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

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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.