Corrosion-Electrochemical Properties of Zirconium Intermetallics

Abstract

Alpha-zirconium is a very poor solvent for most alloying metals. Moreover, it has a high affinity for these metals. Consequently, intermetallics are easily formed and highly visible in zirconium and its alloys. Many researchers believe that the corrosion resistance of zirconium and its alloys depends strongly on the distribution and morphology of these intermetallics. Corrosion problems, such as nodular corrosion and intergranular corrosion, are often associated with intermetallics. Numerous papers have been published concerning the role of intermetallics in nodular corrosion of Zircaloys. Several mechanisms have been proposed for nodule initiation and growth. They include one or more of the following factors: local solute depletion, electrochemical effects, oxide ductility, electronic and ionic conductivities of the surface oxide, induced stresses, and oxide structure transformation. However, very limited studies have been directly done on the corrosion properties of these intermetallics. Therefore six intermetallics (Zr2Fe, Zr3Fe4Cr2, Zr10Fe3Ni2, Zr4Sn, ZrCr2, and 3Zr2Ni) were prepared for corrosion and electrochemical tests. These intermetallics were chosen since tin, iron, chromium, and nickel are the principal alloying elements in Zircaloys, and the selected intermetallics have been identified in the alloy matrix. In addition to these intermetallics, Zircaloy-2, Zircaloy-4, and crystal-bar zirconium were also included in this study. Corrosion and electrochemical tests on selected materials at both ambient and elevated temperatures were performed at Teledyne Wah Chang Albany and at Siemens AG-KWU Group. Selected materials were characterized using SEM/EDX examinations, potential measurements and autoclave tests. From this information the role(s) of intermetallics on corrosion resistance in water and steam are discussed. A new electrochemical-mechanical-passivity (EMP) model is offered to explain observed oxidation of Zircaloy-2 and Zircaloy-4.

Effect of Laser Surface Treatment on the Corrosion Resistance of Zircaloy-4 at High Temperature

“…In Figure 5, we can see that the Fe-Cr precipitates are dissolved and disappear in the LST layer. It is well known that the oxidation rates of the precipitates in zirconium alloys are generally slower than those of α-Zr [45][46][47][48]. Therefore, the precipitates are incorporated into the oxide film.…”

Effect of Cu on microstructure and corrosion behavior in 360°C lithiated aqueous solution of Zr–Cu alloys

“…According to the existing oxidation theories and models, [ 25–27 ] it is known that during the corrosion of Zr alloys, the oxygen ions diffuse toward the O/M interface (or the oxygen ion vacancies diffuse toward the specimen surface) through the oxide layer, leading to the continuous growth of the oxide film. Therefore, the diffusion of oxygen ions plays a key role in the corrosion of Zr alloys.…”

The Influence of Different Contents of Bi Addition on the Corrosion Behavior of Various Zirconium-Based Alloys

“…From another angle, the corrosion of zirconium alloys in deionized water or in superheated steam with high temperature and pressure is also an electrochemical process. The SPPs at the Zr/ZrO 2 interface and α-Zr matrix constitute many micro batteries during oxidation, and α-Zr matrix is preferentially oxidized as anode [23]. On one hand, the Bi dissolved in α-Zr matrix may change the potential of matrix, and reduce the potential difference between the matrix and SPPs, which will slow down the process of electrochemical corrosion and improve the corrosion resistance of alloys; On the other hand, the addition of Bi change the composition and type of SPPs, and the potentials of various SPPs exist diffidence.…”