The present work is the first study investigating the effects of accident tolerant coatings on the low-cycle fatigue life of the Zr-4 alloy. Zr-4 alloy with different accident tolerant coatings, i.e., a Cr coating or a TiCrAlN coating by multi-arc ion plating, were studied at 400°C by in-situ fatigue testing with a scanning electron microscope (SEM). It was surprisingly found that the Cr coating improved the fatigue life of the Zr-4 alloy significantly, whereas the TiCrAlN coating decreased the fatigue life dramatically. The fatigue life variation was closely related to the ratcheting strain of each type of sample in this study. Further, in-situ SEM observations indicated that the Cr coating exhibited a good capacity for plastic deformation with the Zr-4 substrate until the late stage of fatigue life. In contrast, for the TiCrAlN coating, multiple cracks formed during the early stage of fatigue life. The distinct effects of the two coatings were confirmed by analysis of the fracture surfaces and longitudinal section microstructure. Hence, variations in the fatigue life of the coated Zr-4 samples was attributed to the cyclic deformation and cracking behavior of each coating. Finite element simulations based on the cohesive element method indicated that the pre-failure of the brittle TiCrAlN coating (with its low fracture toughness) promoted early crack initiation in the Zr-4 substrate, leading to a short fatigue life. For the Cr coating (with its high fracture toughness and good plasticity), the crack initiation in the substrate was postponed, leading to a longer fatigue life.

目前的工作是研究耐事故涂层对Zr-4合金低周疲劳寿命的影响的第一项研究。通过扫描电子显微镜（SEM）的原位疲劳测试，研究了具有不同耐事故涂层的Zr-4合金，即采用多弧离子镀的Cr涂层或TiCrAlN涂层。令人惊讶地发现，Cr涂层显着改善了Zr-4合金的疲劳寿命，而TiCrAlN涂层显着降低了疲劳寿命。在这项研究中，疲劳寿命的变化与每种样品的棘轮应变密切相关。此外，原位SEM观察表明，Cr涂层表现出良好的塑性变形能力，直到疲劳寿命的后期，Zr-4基体均具有塑性变形。相比之下，对于TiCrAlN涂层，在疲劳寿命的早期阶段形成了多个裂纹。通过分析断裂表面和纵向截面的微观结构，证实了两种涂层的独特作用。因此，涂层Zr-4样品疲劳寿命的变化归因于每个涂层的周期性变形和开裂行为。基于内聚元法的有限元模拟表明，脆性TiCrAlN涂层的预破坏（具有低的断裂韧性）促进Zr-4基底中的早期裂纹萌生，从而导致较短的疲劳寿命。对于Cr涂层（具有高的断裂韧性和良好的可塑性），延缓了基材中的裂纹萌生，从而延长了其疲劳寿命。通过分析断裂表面和纵向截面的微观结构，证实了两种涂层的独特作用。因此，涂层Zr-4样品疲劳寿命的变化归因于每个涂层的周期性变形和开裂行为。基于内聚元法的有限元模拟表明，脆性TiCrAlN涂层的预破坏（具有低的断裂韧性）促进Zr-4基底中的早期裂纹萌生，从而导致较短的疲劳寿命。对于Cr涂层（具有高的断裂韧性和良好的可塑性），延缓了基材中的裂纹萌生，从而延长了其疲劳寿命。通过分析断裂表面和纵向截面的微观结构，证实了两种涂层的独特作用。因此，涂层Zr-4样品疲劳寿命的变化归因于每个涂层的周期性变形和开裂行为。基于内聚元法的有限元模拟表明，脆性TiCrAlN涂层的预破坏（具有低的断裂韧性）促进Zr-4基底中的早期裂纹萌生，从而导致较短的疲劳寿命。对于Cr涂层（具有高的断裂韧性和良好的可塑性），延缓了基材中的裂纹萌生，从而延长了其疲劳寿命。涂层Zr-4样品疲劳寿命的变化归因于每个涂层的周期性变形和开裂行为。基于内聚元法的有限元模拟表明，脆性TiCrAlN涂层的预破坏（具有低的断裂韧性）促进Zr-4基底中的早期裂纹萌生，从而导致较短的疲劳寿命。对于Cr涂层（具有高的断裂韧性和良好的可塑性），延缓了基材中的裂纹萌生，从而延长了其疲劳寿命。涂层Zr-4样品疲劳寿命的变化归因于每个涂层的周期性变形和开裂行为。基于内聚元法的有限元模拟表明，脆性TiCrAlN涂层的预破坏（具有低的断裂韧性）促进Zr-4基底中的早期裂纹萌生，从而导致较短的疲劳寿命。对于Cr涂层（具有高的断裂韧性和良好的可塑性），延缓了基材中的裂纹萌生，从而延长了其疲劳寿命。