Dynamic evolution analysis on molten pool: LMD experiment and simulation

Laser melting deposition is an advanced additive manufacturing technology, wherein molten pool as the fundamental building block endures melting and solidification with complex heat and mass transfer, thereby significantly affecting microstructures of the formed parts. Through deposition experiments and numerical simulations, dynamic evolution of molten pool is investigated from initial molten status to final stable deposition, and microstructures generated there are illustrated by experimental morphological assessment and predicted based on numerical analysis of temperature gradient and solidification rate. Results show that molten pool presents the lengthy elliptical form, and temperature field appears elliptical with a trail at the rear portion, and temperature gradient perpendicular to the scanning direction is relatively higher. Marangoni vortices emerge at the onset of the flow field and subsequently transition into lateral flow and longitudinal vortex. Microstructures grow from planar grains and epitaxial columnar grains to equiaxed grains from bottom to top of molten pool.

激光熔覆沉积（Laser Melting Deposition）是一种先进的增材制造技术，其以熔池（molten pool）作为基本构建单元，熔池会经历熔融与凝固过程，并伴随复杂的热质传递现象，这会对成形零件的显微组织造成显著影响。本研究通过沉积实验与数值模拟，探究了熔池从初始熔融状态至最终稳定沉积层的动态演化过程；同时结合实验形貌表征对熔池内部生成的显微组织进行可视化展示，并基于温度梯度与凝固速率的数值分析完成组织预测。结果表明，熔池整体呈现长椭圆形，温度场同样呈椭圆形且尾部带有尾迹，垂直于扫描方向的温度梯度相对更高。流场初始阶段会产生马兰戈尼涡，随后逐渐转变为横向流与纵向涡。从熔池底部到顶部，显微组织依次由平面晶、外延柱状晶生长为等轴晶。