Analyses of interfacial microstructures and mechanical properties of low-temperature bonded copper/graphite joints

Graphite was bonded to copper at low temperature by a surface-reaction metallization method. The effect of temperature on the morphography of metallization layer was studied,also the mechanical properties of bonded copper/graphite joints were tested. In metallization process,Cr element reacts with graphite to form Cr₃C₂ interfacial layer,which makes it possible to obtain a metallization layer in β-Sn matrix.With the increase of temperature,the reaction between Cr and graphite is enhanced,which results in that discontinuous interfacial layer becomes continuous and its thickness increases to 2 μm. The typical interfacial microstructures of joint are copper/Cu₆Sn₅/β-Sn/Cr₃C₂/graphite. At longer holding time,the thickness of bonded seam decreases,whereas the shear strength increases first and then decreases. All of the joints fracture in graphite substrate in tests. The highest shear strength of 25 MPa is achieved at 80 s and the proper seam thickness has the most favorable effort to release the residual stress.