Characterisation of porous coatings formed on titanium under DC plasma electrolytic oxidation

¹ Division of BioEngineering and Surface Electrochemistry, Department of Engineering and Informatics Systems, Faculty of Mechanical Engineering, Koszalin University of Technology, Racławicka 15-17, PL 75-620 Koszalin, Poland
² HORIBA Jobin Yvon S.A.S., Avenue de la Vauve - Passage Jobin Yvon, CS 45002 - 91120 Palaiseau, France
³ Department of Physics, Norwegian University of Science and Technology (NTNU), Realfagbygget E3-124 Høgskoleringen 5, NO 7491 Trondheim, Norway
⁴ Hochschule Wismar-University of Applied Sciences Technology, Business and Design, Faculty of Engineering, DE 23966 Wismar, Germany
⁵ Manufacturing Engineering, Technical University of Moldova, str. Studenţilor, 9/8, blocul de studii nr. 6, Chisinau, Republic of Moldova

^* Corresponding author: rokosz@tu.koszalin.pl

Abstract

Porous coatings on titanium may be obtained by AC or DC Plasma Electrolytic Oxidation (PEO) process. One has to point out that depending on the plasma treatment the ranges of voltages used are different. It has been found that for DC PEO processing the voltage must be higher than that in the case of AC PEO treatment. In addition, the shape and frequency of the voltage signal have also an impact. Produced coatings were examined with scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and glow discharge optical emission spectroscopy (GDEOS). It was found that it is possible to obtain the porous coatings enriched with phosphorus and copper by use of DC-PEO at 500, 575 and 650 VDC, whereas increasing the PEO voltage results in an increase of Cu/P (copper-to-phosphorus) atomic ratio. Furthermore, based on GDEOS data, three sublayers with different elements concentrations were detected ranging as follows 0-350, 350-2100, 2100-2900 seconds of sputtering time for 575 VDC. Based on XPS results the top 10 nm layer, consisted mainly of titanium (Ti⁴⁺), copper (Cu⁺ and/or Cu²⁺), and phosphates (PO₄^3–, HPO₄^2–, H₂PO₄^–, P₂O₇^3–).