Development of copper-enriched porous coatings on ternary Ti-Nb-Zr alloy by plasma electrolytic oxidation

In this paper, a preparation method and characteristics of porous coatings enriched in copper distributed in the whole volume on a ternary Ti-Nb-Zr alloy biomaterial obtained by plasma electrolytic oxidation (PEO) in an electrolyte containing H3PO4 within Cu(NO3)(2) at potentials of 180 and 450 V are presented. It has been shown that the PEO potential has impact on the thickness of the coatings, i.e., the higher the potential used, the thicker the coating obtained. Using XPS study, it was shown that copper inside the coating appears as Cu+ and Cu2+ ions, while titanium, niobium, and zirconium appear as Ti4+, Nb5+, and Zrx+ (x <= 2), respectively. It was also found that the roughness of PEO coating formed at 450 V is higher than the one obtained at 180 V, and it is well correlated with bigger pores after the PEO treatment. Additionally, in this paper two PEO coating models composed of three sub-layers are presented. The thickness of the outer top porous sub-layer obtained after PEO oxidation at both 180 and 450 V equals to about 2 mu m, while the semi-porous as well as transition sub-layers are thicker after PEO processing at 450 V (5 mu m) than those obtained at 180 V (4 mu m thick). The creation of the top porous and transition compact sub-layer of PEO coating may be explained by switch-on and switch-off of the PEO potential, while the middle and semi-porous sub-layers are most likely formed during the stable voltage conditions of PEO treatment.