John E. Holowczak

Development and Evaluation of Environmental Barrier Coatings for Silicon Nitride

Environmental barrier coatings (EBCs) are required for applications of silicon nitride (Si3 N4 ) and silicon carbide (SiC) based materials in gas turbine engines because of the accelerated oxidation of Si3 N4 and SiC and subsequent volatilization of silica in the high temperature high-pressure steam environment. EBC systems for silicon carbide fiber reinforced silicon carbide ceramic matrix composites (SiC/SiC CMC’s) were first developed and have been demonstrated via long-term engine tests. Recently, studies have been carried out at United Technologies Research Center (UTRC) to understand the temperature capability of the current celsian-based EBC systems and its suitability for silicon nitride ceramics concerning thermal expansion mismatch between the EBC coating and silicon nitride substrates. This paper will present recent progress in improving the temperature capability of the celsian –based EBC systems and discuss their effectiveness for silicon nitride.Copyright

Development and Evaluation of Environmental Barrier Coatings for Si-Based Ceramics

Environmental barrier coatings (EBCs) are being developed for silicon carbide (SiC) based composites and monolithic silicon nitride (Si3 N4 ) to protect against the accelerated oxidation and subsequent silica volatilization in high temperature, high-pressure steam environments encountered in gas turbine engines. While EBCs for silicon carbide (EBCSiC ) have been demonstrated in combustor liner applications, efforts are ongoing in the development of EBC systems for silicon nitride (EBCSiN ). The challenges of adapting EBCSiC to monolithic Si3 N4 are discussed in this paper. Progress in the area of EBCSiN including development and performance during field tests and tests simulating engine conditions are reviewed.Copyright