Force transmission and its effect on structural changes in plasma-sprayed lamellar ceramic coatings

In this study, thermal mismatch strain-induced structural changes in plasma-sprayed lamellar ceramic coatings upon heating were investigated. Experimental results showed that the main structural change is the propagation of inter- and intra-splat cracks along their tips. Correspondingly, significant changes in properties were observed. A lamellar model with connected inter- and intra-splat cracks was developed. The modeling results suggested that shear stress would be primarily concentrated at the interface between two layers, accounting for the propagation of the inter-splat cracks. Subsequently, the stress was transmitted through the residual bonding areas into the upper layer, and thus a tensile effect was generated inside the splat segment. This can be responsible for the propagation of the intra-splat cracks. In addition, dependence of the crack propagation behavior on the structural parameters is discussed. These microscopic structural changes may provide fundamental understanding on the global structural evolution and failure mechanism of coating/substrate systems during service conditions.