热、力耦合作用下热障涂层的失效机制

Failure process of thermal barrier coatings under thermal and mechanical loading

针对热障涂层服役环境中热物理化学环境与机械载荷耦合作用的特点 ,采用交流阻抗谱法与声发射法对热障涂层在恒定外载荷 (高温蠕变 )以及交变载荷 (高温低周疲劳 )作用下的失效过程进行了考察分析 ,研究发现 ,交流阻抗谱中低频段阻抗值的变化可以有效地反映热障涂层热氧化层内横向裂纹的萌生及扩展 ;有无外机械载荷作用下热障涂层的热循环失效的模式截然不同 ,在高温蠕变条件下 ,热障涂层的裂纹并不产生在热氧化层内 ,而是产生在热氧化层与柱状晶之间的等轴晶区 ;而在高温低周疲劳条件下裂纹是在粘结层与高温合金基体的扩散层处 .

High temperature behaviors of thermal barrier coating (TBC) prepared by electron beam physical vapor deposition were investigated under mechanical loading. The change in microstructure and the formation of microcrack were studied by means of impedance spectroscopy (IS) and acoustic emission (AE) methods. The impedance value is very sensitive to the microcrack in the thermally grown oxidation (TGO) layer in the low frequency range. The formation and propagation of microcracks can be monitored by comparing the change of impedance value combined with acoustic emission. It has been found that the failure mode was quite different for TBC samples tested with or without mechanical loading. When TBCs were tested during high temperature creep, the microcracks formed in the equiaxial crystalline area between TGO layer and columnar structure of YSZ top coat, instead of in TGO layer during thermal cyclic testing without mechanical loading. However, cracks initialized in the diffusion layer between substrate and bond coat when TBCs were tested with low cycle fatigue at high temperature.