交流阻抗谱法检测热障涂层中热致氧化层的厚度

Development of measuring method for the thickness of TBC oxide scale by AC impedance spectroscopy

摘要:

热障涂层材料(TBCs)的应用提高了燃气轮机的工作温度并延长了使用寿命。热障涂层主要由超高温合金基底,金属连接层,热致氧化层(TGO)以及陶瓷层(YSZ)组成。涂层服役期间在金属连接层和陶瓷层界面生成的热致氧化层是导致涂层失效剥落的主要原因。涂层失效将导致叶片暴露于高温气体中带来严重后果,因此,TBCs中氧化层厚度的无损检测对于TBCs的寿命预测至关重要。本实验采用交流阻抗谱法对1000℃高温氧化的TBCs样品进行分析。实验结果显示氧化时间100h后,致密氧化物层形成,其厚度随氧化进程增加且成分也由氧化铝向混合氧化物转变。通过等效电路模拟对交流阻抗测试结果进行分析,得到了TGO层电容与厚度倒数的正比例关系,实现了对TGO层厚度的检测。

Abstract:

In gas turbine, thermal barrier coating system (TBCs) is usually used to increase the operation temperature and protect the turbine components like blades and vanes. A TBC system consists typically of a superalloy substrate, a metallic bond coat, the thermally grown oxide and a heat-insulating ceramic top coat. The thermally grown oxide(TGO) grows at bond coat / top coat interface is a dominate factor leading to the failure of TBCs, thus determining the thickness of TGO non-destructively is essential for monitoring the performance of TBCs and predicting the lifetime of TBCs in service. Our work here uses impedance spectroscopy to analysis the TBCs samples with 0.1mm YSZ top coat after oxidation at 1000℃. The SEM and EDS result shows that a continuous alumina layer formed after 100h oxidation and the thickness increases with increasing oxidation time, meanwhile, the chemical composition changes from alumina to mixed oxides. The oxidation kinetics demonstrates that the oxidation procedure is controlled by diffusion. By equivalent circuit model analysis, we obtain the direct proportional relationship between TGO thickness and capacitance, so the TGO thickness can be measured.