Modelling crack propagation in particle-dispersed self healing thermal barrier coatings

A computational study to identify the critical material properties and optimal spatial distribution of capsules containing a reactive healing agent for a brittle (ceramic) matrix is presented. The study focusses on the so called self-healing thermal barrier coating (TBC) system in which suitable healing particles are dispersed in the coating layer with the goal of improving the lifetime of the TBC systems. For successful triggering of the healing process, a primary requirement is that the initiated micro cracks in the TBC matrix should get attracted to the healing particles and, in addition, the cracks should open the particles. Consequently, the interaction between a crack and a healing particle becomes the crucial issue governing the behavior of such systems. The key objective of this chapter is to identify and assess the critical parameters that control the fracture process in the healing particle-matrix system. To achieve this, cohesive element-based finite element fracture analyses were conducted on two different particle/matrix systems, namely an idealized single healing particle-matrix system and a microstructure based system with a random distribution of healing particles in the matrix. The effect of mismatch in elastic and fracture properties between the healing particle and the matrix and the effect of particle/matrix interface properties on the crack path were examined quantitatively. Optimal configurations in terms of mechanical properties of the particles and the particle/matrix interface relative to the matrix material (fracture strength, toughness) to trigger the healing reaction were identified.