GOALI: Multilayered Oxide Fiber Coating Concept for Environmentally Durable SiC/SiC Composites

这个GOALI项目是史蒂文斯理工学院和通用电气公司研发部门的合作项目，将探索一种新的纤维涂层概念，该概念可以使SiC/SiC陶瓷基复合材料在飞机发动机、空间推进系统、公用事业燃气轮机和工业热交换器等高温环境中可靠地使用。与传统的脆性陶瓷材料不同，SiC/SiC复合材料通过加入BN纤维涂层，使其具有韧性和耐损伤性，BN纤维涂层作为纤维/基体界面区域的弱界面来偏转裂缝。首席研究员和他的合作者最近进行了有趣的观察，发现氧化纤维涂层可以为SiC/SiC复合材料提供所需的弱界面行为，而不会明显降低纤维强度。这种特性以前从未报道过氧化物基纤维涂层。这项新发现的基础是一个相当非常规的概念，即使用两种不同但热化学相容的氧化物材料来形成多层氧化物涂层。例如，化学气相沉积（CVD）制备的含有SiO2/ZrO2/SiO2层的纤维涂层的初步结果明确表明，在多层界面区域内存在“优雅”的拉伸行为和广泛的裂纹挠曲，可能是由于SiO2和ZrO2层的热膨胀系数（CTE）的显著不匹配。此外，正如所期望的那样，氧化纤维涂层在应力氧化后仍保留了许多复合材料的特性。从技术角度来看，这种新的涂层概念可能为应力氧化问题提供独特的解决方案，特别是如果在实际开发之前可以测试该概念的通用性。这个GOALI项目将：(1)证明明显的弱界面行为是由CTE不匹配引起的，(2)评估如何通过选择合适的氧化物成分来维持这种类型的主动界面控制到1200摄氏度，(3)确定CVD SiO2层对纤维强度的影响。本着GOALI计划的精神，史蒂文斯和GECRD的独特研究技能和设施被整合在一起。涂层工艺优化和界面表征研究将由教授进行。李和利伯拉分别在史蒂文斯。在工业科学家王博士的指导下，GECRD的气氛控制拉伸测试仪将提供给史蒂文斯的研究生。更重要的是，GECRD在制造SiC/SiC组件方面的工业专业知识将用于预测这种高风险，高增益涂层概念的可行性，以解决美国工业的应力氧化问题。该项目由美国国家科学基金会材料研究部陶瓷项目、数学与物理科学理事会多学科活动办公室和赖特-帕特森空军基地空军研究实验室陶瓷研究小组共同资助

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.***