Oxide Fiber Composites with three dimensional fiber architectures

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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.