In-vitro degradation behavior of Mg alloy coated by fluorine doped hydroxyapatite and calcium deficient hydroxyapatite
(1. Department of Materials, Manufacturing and Industrial Engineering, Faculty of Mechanical Engineering,
Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia;
2. Materials Engineering Department, Najafabad Branch, Islamic Azad University, Najafabad, Isfahan, Iran;
3. Department of Mechanical Engineering, Concordia University, 1455 De Maisonneuve Blvd. West,
Montreal, QC H3G 1M8, Canada)
Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia;
2. Materials Engineering Department, Najafabad Branch, Islamic Azad University, Najafabad, Isfahan, Iran;
3. Department of Mechanical Engineering, Concordia University, 1455 De Maisonneuve Blvd. West,
Montreal, QC H3G 1M8, Canada)
Abstract: Fluorine-doped hydroxyapatite (FHA) and calcium deficient hydroxyapatite (CDHA) were coated on the surface of biodegradable magnesium alloy using electrochemical deposition (ED) technique. Coating characterization was investigated by X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The result shows that nano-FHA coated sample presents nano needle-like structure, which is oriented perpendicular to the surface of the substrate with denser and more uniform layers compared to the nano-CDHA coated sample. The nano-FHA coating shows smaller crystallite size (65 nm) compared to the nano-CDHA coating (95 nm); however, CDHA presents thicker layer (19 μm in thickness) compared to the nano-FHA (15 μm in thickness). The corrosion behaviour determined by polarization, immersion and hydrogen evolution tests indicates that the nano-FHA and nano-CDHA coatings significantly decrease corrosion rate and induce passivation. The nano-FHA and nano-CDHA coatings can accelerate the formation of bone-like apatite layer and significantly decrease the dissolution rate as compared to the uncoated Mg alloy. The nano-FHA coating provides effective protection to Mg alloy and presents the highest corrosion resistance. Therefore, the nano-FHA coating on Mg alloy is suggested as a great candidate for orthopaedic applications.
Key words: magnesium alloy; fluorine-doped hydroxyapatite; calcium deficient hydroxyapatite; electrodeposition; corrosion behavior