Wire arc additive manufacturing of Inconel 718: Constitutive modelling and its microstructure basis

Wire arc additive manufacturing (WAAM) has become a promising method to fabricate large-scale components thanks to its high deposition rate and low cost. An accurate constitutive model is essential for analyzing the deformation behavior of WAAM components intended for high temperature and dynamic or quasi-static conditions. In this study, a wall-shaped Inconel 718 (IN718) part was successfully fabricated by WAAM. The heterogeneous microstructure and chemical segregation inherited from the as-deposited (As-Dep) WAAM sample was improved through a modified solution and aging process. This modified heat treatment (MHT), which introduces massive uniformly dispersed γ’/γ” phases, leads to little change in grain structure of the WAAM sample but significantly eliminates its anisotropy. The relationship between the tensile properties and resultant microstructure was exploited. The insufficiency of the classical Johnson-Cook (J-C) model to describe the flow stress of the heat-treated WAAM IN718 alloy components at different deformation temperatures and strain rates was demonstrated. A modified J-C model, which considers the coupled effects of the temperature and strain rate, was successfully built for WAAM-IN718. The prediction accuracy of the established J-C model was verified, yielding a deviation of less than 1.71% between experimental and predicted values.