Zr-xNb-0.15Fe-0.05Cu-0.05Ge合金在400℃/10.3 MPa过热蒸汽中的耐腐蚀性能

Corrosion Resistance of Zr-x Nb-0. 15Fe-0. 05Cu-0. 05Ge Alloys in 400 ℃/10. 3 MPa Superheated Steam

利用高压釜腐蚀试验研究了Zr-xNb-0.15Fe-0.05Cu-0.05Ge(x=0.7,1,1.3,1.6,质量分数,%)合金在400℃/10.3MPa过热蒸汽中的耐腐蚀性能。使用SEM和TEM分别观察了合金和氧化膜的显微组织。结果表明:随着Nb的质量分数从0.7%增加至1.6%,试验合金的耐腐蚀性能逐渐下降。合金中的第二相为体心立方结构的β-Nb(bcc-β-Nb)相与含有Cu和Ge的密排六方结构的Zr(Nb,Fe)2(hcp-Zr(Nb,Fe)2)相,随着Nb含量的增加,主要第二相由Zr(Nb,Fe)2相逐渐转变为β-Nb相,且呈条带状。Zr(Nb,Fe)2和β-Nb第二相相对含量的变化对合金的耐腐蚀性能有较大影响。具有较大P.B.比、且呈条带状分布的β-Nb相促进了氧化膜中微裂纹的扩展,而且大量的β-Nb相氧化所产生的体积膨胀会影响氧化膜柱状晶的生长,增加了氧化膜中的内应力,促进孔隙和微裂纹形成,从而降低了合金的耐腐蚀性能。

Corrosion resistance of Zr-x Nb-0.15Fe-0.05Cu-0.05Ge(x=0.7,1.0,1.3,1.6,mass fraction,%)alloys exposed to superheated steam at temperature of 400℃and under pressure of 10.3 MPa was studied by autoclave test.The microstructures of alloy and oxide film were observed by SEM and TEM.The results showed that as the mass fraction of Nb increasing from 0.7% to 1.6%,the corrosion resistance of the tested alloys decreased gradually.The second phase particles in the tested alloys wereβ-Nb(bcc-β-Nb)phase of the bcc structure and Zr(Nb,Fe)2(hcp-Zr(Nb,Fe)2)phase of the hcp structure which contained Cu and Ge.With the increase in Nb content,the main second phase changed from Zr(Nb,Fe)2 intoβ-Nb asuuming banded distribution.The change in relative amount of the Zr(Nb,Fe)2 andβ-Nb second phases had greater influence on corrosion resistance of the alloy.Theβ-Nb phase with larger P.B.ratio and asuuming banded distribution promoted the propagation of cracks in oxide film.The volume expansion resulting from large amounts ofβ-Nb phase oxidation disturbed the growth of columnar grains and increased the internal stress in the oxide film,promoted the formation of pores and micro-cracks in oxide film,thereby reducing the corrosion resistance of the alloy.