Microstructure and mechanical properties of Copper/Al interlayer/Graphite joint prepared utilizing “two-stage method” vacuum diffusion bonding

The high property Copper/Graphite joint with Al foil as intermediate layer has been prepared utilizing the "two-stage method" diffusion bonding. At stage I, the Cu-Al diffusion alloying behavior occurs, and when the alloying temperature reaches to 500 °C, the stable Cu9Al4 layer is formed on the surface of Cu substrate. At stage II, Cu (with Cu-Al alloying layer) and Graphite were diffusion bonded, and the microstructure of joint is composed of Cu /Cu9Al4 alloyed layer/Graphite. The C atom diffuses into the Cu9Al4 alloyed layer, which improves the joint property. With the temperature increases from 600 to 900 °C, the diffusion distance of C atom in Cu9Al4 increases from 5.8 μm to 11.4 μm. And the tensile strength of joint increases 25.8 MPa to 38.6 MPa. During the diffusion bonding processing, there are three routes for C atom from graphite diffusing in Cu9Al4 alloyed layer, which are OIⅠ→OIⅡ, OIⅠ→TI→OIⅡ and TIⅠ→TIⅡ routes, respectively. The diffusion coefficient of C atoms diffusion along OIⅠ →OIⅡ route is the largest, indicating that OIⅠ→OIⅡ is the preferential diffusion route for C atom diffusing in alloyed layer, and playing the decisive role in the microstructure and properties of joint utilizing two-stage method diffusion bonding.