Micro-Mixing Injector Manufacturing in Refractory Metal Using Laser Powder Bed Fusion Process

Abstract The decarbonization and reduction of pollutant emissions are at the core of research in the field of gas turbine combustion. One of the hot topics in this regard is the integration of hydrogen, which comes with design challenges and combustor operability limits due to its higher flame temperatures and its propensity to form nozzle-attached flames. These characteristics lead to higher operating temperature requirements for hydrogen fuel injectors to extend their operability. Refractory metals are interesting because their melting temperatures are significantly higher than the combustor outlet temperatures, which opens up new design possibilities. However, multiple challenges, such as oxidation and manufacturing issues, arise with refractory metals. The laser powder bed fusion (LPBF) process is gaining momentum in the manufacturing of micro-mixing injectors because of its suitability to produce complex geometry parts. This additive manufacturing process can be applied to refractory metals, opening up new perspectives for micro-mixing injector designs. In this paper, a small-scale micro-mixing injector in molybdenum was manufactured using the LPBF process to demonstrate the printability of such parts in refractory metals. The geometric precision achieved was acceptable for micro-mixing combustion requirements. Small holes with a nominal size of 0.3 mm, representing injection nozzles, and 0.3 mm-thin walls, demonstrating the possibility to print complex geometries, were successfully produced. An environmental barrier coating (EBC) was developed in parallel to explore the challenges of protecting complex LPBF parts from high-temperature oxidizing environment.