SiC/SiC Composites for Aerospace

航空航天用 SiC/SiC 复合材料

• 批准号: 2267233
• 金额: --
• 依托单位: University of Oxford
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2019
• 资助国家: 英国
• 起止时间: 2019 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2267233
• 关键词: SiC; Composites; Aerospace

CMC's (Ceramic Matrix Composites) consist of fibres imbedded in a matrix, bonded by an interphase - either carbon or boron nitride. CMC's have been suggested for use in multiple markets over the years for their high-performance mechanical and thermal properties - amongst other benefits. In aerospace applications they are in directed competition with titanium alloys (which have limited temperature usability) and nickel-based super alloys (which add significant weight to the engines). However to be deployed in service- in particular in aeroengines further research is required. In particular the reliability and predictability of CMC properties are major obstacles to immediate engine implementation - this is because CMC fibre macrostructures demonstrate complexity, and their microstructural toughening mechanisms not fully understood. This project is in collaboration with Rolls Royce and will further develop the understanding of these materials and move them towards market.Despite being built of brittle ceramic materials, CMC's have great creep resistance and distinct toughening mechanisms (including fibre pull-out) which upgrade their fracture behaviour to quasi-brittle / pseudo-ductile. Fibre pull-out makes use of an interlayer between the fibre and matrix with distinct tribological properties, which enable transfer of any load from one to the other3. Successful load transfer is characterised by high strains and premature 'yields'4. Fibres are able to slide along the interface, providing a source of displacement and therefore absorption of elastic energy5 and lowering of thermal stresses at any crack tip. Whilst the mechanisms of fibre sliding and toughening are comparatively well understood at room temperature, these materials can develop significant changes in mechanical properties at elevated temperatures. This is due to the reaction of the interlayer with the water vapour present in combustion. This produces a variety of microstructural changes - often the formation of glassy phase and the evolution of gasses based around compounds of boron, nitrogen, oxygen and carbon. This project will use advanced microscopy based tools to study the degradation of the interlayer as a function of water vapour partial pressure, over stress and cyclic loadings. This will combine high resolution electron microanalysis methods, thermal gravational analysis and secondary ion mass spectrometry. Allowing both the left behind reaction product and the evolved gas to be studied. This is important as the evolved gas can degrade metallic components further back in the engine - and an understanding of this will be vital to build a safety case for these materials. The mechanical properties post exposure will be correlated with the observed microstructures. This will be the first time these techniques have been used together to understand degradation and failure in these materials. In particular no one knows what gasses are evolved and what they may do to other components. This work fits into the engineering and manufacturing the future themes.

CMC（陶瓷基复合材料）由嵌入基质中的纤维组成，通过碳或氮化硼界面结合。多年来，CMC因其高性能的机械和热性能而被建议用于多个市场-以及其他益处。在航空航天应用中，它们与钛合金（具有有限的温度可用性）和镍基超级合金（显著增加发动机重量）直接竞争。然而，要部署在服务中-特别是在航空发动机中，需要进一步的研究。特别是CMC性能的可靠性和可预测性是直接发动机实施的主要障碍-这是因为CMC纤维宏观结构表现出复杂性，并且其微观结构增韧机制尚未完全理解。该项目是与罗尔斯·罗伊斯公司合作的，将进一步发展对这些材料的理解，并将其推向市场。尽管CMC是由脆性陶瓷材料制成的，但它具有很强的抗蠕变性和独特的增韧机制（包括纤维拔出），使其断裂行为升级为准脆性/伪韧性。纤维拔出利用纤维和基体之间具有不同摩擦学特性的夹层，可将任何载荷从一个传递到另一个3。成功的负荷转移的特点是高应变和过早的"屈服" 4。纤维能够沿着界面滑动，提供位移源，从而吸收弹性能量5并降低任何裂纹尖端的热应力。虽然在室温下纤维滑动和增韧的机制相对较好地理解，但这些材料在高温下的机械性能可能会发生显着变化。这是由于夹层与燃烧中存在的水蒸气反应。这产生了各种微观结构的变化-通常是玻璃相的形成和基于硼、氮、氧和碳的化合物的气体的演变。该项目将使用先进的显微镜为基础的工具来研究作为水蒸气分压，过度应力和循环载荷的功能的夹层的降解。这将结合联合收割机高分辨率电子显微分析方法，热重力分析和二次离子质谱。从而可以对遗留的反应产物和释放的气体进行研究。这一点很重要，因为产生的气体会使发动机中的金属部件进一步退化-了解这一点对于为这些材料建立安全案例至关重要。暴露后的机械性能将与观察到的微观结构相关。这将是第一次将这些技术结合起来，以了解这些材料的降解和失效。特别是，没有人知道会产生什么气体，以及它们对其他成分有什么影响。这项工作符合工程和制造未来的主题。