Microstructure and mechanical properties

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With their joint proposal Reactive Air Brazing of Metal-Ceramics Compounds,IWM (RWTH Aachen University) and IEK-2 (Forschungszentrum Jülich) apply for a second two-year funding period. During the first project phase, the mechanical behavior of reactive air brazed metal-ceramics compounds, the adhesion mechanisms in the interfaces between braze metal and joined components and the damage mechanisms depending on chemistry, processing and thermal ageing were investigated. During the proposed second funding period, an in-depth analysis of damage induced by thermal ageing is planned with special focus on the formation, composition and mechanical properties of the strength-limiting reaction layers formed at the interfaces of the brazed joint during processing and high temperature exposure. For these investigations, mechanical testing and in-depth scanning and transmission electron microscopy studies are planned at brazed joint variants selected according to the results of the first project phase. At the same time, the existing FEM model of brazed joints will be extended in order to simulate the reaction zones at the interfaces, especially their influence on mechanical strength of the brazed joint. This model will be used to predict the mechanical behavior of several metal/ceramic compounds, especially compounds with large thermal expansion mismatch. Extensive mechanical characterization (i.e. by bending, compound tension and double shear testing of brazed joints) of metal-ceramic compounds in the as-received state and after isothermal ageing or thermal cycling allows calibration and validation of the FEM model. Additionally, so called mechanically assisted diffusion bonding, which proved -according to preliminary investigations during the first project phase- to be a promising alternative joining process will be used to produce compounds with large thermal expansion mismatch of their components. Adhesion and shear strength of these compounds will be measured and microscopic investigation, especially of the interface regions is planned