The Hot Corrosion Behavior In Vanadate Environment And Thermal Cycling Behaviors Of Ytz And 2gytz For Thermal Barrier Coating Applications

A preliminary examination was carried out for hot corrosion resistance to V2O5 and thermal cycling behaviors of two alternative materials: zirconia co-doped with 16 mol% YO1.5 + 16 mol% TaO2.5 (YTZ) and zirconia co-doped with 14 mol% YO1.5+ 2 mol% GdO1.5 + 16 mol% TaO2.5 (2GYTZ). The compositions and microstructures of the samples were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). Results showed ZrV2O7 and YVO4/GdVO4 were the main reaction products at 750 degrees C and 850 degrees C for 2 h, while YVO4 and m-ZrO2 were detected as the main corrosion products at 850 degrees C for 10 h or rising temperature to 950 degrees C. With the depletion of V2O5, ZrV2O7 disappeared and decomposed into m-ZrO2 and V2O5. The hot corrosion mechanisms are similar for YTZ and 2GYTZ ceramics. However, the amount of m-ZrO2 in the 2GYTZ was much more than that in the YTZ at the same corrosion conditions. The weaker bonds due to partial substitution of Y3+ with larger size of Gd3+ and the size misfit between Gd3+ and Zr4+ resulted in decreasing the anti-corrosion capability of 2GYTZ ceramic. The tetragonal phase was very stable for YTZ and 2GYTZ coatings during high temperature heat treatment. The thermal durability of the YTZ and 2GYTZ TBCs can be significantly improved by using the YSZ buffer layer. While the cycling lifetimes for 2GYTZ coating was much shorter than that of YTZ coating whether designed for single-ceramic-layer structure or double-ceramic-layer structure. Failure of the 2GYTZ coating mainly resulted from the thermal expansion mismatch stress, concentrated thermal stress introduced by the severe sintering and low fracture toughness.