Microstructural evolution and hot corrosion behavior of La0.8Ba0.2TiO3–δ-YSZ double-layer thermal barrier coatings in Na2SO4 + V2O5 molten salt at 900 °C

Abstract In this work, hot corrosion behavior of air plasma sprayed La0.8Ba0.2TiO3-δ (LBT)-YSZ double-ceramic-layer thermal barrier coating exposed to Na2SO4 + V2O5 molten salt at 900 °C for 20 h was investigated. The phase characterization and microstructural evolution analysis of the coating was carried out after the hot corrosion test by using X-ray diffraction (XRD), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). The results showed that the LBT-YSZ coating possessed excellent hot corrosion resistance compared with the conventional pure YSZ coating. The conventional pure YSZ coating was completely destroyed after the 10 h test due to the volume change resulting from the adverse phase transition. However, the situation for the LBT-YSZ coatings is completely opposite. The LBT-YSZ coating could prevent the YSZ interlayer underlying the LBT overlayer from densification for at least 20 h. In the LBT overlayer, the double-reaction-layer composed of under dense layer and upper porous layer was formed. In particular, the continuous dense layers with a thickness of ~100 μm formed after 10 h, effectively arresting further penetration of the molten salt. In addition, affected by the diffusion extent of SO3 gas, the corrosion products of porous layer were composed of Ba2V2O7, LaVO4, TiO2 and BaSO4, while those of dense layer consisted of Ba2V2O7, LaVO4 and TiO2. The specific mechanism by which the corrosion reaction occurred was proposed based on Lewis acid-base rule and thermodynamics.