In this study, surface characterization of Mg-doped hydroxyapatite coatings on Ti-25Ta-xHf alloys after plasma electrolytic oxidation(PEO) for dental implants was researched using various experimental instruments. To manufacture the Ti-25Ta-xHf alloys, Ti with 25 wt. % Ta and Hf were prepared and then melted in arc-melting furnace. In order to homogenize for the manufacturing of alloys, these samples were heat treated at 1050 °C for 2 h in an argon atmosphere and then water quenched. Micro-pore was formed by PEO method with various voltages, the reaction was carried out in 2.5 mM Ca(NO3)2?4H2O + 1.5 mM NH4H2PO4 solution. HA and Mg-HA were deposited on the Ti-25Ta-xHf alloys by electrochemical deposition with implement cyclic voltammetry in solution containing various Mg contents. Morphology and structure were researched by field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). Microstructure and chemical composition of coated layer and corrosion properties were characterized by fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS). In vitro studies were performed with MG63 cell to investigate the effect of biological change on different surface conditions.

The results were as follows:

1. The microstructures of the Ti-25Ta-xHf alloy showed a needle-like and equiaxed structure. The needle-like structure(α''- phase) changed to an equiaxed grain structure(α"-phase) with increase of Hf content to Ti-25Ta-15Hf alloy.

2. The corrosion potential of Ti-25Ta-xHf alloy increased, whereas the corrosion current density decreased, as Hf content increased. Polarization resistance of PEO treated Ti-25Ta-15Hf alloy at 300V was higher than those of non-PEO treated and PEO treated Ti-25Ta-15Hf alloys at 240V and 270V.

3. From the results of surface properties of anodized layer, as applied voltages increased, pore size increased and showed highly ordered distribution. Ca and P ratio increased with increasing anodization voltage and Hf content. PEO treated surface showed the anatase structure with large crystallite size, as applied voltage increased, and microcrack showed in the case of higher applied voltage(300V).

4. The morphology of HA particles showed the rod-like shape on bulk alloys, however, the rod-like shape changed to plate-like shape with increase of Mg content on micro-pore structured Ti-25Ta-xHf alloys. Also, the surface roughness of HA and Mg-HA coatings increased with Mg content.

5. From the cell culture test, cell proliferation and growth on the pore formed and nano-scaled surface increased predominantly compared to the others, especially, 20Mg-HA coatings on the Ti-25Ta-15Hf alloy showed a good cell growth and proliferation.

In conclusion, it is confirmed that Mg-precipitated surface on pore formed surface with nano-scale structure could be served for increasing the osseointegration at interface between bone and implant surface. This process of surface treatment can be applied to improve the implant surface.