Zr合金表面电沉积Ni/Cr涂层的高温氧化行为研究

Study of high-temperature oxidation behavior of electrodeposited Ni/Cr coatings on Zr alloy surfaces

摘要:

日本福岛核事故后，耐事故燃料（Accident Tolerant Fuel, ATF）包壳技术引起业界广泛关注。在核反应堆堆芯核燃料包壳用锆（Zr）合金表面包覆Cr涂层被认为是短期内最有可能投入商业应用的技术。目前多数Cr涂层的制备方法存在设备昂贵负责、沉积速率偏低、形状适应性偏弱等缺点，而熔盐电沉积技术具有阴极电流效率高、电沉积速度快、基体形状适应性强等优点，有望解决包壳Zr合金表面高质量Cr涂层的高效低成本制备难题。为实现Zr合金表面Cr涂层的熔盐电沉积制备，本文采用水溶液电沉积和熔盐电沉积方法依次在Zr合金基体表面制备Ni过渡层和Cr涂层，对制备得到的Zr/Ni/Cr试样进行组织结构表征、结合力和纳米硬度测试及高温氧化行为研究。结果表明，Zr合金表面的Ni/Cr涂层均匀致密，与基体间的结合力约为151 N。Zr/Ni/Cr从内到外各层的硬度和弹性模量均逐渐升高，呈准梯度过渡。其中Cr涂层的表面粗糙度约为2 μm，硬度和弹性模量分别为2.86 GPa和172.86 GPa。Zr/Ni/Cr试样在1000℃和1200℃高温蒸汽氧化过程中分别表现出近抛物线和近线性规律，表明Ni/Cr涂层能够在1000℃下对Zr合金基体起到良好的保护效果。Zr合金表面Ni/Cr涂层的高温氧化失效机制与Ni过渡层的快速扩散、Cr层的氧化和扩散消耗以及Zr沿Cr晶界快速扩散导致的Cr层性能弱化密切相关。

Abstract:

After the Fukushima nuclear accident in Japan, accident tolerant fuel (ATF) cladding technology has attracted widespread attention in the industry. The cladding of Cr coatings on zirconium (Zr) alloys for nuclear fuel cladding in nuclear reactor cores is considered to be the most likely technology to be commercially available in the near future. At present, most of the preparation methods for Cr coatings have the disadvantages of expensive equipment, low deposition rate and weak shape adaptability. And the molten salt electrodeposition technology has the advantages of high cathodic current efficiency, fast electrodeposition speed, and strong adaptability of substrate shape, which is expected to solve the problem of efficient and low-cost preparation of high-quality Cr coatings on the surface of cladding Zr alloys. In order to realize the preparation of Cr coating on the surface of Zr alloy by molten salt electrodeposition, this paper adopted aqueous solution electrodeposition and molten salt electrodeposition methods to prepare Ni transition layer and Cr coating on the surface of Zr alloy substrate sequentially, and carried out the characterization of the organization structure, the bonding force and nano-hardness test as well as the study of the high-temperature oxidation behavior of the Zr/Ni/Cr specimens obtained from the preparation. The results showed that the Ni/Cr coating on the surface of Zr alloy was uniform and dense, and the bonding force between the coating and the substrate was about 151N. The hardness and modulus of elasticity of Zr/Ni/Cr increased gradually from inner to outer layers with a quasi-gradient transition. The surface roughness of the Cr coating was about 2 μm, and the hardness and modulus of elasticity were 2.86 GPa and 172.86 GPa, respectively. The Zr/Ni/Cr specimens showed nearly parabolic and nearly linear patterns during steam oxidation at high temperatures of 1000°C and 1200°C, respectively, indicating that the Ni/Cr coatings were able to provide good protection to the Zr alloy matrix at 1000℃. The high-temperature oxidation failure mechanism of Ni/Cr coatings on Zr alloy surfaces was closely related to the rapid diffusion of the Ni transition layer, the oxidation and diffusion depletion of the Cr layer, and the weakening of the Cr layer due to the rapid diffusion of Zr along the Cr grain boundaries.