材料期刊网

综述了近年来在核电高温高压水中不锈钢和镍基合金的腐蚀电化学行为规律, 以及材料表面膜的成分、组织结构和电子特征. 通过系统分析水介质化学和材料微观结构对表面膜的影响, 试图把膜的特性与腐蚀电化学行为联系起来. 讨论了核电高温高压水中材料的腐蚀机制, 提出核电高温高压水中不锈钢和镍基合金的腐蚀机制与常温时不同, 高温下是由电化学与氧化联合控制, 而不是传统意义上常温下的纯电化学腐蚀. 表面膜为双层结构, 外层疏松, 而内层是由纳米晶构成的具有半导体性质的膜层, 内层是控制腐蚀的关键. 材料的微观成分与组织结构、表面加工状态、水化学参数是影响核电用材料高温高压水中腐蚀的重要因素. 腐蚀产生的氧化物的楔形力导致缺陷前端产生局部拉应力, 即使在宏观压应力区, 缺陷前端的局部拉应力仍可导致应力腐蚀开裂的发生与扩展. 氧化物楔形力的作用是促进压应力下产生应力腐蚀开裂的重要原因.

The electrochemical corrosion behavior and the chemical components, structures and electronic characters of oxide films for stainless steels and Ni base alloys used in nuclear power plant were reviewed. The effects of water chemistry and microstructure of materials on oxide films were analyzed in order to relate the oxide film properties with electrochemical behaviors. The corrosion mechanism of the materials used in high temperature pressurized water is different with that used in room temperature water. The corrosion mechanism of the materials in high temperature pressurized water is controlled by electrochemistry and oxidation, whereas in room temperature water it is controlled only by electrochemistry. Oxide films has double-layer structure. The outer layer is porous, and the inner layer is composed by nano-crystalline and has semiconductivity which controlled the corrosion process. The microstructure, chemical composition, surface status of materials and water chemistry parameters are the key parameters which affect corrosion. The wedging stress of oxide inside the flaw could induce localized tensile stress at the tip of the flaw, which caused stress corrosion cracking initiation and propagation even in macro-compressive stressed region. The wedging stress of oxide is the key factor to induce stress corrosion cracking in compressive stressed region.