**4. Conclusions**

The present work focused on the production of LPBF samples with a desired orientation towards enhancing their properties in a specific direction. 17-4PH SS powder has been used for the production of the samples, being a widely used material for aeronautical applications, such as landing gear components wing spars and engine mounts, as well as for producing control rods, exhaust components, cockpit fasteners or even simple brackets. Such parts are predominantly loaded in one direction. By optimizing the properties of an additively manufactured 17-4PH alloy, it may be possible to produce parts with lighter and more efficient designs that can replace conventional parts made using traditional manufacturing methods. The properties of the produced specimens have been compared with those of corresponding parts from the literature made via traditional manufacturing methods and other AM processes. While the aviation industry places high standards on conventional crafting methods, their potential for increased complexity is limited. However, powder-based methods offer a significant improvement in this regard. Based on the results of the tensile tests, notable differences in characteristics are observed between parts made conventionally and those produced using our AM process. CP parts, in their as-made condition, exhibit superior tensile strength properties but lack elongation. On the other hand, LPBF-produced parts, when subjected to treatment, demonstrate competitive properties in this aspect. Moreover, the narrow standard deviation of the LPBF values indicates the stability of this manufacturing method. Our findings also suggest that additional treatments can enhance the potential applicability of these powder-based parts, particularly in terms of ultimate tensile strength (UTS) and yield strength (YS). This aligns with the requirement stated in MIL-STD-1530D, which specifies no yielding at the 100% design limit load [6] while still allowing for optimal design freedom to achieve greater complexity. Despite the printing jobs not being 100% accurate in terms of surface finish and the occasional presence of unmelted particles resulting in 2-3% porosity, the results are remarkable compared to other AM technologies, as supported by values reported in the literature. These unmelted zones were subsequently minimized by annealing and aging heat treatments. In conclusion, additively manufactured 17-4 PH parts have the potential to find application in the aviation sector, although further investigations are necessary to assess their actual applicability. Future research endeavors may focus on improving the stability of 3D printing jobs or exploring alternative heat treatment methods, considering their potential impact on the mechanical properties of AM parts. Additive manufacturing (AM) has the potential to revolutionize the way parts are designed and produced, particularly in industries like aerospace in which weight reduction is a critical factor in improving performance and fuel efficiency, which is also emphasized in US Army Directive 2019-29 [39]. By using AM to produce parts with reimagined, lighter geometries, it may be possible to reduce the overall weight of aircraft and spacecraft, resulting in significant improvements in fuel efficiency and cost savings. Moreover, the utilization of AM for part production brings additional advantages, including decreased material waste, enhanced design flexibility and expedited production times. These benefits make AM a promising alternative to conventional manufacturing methods in various industries, including aerospace. Nevertheless, it is important to acknowledge that the adoption of AM in the aerospace sector presents certain challenges that must be overcome. Quality control, certification processes and material limitations are among the key issues that need to be addressed before AM can be widely embraced in the industry.

**Author Contributions:** Conceptualization, Z.G. and T.M.; methodology, S.E.K.; software, S.E.K. and T.M.; validation, S.E.K. and T.M.; formal analysis, S.E.K., T.M., D.M. and E.T.; investigation, S.E.K. and T.M.; resources, S.E.K., T.M. and Z.G.; data curation, S.E.K., T.M., D.M. and E.T.; writing—original draft preparation, S.E.K.; writing—review and editing, T.M., D.M., E.T. and D.P.; visualization, S.E.K. and T.M.; supervision, Z.G. and L.V.; project administration, G.G.; funding acquisition, Z.G. All authors have read and agreed to the published version of the manuscript.

**Funding:** The work was carried out as part of the UMA3 project funded by the European Union's Horizon 2020 research and innovation program under grant agreement No 952463.

**Data Availability Statement:** The data presented in this study are available in the following paper: "Additive Manufacturing of 17-4PH Alloy: Tailoring Printing Orientation for Enhanced Aerospace Application Performance".

**Acknowledgments:** The experiments were carried out at the University of Miskolc, Faculty of Materials and Chemical Engineering, Institute of Physical Metallurgy, Metalforming and Nanotechnology and Institute of Foundry Engineering.

**Conflicts of Interest:** The authors declare no conflict of interest.
