In this study, a La 0.8 Ba 0.2 TiO 3− δ (LBT) upper layer was deposited on an yttria-stabilized zirconia (YSZ) thermal barrier coating (TBC) through atmospheric plasma spraying . The thermal cycling behaviors of the YSZ single-ceramic-layer and LBT–YSZ double-ceramic-layer coatings at 1000 °C were investigated through a water quenching method. Moreover, phases, microstructural evolution , and elemental distributions were studied through by X-ray diffraction and scanning electron microscopy–energy-dispersive X-ray spectroscopy. The results showed that the thermal cycling lifetime of the LBT–YSZ coating was 27% higher than that of conventional YSZ coating. The conventional YSZ coating failed after 251 cycles because of the joining of the continuous horizontal and vertical cracks caused by the formation of thermal growth oxides and the bending effect of the single-ceramic-layer structure. The thermal cycling behavior of the LBT–YSZ coating was different from that of the YSZ coating at the edge and center. Although the former was similar to the failure behavior of the YSZ coating, the cracks in the vertical direction were deflected as a result of the bending effect of the double-ceramic-layer structure during quenching. This deflection led to the formation of slope cracks with longer propagation paths and slope spallation zones. The latter showed small-debris spallation on top of the LBT upper layer due to the lower fracture toughness of the LBT, which protected the central coating from the structural damage of the ceramic coating . These two behaviors would either release the thermal stress or increase the crack-propagation energy requirement in the ceramic coating, consequently improving the thermal cycling lifetime of the LBT–YSZ coating. In summary, depositing an LBT upper layer could potentially improve the thermal cycling lifetimes of TBCs.
Yongchao Fang,Xiufang Cui,Guo Jin,Erbao Liu,Dan Zhang,Xin Wen,Qingbo Mi
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.
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