On the Inability of the Moving Interface Model to Predict Isothermal Solidification Time During Transient Liquid Phase (TLP) Bonding of Ni-Based Superalloys

Understanding diffusion-induced isothermal solidification time during transient liquid phase bonding is vital in producing intermetallic-free robust joints. The isothermal solidification completion time is overestimated by the existing analytical models, even by the closest one to the real bonding conditions, known as the moving interface model. It was found that the boride formation in the diffusion affected zone of Ni-based superalloy upon using B-containing filler metals is one of the reasons behind the inability of the moving interface model to predict the isothermal solidification completion time accurately, which has received scant attention in the literature. Moreover, simplified assumptions in deriving the moving interface model such as constant interfacial solute concentration, which is only valid for binary systems, along with the independency of diffusion coefficient to concentration introduce errors when estimating the isothermal solidification time using the moving interface model. The significant discrepancy between the predicted and experimentally obtained isothermal solidification times reinforces the idea that the existing moving interface analytical model needs to be modified.