Insights into microstructural variations in GH4169 thin-walled parts by laser powder bed fusion: a coupling finite-element/cellular-automaton study

The complex characteristics of thin-walled parts fabricated by laser powder bed fusion (LPBF), particularly the dependence of their microstructures on wall thickness and scanning strategies, pose significant challenges for this technology. This paper presents a predictive model for microstructural evolution of LPBF-fabricated thin-walled components, integrating three-dimensional cellular automaton (CA) with finite element (FE) analysis. The FE method is employed to solve the temperature field of thin-walled components during LPBF, and the resulting temperature history is used to predict microstructural evolution in the CA model. Experimental validation via electron back scatter diffraction (EBSD) on a 4 mm-thick specimen confirms a high degree of agreement between model predictions and experimental results. The study reveals that when the thickness of samples prepared by LPBF is reduced from 4 mm to 0.4 mm, there is a significant coarsening of grain size. Additionally, grains at the bottom are observed to be coarser compared to those at the top, which is attributed to epitaxial growth and remelting. Furthermore, the study explores microstructural changes induced by manipulating laser power and scanning speed, while maintaining constant energy density. The findings indicate that grain morphology and size remain consistent across varying parameters, emphasizing the dominant influence of energy density. Within a predefined scanning strategy, an upsurge in laser energy density leads to an enlargement of the average grain size. Notably, the implementation of a cross-scanning strategy alters the melt pool orientation, disrupting the directional grain growth and fostering the formation of finer grains. This underscores the crucial significance of processing techniques in LPBF.