Research On Reinforcements Synthesized With In-situ For Joining Of Carbon/Copper

Joining of carbon to copper has potential applications in the fabrication of carbon automobile commutators and plasma-facing components. However, the mismatch of coefficient of thermal expansion（CTE） between carbon and copper can lead to the generation of large residual thermal stresses in joints after cooling. Reinforcements synthesized with in-situ in fillers can contribute to the relaxation of thermal residual stresses. In this research, joining of graphite to copper has been realized in vacuum with the composite filler composed of Cu-50 Ti H₂ and reactive powders. The effects of reinforcements on the properties and the microstructure of joints have been investigated.The shear strength of graphite/copper joints increases with the boron powders in the composite filler. The maximum average shear strength of the joint brazed with 15 vol.% B addition is 19.77 MPa, which is equivalent to 92% of the strength of graphite. Microstructural analysis shows the sound interfacial bonding for graphite/copper joint brazed with（Cu-50 Ti H₂）+15B composite filler. Ti B whiskers are in-situ synthesized by the reaction of boron and Ti decomposed from Ti H₂ in the filler. Filler layer is mainly composed of Ti-Cu intermetallic compounds, Cu-based solid solution and Ti B whiskers. Meanwhile, a thin Ti C reaction layer has been developed between graphite and filler layer by the reaction of Ti and graphite substrate. Ti B₂ with block shape rather than Ti B whiskers are formed in the filler layer with boron content higher than 15 vol.%, leading to deterioration of the joints.The content of C powder in the composite filler has a great influence on the shear strength of the graphite/copper joints. The obtained average shear strength of the joint brazed with 5 vol.% C powders is 17.98 MPa. Microstructural analysis indicates that the filler layer is mainly composed of Cu-based solid solution, intermetallic compounds of Ti₂ Cu and Ti Cu₄, and Ti C particles synthesized in-situ. The average shear strength of the graphite/copper joint is 19.2 MPa with the Si C content of 10 vol.% in the（Cu-50 Ti H₂）+Si C composite filler. Microstructural analysis shows that the reaction products composed of Ti C, Ti₅Si₃ and Ti₃ Si C₂ are developed by the in-situ reaction between Ti and Si C powders.The reaction products including Ti B, Ti C, Ti₅Si₃ and Ti₃ Si C₂ are in-situ synthesized by the reaction of reactive powders with Ti decomposed from Ti H₂ in the filler. The reaction products with the form of whiskers and particles uniformly distribute in the filler layer of joints, which could serve as reinforcements, contributing to the improvement of graphite/copper joints. On the other hand, Ti₃ Si C₂ with the ability of plastic deformation at high temperature could relax the thermal stresses of joints. Furthermore, the reinforcements synthesized in-situ with low CTE could decrease the CTE mismatch between graphite and filler layer, which will benefit the relaxation of thermal residual stresses of joints.