Volume 7, Issue 7 (July 2010)
The Evolution of Microstructure and Deformation Stability in Zr–Nb–(Sn,Fe) Alloys Under Neutron Irradiation
A review is given on the effect of neutron irradiation on the microstructure and properties of Zr–Nb and Zr–Nb–Fe (Sn,O) alloys. The in-reactor performance of Zr alloys is dependent on their composition and microstructure, and even small changes in the composition and processing lead to substantial changes in properties as a result of evolution of precipitates and matrix composition. The development of a new generation of alloys of Zr–Nb–Fe (Sn,O) system (that show higher resistance to the irradiation-induced growth, creep, and corrosion) required an examination of their microstructure during the manufacturing process and evolution after neutron irradiation. The basic irradiation phenomena involve irradiation-induced damages (formation of the a- and c-component dislocations) and redistribution of alloying elements. The influence produced by precipitates containing Zr, Nb, and particularly Fe on the properties under irradiation is demonstrated. Relationships between composition, microstructure, and irradiation-induced growth of the Zr–Nb–Fe–Sn are described. An increased content of iron (over limit of the solubility) in Zr–Nb alloys leads to lower irradiation growth and creep and to strengthening of the matrix as a result of Fe leaving Laves phase (HCP) particles with their transformation into β-Nb (bcc). β-Nb precipitates become depleted in niobium (or enriched in zirconium), and finely dispersed irradiation-induced secondary particles enriched in niobium are formed. The basic microstructures that illustrate neutron damage structures, precipitates instability, evolution, and irradiation growth are shown and discussed.