Fatigue behavior is strongly correlated with the residual stress state within thermal spray coatings, with neutral or compressive residual stresses being favorable for fatigue-sensitive applications. However, determination of the coating’s residual stress state is predominately made prior to subjection of the coating to cyclic loading and does not give insight into possible changes to the residual stress state once in service. In this work, high-velocity, oxy-fuel nickel coatings were subjected to a partial fatigue loading regime, via both rotating bend fatigue and cantilever fatigue, targeting 99% of the total system fatigue life. Neutron diffraction was used to measure changes between the initial compressive residual stresses and after partial fatigue loading and was compared with the residual stress measurements made via beam curvature techniques during deposition. Results indicate that the fatigue credit typically associated with compressive residual stress coatings was partially dependent on the mode of loading and that there was a change in the residual stress magnitude due to changes during fatigue cycling. Additionally, metallographic assessment of the fracture surface was used to determine final fatigue failure within the substrate and crack propagation within the coating crossing through the substrate interface into the substrate.

中文翻译：

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结构集成热喷涂镍涂层残余应力和疲劳行为的观察

疲劳行为与热喷涂涂层内的残余应力状态密切相关，中性或压缩残余应力有利于疲劳敏感应用。然而，涂层的残余应力状态的确定主要是在涂层经受循环载荷之前进行的，并且不能深入了解使用后残余应力状态的可能变化。在这项工作中，高速氧燃料镍涂层通过旋转弯曲疲劳和悬臂疲劳承受部分疲劳载荷，达到系统总疲劳寿命的 99%。中子衍射用于测量初始压缩残余应力和部分疲劳加载后的变化，并与沉积过程中通过梁曲率技术进行的残余应力测量进行比较。结果表明，通常与压缩残余应力涂层相关的疲劳信用部分取决于加载模式，并且由于疲劳循环期间的变化，残余应力大小会发生变化。此外，断裂表面的金相评估用于确定基材内的最终疲劳失效和涂层内的裂纹扩展穿过基材界面进入基材。结果表明，通常与压缩残余应力涂层相关的疲劳信用部分取决于加载模式，并且由于疲劳循环期间的变化，残余应力大小会发生变化。此外，断裂表面的金相评估用于确定基材内的最终疲劳失效和涂层内的裂纹扩展穿过基材界面进入基材。结果表明，通常与压缩残余应力涂层相关的疲劳信用部分取决于加载模式，并且由于疲劳循环期间的变化，残余应力大小会发生变化。此外，断裂表面的金相评估用于确定基材内的最终疲劳失效和涂层内的裂纹扩展穿过基材界面进入基材。