Characterization of hot corrosion performance and TGO behavior in APS-BC and HVOF-BC thermal barrier coatings

Hot corrosion and thermally grown oxide (TGO) formation are destructive factors in thermal barrier coatings (TBCs) that lead to coating failure under operational conditions. In the present study, the hot corrosion behavior and TGO evolution for TBCs whose Bond coat by deposited by atmospheric plasma spraying (APS) and high velocity oxygen fuel (HVOF) thermal spray methods were evaluated. Both types of coatings were subjected to cyclic hot corrosion testing at a temperature of 1100°C in the presence of molten salts of Na2SO4 and V2O5 under identical conditions. Subsequently, their microstructures were examined using scanning electron microscopy (SEM) and X-ray diffraction (XRD) images. Additionally, changes in TGO thickness were measured across different cycles using Image J software and SEM images. The results indicate that TBCs deposited using the HVOF method for the bond coat exhibit better performance compared to those deposited using the APS method. The results show that a phase change from tetragonal to monoclinic has occurred for zirconia with the penetration of corrosive salt melt and its reaction with the YSZ layer, and also with the depletion of yttria from the coating structure, YVO4 reaction products have been formed for TBCs. The endurance of hot corrosion cycle of TBCs and the growth behavior of TGO show that the coatings whose interface layer is applied by the HVOF method show better performance than the APS method.