Research On Wettability Of Cu-Ti Alloy On Reinforcements In The Composite Filler For Joining Of Carbon/Cu

The carbon/copper joints can find important applications in fabrication of carbon commutators and plasma facing components. However, the residual thermal stresses of joints are generated due to the big mismatch of physical properties between carbon materials and copper, which results in the deterioration of joints. One of the solutions for relaxation of residual stresses is to introduce the reinforcements with low thermal expansion coefficient in the active brazing filler. Furthermore, the reinforcements introduced can improve the brazing ability of liquid filler and strength the filler layer, contributing to the improvement of joints. Thus, research on the wettability of brazing alloy on reinforcements will contribute to the optimization of the composite filler and the behavior and strengthening mechanism of the reinforcements during joining of carbon/copper. The wetting of Cu-Ti alloy on the reinforcements including carbon materials, hexagonal BN(h-BN), TiB2 and pressureless sintered SiC ceramics has been realized in this research. Meanwhile, based on the interfacial reactions and spreading dynamics, the behavior of wetting spreading for all systems has been investigated.The initial contact angles of Cu22Ti(containing 22 wt.% Ti in the alloy) alloy on graphite and on carbon fiber reinforced carbon composites(CFC) are 110° and 113°, respectively. The equilibrium contact angle is 30° for Cu22Ti/graphite and 26° for Cu22Ti/CFC, respectively. The wettability of Cu50Ti(containing 50 wt.% Ti in the alloy) alloy on the graphite and CFC substrates is better than that of Cu22 Ti. The equilibrium contact angle for both Cu50Ti/graphite and Cu50Ti/CFC systems is 9°. The reaction layer of TiC has been developed by the reaction of Ti with carbon substrates in the interfacial area for Cu-Ti alloy/carbon wetting system. The TiC reaction layer could improve the wettability of Cu-Ti alloy on carbon materials. The investigation on the wetting and spreading dynamic for Cu-Ti alloy/carbon systems shows that in the early stage of wetting, the spreading of Cu-Ti alloys on the carbon substrates is controlled by the action of element Ti with carbon substrates in the triple-phase line. In the later stage, the diffusion of Ti from the liquid alloys to triple-phase line controls the wetting and spreading.The initial contact angles for the wetting of Cu50 Ti alloy on h-BN, TiB2 and SiC ceramics are 42°, 57° and 61°, respectively. The corresponding equilibrium contact angles are 8°, 3° and 11°, respectively. The precursor films with Cu and Ti rich are observed in front of the triple-phase line for both Cu50Ti/h-BN and Cu50Ti/TiB2 systems. The spreading dynamics for the wetting of Cu50 Ti alloy on h-BN, TiB2, and SiC systems are in accordance with the model that the wetting and spreading are controlled by the reaction products. The spreading for the wetting of Cu50 Ti alloy on both h-BN and SiC substrates is controlled by the reaction of Ti with ceramics in the triple line. For the wetting of Cu50Ti/TiB2, the spreading kinetics are controlled by the reaction Ti with TiB2 in the early stage, and by the diffusion of Ti into the triple line in the later stage together with a transition in the intermediate stage.