SBIR Phase I: Novel Environmental Barrier Coatings for High-Temperature Metals and Ceramic Matrix Composites

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This Small Business Innovation Research Phase I project proposes two approaches to develop a thin, low cost, protective coating for SiC-based ceramic composites and refractory and other high-temperature metal alloys reaching 1200 C. Protective coatings are required for metals and ceramics to prevent accelerated fatigue from oxidation and corrosion. A novel SiCN coating will be synthesized via metal doping of thermoset polysilazanes, exhibiting low volumetric shrinkage, high bond strength, and excellent hermiticity. Zr/Ti and Zr/Al doped polysilazanes will be powder coated, thereby increasing ceramic yield by limiting volatile content. Doped SiCN coatings offer lower Young's modulus and tailorable coefficients of thermal expansion (TCEs) and surface chemistries, increasing the coatings' durability during thermal cycling. The second proposed coating system involves a sol-gel or polymer derived ZrSiO4 oxygen barrier with a sol-glass top layer for moisture protection. Zircon functions as a bond coat for the protective Y-Zr-Al-Si-O. The zircon phase will either be spin/dip cast via a standard sol synthesis or derived from the condensation of Zr and Si thermoset polymers. The applications of the novel coatings in this proposal are not limited to protecting SiC-based ceramic composites, but also can be used for silicon nitride, silicon-based monolithic ceramics, and high-temperature metal alloys. The broader impact/commercial potential of this program involves innovative material solutions to improve the performance, durability, and life expectancy of metal, ceramic, and composite components within propulsion and power generation heat engines. Thermal cycling and accelerated corrosion dramatically reduce the lifetime of high-temperature materials, which are experiencing increasingly harsh operating conditions. Protecting ceramic and metal components during service in elevated temperature regimes has been identified as a 21st century materials science priority. Current protective coatings for both metals and ceramics consist of thick layers (100s of microns) of materials of varying composition, increasing the complexity and cost of production of high-temperature materials intended for long-lifetime applications. Achieving this with low-cost, easily processable materials through innovative chemistry will reduce the exorbitant costs of corrosion. The coating approaches being developed offer the potential for quick inspection and servicing through reapplication of the coating system. Ceramic, metal, and composite structural materials operating under high thermo-mechanical loads in corrosive or oxidative environments would benefit from the low-cost coating systems to be developed.