Analysis of growth behavior of intermetallic compound in diffusion bonding of Ti alloy/Cu/stainless steel

The mechanical properties, the generation types, the formation order and the growth thickness of the Ti-6Al-4V/Cu/304 vacuum diffusion welded joint were investigated and studied by means of tensile, SEM scanning, energy spectrum analysis, XRD test and thermo kinetic analysis. The results show that under the bonding pressure of 5 MPa, the tensile strength of the joint increases first and then decreases with the increase of the bonding temperature and time, and the maximum joint is 163 MPa at the bonding temperature of 1 223 K and the time of 3.6 ks, and the excessive temperature and time are unfavorable to the joint performance. With copper foil as the intermediate layer, intermetallic compounds are not formed at the Cu/304 interface. However, a multilevel transitional tissue consisting of solid solution, intermetallic compound Ti_xCu_y, Ti_xCu_y, ect. is formed between the titanium alloy/Cu interface. The evolution of the structure from titanium to stainless steel side is as follows Ti₂Cu, TiCu, TiCu₂, TiCu₃, TiCu₄, Ti₂Fe, FeTi, and TiFe₂ intermetallic compounds. The order of the generation of the reactant is the lowest priority of the value of the ΔG; The effect of Ti_xCu_y on the joints strength of the intermetallic compound is slightly stronger than that of Ti_xCu_y compound. The fracture is caused by the fracture of the Ti₂Cu intermetallic compound in the zone Ⅱ of the titanium alloy side, which extends into the diffusion layer of intermetallic compounds at the boundary of the zone Ⅱ-Ⅲ and is brittle fracture. Therefore, improving the interface structure from the titanium alloy/Cu side is the main way to improve the joints strength. According to the empirical formula, the layer thickness of the intermetallic compound can be controlled by adjusting the temperature and time.