Characterisation of porous coatings formed on titanium under AC 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

The Plasma Electrolytic Oxidation (PEO) process may be used to fabricate porous coatings on titanium. The ranges of voltages used in case of these plasma treatments 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 influence. In the paper scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and glow discharge optical emission spectroscopy (GDEOS) were used to characterise obtained coatings. It was found that it is possible to obtain the porous coatings enriched with phosphorus and copper by use of AC-PEO at only 200 Vpp, while increasing the PEO voltage results in non-porous and cracked coatings. Based on GDEOS for 200 Vpp three sublayers were used, with ranges of 0-400, and 400-2400, and 2400-3600 seconds of sputtering time for first, and second, and transition sublayers respectively. XPS spectra for sample processed at 200 Vpp indicate in top 10 nm layer presence of titanium as Ti⁴⁺ and phosphorous as phosphates (most likely PO₄^3–, HPO₄^2–, H₂PO₄^–, P₂O₇^3–).