Oxide Fiber Composites with three dimensional fiber architectures

在腐蚀性大气中工作温度在1000℃以上的结构材料是能源转换、运输和冶金发展的关键要素。对于这些应用，氧化物纤维复合材料(OFC)是注定的。CMC具有化学稳定性和在氧化环境中的耐受性。在高温和大温度梯度下，CMC表现出损伤容限断裂行为。它们的密度不到3克/厘米，质量比机械性能超过金属高温合金。然而，CMC的生产仍然存在严重的缺陷。目前，人们研究了两个概念来实现OFC的损伤容限断裂行为。在第一个概念中，通过纤维涂层来降低弱纤维与基质的结合。然而，纤维涂层的长期耐温性以及均匀性往往是不够的。第二个概念是所谓的弱矩阵系统。弱基质从机械上使纤维长丝解耦，使其具有损伤容限断裂行为。弱基质概念的缺点是与纤维涂层复合材料相比，层间强度较低。为了克服这一问题，制造三维光纤结构和调整矩阵设计是本研究项目的主题。这就是为什么一种新的氧化物纤维复合材料首次可以用于结构应用，如燃气轮机、热交换器和医疗工程。制备此类结构的唯一纺织制造工艺是3D编织。将三维编织技术应用于超脆性陶瓷纤维的加工，以及对陶瓷基材进行低收缩改性是本项目的重点。这一研究项目将证明制造三维增强CMC结构是可能的，并且力学性能优越。特别令人感兴趣的是z轴上的钢筋与剪切强度之间的相关性。总之，这项工作为OFC的纤维加工和制造提供了重要的概念和结论。

Structural materials for operation temperatures above 1000 °C in corrosive atmospheres are key elements for developments in energy conversion, transportation and metallurgy. For these applications, oxide fiber composites (OFC) are predestined. CMC are chemically stable and resistant in oxidizing environment. At high temperatures and large temperature gradients CMC show damage-tolerant fracture behaviour. They have a density of less than 3 g/cm³ and mass-specific mechanical properties that exceed those of metallic superalloys. However, there are still significant deficits in the production of CMC.Currently two concepts are investigated to realize damage-tolerant fracture behaviour of OFC. In the first concept a weak fiber-matrix bonding is set low by a fiber coating. However, often the long-term temperature resistance as well as to the homogeneity of the fiber coating is insufficient. The second concept is the so called weak matrix system. The weak matrix decouples the fiber filaments mechanically and enables the damage tolerant fracture behaviour. The drawback of the weak matrix concept is the low interlaminar strength compared to composites with fiber-coating. To overcome this problem, the manufacturing of a three-dimensional fiber architecture and an adjusted matrix design is the topic of this research project. That is why in the first time a new oxide fiber composite material can be used in structural application like gas turbines, heat exchangers and in medical engineering.The only textile manufacturing process for the preparation of such structures is the 3D-Braiding. The adaptation of the 3D braiding for the processing of the extremely brittle ceramic fibres as well as the modification of the ceramic matrix towards lower shrinkage is the focus of this project. This research project will demonstrate that the manufacturing of a three-dimensional reinforced CMC structure is possible, and that the mechanical properties are superior. Of particular interest is the correlation between the reinforcement in the z-axis and the shear strength. Overall, this work provides important concepts and conclusions in the fiber processing and manufacturing of OFC.