Mechanisms of crack healing in reactive MAX phase ceramic composites

该项目的目的是探索陶瓷复合材料的裂纹愈合机制，以便在损伤之前再生其力学性能。该项目旨在了解在含有复合陶瓷的MAX相中控制愈合反应激活和物质向反应位点运输的机制。选择Ti-A-C体系中A = Al， Sn的MAX相作为模型体系，因为它们具有独特的纳米层状晶体结构。陶瓷[Ti6C]-八面体层的高键能和a -金属层的低键能之间的显著差异可以用来引发扩展的裂纹偏转和裂纹桥接，从而在裂纹后产生高反应表面积。用低熔点金属（Sn）取代a金属层位置上的Al有望增强变形和断裂时金属的活化。裂纹愈合将通过活化金属与氧化物（MgO）或非氧化物（ZrC1-x）修复填充物的反应来实现，这些填充物恢复了连接断裂裂纹界面的固体韧带。将原子水平上的晶体化学方法与通过周期性组装空间填充构建块形成微观结构的新概念相结合，其中MAX相和修复填料位于界面边界，被认为是一种具有自修复能力的新型复合材料的有远见的方法。

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.