CMAS对热障涂层界面裂纹和残余应力的影响

Effect of CMAS on Interfacial Crack and Residual Stress of Thermal Barrier Coatings

摘要:

随着航空发动机涡轮叶片工作温度的提升,使得一种主要由CaO,MgO,Al₂O₃和SiO₂组成的玻璃态物质(CMAS)对热障涂层的危害越来越严重,从而对热障涂层的性能和耐久性有了更高的要求。本文以电子束物理气相沉积热障涂层为研究对象,利用有限元方法研究了CMAS的渗入对界面裂纹扩展及CMAS对陶瓷层(TC)内部残余应力的影响规律。采用波长固定、振幅变化的正弦曲线表示不同粗糙度的涂层界面,同时考虑了CMAS的弹性模量变化的影响及不同界面形貌与CMAS之间的相互作用。结果表明：CMAS弹性模量的增加对界面裂纹具有抑制作用,并且TGO幅值和厚度越小,抑制作用越明显。CMAS弹性模量对TC层最大残余应力S₂₂的影响存在临界点,在临界点之前,CMAS弹性模量的变化对TC层最大残余应力的影响较大,随着CMAS弹性模量的增加,TC层最大残余应力大幅度减小；在临界点之后,TC层最大残余应力基本不受CMAS弹性模量变化的影响。这些结果对电子束物理气相沉积喷涂的热障涂层失效机理的研究具有重要意义,可以为热障涂层界面的优化提供指导。

Abstract:

With the increase of operating temperature in aero-engine turbine blades, a vitreousSmaterial (CMAS) consisting mainly of CaO, MgO, Al₂O₃ and SiO₂ were increasingly harmful to the thermal barrier coatings deposited on the blade. Therefore, the performance and durability of thermal barrier coatings should meet higher requirements. In this study, the influence of CMAS penetration on interfacial crack propagation and residual stress in the electron beam physical vapor deposition thermal barrier coatings was investigated by using finite element method. The sinusoidal curves with fixed wavelength and varying amplitude were used to model the interfaces with different roughness. At the same time, the effect of the elastic modulus of CMAS and the interaction between interface morphology and CMAS were taken into account. The results show that the increase of CMAS elastic modulus has an inhibitory effect on interfacial cracks, and the smaller the TGO amplitude and thickness, the more obvious the inhibition. There is a critical point for the effect of CMAS elastic modulus on the maximum residual stress S₂₂ in top coat (TC) layer. Before the critical point, the change of CMAS elastic modulus has a greater influence on the maximum residual stress of TC layer, and with the increase of elastic modulus of CMAS, the maximum residual stress of TC layer decreases greatly; after the critical point, the maximum residual stress of TC layer is hardly affected by the change of elastic modulus of CMAS. These results are of great significance for the study of the failure mechanism of thermal barrier coatings by electron beam physical vapor deposition, it can provide guidance for the optimization of the interface of thermal barrier coatings.