目的 本研究旨在提高燃料元件Zr-4合金在高温高压水环境中的服役可靠性,并为耐事故燃料包壳表面防护层的材料选择与结构设计提供实验依据。方法 研究以Zr-4合金为基体,采用激光熔覆技术制备NiCr/Mo、NiCrMo/Mo复合涂层,通过调控Cr、Ni、Mo含量并结合工艺优化,获得了平整、致密、结合良好的涂层结构。基于已制备的涂层体系,在360 ℃、18.6 MPa条件下,分别于除氧水（DO<10 μg/L）和溶氧水（DO≈400 μg/L）环境中开展了为期100 d的长期高温高压水腐蚀试验,并结合SEM、EDS及质量变化测试,对涂层在高温高压水环境中的腐蚀行为进行了系统分析。结果 Mo中间层可有效缓冲热膨胀失配并抑制元素互扩散,使涂层在短期腐蚀中保持较好的完整性,腐蚀后表面主要出现纳米级氧化颗粒和局部选择性氧化。长期腐蚀中,6种复合涂层均优于Zr-4基体,且不同配比在2类水化学环境下表现出明显差异。除氧水中,Ni55Cr40Mo5/Mo涂层的减重最小,100 d减重速率为-129.24 mg/dm2,耐蚀性最佳,而Ni59Cr40Mo1/Mo减重最明显,100 d减重速率为-277.64 mg/dm2,耐蚀性较差;溶氧水中,Ni60Cr40/Mo减重最小,100 d减重速率为-242.00 mg/dm2,Ni55Cr40Mo5/Mo次之,为-257.64 mg/dm2,而Ni59Cr40Mo1/Mo仍最差,100 d减重速率达到-306.44 mg/dm2。结论 Mo、Ni与Cr的协同设计能够显著改善涂层对高温水腐蚀的适应能力,其中氧化产物的均匀分布和界面稳定性是维持长期防护性能的关键;该结果也表明,涂层性能优化必须同时考虑成分配比与水化学环境差异,后续仍需在更长周期和多场耦合条件下进一步验证其工程适用性。
Abstract
The work aims to improve the service reliability of Zr-4 alloy fuel cladding in high-temperature and high-pressure water environments and provide experimental support for the material selection and structural design of surface protection coatings for accident-tolerant fuel cladding. With Zr-4 alloy as the substrate, NiCr/Mo and NiCrMo/Mo composite coatings were prepared by laser cladding. By adjusting the contents of Cr, Ni, and Mo and combining these compositional modifications with process optimization, coating systems with smooth surfaces, dense microstructures, and good interfacial bonding were successfully obtained. To evaluate the corrosion behavior of the coatings under high-temperature and high-pressure water environments relevant to reactor service conditions, long-term corrosion experiments lasting 100 days were conducted at 360 ℃ and 18.6 MPa in deoxygenated water (DO<10 μg/L) and oxygenated water (DO≈400 µg/L). After corrosion exposure, the surface morphologies, elemental distributions, and mass variations of the coatings were comprehensively characterized by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and mass-change measurements. The results showed that the Mo interlayer played an important role in improving coating stability. It effectively alleviated the thermal expansion mismatch between the coating and the Zr-4 substrate and suppressed elemental interdiffusion at the interface. As a result, the composite coatings maintained relatively good structural integrity during short-term corrosion. After exposure, the corroded surfaces were mainly covered with nanoscale oxide particles, accompanied by localized selective oxidation, indicating that the coatings retained their overall continuity and did not undergo severe early-stage degradation. During long-term corrosion, all six composite coatings exhibited better corrosion resistance than the Zr-4 substrate, although their performance differed significantly depending on composition and water chemistry. In deoxygenated water, the Ni55Cr40Mo5/Mo coating showed the smallest mass loss, with a 100-day weight-loss rate of -129.24 mg/dm2, indicating the best corrosion resistance among the tested coatings. In contrast, the Ni59Cr40Mo1/Mo coating exhibited the largest mass loss, with a weight-loss rate of -277.64 mg/dm2, and therefore showed the poorest corrosion resistance. This result suggested that an appropriate amount of Mo was beneficial for corrosion protection in a low-oxygen environment. In oxygenated water, the ranking of corrosion performance changed. The Ni60Cr40/Mo coating showed the lowest mass loss, with a 100-day weight-loss rate of -242.00 mg/dm2, while the Ni55Cr40Mo5/Mo coating ranked second, with a value of -257.64 mg/dm2. The Ni59Cr40Mo1/Mo coating again performed the worst, with a weight-loss rate of -306.44 mg/dm2. These results indicated that the optimal coating composition was strongly dependent on the water chemistry, and that coatings performing well in deoxygenated water did not necessarily remain the best in oxygenated conditions. Overall, the work demonstrates that the synergistic design of Mo, Ni, and Cr can significantly enhance the corrosion resistance of laser-cladded coatings in high-temperature water environments. The uniform distribution of oxidation products and the stability of the coating/substrate interface are key factors in maintaining long-term protective performance. These findings indicate that the optimization of protective coatings must consider both compositional design and environmental water chemistry. The results also provide useful experimental evidence for the development of surface protective layers for accident-tolerant fuel cladding, while further verification under longer exposure times and coupled service conditions is still needed.
关键词
Zr-4合金 /
激光熔覆 /
NiCr/Mo复合涂层 /
高温高压水腐蚀 /
长期耐蚀性 /
界面扩散
Key words
Zr-4 alloy /
laser cladding /
NiCr/Mo composite coatings /
high-temperature and high-pressure water corrosion /
long-term corrosion resistance /
interface diffusion
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基金
中核集团领创科研项目（CNNC-LCKY-202231）
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