The failure behavior of ceramic matrix composites (CMC) is largely determined by the adhesion between the ceramic fiber and the ceramic matrix. Damage-tolerant failure with high fracture toughness and a high proportional limit is desired. The fiber-matrix bond is determined by the boundary zone between the two components, the so-called interphase, and can be adapted, for example, by applying ceramic fiber coatings. In so-called weak interface composites, a weak fiber-matrix adhesion allows the detachment of fibers and matrix on a microscopic scale in the event of failure, which leads to the desired damage-tolerant failure. The fiber coating can also serve to protect the fibers during CMC processing and during the use phase in aggressive environments.

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The research of the "Interfaces & Interphases" working group aims to gain a detailed understanding of the interphase properties of the CMC and their correlation to failure behavior. The interphase is specifically modified by coatings and investigated with the highest resolution. Microscopic methods such as transmission electron microscopy are used. In addition, the failure behavior of the CMC materials is investigated on a microscopic and macroscopic scale. Relevant here are, for example, fracture mechanics investigations or micromechanical single-fiber push-out tests.

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Another research focus of the "Interfaces & Interphases" working group is the repair of CMC materials. The removal of damaged areas and the filling with preceramic polymers or ceramic inlays is being investigated. Once again, the interface between two materials is of crucial importance, as the adhesion between the filling and the surrounding material determines the quality of the repair.

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The "Interfaces & Interphases" working group also deals with the adaptation of the surface of ceramic fiber composites in order to bond external corrosion protection layers with long-term stability.