Effect of S Addition on the Second Phase Particles of Zr-Sn-Nb-Fe Zirconium Alloy

To study the effect of S on the second phase particles (SPPs) of zirconium alloys, alloy samples were prepared by adding different contents of S (26 similar to 570 mu g/g) into Zr-0.70Sn-0.35Nb-0.30Fe alloys. SEM and TEM with EDS were used to investigate the composition and crystalline structure of SPPs. The results show that in Zr-0.70Sn-0.35Nb-0.30Fe alloy, there exists Zr(Nb,Fe)(2) SPPs with hexagonal close packed structure, while in the alloys containing S, orthogonal Zr3Fe SPPs appear besides Zr(Nb,Fe)(2) SPPs and the Zr3Fe SPPs increase in amount with increasing S content. Zr9S2 SPPs occur when the S content reaches 190 mu g/g, and also increase in amount with further increasing S content. The ratio of Nb/Fe decreases with the increase of SPPs' size in the same zirconium alloy. It is indicated that the S content dissolving in alpha-Zr matrix is between 26 mu g/g and 190 mu g/g for the alloys in this study and the excess S dissolving in alpha-Zr matrix is precipitated as Zr9S2 SPPs rather than entering into other SPPs.