Understanding non-parabolic solidification kinetics in Ni-based alloys during TLP bonding via thermo-kinetic modelling

Abstract

Through a diffusion controlled solidification process, transient liquid phase (TLP) bonding is widely exploited to repair or join materials in different industry areas for decades. However, a lack of modeling on the TLP process of multi-component systems makes design of the TLP process an expensive trial and error process. Here, by coupling with experiment, we developed a set of self-consistent kinetic model parameters, which are used to simulate the TLP process of AWS A5.8 BNi-9 (filler)/Inconel 718 (base metal) at 1090 °C such as the solidification kinetics, diffusion profile and the precipitated borides in the Diffusion Affected Zone (DAZ). Consistent with experiment results by X-ray diffraction (XRD) and scanning electron microscopy (SEM), our simulation demonstrate four types of boride precipitated in the DAZ: MB2, MB, M5B3 and M3B2, which consequently results in the non-parabolic solidification behaviors in the brazing system. Based on the calculations using the developed models, we predict that a post heat treatment at 1090 °C for 3500s will homogenize the boride phase distribution in the DAZ, thus increasing the strength of the brazing joint. The developed model parameters may be extended to the other Ni-based alloys.