Effect of Final Annealing Temperature on Corrosion Resistance of SZA-6 Zirconium Alloy Cladding Tubes

Abstract

The corrosion resistance of SZA-6 zirconium alloy(Zr-0.5Sn-0.5Nb-0.3Fe-0.015Si) cladding tubes finally annealed at 480°C, 510°C and 560°C were studied by static autoclave in 360°C/18.6 MPa pure water and 360°C/18.6 MPa/0.01 mol/L LiOH aqueous solution. The microstructure of the samples before and after corrosion were analyzed by EBSD, TEM and SEM. The results showed that the corrosion weight gains of the three SZA-6 alloy samples were lower than that of Zr-4 alloy after 500 days corrosion in both hydrochemical mediums. After long-term corrosion, the corrosion weight gains of SZA-6 alloy in pure water and LiOH aqueous solution increased obviously with the final annealing temperature, while the corrosion weight gain of unstressed Zr-4 alloy was higher than that of recrystallized under the same condition. With the increase of the final annealing temperature, the high-angle grain boundaries in the alloy larger than 15° became more and recrystallization degree also increased. The Second Phase Precipitates (SPPs) were fine, uniform, and dispersively distributed with an average diameter of about 120 nm. Although the size and distribution of the SPPs were similar, the Nb/Fe ratio in the SPPs increased. The long-term corrosion weight gain of zirconium alloy was related to the number of parallel cracks in the oxide film and the uneven growth degree of the oxide film on the interface of the oxide film/matrix. The corrosion resistance of the alloy in two hydrochemical mediums was related to the degree of recrystallization and the content of Nb in the SPPs. Increasing the final annealing temperature would promote the formation of fine and uniform recrystallized grains, which was benefit to the corrosion resistance, but at the same time it would reduce the content of solid solution Nb in the αZr matrix, which in turn would be detrimental to the corrosion resistance.

Temperature sensitivity and transition kinetics of uniform corrosion of zirconium alloys in superheated steam

“…N36 alloy has the largest weight gain, N3 alloy in the intermediate and N2 alloy the smallest. Whereas, the corrosion resistance of Zr-4 obviously changes from the worst in 360 °C pure water [ 5 , 26 ], the intermediate at 390 °C/10.3 MPa and 416 °C/10.3 MPa, to the best at 455 °C/10.3 MPa in superheated steam, which suggests that the temperature-sensitivity of uniform corrosion are quite different between Zr–Sn–Nb alloys and Zr–Sn alloy.…”

“…However, it is found that Zr-4 alloy is very particular with its temperature-sensitivity behavior because of the intersection in fitting curves of both pre-exponential constant and transition time. Although it is the worst corrosion-resistant alloy in service temperature lower than 360 °C [ 5 , 26 ], as temperature raising, its pre-exponential constant becomes the smallest and the transition time becomes the longest among all the four materials above 427 °C.

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“…Up to now, prediction of time or oxide thickness to transition has been limited by the lack of knowledge about transition kinetics and how transition responds to varied temperature. Although there were research data on corrosion or oxidation of zirconium alloy at different temperature [ 6 , 26 , 27 ], the corrosion atmosphere and alloys deviated from each other, and data was unable to be analyzed together by kinetics method. The only knowledge we have obtained is that transition time dramatically decreases with temperature [ 5 , 6 , 12 ].…”

Hydrogenation Behavior of Cr-Coated Resistance Upset Welds of E110 Zirconium Alloy

“…According to Table 2, the magnetron deposition of the Cr coating on the outer surface of the RUW E110 alloy did not affect its hardness using the applied deposition parameters. The maximal temperature of the RUW alloy during Cr coating deposition (390 °C) was less than the typical annealing temperature of Zr alloy cladding tubes and welds (500-580 °C) [34,35]. The hydrogenation of RUW specimens led to the hardening of both types of specimens (Cr-coated and uncoated) due to a formation of the δ-ZrH phase.…”

Review on chromium coated zirconium alloy accident tolerant fuel cladding

“…Nevertheless, the thermal treatment temperature of the Cr coated Zr alloy should be strictly controlled based on the following three considerations: firstly, the final annealing temperature of the commercially used Zr alloy cladding tubes is about 500 °C [102]. A higher pretreatment temperature of the Cr coated Zr alloy leads the phase transition of the Zr substrate (850 °C), which may affect the mechanical properties and corrosion resistance of the Zr substrate [103]. Secondly, the inter-diffusion between the Cr coating and the Zr substrate would be facilitated by the high temperature, which is one of the main consumption ways of Cr coatings [104].…”