Modeling the Impact of Grain Morphology and Porosity on Creep Anisotropy in Laser Powder Bed Fusion Materials

Understanding the mechanisms responsible for the long-term mechanical behavior of additively manufactured (AM) materials is critical for ensuring their safe operation in high-temperature environments. This work focuses on understanding the role that geometric features, such as grain morphology and pre-existing porosity in the AM microstructure, play in the anisotropic deformation behavior exhibited by AM materials with the help of physics-based simulations using the crystal plasticity finite element method. Realistic meshes representative of AM microstructure are generated using novel meshing techniques to model crystallographic effects and grain boundary effects. Our findings demonstrate that when grain structures are considered in isolation, AM microstructures resulting from the laser powder bed fusion (LPBF) process exhibit a propensity to creep faster in the build direction, while the transverse directions are strengthened by texture and grain boundaries. Furthermore, when grain-boundary porosity and the consequent cavity growth are accounted for in the model, transverse directions start to creep faster, showing similar trends as reported in the literature. Therefore, our study suggests that grain boundary defects (as a result of the build process) need to be considered to model the deformation in LPBF materials correctly.