Design and Manufacture of liquid silicon infiltration based SiC/SiC nozzle guide vanes for high-pressure turbines

Kurzfassung

Increasing the efficiency of jet engines is essential for more environmentally friendly air transport. Higher temperature resistance and lower weight of the combustor and turbine components are key requirements for new materials. Along with adapted environmental coating systems and cooling features, ceramic matrix composites (CMC) are strong candidates for aircraft applications. They can withstand high temperatures in an aggressive environment, while their density is two-thirds lower than that of conventional nickel-based alloys, leading to savings in cooling air and potential improvements in engine efficiency. As part of the DLR project 3DCeraTurb, turbine vanes made of silicon carbide fiber-reinforced silicon carbide composites (SiC/SiC CMC) are developed. One aim of 3DCeraTurb is to design and manufacture ceramic nozzle guide vanes (NGV) for a high-pressure turbine (1st stage), experimentally investigate the vane behavior in a wind tunnel, and evaluate performance, damage and lifetime for later application in an aircraft engine. The focus was the enhancement of the manufacturing process from plate dimensions to more complex three-dimensional components. A ceramic-based design served as a basis for the development and manufacture of a new NGV geometry, considering material- and manufacturing-specific constraints. The liquid silicon infiltration (LSI) process was used to manufacture the SiC/SiC vanes. The process began with the draping and CVI fiber coating of woven fabric layers. During this stage, shaping occurred, and the final component contour was defined. The fiber preform was then infiltrated with a phenolic resin, which acted as a carbon source, using resin transfer molding, followed by high-temperature pyrolysis. The resulting porous carbon matrix was infiltrated with a silicon-boron melt, leading to the conversion of carbon into a SiSiC matrix. The surface was ground, to meet the high requirements for surface roughness and geometric and positional tolerances. Cylindrical, laser-drilled cooling holes were introduced for cooling the trailing edge. In the final step, an environmental barrier coating system (EBC) consisting of yttrium disilicate and yttrium monosilicate layers was applied using PVD processing. Thermal simulations were performed at the highest loads (Take-off End of field). Therefore, computational fluid dynamics (CFD) simulations were coupled with a finite element analysis (FEA). For the determination of thermal and mechanical properties, SiC/SiC plates were manufactured. Safety factors were calculated using the Tsai-Wu criterion. Wind tunnel testing under TRL 4 will be performed and vane performance will be evaluated.