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用高压釜腐蚀实验研究了添加0.05%-0.5%Cu(质量分数)对M5(Zr-1%Nb)合金在500 ℃/10.3 MPa过热蒸汽中耐腐蚀性能的影响; 用TEM和SEM分别观察了合金基体和腐蚀后氧化膜的显微组织. 结果表明: Cu含量低于0.2%时, 随着Cu含量的增加, 合金的耐腐蚀性能得到明显改善; 继续提高Cu含量则对进一步改善合金耐腐蚀性能的作用不明显. Cu含量不超过0.2%时, Cu主要固溶在α-Zr基体中; 当Cu含量高于0.2%时, Cu除了固溶在α-Zr基体中之外, 其余的Cu主要以Zr₂Cu型第二相析出. 固溶在α-Zr基体中的Cu, 在α-Zr被氧化后可以延缓氧化膜中空位扩散凝聚形成孔隙和孔隙发展成为微裂纹的过程, 增加氧化膜的致密度, 从而提高合金的耐腐蚀性能. 可见, 对M5合金耐腐蚀性能影响起主要作用的是固溶在α-Zr中的Cu, 而不是含Cu第二相.

The effect of Cu content on the corrosion resistance of Zr-1%Nb-xCu (x=0.05%-0.5%, mass fraction) was investigated in superheated steam at 500 ℃ and 10.3 MPa by autoclave tests. The microstructures of the alloys and oxide films on the corroded specimens were observed by TEM and SEM, respectively. The results showed that when the Cu content was below 0.2%, the corrosion resistance of the alloys was markedly improved with the increase of Cu content, while further addition of Cu did not lead to a further improvement in the corrosion resistance. When the Cu content was below 0.2%, the Cu mainly dissolved in the α-Zr matrix. And when the Cu content was more than 0.2%, part of Cu precipitated as Zr₂Cu second phase particles. When the α-Zr matrix was oxidized, the Cu dissolved in the α-Zr could delay the process that the vacancies in the oxide film diffused and coalesced to form pores, and the pores developed into micro-cracks. Therefore, the corrosion resistance of the alloys was enhanced. It can be concluded that the Cu concentration in the α-Zr matrix, rather than the second phase particles containing Cu, is the main reason that the addition of Cu improves the corrosion resistance of M5 alloy in superheated steam at 500 ℃ and 10.3 MPa.