Creep-induced redistribution of alloying elements in CZ1 zirconium alloys

Abstract

Introducing minor alloying elements is an effective strategy to improve the corrosion and mechanical properties of zirconium alloys for nuclear applications. During in-reactor service, external environment and stress can affect the distribution of alloying elements, substantially changing the degradation process of zirconium alloys. To date, there is a lack of in-depth understanding of the interaction between creep and microchemistry changes. Here, we conducted systematic transmission electron microscopy (TEM) and atom probe tomography (APT) investigations to address creep-induced redistribution of alloying elements in CZ1 (Zr-Sn-Nb-Fe-Cr-Cu) zirconium alloy with different initial microstructures. Nb, Fe, Sn, and Cu are found to co-segregate at grain boundaries. The higher the intermediate annealing temperature, the larger the Gibbsian interfacial excesses of solute elements are. We further demonstrate that creep can reduce the excess value of Fe at grain boundaries due to the coarsening of Zr-Fe-Cr second phase particles via grain boundary and dislocation pipe diffusion. At the same time, the excess value of Sn is increased by diffusing from the matrix to grain boundaries. Moreover, Cu as a minor element in the concentration range of 0.05–0.3 wt.% is found to segregate at dislocations to form the Cottrell atmosphere and develop Cu-rich nanoclusters for suppressing dislocation motion. The new understanding of the segregation and clustering of minor alloying elements provides guidance for developing zirconium alloys with enhanced creep resistance.