Atom Probe Tomography Study of Fe Segregation at Phase Interface in Zr-2.5Nb Alloy

doi:10.1007/s40195-019-00927-x

Abstract

Abstract:

β-Nb is a typical second phase in Zr-Nb-based alloys used as fuel claddings in water-cooled nuclear reactors. The segregation of alloying element Fe may affect the corrosion resistance of Zr-Nb-based alloys. In this work, the Fe segregation at the interface between β-Nb phase and α-Zr matrix in Zr-2.5Nb alloy was studied using atom probe tomography and focused ion beam. The results suggested that the Fe concentration was much lower than Nb concentration in α-Zr matrix, while Fe selectively segregated at the β-Nb/α-Zr phase interface, leading to a Fe concentration peak at some interfaces. The peak Fe concentration varied from 0.4 to 1.2 at.% and appeared at the position where Zr concentration was approximately equal to Nb concentration. The selective segregation of Fe should be affected by the heat treatment and structure defects induced by cold rolling.

Key words: Zr-Nb alloy, β-Nb phase, Phase interface, Segregation, Atom probe tomography

Xue Liang, Qiang Li, Jiao Huang, Mei-Yi Yao, Hui Li, Qing-Dong Liu. Atom Probe Tomography Study of Fe Segregation at Phase Interface in Zr-2.5Nb Alloy[J]. Acta Metallurgica Sinica (English Letters), 2019, 32(10): 1281-1286.

Figures/Tables 6

Fig. 1 Fabrication process of APT specimen by using FIB: a select an area of 10 μm × 2 μm on the surface; b isolate the volume, weld it to a micromanipulator and lift it out; c move the volume to a silicon post; d weld the volume to the silicon post; e, f cut off the volume with the micromanipulator; g milling stage; h cleaning-up to finish the fabrication of APT tip

Fig. 2 TEM micrograph of Zr-2.5Nb alloy showing spherical β-Nb precipitates and rod-like β-Zr phase in the α-Zr matrix

Fig. 3 APT reconstructed atom maps of Zr, Nb and Fe in the Zr-2.5Nb alloy, showing homogeneous distribution of Zr, Nb and Fe atoms. The size of the volume analyzed is 114 nm × 113 nm × 289 nm

Fig. 4 a-c APT reconstructed atom maps of Zr, Fe and Nb in the Zr-2.5Nb alloy, showing Fe segregation and β-Nb precipitates in the matrix. The size of the volume analyzed is 90 × 88 × 284 nm3, d Fe atom map and 80 at.% Nb iso-concentration surface. All the precipitates are marked by arrows, e, f proxigram profiles for Zr, Nb and Fe of two selected β-Nb precipitates (P1 and P3, respectively) shown in d

Fig. 5 a, b APT reconstructed atom maps of Nb and Fe in the Zr-2.5Nb alloy, c 50 at.% Nb iso-concentration surface showing β-Nb precipitates, d proxigram profiles for Zr, Nb and Fe of the β-Nb precipitates marked by P7 in c

Fig. 6 HRTEM image of interface structure between the large β-Nb phase and α-Zr matrix in the Zr-2.5Nb alloy

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