Laser-Induced Breakdown Spectroscopy for composition monitoring during directed energy deposition of graded Fe-Ni alloys

Approaches for in-situ monitoring elemental composition in the working zone during additive manufacturing (AM) with directed energy deposition are relatively underdeveloped and especially needed for processes with multiple powder delivery feeds, such as laser-based directed energy deposition. In this study, Laser-Induced Breakdown Spectroscopy (LIBS) was explored for monitoring elemental composition of an AM-sintered graded Fe-Ni alloy. Fe and Ni powder feeds were varied during Fe-Ni alloy sample building, and LIBS was used to determine gradient alloy composition, which was also verified by mapping Fe and Ni gradients along the sample build direction with an Energy-Dispersive X-ray Spectroscopy (EDS) technique. An integrated experimental and modeling approach presented in this work rapidly fits Fe and Ni peak LIBS emission data by using a physics-informed emission peak identification algorithm based on an atomic emission spectrum simulation to predict peak occurrences, locations, and significant intensities. The approach allows to considerably reduce the computational time needed for peak identification, labeling, and fitting in experimental recorded spectroscopic data. The performed LIBS experimental measurements using this approach demonstrated a 5-Hz composition analysis data rate. Changes in the Fe and Ni peak intensity areas of the compositionally graded sample were correlated to the externally measured composition using EDS, which yielded a good correlation between LIBS and EDS-measured data. The developed approaches indicate directions for obtaining elemental composition data at speeds comparable with AM process control parameter variations, striding towards in-situ non-invasive composition monitoring and closed-loop process control implementations.