Rapid estimation of microstructure using infrared imaging and solidification modeling in wire-laser directed energy deposition

The widespread deployment of Directed Energy Deposition Additive Manufacturing is limited by the lack of control over the produced material depending on process parameters: in particular, the microstructure resulting from rapid solidification. While cost-efficient numerical simulations have been developed to predict temperature evolution and microstructure, their reliability hinges on high-quality experimental validation. This study first addresses this challenge by introducing a simple and cost-effective infrared measurement procedure that combines a single-band camera and a dual-band pyrometer to quantitatively measure temperature fields during wire-laser DED. To do so, the apparent emissivity field was identified and found to be highly heterogeneous due to localized cover gas and oxidation. In addition, to enable rapid microstructure estimation, fast computational procedures are proposed to (i) calculate the thermal gradient field using Fast Fourier Transform, and (ii) simulate solidification in the melt pool, including competitive growth between columnar dendritic grains, using a recent Voronoi tessellation-based model. The computation time is compatible with the development of an online monitoring procedure. The resulting microstructure predictions were validated against Electron Backscatter Diffraction measurements, demonstrating excellent qualitative agreement. This work validates the proposed approach as a promising tool for closed-loop control of microstructure during DED.