Microstructure of Zr-2.5Nb Alloy Pressure Tubing

Abstract

The microstructure of Zr-2.5Nb nuclear reactor pressure tube material has been studied using electron microscopy. X-ray diffraction, and energy dispersive X-ray spectroscopy techniques. The materials studied contained a range of impurity contents with iron ranging from 300 to 1500 ppm in both the cold-worked and cold-worked + annealed (24 h/560°C) conditions. Cold-worked tubes consisted of deformed α-Zr grains with a network of β-Zr (∼20wt%Nb) surrounding the α-Zr grains. Annealing produced a decomposition of the β-Zr phase into α-Zr and β-Nb (∼83 wt% Nb). Cold-worked tubing with Fe contents ⩾500 ppm also contained a very small volume fraction of Zr2Fe precipitates having a tetragonal structure, β-quenching during fabrication of the tubing appeared to suppress the precipitation of Zi2Fe. On annealing, both Zr(FeCr)2 and Zr2Fe precipitates were formed. The Zr(FeCr)2 precipitates had either the C-15 cubic or C-14 hexagonal Laves phase structure. It is proposed that on annealing at 560°C the β-Zr phase (containing Fe and Cr in solution) transforms to α-Zr + β-Nb + Zr(FeCr)2 phases.

The characterisation of second phases in the Zr-Nb and Zr-Nb-Sn-Fe alloys: A critical review

“…In 1991, Northwood et al reported on the microstructure of Zr-2.5Nb (wt.%) [33]. Whilst the authors noted that their standardless Cliff-Lorimer approach to chemical quantification by energy dispersive X-ray spectroscopy (EDS) could result in an error in Fe measurement of as much as ± 25 at.%, they did not provide any evidence to support their claim that "there is a small amount of Fe and Cr in most of the β particles".…”

Creep properties of annealed Zr–Nb–O and stress-relieved Zr–Nb–Sn–Fe cladding tubes and their performance comparison

“…It is known that Sn atoms in the Zr alloys may suppress grain boundary movement, retarding grain growth and making grains finer [13]. In general, the cold-worked metals are thermodynamically in an unstable state and internal energy accumulated during cold-working process is used as the driving force for recrystallization and grain growth [14]. The smaller grain size in Zr-Nb-Sn-Fe alloy tubes in comparison with that of Zr-Nb-O alloy tubes as seen in Fig.…”

Creep performance of Zr-1Nb-0.75Sn-0.1Fe cladding tubes with optimized Sn content

“…It is known that Sn atoms in the Zr alloys may suppress grain boundary movement, retarding grain growth, and making grains finer [13]. In general, the cold worked metals are thermodynamically in an unstable state, and internal energy accumulated during the cold working process is used as the driving force for recovery, during stress relief heat treatment [14].…”