Christophe Tournier

Hot-wire laser additive manufacturing (DED-LHW) addresses key limitations of conventional cold-wire processes,where excessive laser energy overheats the melt pool and promotes columnar grain growth, degrading microstructuralproperties. In addition, a large fraction of the laser power is lost by reflection at the metallic surface, resulting in lowoverall energy efficiency. DED-LHW introduces electrical current for resistive wire preheating via the Joule effect,complementing laser energy to reduce required laser power and enhance deposition stability. This study developsa critical energy delivery model that quantifies the linear thermal energy supplied to the wire by both laser in athree-beam coaxial configuration and Joule heating. The model precisely predicts and prevents dripping and stubbingdefects, as validated experimentally through comprehensive process mapping for Inconel 718. The effects of laserpower, current, scanning speed, and wire feeding speed on bead morphology and dilution are extensively investigated.Results confirm that the laser must provide at least half of the total wire energy for optimal stability, with Joule heatingas a complementary source. DED-LHW achieves twice the deposition rate at 50% laser power compared to cold-wiredeposition, producing smoother beads, more refined contact angle control, and a finer microstructure. This directlyreduces energy consumption and production time while eliminating defects.

The Additive Manufacturing (AM) ability of AD730® alloy by laser powder bed fusion (PBF-LB) is investigated for comparison with the cast & wrought AD730® alloy developed by Aubert & Duval for gas turbine applications. Several designs of experiments were needed to identify stable manufacturing conditions and build-up strategy in terms of low defect rate and microstructure soundness. In particular, the laser power, the scan speed, the layers' thickness, the hatching distance, and the scanning strategy were determined to successfully produce crack-free samples. The PBF-LB AD730® alloy exhibits columnar grains along the build direction. The resultant texture is close to a singlecrystalline-like cube texture. Upon annealing (solution annealing + single aging treatment), such a strong texture is preserved despite the formation of a network of fine transgranular secondary g' precipitates. Room temperature tensile properties are encouraging with yield stress lying between the coarse and fine grain microstructures of cast & wrought AD730®, for both orientations. An anisotropic mechanical behavior is obtained with higher properties for specimens printed along X and Y orientations than along Z. Finally, no evidence of premature failure due to micro-cracks has been detected in the overall test specimens.

The presence of lattice structures is increasing in the manufacturing domain especially in the air/spacecraft and biomedical applications due to their advantages of high strength-to-weight ratios, energy absorption, acoustic and vibrational damping, etc. Dimensional accuracy of a lattice structure is one of the most important requirements to meet the desired functionality as there could be significant deviations in the as-produced part from the designed one. Evidently, an approach (non-destructive) to evaluate the dimensional accuracy of all the elements and eventually the lattice quality is of great significance. X-ray computed tomography (CT) has emerged as a promising solution in the field of industrial quality control over the last few years due to its non-destructive approach. In this work, we propose a methodology for geometrical evaluations of a lattice structure by measuring the deviation in the shape and size of its strut elements holistically. The acquired CT data of the complete lattice are extracted in the form of a point cloud and then segmented and stored as a single strut element with unique identification so that measurements can be performed on the strut individually. As demonstrated with a metallic BCCz-type lattice structure, the methodology helps in critical evaluation of its quality and the correlation with spatial position of the individual struts; e.g., the lattice exhibits large variations of shape among the inclined struts while the vertical struts possess consistency in their shape.