Collaborative Research: Probing Particle Impact onto Molten Metal Pool in Laser Directed Energy Deposition by Synchrotron Imaging and Process Modeling

激光送粉定向能量沉积（LP-DED）是一种增材制造技术，具有制造功能梯度、多材料零件的潜力，具有位置特异性，可广泛应用于航空航天部件、生物医学设备和能量存储等领域。然而，由于多物理现象交织在一起，长度尺度极端，在LP-DED中，快速运动的微小颗粒如何与激光熔化的金属池相互作用仍然知之甚少，尽管其对制造部件中的缺陷起源有很强的影响。该合作研究项目旨在使用同步加速器X射线成像捕获高速金属颗粒与LP-DED中熔池之间的基本接触，并辅以全面的过程建模，以更好地控制工业规模的LP-DED加工。该奖项还将有助于不同学生群体的劳动力发展，包括与中子和X射线散射研究生国家学校的机会。此外，该团队还将在当地社区联合举办针对女孩和妇女的增材制造推广活动，包括与3D打印中的女性合作，该活动将突出金属增材制造领域的许多女性专家。该合作项目的目标是从根本上了解飞行中的金属颗粒与激光生成的熔池之间的相互作用，其影响LP-DED中的液态金属流动和缠结孔形成。该发现驱动的研究是为了测试两个假设：1）粒子冲击中的更大动能将增加熔池流速，2）熔池流速的增加将减少LP-DED部件中的孔隙形成量。该方法包括一个定制的operando LP-DED设置用于同步加速器监测，其中成像将发生在激光诱导的熔池，空间和时间分辨率分别约为2微米和1微秒，当粉末流入熔池附近时，精确地原位捕获熔池内部的变化。结合基于同步加速器的实验，计算流体动力学模型和离散粒子动力学模型将被耦合来模拟熔池流动速度和温度，以及由于粒子撞击和碰撞而在熔池中的运动。实验将支持多物理模型的校准和验证，而模拟结果将估计局部流速和表面张力，以预测源于颗粒撞击的孔隙形成和生长。高速和小尺度观测的研究将填补LP-DED中孔隙率如何发生的知识空白，以及为什么LP-DED加工组件的微观结构、孔隙率和机械行为会有很大变化。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Laser powder-fed directed energy deposition (LP-DED) is an additive manufacturing technology that is potentially capable of making functionally graded, multi-material parts with location-specific properties for a wide range of applications, including aerospace components, biomedical devices, and energy storage, etc. However, because of intertwined multi-physics phenomena and extreme length scales, how tiny fast-moving particles interact with a laser-melted metal pool in LP-DED is still little known, despite its strong influence to defect origination in fabricated parts. This collaborative research project aims to capture fundamental contacts between high-speed metal particles and a molten pool in LP-DED using synchrotron X-ray imaging complemented by comprehensive process modeling with a goal of better control in industrial-scale LP-DED processing. This award will also contribute to the workforce development of a diverse group of students, including opportunities with the National School on Neutron and X-ray Scattering for graduate students. In addition, the team will jointly host outreach events for girls and women that focus on additive manufacturing in the local community, including with the Women in 3D Printing, which will highlight many female experts in metal additive manufacturing.The objective of this collaborative project is fundamental understanding of the interactions between in-flight metal particles and a laser-generated molten pool, which affect liquid metal flows and entangle pore formation in LP-DED. The discovery-driven research is to test two hypotheses; 1) greater kinetic energy in particle impact will increase melt pool flow velocities and 2) an increase in melt pool flow velocities will decrease the amount of pore formation in LP-DED parts. The approach includes a custom-made operando LP-DED setup for synchrotron monitoring, where imaging will occur at a laser-induced melt pool with spatial and temporal resolutions of about 2 microns and 1 microsecond, respectively, precisely capturing in-situ the changes inside the melt pool when powder flows near and into the melt pool. In conjunction with synchrotron-based experiments, a computational fluid dynamics model and a discrete particle dynamics model will be coupled to simulate melt pool flow velocities and temperatures, as well as the motions in the melt pool due to particle impact and liquefying. Experiments will support calibration and validation of the multi-physics models, whereas the simulation results will estimate local flow velocities and surface tension to predict for pore formation and growth rooted from particle impact. The investigation of high-speed and small-scale observations will fill the knowledge gaps in how porosity occurs in LP-DED as well as why there are large variations in the microstructure, porosity, and mechanical behavior of LP-DED processed components.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.