In multilayer coatings, the bonding mechanisms between the different layers determine the cohesive strength of the coatings, which in turn to a large extent controls the mechanical properties of coatings under different loading conditions. In this study, the interfacial bonding state and adhesive strength of a plasma-sprayed single-layer coating (Al2O3), a double-layer coating (Al2O3/BaTiO3), and a three-layer coating (Al2O3/BaTiO3/Al2O3-40 wt.% TiO2) were investigated, as well as their phase composition and microstructure. Scanning electron microscopy observation showed that the microstructure of the three ceramic coatings was relatively dense with a good interface bonding state. However, micro-cracks were observed in the smooth region of the double-layer coating interface, while pores were observed at the BaTiO3/Al2O3-40 wt.% TiO2 interface in the three-layer coating. Transmission electron microscopy observation revealed that element diffusion occurred at the interface. The diffusion depth at the Al2O3/BaTiO3 and BaTiO3/Al2O3-40 wt.% TiO2 interfaces reached 12 nm and 10 nm, respectively. Therefore, both mechanical interlocking (the dominant mechanism) and limited chemical diffusion contributed to interface adhesion in the multilayer coatings. The adhesion strengths of the double-layer, single-layer, and three-layer coatings were 40.1, 21.8, and 15.3 MPa, respectively. The latter exhibited the lowest adhesion strength mainly because of the relatively weak Al2O3/BaTiO3 interface.

中文翻译：

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等离子喷涂多层陶瓷涂层（Al2O3/BaTiO3/Al2O3-40 wt.% TiO2）的界面微观结构和结合性能

在多层涂层中，不同层之间的结合机制决定了涂层的内聚强度，进而在很大程度上控制着不同载荷条件下涂层的机械性能。在这项研究中，等离子喷涂单层涂层 (Al2O3)、双层涂层 (Al2O3/BaTiO3) 和三层涂层 (Al2O3/BaTiO3/Al2O3-40 wt .% TiO2)，以及它们的相组成和微观结构。扫描电镜观察表明，三种陶瓷涂层的微观结构相对致密，界面结合状态良好。然而，在双层涂层界面的光滑区域观察到微裂纹，而在 BaTiO3/Al2O3-40 wt 处观察到孔隙。% TiO2 界面在三层涂层中。透射电镜观察表明在界面处发生元素扩散。Al2O3/BaTiO3 和 BaTiO3/Al2O3-40 wt.% TiO2 界面的扩散深度分别达到 12 nm 和 10 nm。因此，机械互锁（主要机制）和有限的化学扩散都有助于多层涂层中的界面粘附。双层、单层和三层涂层的附着强度分别为40.1、21.8和15.3 MPa。后者的粘附强度最低，主要是因为 Al2O3/BaTiO3 界面相对较弱。% TiO2 界面分别达到 12 nm 和 10 nm。因此，机械互锁（主要机制）和有限的化学扩散都有助于多层涂层中的界面粘附。双层、单层和三层涂层的附着强度分别为40.1、21.8和15.3 MPa。后者的粘附强度最低，主要是因为 Al2O3/BaTiO3 界面相对较弱。% TiO2 界面分别达到 12 nm 和 10 nm。因此，机械互锁（主要机制）和有限的化学扩散都有助于多层涂层中的界面粘附。双层、单层和三层涂层的附着强度分别为40.1、21.8和15.3 MPa。后者的粘附强度最低，主要是因为 Al2O3/BaTiO3 界面相对较弱。