The feedstock capture efficiency on powder laser directed energy deposition (L-DED) is becoming a big challenge in the industrial use of the L-DED process for the manufacturing of large-scale AM parts. The powder capture efficiency is dependent on process optimization and the toolpath. The current literature presents a vast range of usual powder efficiency, between 3% and 32% and in some specific cases exceeding 90%. In L-DED, the powder-gas jet stream interacts with the laser beam adding material locally onto the substrate. Part of this material is captured by the melt pool. The not captured material that is affected by the laser beam suffers degradation. In the literature, there is a lack of studies related to powder reuse in the L-DED process. This paper presents a comprehensive study on the consequence of laser interaction with SS 316L metal powder particles during the L-DED process using a range of different powder characterization techniques to assess the powder morphology, size distribution, chemical composition, followability, and density. The study was conducted within eight powder reuse cycles, without adding virgin material to the powder batch. Reduction of particle size distribution range, increase in circularity, and improvement in the powder flowability were identified as consequences of powder reuse. The result of laser interaction with particles was further explored by scanning electron microscopy, presenting the continuous modification of the particles across the eight reuse cycles. The oxygen content on the particles was also measured to access the O2 pick-up as a consequence of particle heating.

Additively manufactured martensitic stainless steel components can combine complex geometry with superior mechanical and corrosion performance. In this work, the mechanical performance of AISI 410L processed by laser directed energy deposition (L-DED) additive manufacturing using previously optimized parameters is assessed. Microstructure, hardness, tensile strength, and Charpy impact toughness are evaluated in the as-built and heat-treated conditions. Four heat-treatment routes are investigated: (I) austenitization and water quenched, and austenitization, water quenched, and tempered at (II) 300, (III) 450, and (IV) 600 °C, followed by air cooling. The results show that, for tempering temperatures up to 450 °C, the hardness, yield strength, and ultimate tensile strength show an increasing trend when compared with the as-built condition and reference commercial standard (annealed AISI 410) because of microstructure refinement induced by recrystallization. Tempering at 600 °C, on the other hand, enhances the ductility of the specimens, accounting for an increased deformation until fracture and superior Charpy impact toughness. In summary, this work demonstrates that, for all tested conditions, the tensile strength of the AISI 410L additively manufactured by L-DED outperforms that of the standardized commercial AISI 410 martensitic stainless steel, and that post-processing heat-treatments can be used to further enhance toughness and ductility, making it even more competitive.

The processability of pure Inconel X750 and Inconel X750 mixed with 15 vol. % of titanium carbide particulate through laser-directed energy deposition (l-DED) was evaluated. The powders used had a particle size in a range unusual to l-DED processing (0.18–24.05 μm); this case study presents difficulties in processing thin quadri-modal powder and describes possible measures to mitigate them, while also reporting, likely for the first time, on the l-DED processing of Inconel X750 and such related metal matrix composite (MMC). The choice in reinforcement particle size and composition aimed for a reduction in material density and insertion of additional reinforcement mechanisms. Both powders used were analyzed in an FT4 rheometer and compared to reference Inconel 625 powder. l-DED was made viable, but results show that the powders tested here represent a lower limit for the rheological properties accepted by usual l-DED systems. A methodology to quantify the stability of a given processing condition is presented and validated, also indicating that low powder flows are recommended when processing powders of this sort. Inconel X750 demonstrated sensibility to oxidation during processing as depletion of Al and Ti was detected in the deposits. Neither the MMC nor the pure material cracked or showed excessive porosity.