四点弯曲条件下热障涂层断裂模式的声发射表征

Characterization of Fracture Modes for Thermal Barrier Coatings by Acoustic Emission Under Four-point Bending

采用声发射技术实时监测喷涂态8%Y2O3稳定的ZrO2(8YSZ)在四点弯曲载荷下的损伤断裂行为。采用特征参数分析、聚类分析和小波包变换分析声发射信号结合涂层的微观形貌和应力状态,从而推测出热障涂层系统的失效形式。结果表明:内弯和外弯两种加载模式下,均各有4种失效行为。宏观断裂对应的剥落信号无明显频带,而基底变形、表面垂直裂纹、张开型界面裂纹和剪切型界面裂纹信号对应的主频带可清晰区分为:0~156.25 kHz、156.25~234.375 kHz、312.625~390.625 kHz和390.625~468.75 kHz。热障涂层在外弯载荷下,表面垂直裂纹不断出现,随后扩展到粘结层-陶瓷层界面处并转化为张开型界面裂纹;而在内弯载荷下,则在粘结层-陶瓷层界面附近产生剪切型界面裂纹,仅出现少量的表面垂直裂纹。两种界面裂纹均会引起热障涂层的宏观裂纹和剥落。

The fracture behavior of air plasma-sprayed 8% yttria-stabilized zirconia(8 YSZ) thermal barrier coatings was characterized by analyzing acoustic emission(AE) signals during a four-point bending(4 PB) experiment. Characteristic parameters analysis, cluster and wavelet packet transform combining with micromorphology and stress analysis of TBCs were used to obtain the failure types of TBCs. The results show that there are both four failure types under the two loading models.Macroscopic fracture and spallation signals have no obvious frequency band. However, the dominant frequency bands of deformation of substrate, surface vertical cracks, opening interface cracks and sliding interface cracks signals can be distinguished clearly at 0-156.25 kHz, 156.25-234.375 kHz, 312.625-390.625 kHz, and 390.625-468.75 kHz, respectively.As for the outer bending, surface vertical cracks appear continuously and then transform into opening interface cracks at the interface of bond coat and ceramics top coat. As for the inner bending, however, sliding interface cracks appear near the interface of bond coat and ceramics top coat, presenting only small number of surface vertical cracks. Both kinds of interface cracks can cause macroscopic cracks and spallation of thermal barrier coatings.