Plasma Electrolytic Oxidation (PEO) coatings on a zirconium alloy for improved wear and corrosion resistance

Abstract

Zr oxide coatings were deposited using plasma electrolytic oxidation (PEO) on Zr-2.5wt%Nb (Zr-2.5Nb) alloy, which is currently used for pressure tubes in the CANDU nuclear reactor. The effects of two PEO processing factors, electrolyte concentration and current density, on the microstructure and properties of the coatings were systematically investigated. The coating morphology and chemical composition were determined using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). Potentiodynamic polarization corrosion testing was used to examine the corrosion resistance of the coatings in a dilute aqueous, LiOH solution. Pin-on-disc wear tests were performed under dry and lubricated sliding conditions. SEM was also used to characterize the wear traces on the coated and uncoated surfaces. A 30-day autoclave experiment was carried out to study the corrosion performance of the Zr-2.5Nb substrate, PEO coatings and a commercial autoclaved black oxide coating. Based on the results of this research, recommendations are made as to processing parameters for the production of oxide coatings with improved wear and corrosion resistance.

Plasma Electrolytic Modification of Zirconium and Its Alloys: Brief Review

“…On the alloy Zr-2.5 wt.% Nb, which is applied for pressure tubes of nuclear reactors, oxide coatings were synthesized using plasma electrolytic modification (PEM) [ 77 , 78 ]. The effect of treatment factors such as electrolyte composition and current density on microstructure and coating properties was systematically investigated.…”

“…The authors of [ 77 ] performed gravimetric studies of the modified alloy’s ability to resist oxidation. Figure 7 shows the weight gain changing with the exposure time in the autoclave for up to 30 days at 300 °C and the high pressure of 10 MPa in 0.05 mol/L LiOH solution.…”

Plasma Electrolytic Oxidation Treatment of Zr-2.5%Nb Alloy for Corrosion Resistance Enhancement

“…However, plasma electrolytic oxidation (PEO) coatings attracted attention in the last decade regarding the improvement of wear and corrosion resistance of zirconium nuclear alloys by growing ZrO 2 protective layers during electrochemical oxidation of metal surfaces [11,12]. Additionally, taking into account the limited available literature on PEO-treated Zr alloys, including Zy-2 [13,14], Zy-4 [15,16], Zr-1%Nb [17,18] and Zr-2.5%Nb [19,20], further work will be required to optimize and improve the coating layers in the approach of material-coolant interaction.…”

X-ray Computed Tomographic Investigation of the Porosity and Morphology of Plasma Electrolytic Oxidation Coatings

“…Plasma electrolytic oxidation (PEO) processes are considered to be among the most environmental-friendly surface treatments of aluminum, magnesium, and titanium alloys, providing good wear and thermal and corrosion resistance. − The coatings have potential for applications in a wide range of industry sectors, including aerospace, automotive, textile processing, electronic components, energy, oil and gas, and leisure and sports products . The coatings are further being developed for catalysis, − biocompatibility, , drug release systems, sensors, decorative finishing, and as nanostructured and nanocomposite coating materials. , Furthermore, PEO of zirconium and zirconium alloys is of interest for thermal barriers, for improved wear and corrosion resistance in nuclear applications, and for implants. − Porous ceramic coatings are formed during PEO with the assistance of dielectric breakdown at the sites of short-lived microdischarges. , The conditions employed for carrying out PEO, such as surface pretreatment, electrolyte composition, current density, waveform, and time of the treatment, have significant effects on the discharge characteristics and, hence, affect the morphology, density, and composition of the coating. ,− Typically, the PEO coatings consist of an interfacial barrier-like film, up to 1000 nm thick, an inner denser layer, and an outer porous layer containing large cavities . PEO processes can form coatings across a wide range of thicknesses up to several hundreds of microns, − commonly with a linear dependence on treatment time …”