晶界结构特征对304不锈钢和B10铜镍合金局部氧化物膜的影响

Austenitic alloy is one class of the key tubing materials in ships, offshore engineering, petrochemical sector, and thermal and nuclear power stations. The corrosion resistance of the alloy is generally attributed to the formation of protective oxide film in its service environment. But immature failures of the austenitic alloy tubes are reported frequently. Multiple twining is the main structural characteristic of the austenitic alloy. The traditional research tends to pay close attention to the influence of alloy composition on its corrosion resistance. The common evaluation method of the “grain boundary engineering” (GBE) effect is based only on the intergranular corrosion resistance of the bare surface of the alloy. Up to now little attention is paid to the effect of the alloy microstructure on the formation and evolution of the oxide film. This research focuses on SUS304 stainless steel and the 90-10 copper-nickel alloy, of which the oxide film properties are different in service environment. With the flexible application of the EBSD (Electron Backscattered Diffraction) technique, the scanning Kelvin probe microscope and the micromorphology characterization, the influence of the grain boundary structure on the formation and evolution of the local oxide film in the two alloys is investigated systematically. Emphasis is placed on the establishment of the internal relations between the grain boundary structure and the formation and properties of the local oxide film in the two alloys. The “corrosion-resistant” grain boundaries and the “optimum” grain boundary structure of the two alloys in the film-free solution and in the filming solution are determined respectively. Finally, the different rules of grain boundary structure influenced on the corrosion behavior of the two alloys in the film-free solution and in the filming solution are revealed, which can provide basis for improving the corrosion resistance of the two austenitic alloys in service environment using the grain boundary engineering.

奥氏体合金是海洋工程、核电、石油化工等领域重要的耐蚀管系材料，其耐蚀性能依赖于在服役环境中形成的氧化物膜，但相关腐蚀失效事故时有发生。多重孪晶是奥氏体合金显微组织的主要特点。传统研究多关注合金成分对耐蚀性的影响，以往“晶界工程”有效性的评价方法也仅基于合金裸表面的抗晶间腐蚀性能。奥氏体合金的晶界结构如何影响氧化物膜的形成演化及耐蚀性，目前尚缺少该方面的系统研究。本项目以成膜特征不同的304不锈钢和B10铜镍合金为研究对象，灵活运用EBSD技术、扫描开尔文探针技术和微观形貌表征手段，系统研究晶界结构特征对其局部氧化物膜的影响规律，建立“晶界结构特征-局部氧化物膜特征-耐蚀性能”之间的相互关系，明确两种奥氏体合金在不成膜和成膜环境中的“耐蚀”晶界和“最优”晶界结构，揭示晶界结构特征对其在不成膜和成膜环境中腐蚀行为的影响规律的异同，为从微观结构调控方面提高奥氏体合金抗腐蚀性能提供依据。

在材料四面体中，四个顶点分别是材料的成分、组织结构、合成与加工、服役性能。奥氏体合金是海洋工程、核电、石油化工等领域重要的耐蚀管系材料，其耐蚀性能依赖于在服役环境中形成的氧化物膜，但相关腐蚀失效事故时有发生。晶界结构和晶粒取向是奥氏体合金显微组织特点的两个重要方面。传统研究多关注合金成分对耐蚀性的影响，奥氏体合金的晶界结构和晶粒取向如何影响其腐蚀敏感性和耐蚀性能，目前尚缺少该方面的系统研究。B10铜镍合金，俗称白铜，属面心立方结构，是舰船、海洋工程、滨海电厂等领域重要的海水管路材料，本项目以B10铜镍合金为研究对象，主要关注了其晶界结构、晶粒取向等微观组织结构特征对其耐蚀性能的影响，灵活运用了EBSD技术和扫描开尔文探针技术（AFM/SKPFM），研究了不同ΣCSL 取向的对称倾转晶界的腐蚀敏感性差异，共格孪晶界和非共格Σ3 晶界的腐蚀敏感性差异，并与随机大角度晶界对比，揭示了ΣCSL晶界取向差对B10铜镍合金的晶界腐蚀敏感性的影响规律，弥补了对B10合金的“晶界结构特征-耐蚀性能” 关系认识的不足，为利用晶界工程提高B10铜镍合金的耐腐蚀性能提供了理论指导；研究了晶粒取向对B10铜镍合金腐蚀敏感性的影响规律，建立了B10合金的晶粒取向、表面Volta电势和活性溶解速率之间的关系，并提出了台阶溶解模型，揭示了面心立方金属的密排面的快速溶解机制，弥补了对面心立方金属的“晶粒取向-耐蚀性能”关系认识的不足，为从微观结构调控方面提高B10铜镍合金的耐腐蚀性能提供了理论指导；并研究了B10铜镍合金在海水中的腐蚀产物膜成分、结构和形成机制，在中长期浸泡过程中腐蚀产物膜随时间的演变，以及不同厂家的B10合金管的腐蚀产物膜演化过程的异同，深化了对B10铜镍合金的腐蚀产物膜与其耐蚀性关系的理解与认识。