Environmental degradation of SiC/SiC

关键目标和目的目前由罗尔斯·罗伊斯高温复合材料公司（RRHTC）生产的SiCf/SiC陶瓷基复合材料的变体含有基质添加剂，通过形成低粘度高透氧性硼硅酸盐玻璃来控制氧化降解。这种低粘度玻璃为基质裂纹提供了“自修复”机制，但也导致了氧化和环境抗性行为，这是由于氧化产物的可变化学性质而导致的路径依赖性。该计划将研究这些氧化产物在潮湿和/或海洋环境中的稳定性，以及这如何影响随后的机械性能。具体目标包括：1.量化/定性环境暴露如何影响单调本构性能。确定应变（损伤）的演变是否受到环境暴露的影响。3.在整个疲劳加载方案中，监测氧化/环境暴露影响下的损伤进展。4.表征由于环境暴露而导致的断裂形态，并与最终的机械性能相关联。新方法罗尔斯·罗伊斯和斯旺西大学将共同合作，生成一个适当缩放的测试矩阵，以检查环境暴露对寿命的影响。确定对环境暴露的影响需要比较基线测试数据和检查学生测试的样品。当适用于补充学生评估的新样本时，罗尔斯·罗伊斯将向学生提供以前的测试数据和样本。纤维增强CMC系统的变形和最终失效非常复杂，并吸引了高度复杂和新颖的表征技术来描述力学行为。该项目将扩展我们的实验室专业知识，在使用声发射（AE），数字图像相关（DIC）和电阻监测时，适用于宏观尺度轴向试样。然而，最近采购的原位SEM加载阶段将允许新的实验在微观尺度上，结合DIC的SEM成像记录表面基体开裂，次表面纤维基体的解凝聚力和纤维断裂。高倍率扫描电镜和化学绘图将被用来识别环境诱导的玻璃相。由于这类材料的响应相对较脆，因此需要改进传统的机械测试控制，以准确再现低幅度应变控制的疲劳条件。ExploitationCMC的重点是在航空和陆基燃气轮机的高温阶段的未来应用。本研究中开发的信息和方法将为未来的CMC材料开发提供信息。了解在模拟、高温、氧化、使用环境下发生的变形机制将改进新CMC变体的设计，并为工程师提供未来结构完整性评估的信息。

Key Objectives and AimsCurrent variants of SiCf/SiC ceramic matrix composites produced by Rolls-Royce High Temperature Composites (RRHTC) contain matrix additions that control oxidation degradation via the formation of a low viscosity high oxygen permeability borosilicate glass. This low viscosity glass provides a "self-healing" mechanism for matrix cracks but also results in an oxidation and environmental resistance behaviour that is path dependent due to the variable chemistry of the oxidation product. This program will investigate the stability of these oxidation products in humid and/or marine environments and how this impacts subsequent mechanical performance. Specific objectives include: 1. Quantify/qualify how environmental exposure affects the monotonic constitutive performance.2. Establish whether the evolution of strain (damage) is affected by environmental exposure. 3. Monitor damage progression under the impact of oxidation/environmental exposure throughout fatigue loading regimes.4. Characterise fracture morphology due to environmental exposures and correlate to ultimate mechanical performance.Novel MethodologiesRolls-Royce and Swansea University will collaborate together to generate a suitably scaled test matrix that would examine the impact of environmental exposure on life. Determination of the impact on environmental exposures will require comparison of baseline test data and the examination of the specimens tested by the student. Previous test data and specimens will be provided by Rolls-Royce to the student when it is applicable to supplement the new specimens evaluated by the student.Deformation and ultimate failure in fibre reinforced CMC systems is highly complex and attracts highly sophisticated and novel characterisation techniques to describe mechanical behaviour. This project will extend our laboratory expertise in the use of acoustic emission (AE), digital image correlation (DIC) and electrical resistance monitoring when applied to macro-scale axial test coupons. However, the recent procurement of an in-situ SEM loading stage will allow novel experiments on the micro-scale, incorporating DIC of SEM imaging to record surface matrix cracking, sub-surface fibre-matrix de-cohesion and fibre rupture. High magnification SEM and chemical mapping will be employed to identify environmentally induced glassy phases. Due to the relatively brittle response of this class of material, improvements to traditional mechanical test controls will be required to accurately reproduce low magnitude strain controlled fatigue conditions.ExploitationCMCs are focussed towards future applications in the high temperature stages of aero and land based gas turbines. The information and methods developed in this research will inform future CMC material developments. Understanding the deformation mechanisms that occur under simulated, high temperature, oxidising, service environments will improve the design of new CMC variants and inform engineers of future structural integrity assessments.