添加Bi对Zr-4合金在400℃/10.3 MPa过热蒸汽中耐腐蚀性能的影响

EFFECT OF Bi ADDITION ON THE CORROSION RESISTANCE OF Zr-4 IN SUPERHEATED STEAM AT 400℃/10.3 MPa

在Zr-4合金基础上添加0.1%—0.5%Bi(质量分数)制备成Zr-4+xBi合金,用高压釜腐蚀实验研究了Bi含量对Zr-4+xBi合金在400℃/10.3 MPa过热蒸汽中耐腐蚀性能的影响;用TEM,EDS和SEM观察了合金和合金腐蚀后氧化膜的显微组织.结果表明:随着Bi含量的增加,Zr- 4+xBi合金中第二相的尺寸和形状变化不大,但数量增多,并出现了不同成分的第二相,包括Zr(Fe,Cr)_2,Zr-Fe- Cr-Bi.Zr-Fe- Sn -Bi和Zr-Fe- Cr-Sn-Bi.在Zr -4+0.1Bi合金中检测到了含Bi的第二相,这说明580℃时Bi在Zr- 4+xBi合金α- Zr基体中的固溶度小于0.1%.另外,适量Bi的添加促进了原先固溶在α-Zr基体中Sn的析出.与Zr-4合金相比,在Zr-4中添加0.1%—0.5%Bi后合金的耐腐蚀性能反而下降,并随着Bi含量的增加耐腐蚀性能恶化趋势越显著,这说明Zr-4合金中添加Bi并不能改善合金的耐腐蚀性能,反而产生有害的影响.这应该与含Bi第二相和同时含有Bi,Sn第二相的析出有关.

The effect of Bi contents on the corrosion resistance of Zr-4＋xBi （x=0.1%--0.5%, mass fraction） alloys, which were prepared by adding Bi to Zr-4, was investigated in superheated steam at 400 ℃ and 10.3 MPa by autoclave tests. The microstructures of the alloys and fracture surface morphology of the oxide fihn formed on the alloys were observed by TEM, EDS and SEM. The results show that with the increase of Bi content, the second phase particles （SPPs） are almost the same in size and shape, but increase in amount and vary in composition, including Zr（Fe, Cr）2, Zr-Fe-Cr-Bi, Zr-Fe-Sn-Bi and Zr-Fe-Cr-Sn-Bi. Even in the Zr 4＋0.1Bi alloy, Bi-containing SPPs were detected. This indicates that the solid solubility of Bi in α-Zr matrix of Zr-4＋xBi alloys is less than 0.1% at 580 ℃. Moreover, the addition of Bi promotes the precipitation of Sn which originally dissolved in the α-Zr matrix of Zr-4. Compared with Zr-4, the addition of Bi makes the corrosion resistance worse, and it becomes more obvious with the increase of Bi content. This illustrates that the addition of Bi can not improve the corrosion resistance, on the contrary, it brings a harmful influence. This may be related to the precipitation of the Bi-containing and Bi-Sn-containing SPPs.