La mise en forme de métaux et d’alliages métalliques par fusion laser sur lit de poudre pour applications à haute température

Abstract

For many systems operating at high and very high temperatures, performance improvements come with an increase in operating temperature. Although additive manufacturing processes allow for an expanded range of use for traditional materials, new classes of materials are needed to surpass their inherent limitations. This project focuses on offering an alternative for metals actually used in the combustor and the rotor assembly of an inside-out microturbine. To this end, refractory metals, a next-generation titanium alloy, and a titanium aluminide-based intermetallic have been selected to be processed using the laser powder bed fusion (LPBF) additive manufacturing process. The objective is to reduce the integration constraints of new materials on low-power machines without temperature control in the printing chamber. The project begins by collecting information about the melt pool through both numerical and experimental approaches, then developing a reduced plan of experiments to produce samples for structural analysis and mechanical testing in order to obtain optimized parameter sets specific to each material. Finally, precision parts, others with complex geometries, and initial prototypes are manufactured to test the printability and robustness of the selected parameters. The project starts with tungsten and molybdenum. A numerical model allowed for the quick definition of a reduced plan of experiments and the production of crack-free samples with properties competitive with conventional powder metallurgy. The addition of rhenium to molybdenum and the use of post-processing improved the mechanical properties, although oxidation problems limited high-temperature performance. Printability limits were determined, and a pure molybdenum micro-premixed injector prototype was produced, though it could not be tested in real conditions. Next, due to the complexity of the fusion and solidification phenomena in the next-generation titanium alloy Ti-6Al-2Sn-4Zr-6Mo, the approach was adapted experimentally. This method enabled the definition of reduced ranges of process parameters, ultimately producing high quality samples with optimized parameter sets offering a choice between productivity and precision. However, mechanical testing revealed a critical lack of ductility for this application, which was improved through post-processing at the expense of mechanical strength. Finally, moving to an equivalent capacity equipment highlighted that the architectural difference between the two equipment alone was enough to compromise the obtained properties, justifying the need to adjust the process parameters for each new piece of equipment. Finally, for the titanium aluminide-based intermetallic Ti-22Al-25Nb, modifications to the process parameters were not sufficient to prevent cracking in the parts. A post-processing step after printing allowed for the production of sound samples, but moving to more complex and larger geometries revealed the limits of this solution. However, the data collected allowed for the definition of printability criteria for this alloy, while emphasizing the constraints of printing on machines with limited power and no temperature control in the printing chamber. This project demonstrates that, although promising, the implementation of new metals for high-temperature applications using laser powder bed fusion still faces technical challenges related to the optimization of process and post-process parameters before their integration into functional devices.

Date	12 Dec 2025
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Vladimir Brailovski (Supervisor)