Characteristics of CeO 2 /ZrO 2 -HA composite coating on ZK60 magnesium alloy
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Renguo Song School of Materials Science and Engineering, Changzhou University, Changzhou 213164, China; and Jiangsu Key Laboratory of Materials Surface Science and Technology, Changzhou University, Changzhou 213164, Jiangsu, China (Received 28 October 2016; accepted 19 January 2017)
A CeO2/ZrO2-hydroxyapatite (HA) composite bio-ceramic coating was prepared on ZK60 magnesium (Mg) alloy by using micro-arc oxidation (MAO) and electrophoretic deposition (EPD). MAO coating was done as the basal layer was grown in alkaline electrolyte with the addition of nanoparticles (CeO2 and ZrO2) to improve the mechanical properties of coating. A HA coating as the covering layer was deposited on the surface of MAO coating for improving the biological properties of the coating. The phase compositions and morphology of coatings were monitored with X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Adhesion and wear resistance of coatings were evaluated using a scratch test and a pin-on-disc sliding wear test. The corrosion resistance of coatings was evaluated in a simulated body fluid (SBF) using electrochemical tests at 36.5 6 0.5 °C. The experimental results showed that the CeO2/ZrO2-HA composite coating on Mg alloy effectively improved its mechanical properties and corrosion resistance. Combining MAO and EPD is a promising modification technology for degradable Mg alloys as biomaterials.
I. INTRODUCTION
Mg and its alloys are promising implant materials in orthopedic applications due to their attractive mechanical and biological performances:1–4 (i) the density, elastic modulus, and yield strength of Mg-based materials are much closer to those of natural bone, which can greatly reduce the stress shielding effect; (ii) Mg-based materials are easy to be degraded in the body fluid environment by corrosion, and Mg21 can catalyze new bone tissue growth and bone binding with implants, which make the patients free from a second operation. However, Mg and its alloys have a high degradation rate in the human body fluid, which are possible to lose the mechanical integrity before the tissue haled due to the rapid corrosion.1 To slow down the biodegradation rate of Mg-based materials and improve their mechanical properties, it is necessary to employ a proper treatment technique to improve the surface properties of materials. MAO is a convenient and promising approach to form ceramic coatings on the surface of light metals such as Ti, Al, and Mg. It is an electrochemical technique for the formation Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.48
of an anodic ceramic layer by spark/arc micro discharges in a suitable electrolyte.5,6 After the MAO process, the surface properties, such as corrosion resistance, wear resistance, hardness, and adhesion to substrate can be considerably improved.7–9 However, it is undeniable that the ordinary MAO coating still has some shortcomings, such as micro-pores, micro-cracks, and lack of biological acti
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