Study on reaction kinetics in diffusion bonding of Ti ₂AlNb and GH4169 with Nb+Ni foils as interlayer

The process of reaction kinetics was investigated for vacuum diffusion bonding of Ti ₂AlNb and GH4169 by inserting metal foils of Ni+Nb as interlayer. The results show that there is an optimum thickness (about 3.36 μm) for the reaction layer Ni ₆Nb ₇, which is the main factor that influences the joint's shear strength. The modified effective heat of formation (MEHF) theory and the effective Gibbs free energy theory were applied to predict that Ni ₆Nb ₇ is the primary phase formed during Ni-Nb interface reaction, i.e., Ni ₆Nb ₇ phase inevitably forms during the bonding process. The growth rate of Ni ₆Nb ₇ layer is lower than that of Ni ₃Nb layer. Thus it is possible to control the thickness of Ni ₆Nb ₇ layer by optimizing the processing parameters so as to improve the mechanical properties of the joints. The optimized duration time for the samples bonded at 1050°C under 20 MPa is 49.5 min. This condition issues experimental shear strength of the joint as 468.2 MPa.