Computational Evaluation of the Effect of Build Orientation on Thermal Behavior and in-situ Martensite Decomposition for Laser Powder-Bed Fusion (LPBF) Process

Laser powder bed fusion (LPBF), which is an additive manufacturing method, is a thermomechanical process in which instantaneously varying heat flow rates occur by moving a highintensity laser beam. The high temperatures and cooling rates that occur throughout the process result in microstructures with brittle behavior. The microstructure and mechanical properties may be improved by controlling the cooling rates in the layers via build orientation. Since the process is on a microscale, it requires planning as it does not allow instant intervention. Therefore, numerical analysis can be helpful to determine the effect of different build orientations. In this study, the effect of different build orientations was emphasized. For this purpose, successive layers resulting in narrowing and expanding cross-sectional areas were investigated with a detailed thermal approach. Also, a martensite decomposition case, as a result of changing the build orientation for a geometry, was presented numerically. As a result, it is shown that build orientation has an effect on the heat distribution within the part. Some benefits of expanding the cross-sectional area have been determined. Specifically, it is found that the build orientation may also enable local martensite decomposition, contributing to a lamellar microstructure.