Physical chemistry of self-organization and self-healing in metals

Wear occurs at most solid surfaces that come in contact with other solid surfaces. While biological surfaces and tissues usually have the ability to repair minor wear damage, engineered self-healing materials only started to emerge recently. An example of a smart self-healing material is the material with imbedded microcapsules or microtubes, which rupture during crack propagation and release a healing agent that repairs the crack. Self-healing mechanisms are hierarchical in the sense that they involve interactions with different characteristic scale lengths. While traditional models of self-healing require equations with many degrees of freedom, taking into account the hierarchical organization allows us to reduce the number of equations to a few degrees of freedom. We discuss the conditions under which the self-healing occurs and provide a general theoretical framework and criteria for self-healing using the concept of multiscale organization of entropy and non-equilibrium thermodynamics. The example of a self-healed Al alloy reinforced with microtubes filled with Sn60Pb40 solder is discussed as a case study.