EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

During an alloy Additive Manufacturing (AM) process, just after the melting of feedstock, the molten material undergoes melt-pool dynamics and rapidly solidifies (typically, within a few milliseconds). Then, for the remaining build time, it undergoes multiple heating-cooling cycles in the solid-state, i.e. Solid-State Thermal Cycling (SSTC) or intrinsic heat treatment, at varying temperature amplitudes and rates. The thermo-mechanical driving forces during SSTC can trigger a plethora of mechanisms such as dislocation dynamics and defect interactions, solid-state phase transformation, recrystallization, grain growth, etc., which manifest as microstructural changes in the form of texture evolution, grain morphology, grain boundary evolution, low-angle grain boundary formation, etc.

Currently, most research efforts in AM microstructure modelling are focused on understanding microstructure formation during solidification. In this work, we are interested in understanding what happens to the microstructure during SSTC. To that end, we propose a Thermal Elasto-ViscoPlastic (T-EVP) polycrystalline (crystal plasticity) model that captures the effect of strong thermal gradients on the local and macroscopic elasto-viscoplastic response of a material. The model is designed in such a way that it can be straightforwardly coupled/extended with other physics based-models, e.g. recrystallization/grain growth, to better capture microstructure evolution during SSTC. This model is numerically implemented via a Finite Element (FE) method to give the T-EVP-FE model.

In this talk, we first present the governing equations of the T-EVP-FE model and its numerical implementation. Then, we present the results of a series of simulations where a polycrystalline microstructure is subjected to SSTC that occurs during an AM process. These results are then analysed to understand the combined effect of thermo-mechanical boundary conditions on the local and macroscopic response of a stainless steel.