Variations in morphology and microstructure caused by different melt pool dynamics in laser powder bed fusion of ultrathin walls
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The microstructure and morphology of lightweight parts produced with the laser powder bed fusion (PBF-L) are strongly affected by the processing parameters such as the scan velocity, beam size and power, as well as the scanning strategy. As the building process progresses layer after layer, instabilities in the melt pool can give rise to the morphological defects, inhomogeneous temperature distribution, and affect the grain microstructure of the part~\cite{Mohammadpour}. Previously, we have shown that numerical simulations of the PBF-L on the mesoscopic level can serve as a predictive tool for the morphology of thin walls. In this contribution, we go beyond the morphology and demonstrate the crucial role of melt pool dynamics in defining both morphological and microstructure features of the thin wall structures. For this purpose, we incorporate the cellular automata model for grain microstructure simulation in KiSSAM, a high-performance simulation software for additive manufacturing, developed previously by the authors of this Contribution, which enables rapid simulation of both the morphology of thin walls and their resulting microstructure. We apply the developed model to a study of the influence of the scanning strategy and processing parameters on the morphology and microstructure of single-pass thin walls fabricated by PBF-L. We investigate the regimes with the longer and shorter melt pools for two different scanning strategies: a) single scanning direction for all the layers of the wall; b) alternating scanning directions for successive layers. The results suggest that a) the morphology of a single track does not allow conclusions to be drawn about the structure of the entire wall; b) the scanning strategy mainly affects the morphology of the wall, while it is the set of the basic processing parameters that governs the formation of the grain microstructure.