Microstructure of an Oxide Ceramic Matrix Composite (Cross Section)
Profound characterization is mandatory for successful development of structural and functional ceramics. Characterization is performed by means of state-of-the-art analytic methods on a very broad length scale: atomic or crystal structures are investigated be means of X-ray or electron diffractometry which reveal grain orientations, strains, and phase transformations. Imaging methods such as scanning and transmission electron microscopy reveal the microstructures of materials and effects caused by deformation, corrosion, and the like.
A more macroscopic examination of materials and components is performed by non-destructive methods such as scanning ultrasound analysis or X-ray computed tomography. Standard characterization methods include thermal conductivity, thermal expansion, micro-hardness and permeability.
Mechanical Characterization of an All-oxide Ceramic Matrix Composite (Tensile Test)
The design of CMC components is performed on the basis of mechanical properties which are analyzed by room- and high-temperature fracture mechanics. Thereby the definition of failure criteria for CMC under complex thermal-mechanical loads is a primary R&D goal. Experiments are accompanied by computational methods allowing a simulation of material properties. Key properties of our oxide CMC are closely linked to the properties of oxide ceramic fibers. Therefore, properties like tensile strength or creep behavior of oxide fibers consisting of alumina and/or mullite are thoroughly investigated, also upon thermal treatment or corrosive attack. Specific laboratory equipment allows testing of single, only 10 micron thick ceramic fibers up to 1500°C. Fibers are also analyzed by scanning and transmission electron microscopy. The combination of analytic methods provides an insight in fiber damaging and its associated physical-chemical effects.
Beyond basic laboratory work the behavior of ceramic materials is studied under complex conditions mimicking real applications. This includes experiments in (turbine) combustor rigs, (hypersonic) wind tunnels, solar- or radiation furnaces, etc. which is habitually performed in co-operation with other DLR research institutes.