B10铜镍合金管的晶界工程设计及其海水腐蚀机制研究

Domestic demand for the copper-nickel tubing is great, as it is one of the key materials widely used as heat exchangers and condensers in ships and other marine environments, among which the 90Cu-10Ni (CuNi10Fe1Mn, UNS C70600) tubing is the most widely used. But the corrosion of the 90Cu-10Ni tubes has plagued the shipbuilding and other marine industries for long. The corrosion failures are generally attributed to intergranular corrosion, erosion corrosion or pitting, all of which are associated with local failure of the corrosion product film. As multiple twining is the main structural characteristic of the 90Cu-10Ni alloy, the grain boundary structure becomes the primary factor affecting its corrosion resistance when the alloying elements and impurities are well controlled. Therefore, it is of great significance to explore the possibilities of restraining intergranular corrosion and pitting and thereby improving the corrosion resistance of the 90Cu-10Ni tube by adjusting the grain boundary structure through the grain boundary engineering (GBE). In this research, the special thermal mechanical processes will be introduced into the manufacturing route of the 90Cu-10Ni tube to adjust the grain size, grain boundary characteristic distribution, and the connectivity of random high angle boundaries. The relationship between the GBE parameters and the grain boundary structural characteristics will be established. With the flexible applications of the electron backscatter diffraction (EBSD), the atomic force microscope/scanning Kelvin probe force microscope (AFM/SKPFM), the scanning vibrating electrode technique (SVET) and the transmission electron microscope (TEM), the influences of local grain boundary structure on the propensity for intergranular corrosion, pitting and precipitation at grain boundary will be investigated. The short-term immersion in simulated seawater combined with AFM/SKPFM scanning, and the long-term immersion in natural seawater followed by the erosion corrosion test and the cross section EBSD/SEM will be employed on the GBE-tube and the as-received tube. The focus is on the effects of the grain boundary structure of the underlying substrate on the formation and degradation of the corrosion product film. The aim of this project is to build the connections between the GBE parameters, grain boundary structure, and the corrosion properties, and thereby to lay the foundation for enhancing the corrosion resistance of the 90Cu-10Ni tubing by GBE.

铜镍合金管广泛用于海水热交换器和冷凝器，是舰船和海洋工程的关键材料，其中B10管用量最大，但其耐蚀性不稳定，腐蚀泄露一直困扰上述行业，腐蚀失效多被归因于晶间腐蚀、冲刷腐蚀、点蚀等，均涉及腐蚀产物膜的局部破坏。多重孪晶是B10合金显微组织的主要特点，当合金成分和夹杂物控制合格时，晶界结构成为影响耐蚀性的首要因素。本项目在B10合金管的工艺末端进行不同的“冷变形+热处理”，对其晶粒度、晶界特征分布、随机晶界网络连通性进行调控，确定晶界工程参数与晶界结构特征的对应关系；借助EBSD、TEM及AFM/SKPFM、SVET研究晶界析出物、点蚀、晶间腐蚀倾向与局部晶界结构的关系；通过模拟海水短期腐蚀、实海长期腐蚀、冲蚀实验和截面EBSD、SKPFM方法研究晶界结构特征对腐蚀产物膜形成及冲蚀退化行为的影响及机制，目的是建立“工艺参数-晶界结构-耐蚀性能”的联系，为利用晶界工程提高B10管耐蚀性奠定基础。

铜镍合金管广泛用于海水热交换器和冷凝器，是舰船和海洋工程的关键材料，其中B10管用量最大，B30管用在环境更苛刻的关键部位。B10和B30海水管路的腐蚀泄露频发，一直困扰上述行业。铜镍合金管的腐蚀失效多被归因于晶间腐蚀、冲刷腐蚀、点蚀等，均涉及腐蚀产物膜的局部破坏。铜镍合金是单相面心立方固溶体，晶界和晶粒取向是它的主要微观组织特征。当合金成分和夹杂物控制合格时，微观组织特征成为影响耐蚀性的首要因素。本项目在B10合金管的工艺末端进行“冷变形+热处理”的晶界工程工艺，获得了晶粒度适中、低Σ晶界含量高、随机晶界网络连通性低的“GBE-B10管”；研究了不同ΣCSL晶界的腐蚀敏感性差异。此外，本项目还研究了晶粒取向对B10合金的活性溶解行为和成膜行为的影响规律，发现活性溶解速率和成膜速率都遵循(111)>(101)>(001)的顺序，采用第一性原理计算解释了各向异性腐蚀行为的形成机制，并提出了构筑表层织构提高传统合金耐蚀性的新思路。本项目还设计搭建了一套可模拟铜及铜镍合金管内壁轴向冲刷的管流式实验装置，利用该装置研究了TP2紫铜管和B10、B30铜镍合金管的冲蚀退化行为与晶间腐蚀的关系，揭示了流速对腐蚀产物层演化的影响以及腐蚀产物层演化与电化学行为之间的关系，在TP2紫铜管中首次发现了冲蚀损伤沿晶间发生并形成了部分氧化的呈坚果结构的铜晶粒，深化了对铜及铜合金海水管路腐蚀行为的认识。本项目还探索了预浸泡成膜对B10和B30铜镍合金管冲蚀抗力的影响，明确了温度和供氧条件对B10和B30管的腐蚀产物膜形成及其保护性的影响，相关结果对于指导船厂等用户制定铜镍合金海水管路的运行维护保养规范有重要价值。