Microstructure of Bi-containing zirconium alloys

Abstract

The effect of Bi addition (0.05 wt%–0.50 wt%) on the microstructure of zirconium alloys, including T5 (Zr–0.7Sn–1.0Nb–0.3Fe–0.1Cr), S5 (Zr–0.8Sn–0.35Nb–0.4Fe–0.1Cr), Zr–4(Zr–1.5Sn–0.2Fe–0.1Cr) and Zr–1Nb, was investigated by transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS) and selected area electron diffraction (SAED). Results show that with the increase in Bi content, h-Zr(Fe,Cr,Nb)2, o-Zr(Fe,Sn,Bi)2 and Zr–Fe–Cr–Nb–Sn–Bi second-phase particles (SPPs) precipitate successively in the T5 + xBi and S5 + xBi alloys; in the Zr–4 + xBi alloys, h-Zr(Fe,Cr)2, o-Zr(Fe,Sn,Bi)2, Zr–Fe–Cr–Sn–Bi and Zr–Fe–Cr–Bi SPPs are detected successively. While as for Zr–1Nb + xBi alloys, Bi-free SPPs appear. The addition of Bi promotes the precipitation of SPPs with Sn in the alloys. The concentration of Bi dissolved in α-Zr matrix increases with the decrease in Sn content in the alloys. Adding reasonable Bi has little influence on the solid solution content of Nb in α-Zr matrix.