Hot corrosion performance and electrochemical study of CoNiCrAlY/YSZ/YSZ-La2O3 multilayer thermal barrier coatings in the presence of molten salt

One of the effective methods to prevent materials degradation at high temperatures is thermal barrier coating (TBC). In this research, a multilayer (CoNiCrAlY/YSZ/YSZ-10 wt%La2O3) TBC system was deposited on the IN738 superalloy using the high-velocity oxy-fuel (HVOF) and atmospheric plasma spray (APS) techniques. Hot corrosion behaviors were studied in the presence of Na2SO4-20 wt% V2O5 molten salt at 880 °C for 400 h. Hot corrosion kinetics were determined by measuring the thermal grown oxide (TGO) thickness of the specimens at regular intervals. Afterward, the electrochemical behavior of the coated and hot corroded samples was investigated by electrochemical polarization method. Phase identification, TGO, surface morphologies and elemental distribution of the coated samples were also studied during hot corrosion by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The results showed that the multilayer YSZ/YSZ-10 wt%La2O3 ceramic top coat led to a reduction in the penetration of corrosive components into the coating; thereby, delaying the formation of destructive YVO4 phases and postponing the monoclinic-ZrO2 phase transformation.