Effects of Interlayer Thickness on Interfacial Microstructure and Joint Performance of Transient Liquid Phase Bonded TC4 Titanium Alloy

Transient liquid phase (TLP) diffusion bonding of TC4 titanium alloy was realized using an electrodeposited Ni/Cu layer as interlayer. The effects of Cu interlayer thickness on interfacial microstructure and mechanical property of TC4 joint were studied by SEM, EDS and XRD, and the reaction mechanism was clarified by Ti-Cu and Ti-Ni binary phase diagrams. The results show that the typical interfacial microstructure of the joint is TC4/alpha-Ti+Ti-2( Cu, Ni)/TC4. With the increase in the thickness of electrodeposited Cu layer, the width of diffusion layer and welding seam increase, and the voids in the center of the joint disappear. Continuous Ti-2(Cu, Ni) intermetallic layer appears in the reaction layer and its width increases gradually. The tensile strength of the joint increases firstly and then decreases with the increase in interlayer thickness, reaching the maximum value of 500 MPa when the thickness of Cu layer is 15 mu m. Fracture analysis shows that all of the bonded joints are fractured at the welding seams in the form of cleavage mode.