Project Details
Description
This GOALI project, a collaboration between Stevens Institute of Technology and General Electric Corporate Research and Development, will explore a novel fiber coating concept which may enable the reliable use of SiC/SiC ceramic matrix composites in high-temperature environments encountered in aircraft engines, space propulsion systems, utility gas turbines, and industrial heat exchangers. Unlike traditionally brittle ceramic materials, SiC/SiC composites are made to be tough and damage-tolerant by incorporating a BN fiber coating which serves as a weak interface to deflect cracks at the fiber/matrix interface region. The Principal Investigator and his collaborators have recently made intriguing observations that an oxide fiber coating can provide the desired weak interface behavior for SiC/SiC composites without apparent degradation of fiber strength. Such characteristics have never been reported previously for an oxide-based fiber coating. The basis of this new discovery was a rather unconventional concept of using two dissimilar, but thermochemically compatible oxide materials to form a multilayered oxide coating. For example, initial results with a fiber coating containing SiO2/ZrO2/SiO2 layers prepared by chemical vapor deposition (CVD) showed definitive evidence for 'graceful' tensile behavior and extensive crack-deflection within the multilayered interface region, presumably due to the significant mismatch in the coefficient of thermal expansion (CTE) of the SiO2 and ZrO2 layers. Furthermore, as expected of the oxide-based fiber coating, much of the composite characteristics was retained after stress oxidation. From a technological perspective, this new coating concept may offer an unique solution to the stress oxidation problem, particularly if the generality of the concept can be tested prior to practical development. This GOALI project will: (1) prove that the apparent weak interface behavior is caused by the CTE mismatch, (2) evaluate how this type of proactive interface control can be sustained up to 1200 degrees C by selecting appropriate oxide constituents, and (3) determine the effect of the CVD SiO2 layer on fiber strength.
In the spirit of the GOALI program, unique research skills and facilities at Stevens and GECRD are integrated. Coating process optimization and interface characterization studies will be conducted by Profs. Lee and Libera, respectively, at Stevens. An atmosphere-controlled tensile tester at GECRD will be available to Stevens' graduate students under the direction of Dr. Wang, the industrial scientist. More importantly, GECRD's industrial expertise in manufacturing SiC/SiC components will be used to project the viability of this high-risk, high-gain coating concept for solving the stress oxidation problem for the U.S. industry. This project is co-funded by the Ceramics Program of the Division of Materials Research, the Office of Multidisciplinary Activities of the Mathematical and Physical Sciences Directorate, both at NSF, and the Ceramics Research Group at the Air Force Research Laboratory at Wright-Patterson Air Force Base.
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Status | Finished |
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Effective start/end date | 15/07/99 → 30/09/02 |
Funding
- National Science Foundation