Phase field model for multiphase alloys under arbitrary thermal history: An application to IN718 super-alloy

Abstract

Currently, it is still a significant challenge to predict the microstructural evolution of multiphase alloys in complex manufacturing processes such as joining, welding and additive manufacturing due to their complex thermodynamics and thermal history. In this work, we present a phase-field framework, aiming to predict the evolution of precipitate microstructure under arbitrary thermal history. Our model incorporates nucleation, growth and transformation by taking into account interfacial, chemical and elastic energies. In order to quantitatively describe the nucleation of phases, we leverage on experimental time-temperature-transformation data to parameterize the classical nucleation model. For demonstration, we employ super-alloy IN718, where thermodynamic and kinetic data is obtained using CALPHAD method and major precipitate phases, i.e. γ′,γ″ and δ and their variants are considered. The predicted continuous-cooling-transformation diagram is consistent with data existing in literature, thus validating the approach. We further predict the precipitate evolution under rapid thermal cycling to mimic a typical additive manufacturing process.