Laser beam shaping significantly influences solidification microstructure evolution in directed energy deposition (DED-LB), with distinct effects on grain morphology and crystallographic texture. To enable quantitative prediction and mechanistic understanding of these beam shaping effects on solidification microstructure evolution in both welding and metal additive manufacturing, an optimized thermal-fluid – microstructure coupling framework was developed. The integrated model incorporates novel features, including spatiotemporal optimization, efficient thermal-to-microstructural data interpolation (158x faster), CPU-parallelized grain growth algorithms (3.17x speedup), and adaptive time-step size calculation. Single-track experiments and corresponding simulations were performed for both laser-induced melting and laser-based directed energy deposition (DED-LB) using uniform circular and uniform square laser beam intensity profiles. The resulting crystallographic texture and grain morphology were quantitatively characterized through cross-sectional analysis, pole figures, and statistical distributions. Excellent agreement was achieved between experiments and simulations, with texture index deviations below 10.8% and accurate reproduction of grain size distributions demonstrating the model's fidelity. For the chosen process parameters, the two beam shapes have measurable but limited influence on texture development, with variations ranging from −5.3% to +5.1%. However, beam shape had a much stronger impact on grain morphology than on texture: circular beams refined the bulk grain-area and aspect-ratio distributions relative to square beams, while square beams yielded smaller mean grain areas, highlighting the need for distribution-level metrics beyond simple averages. By linking these morphological trends to beam-shape-dependent variations, the presented framework serves as a predictive tool for microstructure-aware process optimization in laser-based additive manufacturing.

Modeling the thermal and fluid flow fields in laser-based directed energy deposition (DED-LB) is crucial for understanding process behavior and ensuring part quality. However, existing models often fail to accurately predict these fields due to simplifying assumptions, particularly regarding powder particle-induced attenuation in laser power and energy density distribution, and the variable material properties and process parameters. The present work introduces a high-fidelity multi-phase thermal-fluid model driven by a combination of the discrete element method (DEM) and the finite volume method (FVM). Incorporating an enhanced attenuation model for laser energy enables a more precise approximation of powder particle-induced attenuation effects in the laser power and energy density distribution. The study focuses on the influence of laser beam intensity profiles during DED-LB of austenitic stainless steel (AISI 316 L), with model validation conducted through experimental measurements of deposited track dimensions for different beam shapes. The results of numerical simulations demonstrate the critical impact of powder-induced attenuation on the laser power and intensity profiles. Neglecting laser energy attenuation, a common assumption in numerical simulations of DED-LB, leads to overestimations of the absorbed energy of the laser beam, affecting thermal and fluid flow fields, and melt pool dimensions. The present study unravels the complex relationship between the attenuation coefficient (due to the powder stream) and powder stream characteristics, describing the variations of the attenuation coefficient with changes in the powder mass flow rate and powder stream incidence angle. The findings show the critical effects of laser beam shaping on melt pool behavior in DED-LB, with square beams inducing larger melt pool volumes and circular beams creating smaller but deeper melt pools. The proposed enhanced thermal-fluid modeling framework offers a robust approach for optimizing laser-based additive manufacturing across diverse materials and laser systems.

Laser beam shaping offers remarkable possibilities to control and optimise process stability and tailor material properties and structure in laser-based welding and additive manufacturing. However, little is known about the influence of laser beam shaping on the complex melt-pool behaviour, solidified melt-track bead profile and microstructural grain morphology in laser material processing. A simulation-based approach is utilised in the present work to study the effects of laser beam intensity profile and angle of incidence on the melt-pool behaviour in conduction-mode laser melting of stainless steel 316L plates. The present high-fidelity physics-based computational model accounts for crucial physical phenomena in laser material processing such as complex laser–matter interaction, solidification and melting, heat and fluid flow dynamics, and free-surface oscillations. Experiments were carried out using different laser beam shapes and the validity of the numerical predictions is demonstrated. The results indicate that for identical processing parameters, reshaping the laser beam leads to notable changes in the thermal and fluid flow fields in the melt pool, affecting the melt-track bead profile and solidification microstructure. The columnar-to-equiaxed transition is discussed for different laser-intensity profiles.