Wavy microstructure for improvement of bonding strength in titanium to carbon steel brazed joints

Multi-interlayer composed of Ni and microcracked Cr (MC-Cr), formed by electrochemical deposition, was applied to induce the formation of wavy microstructure enhancing bonding strength of titanium to carbon steel brazed joints with BAg45CuZn filler. Effect of microcrack density in Cr layer on microstructure evolution and mechanical properties of joints has been studied. Phase identification and formation mechanism of joints were analyzed systematically. Introducing multilayer with microcracks avoided the formation of brittle Ti-C and Fe-Ti phases near carbon steel substrate. During bonding, the diffusion of Ti atoms was hindered by compact Cr while promoted by Ni at microcracks. The inhomogeneous diffusion of Ti atoms led to the generation of a wavy microstructure unit that is crater-shaped structure, accompanied by the enrichment of β-CuZn, Fe_0.2Ni_4.8Ti₅ and Cu₂TiZn phases. The fracture results showed that these structures improved the shear strength of joints up to 242 MPa by altering the direction of crack propagation.