Abstract
A strontium (Sr)-doped hydroxyapatite-like coating was deposited on α-Ti alloy via the growing integration layer (GIL) method at various applied voltages. We added 0.03 M strontium hydroxide (Sr(OH)2·8H2O) to a solution containing calcium acetate and sodium dihydrogen phosphate to produce Sr-doped hydroxyapatite (Sr-HA) coatings. The scanning electron microscope (SEM) images of these coatings showed that all various features, such as average pore size, coating thickness, micro-hardness, and roughness, were similar to those of HA. As the voltage increased from 250 to 300 V, the amount of micro cracks decreased, and there were eliminated at 350 V. The SEM images also showed that the Sr-HA coatings were closely integrated with the alloy: without any gaps between the oxide layers and the alloy. In addition, energy-dispersive X-ray spectroscopy verified the Sr integration from the bottom up. X-ray diffraction patterns confirmed Sr-HA formation instead of calcium phosphate, even at the lowest voltage of 250 V. The value of Ecorr increased by 6.6% after raising the voltage from 250 to 350 V. The electrochemical impedance spectroscopy analysis confirmed that the adequate corrosion resistance of Sr-HA coatings, especially at the highest voltage of 350 V. In addition, the GIL treatment increased the layer resistance measured by Rp/Rc. Optimally, the GIL method used the highest voltage of 350 V to produce higher quality of Sr-HA-rich coatings.
Highlights
A strontium (Sr)-doped hydroxyapatite-like coating was deposited on α-Ti alloy via the growing integration layer (GIL) method at various applied voltages
This paper demonstrates that the micro-structure, composition, and corrosion resistance can be controlled through the voltage applied to grow Sr-doped hydroxyapatite (Sr-HA) coatings on the surface of an α-Ti alloy in Ca- and P-ion rich electrolyte
The crack occurrence is easy to find after surface modification process such as micro-arc oxidation (MAO) or plasma sprayed method[16,26]
Summary
A strontium (Sr)-doped hydroxyapatite-like coating was deposited on α-Ti alloy via the growing integration layer (GIL) method at various applied voltages. The GIL treatment increased the layer resistance measured by Rp/Rc. Optimally, the GIL method used the highest voltage of 350 V to produce higher quality of Sr-HA-rich coatings. We proposed a novel coating method called growing integration layer (GIL)[19,20,21] for the direct formation of coating layers on the Ti alloys via electrochemical reactions in solution at low temperature. GIL forms integrated layers from the bottom up, called “growing integration layer” method If necessary, another coating layer can be produced on the substrate body by using another solution and interface reaction. They were reported that high doses of Sr cause bone abnormalities[29,30]
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