Evolution of mechanical properties of thermal barrier coatings subjected to thermal exposure by instrumented indentation testing

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• 作者：C.C. Li ; T. Wang ; X.J. Liu ; Z.H. Zheng ; Q. Li ; ^{qli@fzu.edu.cn" class="auth_mail" title="E-mail the corresponding author}
• 关键词：Thermal barrier coatings ; Instrumented indentation testing ; Young's modulus ; Fracture toughness ; Residual stress
• 刊名：Ceramics International
• 出版年：2016
• 出版时间：June 2016
• 年：2016
• 卷：42
• 期：8
• 页码：10242-10250
• 全文大小：5351 K

文摘

The evolution of mechanical properties, namely Young's modulus, hardness, fracture toughness and residual stresses of air plasma-sprayed 8 wt% Y₂O₃-stabilized ZrO₂ thermal barrier coatings (TBCs) subjected to thermal exposure at 1100 °C, was evaluated based on an instrumented indentation testing system. It is found that the variation of Young's modulus and hardness with the increase of thermal exposure time can be divided into two regimes: a rapid initial increase, followed by a more gradual increase. Conversely, fracture toughness decreased from the initial value of 1.48–1.05 MPa m^1/2 after 350 h, indicating the degradation of TBCs. And the corresponding residual stress in top coat varied from the deposition stress of −29.9 MPa to a maximum of −56.0 MPa within 100 h, and then decreased to −15.0 MPa after 350 h. The evolution of mechanical properties was correlated with microstructural changes in the top coat. Microstructure observations revealed that thermally grown oxide (TGO) formed at the interface between ceramic coat and bond coat, and was predominantly comprised of Al₂O₃ layer, along with some oxide clusters of (Cr, Al)₂O₃, (Co, Ni)(Cr, Al)₂O₄ and NiO. The growth of TGO followed a parabolic law with a rate constant of 0.13236 μm²/h. After 350 h, porosity in 8YSZ coatings was reduced from 8.39% to 5.79% as a result of activated diffusion-controlled sintering.