Meso-scale solidification models for metallic additive manufacturing processes

Our ambition is to develop a multi-scale approach to model the powder bed fusion process from melting to solidification: grain nucleation, growth and impingement, residual stresses and porosity. In order to feasibly predict microstructural features at the scale of an entire part, trade-offs need to be made between accuracy and efficiency. Hot cracking and porosity are the main culprits responsible for the relatively poor fatigue performance of AM produced parts. Rapid and anisotropic thermal contraction during solidification and subsequent cooling results in regions of localised stress at grain boundaries. As the microstructure develops, pockets of liquid can become cut off from the melt pool and may no longer be sufficiently fed with liquid to account for the volumetric contraction during the liquid to solid phase transformation and further contraction as the surrounding solid cools. Modelling the pressure drop in these intergranular regions during these last stages of solidification is key to predicting the size and distribution of solidification induced porosity. This challenging problem is currently being addressed by the authors.