Second Phase Particles in Zr-Sn-Nb-Fe Alloys: A Review

In the Zr-Sn-Nb-Fe quaternary alloys, the nature and evolution of the second phase particles (SPPs) is critical to the performance of the alloy in the extremely deteriorative environment. The main aim of this review consists in summarizing the fundamental results of the identification and characterization of the SPPs in the Zr-Sn-Nb-Fe alloys. Emphasis was placed on the importance of composition, identification, crystallographic structure, formation mechanism, and state and stability of several SPPs in these alloys. Identical compositions in ternary Zr-Nb-Fe intermetallics have been identified as C14 HCP Zr(Nb,Fe)(2) or C15 FCC (Zr,Nb)(2)Fe structure. Zr(Nb,Fe)(2) is often reported, while, the cubic phase (Zr,Nb)(2)Fe is easily distinguished. The reliability of R* parameter, which is specified by Nb/Fe physical ratio in determining the SPPs types in different composition range of Zr-Sn-Nb-Fe alloys, is discussed with reasons. The influence and the role of O and Cr in the formation and stability of ternary Zr-Nb-Fe intermetallics are also clarified. Finally, thermodynamic stability of SPPs was also taken into consideration in the current review.