are observed and analyzed, and the shear strength of the joints is evaluated. The interfacial morphologies show a good metallurgical combination with no apparent defects. The interfacial transition layer mainly consists of a Cu-based solid solution, Ti-Cu intermetallic compound, and small amounts of TiC near the graphite substrate. The widths of the transition layer are approximate to 25-50 and 490 mu m, respectively, for straight and zigzag interfacial configurations. There is a high hardness region that corresponds to the transition layer close to the graphite matrix. The shear strength of the joint with a zigzag structure interface can reach 17.9 MPa, which increases by 2.75 times compared to that of the straight interface. The zigzag structure between the graphite and the transition layer effectively improves the joint strength due to the increases in the bonding area and deflection of the fracture path.