燃气轮机热障涂层劣化的阻抗研究

Impedance Study of Thermal Barrier Coating Deterioration in Gas Turbines

热障涂层(TBC)的一些固有特性(如多孔性、较薄的厚度、相当高的电阻率)使传统常温无损检测技术存在一定应用局限,为此,提出了一种在高温环境下利用阻抗谱法监测热障涂层中氧化物生长的方法,基于阻抗谱测试原理,通过分析交流阻抗在不同频率域下的响应以及相角信息获得热障涂层中氧化物的生长信息,并结合SEM微观形貌,构建预测模型。结果表明:在1000℃高温氧化不同时间后,发现在陶瓷层和粘接层之间形成了一条致密的深色热生长氧化物(TGO)层,其厚度随着氧化时间的延长而增加,并且呈现出非线性关系。随着氧化时间的延长,TGO层的成分从氧化初期的Al_(2)O_(3)向Al_(2)O_(3)(主要)、Cr_(2)O_(3)、CoO、NiO的混合氧化物过渡。通过建立适当的电路模型拟合阻抗谱数据,建立了TGO层电阻与氧化时间的关系,从而证实了阻抗谱法在热障涂层高温退化过程中进行无损检测的可行性。

Some inherent characteristics of thermal barrier coatings(TBC),such as porosity,thinner thickness and relatively high electrical resistivity,limit the application of traditional room temperature nondestructive testing techniques.Therefore,a method for monitoring oxide growth in thermal barrier coatings using impedance spectroscopy in hightemperature environments was proposed.Based on the principle of impedance spectroscopy test,the growth information of oxides in thermal barrier coatings was obtained by analyzing the response of AC impedance in different frequency domains and phase angle information,and the prediction model was constructed based on the micromorphology of SEM.Results showed that after oxidizing at 1000℃for different times,a dense dark thermally grown oxide(TGO)layer was formed between the ceramic layer and the adhesive layer,and its thickness increased with the prolongation of oxidation time,exhibiting a nonlinear relationship.As the oxidation time prolonged,the composition of the TGO layer transitions from Al_(2)O_(3)in the early stage of oxidation to a mixed oxide of Al2O3(mainly),Cr_(2)O_(3),CoO and NiO.Furthermore,the relationship between the resistance of the TGO layer and the oxidation time was constructed by establishing an appropriate circuit model to fit the impedance spectrum data,which confirmed the feasibility of nondestructive testing using impedance testing technology in the process of hightemperature degradation of thermal barrier coatings.