热障涂层系统的热梯度机械疲劳应力分析

基于IN738高温合金基体上涂覆的热障涂层系统(Thermal barrier coating system,TBCs),分析热循环和热梯度机械疲劳加载条件下涂层的应力分布及演变。通过有限元分析研究了热生长氧化层(Thermally growth oxidation,TGO)的应力分布,以预测不同载荷作用下TBCs的失效行为。结果可知,在热循环的基础上施加应变载荷会造成TGO应力性质及大小的改变。只施加温度载荷,在加热过程中TGO/粘结层(Bond coat,BC)界面波峰位置会承受轴向较大的拉伸应力,裂纹多会在此处萌生,且以层间开裂的方式失效。而在温度与机械载荷的共同作用下,冷却过程中会承受较大的拉伸应力,显著增大的轴向应力与径向应力共同作用,使垂直于TGO/BC界面的裂纹沿着界面方向扩展,从而造成陶瓷层(Top coat,TC)剥落。进一步对比分析了同相和反相加载时的应力分布,结果表明反相加载时一次循环周期内会产生拉伸平均应力,更易发生TBCs的失效。

Analysis on Stress Distribution of Thermal Barrier Coating System with Thermal Gradient Mechanical Fatigue

The thermal barrier coatings systems (TBCs) were deposited on the IN738 nickel-based superalloy substrate, and the stress distribution and evolution under the thermal gradient cyclic loading and the thermal gradient mechanical fatigue were evaluated for the TBCs respectively. The stress distribution at the thermally growth oxidation (TGO) was analyzed by the finite element analysis method to predict the failure behavior of the TBCs under different loading conditions. The results show that the peak region of the TGO is subject to the major axial tensile stress during the heating process under the thermal cyclic loading. The fatigue crack started from the peak regions and TBCs fails with the delamination between the layers. The thermal cyclic associated with strain loading leads to the alteration of the characteristic and the amplitude of the axial stress. Under the thermal gradient cyclic loading, the crack normal to the interface propagates primarily in the metallic bond coat parallel to the interface by the combined effect of the remarkably increasing axial stress and radial tensile stress, hence the spallation of the ceramic layer occurrs. The comparative analysis of the thermal mechanical loading with in-phase and out-of-phase demonstrated that the TBCs will be more likely to fail due to the tensile mean stress in a cycle in the opposite phase.