Thermally sprayed ceramic coatings often demand highly performance against high gas temperature, corrosion and wear resistant in the severe environment with coupled conditions including high temperature and complex stresses. However, the complexity of the microstructure of as-sprayed coatings which are significantly affected by defects give arise to the premature coatings failure and consequently reduce their service lifetime as in the case of thermal barrier coatings. This work aims to investigate the mechanisms of failure in air plasma-sprayed alumina coatings deposited on NiCrAlY bond-coat (BC) which in turn was deposited on a stainless-steel substrate. One of the most important failure mechanisms is related to the coating delamination at the alumina/BC interface. A discrete element method (DEM)-based model is proposed for the simulation of the induced stresses and delamination in a thermal barrier coating under mixed mode I and II. The emphasis is devoted on the effect of the mismatch in the coefficient of thermal expansion between the alumina coating and the BC associated with crack propagation within the material. The microstructure taking into account defects namely pores and cracks were built with the help of the image analysis using SEM images of the polished cross-section coatings. The effect of temperature-dependent material properties on the failure mechanisms is considered as well.