锆合金因具有较低的热中子吸收截面、优良的耐腐蚀性能和力学性能，是轻水堆核电站中重要的核反应堆结构材料。然而，在高温及腐蚀条件下，锆合金表面会发生氧化腐蚀，当氧化膜厚度达2~3 μm时，其生长速率会急剧增大，即发生腐蚀动力学转变，限制了锆合金在反应堆中的使用寿命。本工作借助相场动力学方法对锆合金氧化膜中四方相ZrO₂ (t-ZrO₂)向单斜相ZrO₂ (m-ZrO₂)转变及氧化膜-金属体系中裂纹的扩展行为进行了研究。模拟结果表明，氧化膜中发生t-ZrO₂→m-ZrO₂转变时，生成的m-ZrO₂相呈“芒果状”且主要受压应力作用，而基体在沿m-ZrO₂晶粒的长轴和短轴方向上分别受到压应力和拉应力，且应力均随m-ZrO₂的长大而增大。应力下裂纹扩展模拟发现，氧化膜中平行于其与金属界面的横向裂纹，可在垂直于界面的拉伸应力作用下扩展，并可与邻近的横向裂纹及缺陷相互连接，形成缺陷层。氧化膜中垂直于界面的纵向裂纹在扩展至界面后未向金属基体中继续扩展，而是向氧化膜中产生分叉，其继续扩展将促进氧化层从基体上剥落。

Zirconium alloys are considered as important nuclear reactor structural materials owing to their low thermal neutron absorption cross-section, good corrosion resistance, and good mechanical properties in high-temperature and high-pressure water. However, under high temperature and corrosion conditions, an oxide film forms on the surface of zirconium alloys, and its growth rate increases rapidly when the thickness is 2-3 μm, leading to a transition in corrosion kinetics, which limits its service life in the reactor. In this study, the transformation of zirconia from tetragonal (t-ZrO₂) to monoclinic (m-ZrO₂) and the crack propagation behavior in the oxidation layer on zirconium alloys have been investigated using phase-field simulation. During the transformation of t-ZrO₂ to m-ZrO₂ in the oxide film, the t-ZrO₂ matrix undergoes compressive and tensile stresses along the long and short axes of the m-ZrO₂ precipitate, respectively, whereas the m-ZrO₂ precipitate primarily undergoes compressive stress during the transformation. Moreover, the stresses increase with the growth of the m-ZrO₂ grains. The simulations of crack evolution reveal that the cracks in the oxidation layer parallel to the oxide-metal interface expand under applied tensile stress perpendicular to the interface. Such cracks may connect with other isolated cracks and defects forming a defect layer. Upon extending to the oxide-metal interface, surface cracks perpendicular to the interface bifurcate in the oxide rather than penetrate into the metal matrix, which facilitates the peeling off of the oxidation layer from the substrate.