CERAMIC AND METAL ADDITIVE MANUFACTURING OF MONOLITHIC ROTORS FROM SIALON AND INCONEL AND COMPARISON OF AERODYNAMIC PERFORMANCE FOR 300W SCALE MICROTURBINES

The gas turbine industry is continuously developing and testing new materials and manufacturing methods to improve the performance and durability of hot section components, which are subjected to extreme conditions. SiAlON and Inconel 718 are especially desirable for turbomachinery applications due to their high strength and high temperature capabilities. To demonstrate the viability of additive manufacturing for small scale turbomachinery for 300W scale microturbines, a monolithic rotor with a design speed of 450,000 RPM containing radial turbine and compressor was developed considering additive manufacturing constraints. The geometry was manufactured from SiAlON and Inconel 718 using lithographic ceramic manufacturing and selective laser melting, respectively. The additive manufacturing and thermal process parameters as well as material characterization are described in detail. Surface and computerized tomography scans were conducted for both rotors. While the metallic rotor showed undesirable printing artefacts and a large number of defects, the ceramic part achieved a level of relative precision and surface quality similar to large-scale production via casting. To compare turbomachinery performance, an aerodynamic test facility was developed allowing to measure pressure ratios and efficiency of small compressors. The rotors were tested in engine realistic speeds, achieving a compressor rotor pressure ratio of 2.2. The ceramic part showed superior efficiency and pressure ratio compared to the Inconel rotor. This can be explained with lower profile and incidence losses due to a higher fidelity physical representation of the model geometry and better surface finish.