플라즈마 전해 산화된 생체용 Ti 합금의 표면특성

Abstract

In this study, the effects of applied potential on the surface characteristics of plasma electrolytic oxidized (PEO) Ti-6Al-4V alloy for biomaterials were investigated with the applied voltage of 150V, 250V, and 350V in the electrolyte containing Ca and P ions. PEO film was formed in mixed solution of 0.15 M calcium acetate monohydrate and 0.02 M calcium glycerophosphate electrolyte at 150V ~ 350V for 3 minutes using DC power supply. PEO films formed at various applied voltages were examined surface characteristics by roughness test, scratch test, nanoindentation test, wettability test for biocompatibility, and electrochemical test. Surface morphologies and structures of the PEO-treated alloy were determined by field-emission scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffractometer. The results were as follows;

1. The PEO-treated surface with a porous oxide film containing hydroxyapatite (HA) was formed. The size of pores at 150V was smaller compared to others. For 250V, uniform size of pores and HA formation were observed. At 350V, size of pores increased, the number of pore decreased as compared with the surface formed at 150V and 250V. Even cracks on the surface were observed at 350V.

2. From the result of EDS analysis, PEO-treated surface shows that the Ca / P ratio increased as the applied voltage increased, and the uniform distribution of Ca and P elements was noticed over the entire surface.

3. The anatase, rutile, and HA phase were observed on the PEO-treated surface. As the applied voltage increased, the XRD peaks of anatase phase and the HA phase gradually increased. Rutile was observed only at 350V.

4. As a result of the scratch test the films were broken at the load at 5.3N, 2.3N, and 6N for the PEO surfaces formed at 150V, 250V, and 350V. Also, The peeling of film was observed of the loads of 16.4N, 29.6N, and 8.1N, respectively, for the samples prepared at 150V, 250V, and 350V. The oxide film peeled at the highest load for the sample prepared at an applied voltage of 250V.

5. The nano-indentation analysis shows, the hardness of the samples increased and the elastic modulus decreased with increasing applied voltage.

6. From the results of wettability and surface roughness test on the PEO surface, as the applied voltage increased, the contact angle was decreased and the surface roughness was increased.

7. From the electrochemical corrosion test, the corrosion potential decreased and corrosion current density increased with the applied voltage. The polarization resistance was increased from 150V to 250V, and then decreased at 350V.

In addition, it was noticed that small HA particles on the PEO surface formed at an applied voltage of 350V were disappeared, and that the edges of the pores and cracks were smoothened as a result of attack of chloride ions.