燃气热循环下7YSZ热障涂层的微结构演变与阻抗谱特征

在1250℃燃气热循环条件下,测试热障涂层抗冷热冲击性能,以模拟发动机叶片的启动升温与关闭降温循环过程。采用电化学阻抗谱测试和扫描电镜(SEM)系统研究热循环过程中热生长氧化物(TGO)生长与YSZ陶瓷层微结构演变。结果表明:随着热循环次数增加,热障涂层内TGO不断生长变厚,在中频阶段的阻抗谱响应越来越显著。YSZ陶瓷层内部经历了微裂纹的萌生与扩展两个阶段。经过100次热循环后的YSZ层表现出与喷涂态涂层相似的阻抗特征,表明高温下烧结会使YSZ层产生的微裂纹在短时间内愈合。但经过300次热循环后的YSZ层表现出与喷涂态完全不同的阻抗谱,并随热循环次数增加,YSZ颗粒间隙阻抗值不断增加,表明YSZ内层产生了不可愈合的微裂纹,是导致YSZ层最终失效的主要因素。

Microstructure Evolution and Impedance Spectroscopy Characterization of Thermal Barrier Coating Exposed to Gas Thermal-shock Environment

Gas thermal-shock experiment of thermal barrier coatings (TBCs)was carried out in air up to 1250℃ in order to simulate the thermal cycling process of the engine blades during the start heating and shut down cooling.The growth of thermal growth oxide (TGO)layer and microstructure evolu-tion of YSZ layer during thermal cycling process were investigated systematically by electrochemical impedance spectroscopy testing and SEM.The results show that the thickness of TGO layer increases when increasing the frequency of thermal cycling,and the impedance response of middle frequencies is more and more remarkable.Meanwhile,initiation and growth of micro-cracks occur in YSZ layer dur-ing the gas thermal-shock experiment.The corresponding impedance characterization of YSZ layer af-ter 100 cycles is similar to the as-sprayed sample,indicating that micro-cracks in short time could heal since the YSZ micro-cracks sinter at high temperature.But after 300 cycles,the impedance spectros-copy of YSZ layer is quite different to the as-sprayed sample,with the corresponding impedance of particle-gap of YSZ more and more remarkable with the increase of the thermal-shock times,indica-ting that non-healing micro-cracks form in the YSZ layer,which may be the main reason to induce the failure of YSZ layer.