Joining of Graphite to Copper with Nb Interlayer: Microstructure and Mechanical Properties

Reliable joining of graphite and copper is achieved by means of a multilayer structure: niobium, which is used as stress‐relief interlayer, is joined to copper on one side by transient liquid phase (TLP) bonding and to graphite on the other side, using Ti/Cu foils as a filler alloy. The joints prepared by different parameters are analyzed in terms of microstructure, joint strength, and fracture behavior. With low joining temperature and low Ti content, a ductile banded Cu/TiCu 4 layer forms between graphite and Nb by peritectic reaction. The dissolution‐precipitation of Nb in TiC particles can help to reduce the brittleness on graphite interface. The TLP bonding between Nb and copper results in a narrow diffusion layer in copper substrate. The maximum shear strength of joints reaches 32 MPa as using 11.3 wt% Ti at 1000 °C. The fracture modes change from bowl shape cracks in graphite/Cu joints to multi‐step cracks in graphite/Nb/Cu joints.