This paper addresses a numerical framework for modeling site-specific microstructure evolution in Laser Powder Bed Fusion (LPBF), where rapid solidification significantly influences the microstructure and properties of manufactured components. The fine microstructure and rapid solidification can enhance mechanical properties in final parts, yet pose challenges in controlling microstructure and addressing potential defects. In this study, an in-house developed free surface thermo-fluidic Computational Fluid Dynamics (CFD) model is coupled with a binary alloy phase-field model characterized by rapid solidification kinetics. The CFD model considers complex fluid flows related to Marangoni and recoil pressure, laser-material interactions, and rapid melting and solidification of the melt pool. A convergence study for the phase-field model is conducted, comparing simulated partition coefficients with the Continuous Growth Model (CGM) theory. The study investigates the individual effects of temperature gradients and solidification rates on simulated microstructure. Results indicate that, for the same order of magnitude change, the solidification rate has a more pronounced effect on microstructure than temperature gradients. The paper concludes with the simulation of site-specific microstructure evolution within the melt pool, comparing the results with experiments conducted at varied scanning speeds. The predicted microstructure aligns well with experimental measurements, suggesting the potential utility of the developed phase-field model in quantitative microstructural modeling. Overall, this work contributes to understanding microstructure evolution under rapid solidification conditions, providing a fundamental basis for optimizing the LPBF process.

中文翻译：

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激光粉末床熔融过程中快速凝固的建模

本文提出了一种用于模拟激光粉末床熔合 (LPBF) 中特定位置微观结构演化的数值框架，其中快速凝固会显着影响制造部件的微观结构和性能。精细的微观结构和快速凝固可以增强最终零件的机械性能，但在控制微观结构和解决潜在缺陷方面提出了挑战。在这项研究中，内部开发的自由表面热流体计算流体动力学（CFD）模型与以快速凝固动力学为特征的二元合金相场模型相结合。 CFD 模型考虑了与 Marangoni 和反冲压力、激光-材料相互作用以及熔池快速熔化和凝固相关的复杂流体流动。对相场模型进行了收敛性研究，将模拟分配系数与连续增长模型 (CGM) 理论进行了比较。该研究调查了温度梯度和凝固速率对模拟微观结构的个体影响。结果表明，对于相同数量级的变化，凝固速率对微观结构的影响比温度梯度更显着。本文最后模拟了熔池内特定位置的微观结构演化，并将结果与​​不同扫描速度下进行的实验进行了比较。预测的微观结构与实验测量结果吻合良好，表明所开发的相场模型在定量微观结构建模中的潜在效用。总的来说，这项工作有助于理解快速凝固条件下的微观结构演变，为优化LPBF工艺提供了基础基础。