A fully coupled thermal-microstructural-mechanical finite element process model for directed energy deposition additive manufacturing of Ti-6Al-4V

A fully coupled thermal-microstructural-mechanical finite element modelling framework is developed to investigate the distortion and residual stresses during directed energy deposition (DED) of multi-phase Ti-6Al-4V alloy. The Johnson-Cook constitutive model is used to predict the yield strength of each phase as a function of strain, strain rate and temperature where the flow stress is calculated by a linear mixing rule based on the volumetric phase fractions. A thin-walled rectangular sample is chosen as the reference geometry and the results are compared with experimentally measured in situ thermal history and distortion data, where a reasonable agreement is achieved. The proposed modelling framework with physics-based material constitutive model provides useful information for a better understanding of process-microstructure-property relations in additive manufacturing by DED.