采用XRD和Raman光谱技术对NZ2锆合金在360 ℃, 18.6 MPa含锂水和400 ℃, 10.3 MPa蒸汽中腐蚀不同时间后氧化膜的内应力及晶体结构进行测试, 通过SEM对氧化膜的显微结构进行表征. 结果表明, 随着腐蚀时间的延长, NZ2合金氧化膜中四方相含量不断降低, 单斜相含量不断升高, 发生四方相向单斜相转变. 当氧化膜厚度达到2 mm时, 出现了立方相. 氧化膜中四方相含量越高, 锆合金的耐腐蚀性能越好. 氧化膜内应力及显微结构的研究结果表明, NZ2合金氧化膜内有高的压应力存在. 氧化开始阶段, 随着腐蚀过程的进行, 氧化膜内部压应力增加. 当氧化膜厚度达到2 mm时, 氧化膜中压应力超过临界值, 氧化膜发生破裂, 应力释放发生. 裂纹降低了氧化膜的保护性, 腐蚀转折发生. 转折后氧化膜内压应力很低, 而且基本保持恒定. 因此, 腐蚀转折与氧化膜内压应力的突然释放密切相关. 氧化膜中压应力越高, 四方相越稳定, 耐腐蚀性能越好. 同时, 探索了氧化膜中四方相和立方相的稳定机理, 建立了新锆合金的腐蚀机理模型.

The corrosion resistance of new zirconium alloys containing Nb, used as the fuel cladding materials in water-cooled nuclear power reactors, is closely related to the characteristics of the oxide films, including the internal stresses and the crystal structure. However, the relation of the corrosion kinetics to the internal stresses and the crystal structure of the oxide films has not been well understood, also the corrosion mechanism of new zirconium alloys has not been confirmed. Therefore, it is helpful to solve the above problems, furthermore improve the corrosion resistance of new zirconium alloys, to characterize the internal stresses and the crystal structure of the oxide films accurately. The internal stresses and the crystal structure of the oxide films of NZ2 zirconium alloy, corroded in 360 ℃, 18.6 MPa lithiated water and 400 ℃, 10.3 MPa steam, were tested by XRD and Raman spectroscopy, and the microstructure of the oxide films was investigated by SEM. The results of the crystal structure show that tetragonal ZrO₂ (t-ZrO₂) content in the oxide films of NZ2 alloy decreases, monoclinic ZrO₂ (m-ZrO₂) content increases with the prolongation of the corrosion time, t-ZrO₂ transforms into m-ZrO₂. And cubic ZrO₂ (c-ZrO₂) appears in the oxide films when the thickness of the oxide films reaches 2 mm. Corrosion resistance of NZ2 alloy is improved when the content of t-ZrO₂ in the oxide films increases. The results of the internal stresses and the microstructure of the oxide films indicate that the high compressive stresses exist in the oxide films. At the beginning of the corrosion, the compressive stresses in the oxide films increase with the corrosion time. When the thickness of the oxide films reaches 2 mm, the compressive stresses exceed the critical value and the stresses are released. The stress relaxation leads to the formation of the cracks, which reduces the protection of the oxide films, therefore the corrosion transition occurs. After the transition, the compressive stresses of the oxide films are constantly low. So the corrosion transition is closely related to the relaxation of the compressive stresses. The high compressive stresses and t-ZrO₂ content are corresponding to the good corrosion resistance. Also the stabilization mechanisms of t-ZrO₂ and c-ZrO₂ are explored, finally the corrosion mechanism of new zirconium alloys is established.