基于声发射技术的热障涂层拉伸失效模式研究

Research on Crack Failure Modes of Thermal Barrier Coatings Based on Acoustic Emission Technique

热障涂层是一种典型的脆性、非均质、多层结构的材料。服役过程中受热-力载荷的作用,将会导致涂层过早的剥落失效,其主要的失效形式为陶瓷层开裂和界面剥落失效。热障涂层的失效主要是微裂纹萌生、扩展及连通导致。利用声发射技术结合微观形貌观察,研究了拉伸载荷下热障涂层的失效过程,并识别热障涂层裂纹损伤模式。根据不同载荷下的微观形貌观察,研究拉伸载荷下热障涂层的失效过程;利用声发射特征参数分析法(如声发射事件数、幅值),将热障涂层的失效过程分为几个不同阶段,并结合形貌观察,建立声发射特征参数与裂纹损伤失效信息之间的联系;利用快速傅里叶变换(Fast Fourier transform,FFT)识别热障涂层的损伤模式。结果表明:热障涂层拉伸失效过程为裂纹首先在陶瓷层表面萌生,随后向陶瓷层/粘结层的界面处扩展,到达界面后,裂纹将沿着界面生长与扩展,最终导致热障涂层分层剥落;将热障涂层的失效过程分为四个阶段;频谱分析结果表明基体频率成分大约在0.020MHz,表面裂纹的频率成分在0.20~0.25MHz,界面裂纹的频率成分在0.15~0.20MHz。

Thermal barrier coatings(TBCs)is a typical brittle,heterogeneous,multilayer structure material.The heat-loading effect during service will lead to premature peeling failure of the coating.The main failure modes are ceramic coating cracking and interface spalling failure.The failure of TBCs is mainly the accumulation of micro-cracks,the expansion and the accumulation of connectivity results.The failure process of TBCs under tensile load is studied by using acoustic emission(AE)technique combined with microscopic morphology observation,and the crack damage mode of TBCs is identified.According to the microscopic morphology observation under different loads,the failure process of the TBCs under tensile load is studied.The TBCs is applied by the AE characteristic parameter analysis method(such as AE events,AE amplitude).The failure process is divided into several stages,and the relationship between AE characteristic parameters and crack damage failure information is established based on the observation of morphology.The TBCs failure modes is identified by fast Fourier transform(FFT).The results show that the tensile failure process of the TBCs is that the crack firstly sprouts on the surface of the ceramic coating and then spreads to the interface of the ceramic coating/bond coating.After reaching the interface,the crack will grow and propagate along the interface,eventually leading to ceramic coating is peeled off.The failure process of the TBCs is divided into four steps;the spectrum analysis shows that the frequency component of the substrate is around 0.020 MHz,the frequency component of the surface crack is 0.20-0.25 MHz,and the interface crack is 0.15-0.20 MHz.