Effect of DC Plasma Electrolytic Oxidation on Surface Characteristics and Corrosion Resistance of Zirconium.

Maciej Sowa,Wojciech Simka

doi:10.3390/ma11050723

Maciej Sowa, Wojciech Simka

Open Access

https://doi.org/10.3390/ma11050723

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Abstract

Zr is a valve metal, the biocompatibility of which is at least on par with Ti. Recently, numerous attempts of the formation of bioactive coatings on Zr by plasma electrolytic oxidation (PEO) in solutions that were based on calcium acetate and calcium β-glycerophosphate were made. In this study, the direct current (DC) PEO of commercially pure zirconium in the solutions that contained Ca(H2PO2)2, Ca(HCOO)2, and Mg(CH3COO)2 was investigated. The treatment was conducted at 75 mA/cm2 up to 200, 300, or 400 V. Five process stages were discerned. The treatment at higher voltages resulted in the formation of oxide layers that had Ca/P or (Mg+Ca)/P ratios that were close to that of hydroxyapatite (Ca/P = 1.67), determined by SEM/EDX. The corrosion resistance studies were performed using electrochemical impedance spectroscopy (EIS) and DC polarization methods. R(Q[R(QR)]) circuit model was used to fit the EIS data. In general, the coatings that were obtained at 200 V were the most corrosion resistant, however, they lacked the porous structure, which is typical for PEO coatings, and is sought after in the biomedical applications. The treatment at 400 V resulted in the formation of the coatings that were more corrosion resistant than those that were obtained at 300 V. This was determined mainly by the prevailing plasma regime at the given process voltage. The pitting resistance of Zr was also improved by the treatment, regardless of the applied process conditions.

Highlights

There are many requirements posed implantable medical materials, like sufficient mechanical strength, good biocompatibility, and chemical stability
1a), at the microscopic scale, the grained structure was revealed (Figure 1b). Such a long long etching time (2 min) was necessary since shortening of this process resulted in the formation etching time (2 min) was necessary since shortening of this process resulted in the formation of dark of dark residue composed of corrosion products of Zr and the remainder of the SiC particles after residue composed of corrosion products of Zr and the remainder of the SiC particles after the the grinding
The work that was described here was concerned with the direct current plasma electrolytic oxidation of commercially pure zirconium performed in a galvanostatic/potentiostatic manner

Summary

Introduction

There are many requirements posed implantable medical materials, like sufficient mechanical strength, good biocompatibility, and chemical stability. Polymeric biomaterials are gradually increasing their significance in the biomedical applications [1,2], metals and alloys are still unparalleled as dental and orthopedic implants [3]. Titanium and its alloys are among the most popular metallic biomaterials because of the excellent corrosion resistance and their very good strength-to-weight ratio. Ti-6Al-4V, in particular, is extensively used due to the presence of α+β Ti phase, improving its mechanical strength even further. The presence of V in the alloy caused concern because of its cytotoxicity [4], while Al is known to be neurotoxic and it might be responsible for Alzheimer’s disease [5]. More interest has been given to β phase Ti alloys, which exhibit lower Young modulus, thereby decreasing the stress-shielding effect [6,7,8]

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