Effect of NiTi Addition on the Hot Corrosion Resistance of YSZ TBC

The purpose of this research is to improve the quality and efficiency of Yttria-stabilised zirconia (YSZ) thermal barrier coating (TBC) in Na2SO4-V2O5environments through the addition of NiTi powder. For this purpose, YSZ coatings with and without 5 Wt.% NiTi powder were deposited by atmospheric plasma spray (APS) technique on a Ni-based superalloy (IN738LC) substrate as a top coat with a CoNiCrAlY bond coat. The hot corrosion resistance of the samples was investigated in a furnace by cyclic mode in Na2SO4-55 wt. % V2O5 salts. Each cycle consists of 4 h heating at 950°C. The results indicated that the molten salts at the working temperature can react with Yttria, the stabilizing compound of YSZ, and cause the transformation of tetragonal zirconia to monoclinic phase during cooling. This transformation results in a volumetric expansion which can lead to cracking and spallation of the surface layers of the thermal barrier coatings. Microstructural and phase studies of coatings before and after hot corrosion tests confirmed the better hot corrosion resistance of YSZ-5Wt.%NiTi composite coating compared to YSZ due to delay in crack propagation and the tetragonal phase transformation to the monoclinic