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Compact military-grade jet engines offer many potential applications, including use in remotely piloted vehicles, but can be expensive to use for research and development purposes. A study aimed at increasing the power and thrust output of an inexpensive commercial compact engine found a material limitation issue in the turbomachinery. To gain the additional power, hotter turbine inlet temperatures were required. This temperature increase exceeded the limit of current uncooled metal turbine rotors but could be achieved through turbine rotors made from ceramics, such as silicon nitride, which would allow an increase in the thrust and power output by a factor of 1.44. Current ceramic turbine manufacturing methods are costly and time consuming for rapid prototyping, but recent breakthroughs in ceramic additive manufacturing have allowed for cheaper methods and faster production which are beneficial for use in research and development when designs are being rapidly changed and tested. This research demonstrated, through finite element analysis, that a silicon nitride turbine rotor could meet the increased turbine inlet temperature conditions to provide the desired thrust and power increase. Further, as a proof of concept, an additively manufactured drop-in replacement alumina turbine rotor was produced for the JetCat P400 small-scale engine in a manner that was cost-effective, timely, and potentially scalable for production. This compact engine was used to demonstrate that a cost-effective ceramic turbine could be manufactured. At the time of publication, the desired ceramic material, silicon nitride, was not available for additive manufacturing.

Consolidation of pure molybdenum through laser powder bed fusion and other additive manufacturing techniques is complicated by a high melting temperature, thermal conductivity and ductile-to-brittle transition temperature. Nano-sized SiC particles (0.1 wt%) were homogeneously mixed with molybdenum powder and the printing characteristics, chemical composition, microstructure, mechanical properties were compared to pure molybdenum for scan speeds of 100, 200, 400, and 800 mm/s. The addition of SiC improved the optically determined density and flexural strength at 400 mm/s by 92% and 80%, respectively. The oxygen content was reduced by an average of 52% over the four scan speeds analyzed. Two mechanisms of oxygen reduction were identified as responsible for the improvements: oxidation of free carbon and the creation of secondary phase nanoparticles. This study illustrates the promising influence of nanoparticle additions to refractory metals in laser powder bed fusion.

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