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

In this work, hot corrosion behavior of air plasma sprayed La 0.8 Ba 0.2 TiO 3-δ (LBT)-YSZ double-ceramic-layer thermal barrier coating exposed to Na 2 SO 4  + V 2 O 5 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 SO 3 gas, the corrosion products of porous layer were composed of Ba 2 V 2 O 7 , LaVO 4 , TiO 2 and BaSO 4 , while those of dense layer consisted of Ba 2 V 2 O 7 , LaVO 4 and TiO 2 . The specific mechanism by which the corrosion reaction occurred was proposed based on Lewis acid-base rule and thermodynamics.