Thermal barrier coatings (TBCs) are widely used to further extend the lifetime of turbine blades by protecting the blades from high temperature corrosion and oxidation. However, the mechanical behavior of turbine blades is obviously affected by the TBCs. In this study, microstructures evolution, damage mechanisms and life prediction of coated and uncoated nickel-based single crystal (NBSX) superalloy DD6 under isothermal fatigue load were investigated at 980 °C. The effects of TBCs on fatigue failure behavior and lifetime of DD6 were addressed. The results showed that the fatigue lifetime reduced with the increase of load. The effect of TBCs on the fatigue lifetime was related to the stress amplitude, as the effect was beneficial at high stress but almost negligible at low stress. Fracture morphologies showed that the cracks more likely initiated and propagated from basal defects for both coated and uncoated DD6, and the microstructure evolution also showed stress amplitude dependence. The crack density of uncoated DD6 increased first and then decreased with the increase of stress amplitude. However, the TBCs reduced the number of cracks that penetrate into the DD6 substrate, and the stress amplitude exerted a significant effect on crack propagation paths. In addition, the rafting behaviors of the DD6 substrate of coated and uncoated samples was compared, and results showed that TBCs could reduce the rafting degree of DD6. Finally, the fatigue lifetime of coated samples was predicted based on the modified Basquin model, and the prediction results fitted well with the experimental results.

中文翻译：

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涂层和非涂层镍基单晶高温合金 DD6 的高温疲劳行为：微观结构演变、损伤机制和寿命预测


热障涂层 （TBC） 广泛用于通过保护叶片免受高温腐蚀和氧化来进一步延长涡轮叶片的使用寿命。然而，涡轮叶片的机械性能明显受到 TBC 的影响。本研究在 980 °C 下研究了等温疲劳载荷下涂层和无涂层镍基单晶 （NBSX） 高温合金 DD6 的微观组织演变、损伤机制和寿命预测。 解决了 TBC 对 DD6 疲劳失效行为和使用寿命的影响。结果表明：疲劳寿命随着载荷的增加而缩短;TBC 对疲劳寿命的影响与应力幅值有关，因为这种影响在高应力下是有益的，但在低应力下几乎可以忽略不计。断裂形态表明，对于涂层和未涂层的 DD6，裂纹更有可能从基底缺陷开始和传播，并且微观结构演变也显示出应力幅值依赖性。无涂层 DD6 的裂纹密度随应力幅值的增加呈先增加后减小的趋势。然而，TBC 减少了渗透到 DD6 基材中的裂纹数量，并且应力幅值对裂纹扩展路径产生了显着影响。此外，比较了涂覆和未涂覆样品的 DD6 基材的漂流行为，结果表明 TBCs 可以降低 DD6 的漂流程度。最后，基于改进的 Basquin 模型预测涂层样品的疲劳寿命，预测结果与实验结果吻合较好。