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

Abstract

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 film 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 a-Zr matrix of Zr-4+xBi alloys is less than 0.1%at 580°C.Moreover,the addition of Bi promotes the precipitation of Sn which originally dissolved in theα-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.