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

激光送粉定向能沉积(LP-DED)是一种添加剂制造技术，它具有制造功能梯度、具有特定位置特性的多材料零件的潜力，可广泛应用于航空航天部件、生物医学器件和储能等领域。然而，由于交织在一起的多物理现象和极长的尺度，微小的快速运动的颗粒如何与激光熔化的金属熔池相互作用仍鲜为人知，尽管它对制造零件中缺陷的产生有很大的影响。这一合作研究项目旨在利用同步加速器X射线成像技术捕捉LP-DED中高速金属颗粒与熔池之间的基本接触，并辅之以全面的工艺建模，目的是更好地控制工业规模的LP-DED工艺。该奖项还将有助于不同学生群体的劳动力发展，包括为研究生提供在国家中子和X射线散射学院工作的机会。此外，该团队还将为当地社区的女孩和妇女举办外展活动，重点关注添加剂制造，包括与3D打印中的妇女，这将突出许多金属添加剂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，这些相互作用影响LP-DED中的液态金属流动和缠绕孔洞的形成。这项以发现为导向的研究旨在验证两个假设：1)颗粒碰撞中更大的动能将增加熔池流动速度，2)熔池流动速度的增加将减少LP-DED部件中的气孔生成量。该方法包括为同步加速器监测定制的OPERANDO LP-DED装置，其中成像将在激光诱导熔池进行，空间和时间分辨率分别约为2微米和1微秒，当粉末在熔池附近流动和进入熔池时，精确地原位捕捉熔池内的变化。结合基于同步加速器的实验，将耦合计算流体动力学模型和离散颗粒动力学模型来模拟熔池流动速度和温度，以及由于颗粒碰撞和液化而在熔池中的运动。实验将支持对多物理模型的校准和验证，而模拟结果将估计局部流动速度和表面张力，以预测源于颗粒碰撞的气孔形成和生长。对高速和小规模观测的调查将填补LP-DED中孔隙率如何产生的知识空白，以及LP-DED工艺组件的微观结构、孔隙率和机械行为存在巨大差异的原因。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.