Zr-0.7Sn-1.07Nb-0.32Fe-0.08Cr-xBi合金在400 ℃过热蒸汽中耐腐蚀性能的研究

Corrosion Resistance of Zr-0.7Sn-1.07Nb-0.32Fe-0.08Cr-xBi Alloy in Superheated Stream at 400 ºC/10.3 MPa

摘要:

在Zr-0.7Sn-1.07Nb-0.32Fe-0.08Cr (T5)合金中添加不同含量Bi制备成T5+xBi（x=0.1，0.3，0.5，质量分数，%）合金，用静态高压釜腐蚀试验研究了T5+xBi合金在400 ℃/10.3 MPa过热蒸汽中的耐腐蚀性能。用TEM和SEM分别观察了合金的显微组织和氧化膜断口形貌。结果表明：当添加的Bi含量￡0.3%时，合金中只检测到了密排六方结构的Zr(Nb, Fe, Cr)2第二相；当Bi含量达到0.5%时，合金中除了析出大量的Zr(Nb, Fe, Cr)2第二相外，还发现少量正交结构的ZrBi2型Zr(Bi, Fe, Sn)2和结构未确定的Zr-Nb-Bi-Fe-Cr-Sn第二相。这说明Bi在T5+xBi合金中固溶在α-Zr基体中的最大含量（CBi）为：0.3%￡CBi<0.5%（质量分数）；Bi的添加促进了T5合金中原来固溶在α-Zr基体中的Sn以第二相形式析出。当添加的Bi含量￡0.3%时，耐腐蚀性能得到一定程度的改善，而添加0.5% Bi后耐腐蚀性能反而降低。结合显微组织分析结果可以说明：固溶在α-Zr基体中的Bi可改善合金的耐腐蚀性能，而合金中析出含Bi和Sn的第二相后又会降低合金的耐腐蚀性能

Abstract:

The corrosion resistance of Zr-0.7Sn-1.07Nb-0.32Fe-0.08Cr-xBi (x=0.1, 0.3, 0.5, mass fraction, %) alloys was investigated in superheated stream at 400 oC/10.3 MPa by autoclave tests. SEM and TEM equipped with EDS were employed to investigate the microstructures of the alloys and fracture surface morphology of the oxide film. Results show that when the Bi content is below 0.3%, there exists Zr(Nb, Fe, Cr)2 second phase particles (SPPs) with a hexagonal crystal structure (hcp). And when the Bi content is up to 0.5%, besides many Zr(Nb, Fe, Cr)2 SPPs, there are also a few Zr(Bi, Fe, Sn)2 SPPs with an orthogonal structure and Zr-Nb-Bi-Fe-Cr-Sn SPPs with an unidentified structure. This indicates that the maximum concentration of Bi in α-Zr matrix of T5+xBi alloys is 0.3%￡CBi<0.5%. The addition of Bi promotes the precipitation of Sn as SPPs, which is originally in solid solution in the α-Zr matrix of Zr-0.7Sn-1.07Nb-0.32Fe-0.08Cr alloy. When the Bi content is below 0.3%, the corrosion resistance of the alloys improves with the Bi content, but the addition of 0.5% Bi makes the corrosion resistance worse. It indicates that the solid solution of Bi in α-Zr matrix can improve the corrosion resistance, while the precipitation of the SPPs containing Bi and Sn is harmful to the corrosion resistance.