Effect of pre-existing microcrack on the cyclic displacement instability in thermal barrier coating systems

The displacement instability of the thermally grown oxide (TGO) layer in thermal barrier coating systems is a critical factor inducing the failure of the system by causing large scale delamination and spallation. In this paper, the effect of pre-existing microcracks within the ceramic top-coat (TC) on the cyclic displacement instability under thermal cycling is investigated by a finite element analysis. Stress and the interface morphology are obtained after thermal cycling when the microcracks pre-exist within the TC. The influence of various parameters including crack location, crack length and crack direction on the interface morphology are discussed in detail. It is demonstrated that the existing of microcracks within TC can aggravate the displacement instability and affect the stress state in TC significantly. However, when the crack is perpendicular to the flat interface, the aggravation of it on the instability is weakest.