Short communicationPreparation of bioceramic films containing hydroxyapatites on Ti–6Al–4V alloy surfaces by the micro-arc oxidation technique
Introduction
With increasing demand for a substitute material for the replacement of hard tissue, such as bone, teeth, etc., bioceramic films on titanium/titanium alloy surfaces with appropriate biological activity have become a research focus in the field of materials science [1], [2], [3], [4], [5], [6], [7]. A typical technique for the surface modification of medical titanium and titanium alloys is the plasma spray processing at present, but this technique has some shortcomings. For example, the preparation of coatings on a complicated alloy surface is very difficult. In particular, if bioceramic films are formed and applied at elevated temperatures, they will decompose and hence lead to unexpected poor properties. To overcome these shortcomings, the wet techniques of surface modifications, such as electrophoresis and cathode electrodeposit, have been developed, but they still suffer poor bonding strength between coatings and substrate.
Micro-arc oxidation (MAO) processing [8], [9], [10], [11] is a kind of soft chemical technique. In this technique, the surface modification of metals and alloys is realized at the aqueous solution. However, the bioceramic films reported in the literature mostly contain calcium and phosphorus, which are harmful to human being [12]. Especially, the direct synthesis of hydroxyapatite (HAP) has been reported rarely. Even if HAP could be synthesized by MAO, the previously proposed approach cannot achieve satisfactory applications without the help of other techniques [13].
This study presents a novel method for preparing directly HAP on Ti–6Al–4V alloy surface by MAO.
Section snippets
Experimental
Ti–6Al–4V alloy was chosen as the substrate. Its chemical composition is: 5.50–6.75 wt.%Al, 3.5–4.5 wt.%V, 0.2–0.3 wt.%O, < 0.50 wt.%Fe, < 0.50 wt.% other impurity, and balance titanium. The size of Ti–6Al–4V substrate is 40 mm × 10 mm × 3 mm. Prior to MAO, the surface of Ti–6Al–4V specimen was polished step by step with Nos. 280, 400, and 600 sandpaper, respectively, cleaned with acetone, absolute ethanol, distilled water, and ultrasonic, and dried with heat wind. The surface coatings were prepared using a
The influence of MAO electric current density on bioceramic films
Under the treating time of 25 min and different MAO electric current density, XRD patterns of ceramic films on titanium alloy substrate surfaces are shown in Fig. 1. One can see that under low electric current density (0.3 A/cm2), the intensity of the diffraction peak of titanium is the largest, followed by rutile, while the intensity of anatase TiO2 is the lowest. The intensity of HAP diffraction peak is very low. With the increase of the electric current density (0.7 A/cm2), the intensity of the
Conclusions
- (1)
The bioactive HAP has been synthesized on the titanium alloy surface using the micro-arc oxidation technique in the solution containing calcium and phosphorus ion.
- (2)
MAO time and electric current density play an important role in the formation of phases of ceramic films. The increases of MAO time and electric current density are useful for the formation of bioactive HAP in the ceramic films on titanium alloy surfaces.
Acknowledgements
This work was supported by “Program for New Century Excellent Talents in University”, Department of Education of Jilin Province, and “985 project” of Jilin University of PR China.
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2020, Surface and Coatings TechnologyCitation Excerpt :he MAO technique, easy to form a high-quality ceramic layer on the surface of Ti, Mg, Zr, Al, and their alloys, has aroused considerable attention [11–15]. It also can be a convenience to control the electrolyte composition, electrolyte concentration, or adjust the processing condition to enhance surface properties of metal such as corrosion resistance, bioactivity, and adherence strength with the substrate [12,13,16,17]. Micro-arc oxidation (MAO) processes are a functional surface treatment based on electrochemical reactions to high-voltage in a specific electrolyte, which has been extensively used for the deposition of ceramic coatings on the surface of metal [1,18,19].