The effect of V₂O₅ melt infiltration on the failure of thermal barrier coatings

The use of low quality fuel in land based driven turbine in Saudi Arabia usually results in hot corrosion attack (Type 1) due to the penetration of V₂O₅ into the existing micro pores and cracks on the top coat of thermal barrier coatings (TBCs). As a result of dissolution-precipitation reaction, 4-5% volumetric expansion of the coating occurs due to the tetragonal-to-monoclinic (destabilization) transformation of Zirconia. In the current work, a Phase Field Model that estimates the kinetics of micro-structural evolution during the diffusional tetragonal-to-monoclinic phase transformation in the Melt Infiltrated Reaction Zone of the top coat at 900ºC is developed. The model is sequentially-coupled with constitutive model in order to determine the resulting stress field developed in the top coat. The results show that localized stresses are developed due to the Zirconia-destabilization transformation, and the stresses are found to be higher at the corners and curvatures formed by inter-lamella connection of the micro-pores and micro-cracks.