Diffusion Bonding Of Surface Self-nanocrystallined Ti Alloy And Stainless Steel With A Ni Interlayer

Due to tremendous differences of physical, chemical and mechanical property, thicker intermetallic compounds is yielded easily on the bonding interface, grains grow significantly in the diffusion layer, and residual stress is developed during the diffusion bonding of dissimilar metal, which deteriorated badly mechanical character of joint. To solve these problem, surface self-nanocrystallization (SSNC) was apllied to synthesize nanostructured layer on the bonded surfaces of 0Cr18Ni9Ti stainless steel and TA17 titanium alloy bars, and then pulse-pressuring diffusion bonding (PPDB) with nickel interlayer was carried out on these bars which based on the previous studies.PPDB of titanium alloy to stainless steel was carried out with nickel interlayer with a thickness of 12.5μm after samples SSNCed. Diffusion experiments were processed by adjusting the technical parameters of diffusion bonding (bonding temperature and impulse cyclic times). Microstructure observation, micro-hardness testing, SEM observation, EDS determination and XRD analysis were employed to investigate the structure of the joint. And the potimal technical parameters of the diffusion bonding were obtained. Based on the formation-mechanism of interface-structure and the test results it was found thatα-Ti/β-Ti / Ni₃Ti/NiTi/NiTi₂/ Fe-Ni solid solution/γ-Fe layered structure were formed on the bonding interface.Under conditions of bonding temperature 850℃, pulse pressure 8～50MPa, pulse pressuring cycles 30 cycles, frequency 0.5Hz, preserved temperature for 0s before pulsing and 120s after pulsing, the time for bonding was only 180s under the optimum situation, and the joint strength reached 322.7MPa. Considering the effects of compressibility and the intermetallic, with the impulse cyclic times increase, the joints'property decreased. Base on the test of fracture's breadcrust and the micromechanics of rupture, PPDB joints ruptured around the interface between Ni-Ti inter-metallic compounds layers and nickel interlayer in the tension test.At the same time, nickel interlayer blocked the interdiffusion of Fe and Ti effectually and form the Ni₃Ti/NiTi/NiTi₂ intermatallic phase.Researches showed that application SSNC to diffusion bonding of titanium alloy and stainless steel may increase atoms diffusion coefficient.The jiont and base metal were taken to do electrochemical corrosion test with 5% HCL corrosive liquid, respectively. The results indicated that the corrosion beharvior magnitude jiont > Stainless steel > Ti alloy, and the joint's corrosion beharvior were better than TA17 alloy and 0Cr18Ni9Ti stainless steel.With SSNC treatment before bonding and adding Ni interlayer, the temperature and time of diffusion bond is lowered, the performance of joint of is improved, and the negative effects of intermetallic compounds was reduced as small as possible. Through this research, a improved technology for the bonding of dissimilar materials was developed.