Material Model Fidelity Comparison for the Efficacy of Predicting Residual Stresses in L-PBF Additively Manufactured IN718 Components

Abstract

Internal state variable models are well suited to predict the effects of an evolving microstructure as a result of metal-based additive manufacturing (MBAM) processes in components with complex features. As advanced manufacturing techniques such as MBAM become increasingly employed, accurate methods for predicting residual stresses are critical for insight into component performance. To this end, the evolving microstructural model of inelasticity (EMMI) is suited to modeling these residual stresses due to its ability to capture the evolution of rate- and temperature-dependent material hardening as a result of the rapid thermal cycling present in MBAM processes. The current effort contrasts the efficacy of using EMMI with an elastic–perfectly plastic (EPP) material model to predict the residual stresses for an Inconel 718 component produced via laser powder bed fusion (L-PBF). Both constitutive models are used within a thermo-mechanical finite element framework and are validated by published neutron diffraction measurements to demonstrate the need for higher-fidelity models to predict residual stresses in complex components. Both EPP and EMMI can qualitatively predict the residual stresses trends induced by the L-PBF local raster scanning effects on the component, but the influence of the temperature-dependent yield and lack of plastic strain hardening allowed EPP to perform similar to EMMI away from free surfaces. EMMI offered the most insight at the free surfaces and around critical component features, but this work also highlights EMMI as a process–property-dependent model that needs be calibrated to specimens produced with a similar reference structure for microstructure evolution effects to be accurately predicted.