Evolution of hot corrosion resistance of conventional CSZ and MoSi2 self-healing thermal barrier coatings in Na2SO4+V2O5 at 950 °C

ZrO2-based hot corrosion-resistant thermal barrier coatings (TBCs) with MoSi2+Al2O3 have gained increasing attention. In this research, a novel dual-layer TBC (CSZ: ZrO2-25 wt% CeO2-2.5 wt% Y2O3/MAC: MoSi2 + Al2O3 + CSZ) was developed, and its hot corrosion was compared to a single-layer CSZ. The atmospheric plasma spray (APS) process was utilized to apply CSZ/MAC and CSZ TBCs on NiCrAlY, as a bond coat to nickel-based superalloy (IN738LC). Different investigations, including hot corrosion test, field emission scanning electron microscopy (FESEM/EDS), and X-ray diffraction (XRD) analyses, were used to reveal why the MAC overlayer improves the CSZ hot corrosion behavior. A medium of Na2SO4-55 wt% V2O5 was used to analyze the hot corrosion; a temperature of 950 °C for 2 h was considered in every single cycle. The results exposed that there is a big difference between the hot corrosion resistance of the dual-layer CSZ/MAC TBC in comparison with the single-layer CSZ. Based on the FESEM analysis, this can be related to the very low diffusion of Na2SO4-55 wt% V2O5 into the dual-layer TBC where the infiltration of aggressive molten salt was diminished. According to the XRD results, two reasons are leading to the degradation of the aforementioned TBCs: (i) the tetragonal to the monoclinic transformation of ZrO2 and (ii) the formation of hot corrosion products, i.e., CeVO4 and YVO4 crystals.