Corrosion Behavior Of Zirconium Alloys Research Articles

Effect of microstructure variation induced by processing on corrosion behavior of Zr-Sn-Nb alloy

In order to investigate the effect of microstructure variation induced by processing on corrosion behavior of zirconium alloys, Zr-Sn-Nb alloy original plates were processed by rolling and annealing, and the microstructure and corrosion behavior of both original plates and processed plates were analyzed. It was found that after the original plates were processed, the recrystallized microstructure in original plates was transformed to stress-relieved microstructure in processed plates, with second phase particles ripening. When exposed to pure water and water containing H3BO3 and LiOH, the original plates have better corrosion property than the processed plates, and the corrosion transition of the processed plates happened earlier than that of the original plates. The grain structure differences of original plates and processed plates have two aspects of influence on oxide cracking and corrosion transition. Firstly, there were more defects in processed plates which results in smaller grains and larger grain boundary areas in oxide. Secondly, the strength of processed plates is higher, and this will lead to less stress accommodation of the growing oxide by plastic deformation of the matrix, and higher stress in oxide layer formed during the corrosion process. Both factors caused more cracks in the oxide layer of processed plates, leading to earlier corrosion transition and decreasing corrosion property. Second phase particles and their surroundings are susceptible to cracks during corrosion process, and may become the original source of cracks. However, second phase particle ripening was not closely related to decreasing corrosion property of processed plates.

The effect of chromium-based coatings on corrosion behavior of alloy Zr1Nb in 70ppm Li+ water environment

Recent research indicates that one of the leading candidates for Accident Tolerant Fuels (ATF) are chromium-based coatings deposited on the commercially used zirconium alloys. The chromium-based coatings seem to improve the corrosion kinetics of underlying zirconium in both primary water and steam, where zirconium fails to meet the safety requirements. It is well known that the corrosion kinetics of zirconium can be negatively influenced by high concentrations of lithium ions. To evaluate the effect of chromium-based coatings on corrosion behavior of zirconium alloys in water containing elevated concentrations of lithium, Cr and CrN/Cr multilayer coated Zr1Nb alloy was tested in high temperature water containing 70 ppm Li+. Using Electrochemical Impedance Spectroscopy (EIS), Scanning Electron Microscopy (SEM) and Energy-dispersive X-ray Spectroscopy (EDX), we have found that the chromium coating could have a positive effect on the underlying material as it behaves as a good diffusion barrier for oxygen and Li+ions. On the other hand, CrN/Cr coating, due to not sufficient structural integrity of the multilayer, showed non-protective behavior to the Zr1Nb alloy. Our results suggest that certain chromium coatings can significantly enhance corrosion resistance in lithium containing water environments.

Effect of dissolved oxygen on corrosion behavior of Zr–0.85Sn–0.16Nb–0.37Fe–0.18Cr alloy in 500 °C and 10.3 MPa super-heated steam

Abstract To better understand the role of dissolved oxygen (DO) in affecting corrosion behavior of zirconium alloys, the Zr–0.85Sn–0.16Nb–0.37Fe–0.18Cr (wt.%) alloy was corroded in super-heated steam at 500 °C and 10.3 MPa under 1×10−6 DO and deaeration conditions. The microstructure of the alloy and oxide films was investigated by SEM, TEM, EDS and EBSD. Results show that the corrosion is aggravated under 1×10−6 DO. Compared with the deaeration condition, the oxide film is looser, and has more micro-cracks and more uneven inner surface under DO condition. For the oxide film forming under deaeration condition, the selected area diffraction (SAED) spots of planes (002)m, and (101)t are strong, while those of the (001)m and are weak. However, for the oxide film forming under DO condition, the SAED spots of planes (111)m, (200)m and (101)t are strong, while those of the (100)m and (110)m are weak. The higher DO content in super-heated steam accelerates the growth of oxide films, thus decreasing the corrosion resistance of zirconium alloys.

Research on the existence and stability of interfacial tetragonal zirconia formed on zirconium alloys

Corrosion of zirconium claddings is one of the key properties that must be considered when designing new zirconium alloys. Tetragonal phase is formed on the zirconium matrix during high temperature corrosion and is mainly stabilized near the metal/oxide interface. This phase has a tremendous influence on the corrosion behavior of zirconium alloys. T-ZrO2 phase formed on Zr-0.5Sn-0.15Nb-0.5Fe-0.2 V (N2) and Zr-1.0Sn-1.0Nb-0.3Fe (N36) claddings corroded in 773 K/10.3 MPa steam were studied. A Micro Raman spectrometer was used to analyze the existence and stability of oxide phase before and after dissolution of the zirconium matrix. The result indicates that interfacial t-ZrO2 is not transformed after the removal of the zirconium matrix. Even though most of the stress in m-ZrO2 is released, the lattice distortion in t-ZrO2 still exists, causing this phase to deviate from normal state and maintain its stability. We suggest that the possible reason for stabilizing t-ZrO2 is not the released macroscopic compressive stress, but the existence of small tetragonal grains or large amount of vacancies which can also introduce lattice distortions. The results highlight the important role of oxygen vacancies. Therefore, the stability of t-ZrO2 after matrix dissolution provides us with a chance to observe the microscopic evolution of tetragonal phase at the inner face. T-ZrO2 grows with increasing corrosion time and its intensity drops down after transition. Its microscopic distribution seems to be related to oxide particles and interfacial waviness.

The correlation between tetragonal phase and the undulated metal/oxide interface in the oxide films of zirconium alloys

The transition mechanism is of significance to the corrosion behavior of zirconium alloys. Two important phenomena may be the causes of transition, which are the undulated wavy interface and the existence of tetragonal zirconia at the metal/oxide interface. There is little detailed study on the correlation between these two features. Micro-scale Raman imaging of intensity and Raman shifts was conducted in this study to further evaluate the connection. It was studied based on the oxide films formed on Zr-0.5Sn-0.15Nb-0.5Fe-0.2 V and N36 claddings corroded in 500 °C/10.3 MPa steam. The stress in interfacial tetragonal zirconia has relationship with the amplitude to wavelength ratio of the undulated part and it is always found to be larger at the convex parts of interface. These parts are prone to crack formation. At one convex position that the oxide cracked, t-ZrO2 is found to be preserved beneath and above the crack. Stress is also preserved, but partially released. When interfacial t-ZrO2 exists, the stress in the surrounding monoclinic phase is observed to be small. This provides us a more detailed figure of the stress distribution in oxide film. Tetragonal phase is mainly distributed near the metal/oxide interface. More intense tetragonal signals are frequently found at the convex positions of interface. This might result from large tetragonal grains or aggregation of small t-ZrO2 grains. These grains are stabilized at convex parts because of the large compressive stress and might be unstable once the grain size exceeds a critical value or once cracks are formed at such positions. An illustration of the connection between t-ZrO2 and undulated interface is then proposed. Possible reasons that facilitate the formation of lateral cracks and possible reasons for the existence of t-ZrO2 at the convex positions are discussed.

Influence of dissolved hydrogen on the early stage corrosion behavior of zirconium alloys in simulated light water reactor coolant conditions

The dissolved hydrogen concentration in the water phase represents a key factor for corrosion characteristic of zirconium alloy. A zirconium alloy was oxidized for 100d at two different concentrations, 2.49 and 4.15mg/kg. In situ Raman peaks of the specific oxide phases changed, indicating the occurrence of phase transformation. Moreover, the result of transmission electron microscopy was compared with in situ analysis of the oxide structure formed on the zirconium alloy. The phase stability of the oxide could be influenced by the dissolved hydrogen, and it the phase transformation from tetragonal to monoclinic is influenced by dissolved hydrogen.

Corrosion Behavior of Zirconium Alloys with Nb and Cr Addition

Corrosion Behavior of Zirconium Alloys with Nb and Cr Addition

Corrosion behavior of Zr–Nb–Cr cladding alloys

Zr–Nb–Cr alloys were used to evaluate the effects of alloying elements Nb and Cr on corrosion behavior of zirconium alloys. The microstructures of both Zr substrates and oxide films formed on zirconium alloys were characterized. Corrosion tests reveal that the corrosion resistance of ZrxNb0.1Cr (x = 0.2, 0.5, 0.8, 1.1; wt%) alloys is first improved and then decreased with the increase of the Nb content. The best corrosion resistance can be obtained when the Nb concentration in the Zr matrix is nearly at the equilibrium solution, which is closely responsible for the formation of columnar oxide grains with protective characteristics. The Cr addition degrades the corrosion resistance of the Zr1.1Nb alloy, which is ascribed to Zr(Cr,Fe,Nb)2 precipitates with a much larger size than β-Nb.

1094.ジルコニウム合金の均一腐食および水素吸収に及ぼす析出物の電気化学的役割,(I)

Substantial roles of precipitates such as Zr-Fe-Cr type intermetallic compounds on uniform corrosion and hydrogen pickup of zirconium alloys in pure water autoclave tests were investigated from an electrochemical point of view. This paper describes the roles on corrosion. A corrosion test on precipitate-containing and precipitate-free materials made from pure zirconium and a small quantity of iron and chromium, rest potential measurements on an intermetallic compound of Zr(FeCr)2 and zirconium matrix, and a galvanic coupling test of those were performed. Results showed that corrosion behavior of zirconium alloys could be attributed to the electrochemical properties of intermetallic compounds precipitated in each alloy. Namely, the cathodic and anodic polarization characteristics were associated with anodic protection provided by the precipitates on the alloys and the precipitates degradation in the oxide films, respectively. The mechanism was confirmed through a corrosion test of Zr-X(X=0.2Fe, 0.2Cr, 0.1Fe-0.1Cr) alloys and electrochemical measurements of ZrFe2, ZrCr2, and Zr(FeCr)2 intermetallic compounds.

鋯合金腐蝕行為的研究(1940-1995)Part III.結瘤腐蝕

The present work critically reviewed the nodular corrosion behavior of zirconium alloys. Four import topics are described: the phenomena and behavior, the various factors affect nodular corrosion resistance, the mechanisms of nodular corrosion, and the effects of radiation damage on corrosion behavior.