8YSZ双层热障涂层缺陷演变与微裂纹水浸超声宏观检测

采用PASCAN-64型水浸超声设备并配合扫描电镜对8wt %Y₂O₃-ZrO₂(8YSZ)双层热障涂层热震过程中内部组织结构演变进行了检测。结果表明, 当超声波从垂直陶瓷层方向入射至粘结层反射所获得的回波信号影像主要反映了陶瓷层组织结构演变, 从垂直基底方向入射至粘接层/陶瓷层界面处反射所获得的回波信号影像主要反映了热生长氧化物层组织结构演变, 从垂直陶瓷层方向透射整个试片所获得的回波信号影像综合反映了整个涂层组织结构演变。当陶瓷层中均匀分布着孔隙率<11%、最大横向尺寸<50 μm的孔隙以及热生长氧化物层主要为致密的α-Al₂O₃时, 回波信号的幅值dB<0, 反映在影像中的信号分布均匀, 表明涂层处于良好状态。当陶瓷层中均匀分布着孔隙率>44%、最大横向尺寸>100 μm的孔隙以及热生长氧化物层主要为具有稀疏结构且厚度>5.2 μm的Cr、Co氧化物时, 回波信号的幅值dB>0的区域连接成片, 则预示着涂层即将失效或已失效。可见, 水浸超声技术能够较准确地反映热障涂层内部组织结构演变, 是一种较好的热障涂层内部缺陷的无损检测方法。

Defect Evolution and Microcracks of 8YSZ Double-layer Thermal Barrier Coatings by Water Immersion Ultrasound Macroscopic Detection

Evolution of internal structure of 8wt% Y₂O₃-ZrO₂ (8YSZ) thermal barrier coatings during thermal shock was detected by PASCAN-64 water immersion ultrasonic equipment and scanning electron microscopy. The results show that echo signal obtained by reflection of the ultrasonic wave which is incident from vertical top coating to the bond coating mainly reflect evolution of the structure of top coating, and the echo signal obtained by reflection of ultrasonic wave which is incident from vertical basement to interface between bond coating and top coating mainly reflect evolution of structure of TGO layer, while the microstructure evolution of the whole coating is reflected by transimission signal obtained by transimission of the ultrasonic wave from vertical top coating to substrate. When porosity of the coating top coating is less than 11%, the maximum transverse size of the coating top coating is less than 50 μm and the TGO layer is mainly dense α-Al₂O₃, the amplitude of the echo signal dB is less than 0. Uniform distribution of signals can be observed from corresponding images, indicating that the coating is in good condition. When the porosity of top coating is more than 44%, the maximum transverse size is more than 100 μm, and the TGO layer is mainly composed of oxides of Cr and Co with sparse structure and thickness of more than 5.2 μm. From the image, the area whose amplitude dB is greater than 0 is connected into pieces, which indicates the imminent failure of the coating. Water immersion ultrasound technology can accurately reflect the evolution of internal structure of thermal barrier coatings, and it is a good nondestructive testing method for internal defects of thermal barrier coatings.