Mechanisms of crack healing in reactive MAX phase ceramic composites

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The aim of the proposed project is to explore the mechanisms of crack healing in ceramic composites in order to regenerate the mechanical properties prior to damaging. The project aims to understand the mechanisms controlling the activation of the healing reaction and the transport of matter to the reaction site in MAX phase containing composite ceramics. MAX phases in the system Ti-A-C with A = Al, Sn are selected as a model system due to their unique nanolaminate crystal structure. The pronounced difference between the high bonding energy in the ceramic [Ti6C]-octahedra layers and the low bonding energy of the A-metal layers can be used to initiate extended crack deflecttion and crack bridging giving rise for a high reaction surface area in the wake of a crack. Substitution of Al on the A-metal layer position by a low melting metal (Sn) is expected to enhance mobilisation of the metal upon deformation and fracture. Crack healing will be achieved by reaction of the mobilised metal with oxide (MgO) or non-oxide (ZrC1-x) repair fillers restoring solid ligaments bridging the disruptted crack interface. Combining the crystal chemistry approach on the atomic level with a novel concept of microstructure formation by periodical assembly of space filling building blocs where the MAX phase and the repair filler are located at the interface boundary is considered as a visionary approach for a new class of composites with self healing capacity.