INNOVATIVE, MULTIFUNCTIONAL LAYERED COATINGS FOR HIGH TEMPERATURE CERAMIC MATRIX COMPOSITES
- ReliaCoat Technologies, LLC; ReliaCoat Technologies, LLC
- BROWN UNIVERSITY
- ReliaCoat Technologies, LLC
Efforts throughout this STTR Phase I program have focused on developing and down-selecting various multilayer thermal/environmental barrier coating (T/EBC) coating systems, designed to accommodate future gas turbine environments with ceramic matrix composite (CMC) materials. To address the needs of thermal insulation and environmental protection while retaining mechanical and chemical phase stability, the team proposed a (multi-faceted approach to determine the most feasible T/EBC architectures. These consisted of: (1) spatially optimized multilayer T/EBC, (2) monolithic multifunctional layer, and (3) hybrid multilayer. To ensure thermally stable bond coats the team investigated three different approaches: (1) conventional plasma sprayed silicon, (2) plasma sprayed and high velocity oxygen fuel (HVOF) sprayed MoSi2, and (3) plasma/HVOF sprayed EBC only, without incorporating bond coats. Through careful manufacturing-enabled architecture optimization of each layer the following criteria would be addressed: (1) thermal mechanical and chemical stabile system up to 1700 °C thermal gradient, (2) resistant to moisture and corrosive gases, (3) tolerant to thermal strains, and (4) resistant to erosion and particulates. Through close collaboration with program partners, the team down-selected processes and materials that met the criteria necessary for bond coat, EBC, and TBC structures, among which included an experimental YYbSi2O7 monolithic T/EBC powder. Using ReliaCoat’s analytical models and associated multilayer thermo-mechanical analysis software for predicting T/EBC durability and thermal profiles, select coating materials and architectures were assessed for initial determination of viable T/EBC solutions. Optimized coating processing was enabled for each of the designed architectures using Reliacoat’s integrated diagnostic tools that allow rapid assessment and control of the microstructure and properties to meet the stated design criteria. Throughout the program more than 50 T/EBC specimen variants were processed onto SiC/Hexoloy test substrates. The ability to achieve such high productivity is in part a testament to Reliacoat advanced instrumentation, software and visualization capabilities that allow rapid integration of design, materials and processes. Via process and coating architecture optimization, the team was able to successfully synthesize each of the three proposed T/EBC approaches, including the experimental monolithic T/EBC material. Furthermore, each approach was successfully sprayed with and without bond coats on two types of substrates (Hexaloy SiC and CVD formed SiC). Results indicated that via proper HVOF processes EBC and T/EBC layers could be deposited directly onto SiC; upon thermal testing at 1300 °C and 1700 °C the layer exhibited good adhesion and promising durability in initial tests of upto 200 mins of cycling exposure at 1700 °C surface temperature in a cyclic burner rig test. Additional testing with MoSi2 showed potential for good adhesion with HVOF processing, however additional parametric optimization is necessary. The team further demonstrated the capability to improve EBC layer density and reduce moisture penetration EBC layers by through optimized heat-treating procedures. The various synthesized coating architecture variants were characterized for phase composition, thermal compatibility, and thermal durability (isothermal and thermal gradient). Using X-ray diffraction (XRD) analysis it was confirmed that plasma sprayed EBCs and T/EBC restore their crystallinity with appropriate post-processing annealing procedures. HVOF-processed MoSi2 and EBC layers retained most of their crystallinity compared to as-sprayed plasma sprayed coatings. Freestanding EBC + TBC coatings subjected to 1600 °C thermal compatibility tests exhibited limited interlayer diffusion following 24 hours of exposure. Long-term isothermal durability tests at 1300 °C further suggested TBC layer optimization was critical to preventing sintering-induced cracking and enhancing sample durability. This was later reaffirmed following 1300 °C burner rig thermal gradient testing. Upon , iterative optimization of EBC and TBC architectures, four T/EBC sample variants successfully survived ten 20-minute burner rig cycles of 1700 °C. These included: (1) HVOF EBC + APS YZO, (2) HVOF T/EBC, (3) HVOF T/EBC + APS T/EBC, and (4) HVOF T/EBC + APS YZO. Thermal gradient measurements additionally indicated the potential to reduce substrate temperatures by over 700 °C.
- Research Organization:
- RELIACOAT TECHNOLOGIES, LLC
- Sponsoring Organization:
- USDOE Office of Fossil Energy (FE)
- Contributing Organization:
- Brown University
- DOE Contract Number:
- SC0018726
- OSTI ID:
- 1506973
- Type / Phase:
- STTR (Phase I)
- Report Number(s):
- RCT102401
- Country of Publication:
- United States
- Language:
- English
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