| 引用本文: | 刘艳,张云华,闫秀林,李俊杰,刘进.变形温度对核电用锆包壳管表面Cr涂层开裂行为的影响[J].中国表面工程,2023,36(2):222~230 |
| LIU Yan,ZHANG Yunhua,YAN Xiulin,LI Junjie,LIU Jin.Effect of Deformation Temperature on Cracking Behavior of Cr Coatings on the Surface of Zircalloy Cladding Tube for Nuclear Power[J].China Surface Engineering,2023,36(2):222~230 |
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| 摘要: |
| Cr 涂层能够有效提高核电反应堆锆包壳管的事故容错能力，但在高温下其内部可能会萌生裂纹导致涂层开裂失效，现有 Cr 涂层开裂行为研究多针对常温，因此研究不同温度下 Cr 涂层的开裂行为对于其应用具有重要的理论和工程价值。采用多弧离子镀技术在 N36 锆合金包壳管外表面制备厚度为 14 μm 左右的 Cr 涂层，采用 WDW-100C 万能试验机对涂层管分别进行室温(25 ℃)与高温(100、200、300、400 ℃)拉伸试验，并通过超景深显微镜和扫描电镜(SEM)观察涂层的裂纹表面与截面形貌，对 Cr 涂层在不同温度下的开裂行为与开裂机理进行研究。结果表明，随着温度升高，涂层管的屈服强度从(400±5)MPa 下降到(150±5)MPa，涂层管的总体塑性变化不大；室温下裂纹萌生于涂层内部，其开裂方式为脆性沿晶断裂；100 ℃时涂层开裂方式不变，但表面裂纹数量减少，裂纹尖端出现钝化，由 V 字形转变为 U 字形； 随着温度进一步升高，涂层的塑性变形能力提高，其表面呈流线形塑性变形；200 ℃及以上温度下，涂层表面无明显开裂，仅出现少量微裂纹，塑性的升高导致拉伸过程中涂层的变形量与基体存在差异，裂纹开始萌生于界面处，其断裂方式也由脆性断裂转变为韧性断裂。采用单轴拉伸法研究温度对锆包壳 Cr 涂层开裂行为的影响，可为 Cr 涂层在核电领域的应用提供一定数据与理论支撑。 |
| 关键词: 变形温度 锆合金 铬涂层 开裂行为 |
| DOI：10.11933/j.issn.1007-9289.20220330001 |
| 分类号:TG174 |
| 基金项目:国家重点研发计划资助项目(2018YFB1900105) |
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| Effect of Deformation Temperature on Cracking Behavior of Cr Coatings on the Surface of Zircalloy Cladding Tube for Nuclear Power |
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LIU Yan, ZHANG Yunhua, YAN Xiulin, LI Junjie, LIU Jin
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School of Materials Science and Engineering, Southwest Jiaotong University, Chengdu 610036 , China
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| Abstract: |
| Chromium (Cr) coatings can effectively improve the accident tolerance of zirconium cladding tubes in nuclear power reactors. However, internal cracks may develop at high temperatures, leading to the cracking failure of the coatings. Most studies on the cracking behavior of Cr coatings have been conducted at ambient temperature. Therefore, it is of great theoretical and engineering value to study the cracking behavior of Cr coatings at various high-temperature working environments. Cr coatings with a thickness of approximately14 μm were prepared on the surface of N36 zirconium cladding tubes by multi-arc ion plating technology. The coatings were well formed internally, dense, and without obvious defects, such as pores and cracks. The combination of the coating and substrate was good, and the combination area was flat without obvious defects. The coated tubes were subjected to tensile tests at room temperature (25 ℃) and high temperatures (100, 200, 300, and 400 ℃) using a WDW-100C universal testing machine. The surface and section morphologies of the Cr coatings were observed by an ultra depth-of-field microscope and a scanning electron microscope to determine their cracking behavior at different temperatures. The results show that the yield strength of the coated tube decreased from (400 ± 10) MPa to (150 ± 10) MPa with increasing temperature, while the plasticity changed only slightly. The observation of the fracture surface of the coated tube showed that the coating bonded well with the substrate near the fracture after room temperature and high-temperature stretching, and did not exhibit large-area peeling, showing excellent film-based bonding. Numerous circular cracks perpendicular to the direction of tensile stress formed on the surface of the coated tube at room temperature. The number of cracks on the coating surface was highest at room temperature, and significantly decreased as the temperature increased. The fracture cross-section revealed that cracks initiated inside the coating at room temperature. The cracking mode was brittle intergranular fracture. In addition, tiny cavities were present inside the coating, which could be a source of cracks. At 100 ℃, the cracking mode remained unchanged, but the number of surface cracks decreased. As the plasticity of the coating increased, the crack expansion rate within the coating decreased; the driving force for crack expansion into the substrate also decreased and ultimately decreased the depth of expansion into the substrate; and the crack tip changed from V-shaped to U-shaped. With the increase in temperature, the coating plasticity improved and its surface exhibited linear plastic deformation. At 200 ℃ and above, the coating surface had no obvious cracking; only a few microcracks. During the tensile process, the increased plasticity of the coating resulted in a different deformation from that of the matrix: cracks initiated at the interface and the fracture mode changed from brittle fracture to ductile fracture. This indicates that the tough-brittle transition temperature of the Cr coatings is between 100 ℃ and 200 ℃. Cr coatings inhibited cracking in the zirconium alloy matrix at high temperatures, thus extending the service life of zirconium cladding tubes. In this study, the effect of temperature on the cracking behavior of Cr coatings on zirconium cladding tubes was investigated by a uniaxial tensile method to provide data support for the application of Cr coatings to accident tolerant fuel. |
| Key words: deformation temperature zirconium alloy Cr coating cracking behavior |
