Knowledge based design of crack and erosion damage healing nanolaminates

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Today, the properties of components are designed such that they meet operational demands in various environments for a given time before they have to be repaired “externally” or replaced by new ones. Self-healing materials allow for a design concept based on damage management where damage that is inflicted during operation can be healed autonomously. It has been shown that the MN+1AXN phases Ti3AlC2, Ti2AlC and Cr2AlC exhibit autonomous self-healing behaviour. Cracks are filled and hence healed by oxidation products of the M and A elements in the MAX phase at high operating temperatures. After crack healing the fracture strength is recovered to the level of the virgin material. MAX phases are nanolaminates exhibiting both ceramic and metallic properties. Due to its oxidation and corrosion resistance, it can be used at high temperatures and in aggressive environments. Unlike conventional high temperature materials, MAX phase metallo-ceramics are easily machinable. Furthermore, it has been shown that the MAX phase Cr2AlC exhibits excellent erosion resistance. So far, basic physical and chemical materials design principles for self-healing materials have not been identified. Therefore, this project aims at identifying and understanding these principles to realize knowledge-based design of crack and erosion damage healing materials. Based on ab initio calculations of the stability of Cr2-xMxAl1-yAyC (M = Ti, Hf, Zr; A = Si, B), phases suitable for experiments are determined and synthesized. The crack healing kinetics will be investigated as a function of the concentrations of the elements M and A both experimentally and by means of modelling. In principal, self-healing of erosion damage appears possible, but yet has to be demonstrated experimentally. The long-term vision of this project is to predict the capability of a MAX phases for crack and erosion damage management as a function of composition, temperature, time and environment.