The effect of porosity on the hot corrosion failure of thermal barrier coatings

It has been found that the use of low-grade fuels in land-based turbines results in the hot corrosion (Type-I) degradation of turbine blades in Saudi Arabia. Due to the diffusion of a molten salt, V₂O₅, into the top coat of thermal barrier coatings, volumetric expansion of the coating occurs as a result of the tetragonal-to-monoclinic transformation of zirconia. The top coat material is usually made porous due to the need for higher thermal resistance in the coatings. In the present study, a phase field model that estimates the kinetics of microstructure evolution during the corrosion process is estimated at 900 °C. The transformation-induced stresses are predicted by coupling the phase transformation with elasticity. The governing equations are implemented numerically using the finite element method. The effect of pore size, shape, orientation, and dispersion is also investigated. The result shows that very high compressive stresses are developed within the coating cross-section, which eventually causes the spallation failure of the coating.