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

激光粉末定向能沉积（LP-DED）是一种增材制造技术，具有制造具有特定位置特性的功能梯度多材料部件的潜力，适用于广泛的应用，包括航空航天部件、生物医学设备和能量存储等。然而，由于相互交织的多物理场现象和极端的长度尺度，微小的快速运动粒子如何与LP-DED中的激光熔化金属池相互作用仍然知之甚少，尽管它对制造零件的缺陷起源有很大的影响。该合作研究项目旨在利用同步加速器x射线成像技术捕捉高速金属颗粒与LP-DED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。该奖项还将有助于多样化学生群体的劳动力发展，包括研究生在国家中子和x射线散射学院的机会。此外，该团队将共同为当地社区的女孩和妇女举办外展活动，重点关注增材制造，包括3D打印女性，这将突出许多金属增材制造方面的女性专家。该合作项目的目标是基本了解飞行中的金属颗粒与激光产生的熔池之间的相互作用，这种相互作用会影响LP-DED中液态金属的流动和纠缠孔的形成。以发现为导向的研究是为了检验两个假设；1)颗粒碰撞动能增大，熔池流动速度增大；2)熔池流动速度增大，LP-DED零件孔隙形成量减小。该方法包括一个定制的operando LP-DED装置，用于同步加速器监测，其中成像将在激光诱导的熔池中进行，分别具有约2微米和1微秒的空间和时间分辨率，精确地捕捉熔池内粉末靠近和流入熔池时的变化。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耦合模拟熔池的流速和温度，以及由于粒子撞击和液化而导致的熔池运动。实验将支持多物理场模型的校准和验证，而模拟结果将估计局部流速和表面张力，以预测颗粒撞击导致的孔隙形成和生长。高速和小规模观察的调查将填补LP-DED中孔隙度如何发生的知识空白，以及为什么LP-DED加工部件的微观结构、孔隙度和力学行为会有很大变化。该奖项反映了美国国家科学基金会的法定使命，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.