Interfacial structure and mechanical properties of contact-reaction TC4/ TC4 joint brazed with copper filler

TC4 alloy was brazed by contact reaction brazing without flux in vacuum brazing furnace with copper foil as intermediate layer. The variation of microstructure and strength of the sandwich TC4/Cu/TC4 brazed joints with different brazing temperature were discussed. The results showed that the joint consisted of diffusion zone (R-Ti), interface zone (Ti2Cu) and center zone (a large amount of complex Ti-Cu compounds) with low brazing temperature (920 degrees C). With the increase of temperature, the center zone firstly disappeared, then the interface zone, finally leaving the diffusion zone and little of interface zone (1010 degrees C). After the compression shear testing, it showed that with the increasing brazing temperature, the shear strength of the joints raised, the maximum shear strength can reach 735 MPa at 980 degrees C. Although further increasing the brazing temperature increases the joint strength, the high processing temperature (above the alpha-*R phase transus temperature of about 985 degrees C) deteriorates the properties of the TC4 base metal. The fracture mode with low brazing temperature presented cleavage fracture while the fracture mode with high brazing temperature appeared quasi-cleavage fracture.