Hot corrosion behavior of rare earth zirconates and yttria partially stabilized zirconia thermal barrier coatings

Thermal barrier coatings (TBCs) of yttria stabilized zirconia (YSZ) and rare earth zirconates of La2Zr2O7 (LZ) and La2(Zr0.7Ce0.3)2O7 (LZ7C3) were deposited by electron beam-physical vapor deposition (EB-PVD). The present study compares the hot corrosion performances of YSZ, LZ and LZ7C3 coatings in the presence of molten mixture of Na2SO4 + V2O5 at 1173 K for 100 h. X-ray diffraction (XRD) indicates that the reaction between NaVO3 and Y2O3 produces YVO4, leaching Y2O3 from YSZ and causing the progressive destabilization transformation from t′ to m-ZrO2. The excess La2O3 in the as-deposited LZ coating can aggravate the degradation of LZ coating by both NaVO3 and Na2SO4, resulting in very rapid disintegration of the coating. In contrast, the LZ7C3 coating is still perfect without significant degradation, which exhibits the best performance for hot corrosion resistance among all the coatings. Phase transformation and chemical interaction are the primarily corrosive mechanisms for deterioration of YSZ and LZ coatings.