Corrosion Behavior of Zr-0.8Sn-0.35Nb-0.4Fe-0.1Cr-xBi Alloys in Superheated Steam at 400 ℃/10.3 MPa

An autoclave was employed to investigate the effect of Bi contents on the corrosion resistance of Zr-0.8Sn-0.35Nb-0.4Fe-0.1Cr-xBi (x=0.1%-0.5%, mass fraction) alloys in superheated steam at 400 ℃ and 10.3 MPa. The microstructures of the alloys and oxide films on the corroded specimens were observed by TEM and SEM, respectively. The results show that (0.1%-0.5%) Bi addition can improve the corrosion resistance of the Zr-0.8Sn-0.35Nb-0.4Fe-0.1Cr alloy, but the degree of the improvement effect decreases with the increase of Bi contents. Only Zr(Fe,Cr,Nb)2 second phase particles (SPPs) were detected in the alloy with 0.1% Bi; Zr(Fe,Cr,Nb)2 and Zr-Fe-Sn-Bi SPPs were detected in the alloy with 0.3% Bi. Zr(Fe,Cr,Nb)2, Zr-Fe-Sn-Bi and Zr-Fe-Cr-Nb-Sn-Bi SPPs were detected in the alloy with 0.5% Bi. This implies that the Bi addition promotes the precipitation of Sn as the SPPs and the solid solubility of Bi in α-Zr matrix of Zr-0.8Sn-0.35Nb-0.4Fe-0.1Cr-xBi alloys is not less than 0.1% at 580 ℃. From the above results, it can be concluded that the Bi as solid solution in α-Zr matrix can improve the corrosion resistance, however, the precipitation of SPPs containing Bi and Sn is deleterious to the corrosion resistance.