Role of the Second-Phase Particles in Zirconium Binary Alloys

Abstract

The second-phase particles (SPP) play an important role on the corrosion and hydriding properties of BWR Zircaloy-type materials. It has been proposed that the chemical composition of the SPPs as well as the SPP size distribution strongly affect the in-reactor performance. Zr-Fe, Zr-Cr, and Zr-Ni binary alloys were processed, the size and density of SPP being independently varied through chemical composition and heat treatments. SEM imaging was used to measure the grain size and the SPP size and distribution. Significant differences between binary alloys with iron, chromium, and nickel were observed. Grain sizes depend primarily on size and volume fraction (VF) of SPP. The SPP kinetic growth varies with the alloying element. These observations are compared with corrosion and hydriding data obtained from autoclave experiments at 415 and 500°C, which show that besides the SPP size, their volume fraction is an important parameter (increasing the volume fraction decreases the corrosion rate, whatever the nature of the SPP). On the contrary, air oxidation at 415°C shows very slight influence of SPP type, size, and volume fraction on the corrosion resistance of the material. It should, however, be noticed that the considered test was a short-term test (3 days) and that the oxide layer thickness was less than or around 1 μm for all tested materials. Electrochemical impedance spectroscopy as well as potential sweep and step experiments were used to study the oxidation properties of the binary alloys at room temperature. On samples with large particles, thin compact oxide films are formed. In contrast, on samples with many small particles thick porous oxides are formed. Based on these results and the SPP volume fraction, a tentative mechanism of corrosion and hydriding is proposed, explaining the differences in uniform and nodular corrosion observed between different Zr-based alloys.

Oxidation behaviour of zirconium alloys and their precipitates – A mechanistic study

“…The original reference are stated [6,27]. In certain cases further heat treatment and oxidation is performed in this laboratory.…”

“…A key to answer this question could be to understand the precipitate oxidation behaviour itself, which has been studied for binary [1,2,[5][6][7][8][9][10][11][12][13][14][15][16] and commercial zirconium alloys [14,[17][18][19][20][21][22][23][24][25]. Studies for unirradiated alloys have shown that in the case of Zr 2 (Fe,Ni) precipitates a similar oxidation behaviour to the surrounding matrix has been either reported or can be concluded from the presented results [17][18][19][20].…”

Influence of light ion irradiation of the oxide layer on the oxidation rate of Zircaloy-4

“…This assumption may explain only a part of the high burnup acceleration of the alloy. A second assumption assigned the accelerated corrosion to the amorphisation and the dissolution of the Zr(Fe,Cr) 2 precipitates under irradiation [2,[8][9][10][11][12]. Others authors suggest that the kinetic acceleration is due to the tin distribution in the alloy in service [13][14][15].…”

Corrosion behavior of Zr−Nb alloys in 360°C water and 500°C supercritical water

“…However, most of the effort has been dedicated to improving the performance in the LWR. Moreover, in the open literature, there is no information on the corrosion behavior of Zrbased alloys in the operating condition of a SCWR, although the corrosion resistance in a similar condition such as a 500°C steam has been investigated [4].…”