Fabrication and Characterisation of Porous Coatings Enriched with Copper on CP Titanium Grade 2 under Plasma Electrolytic Oxidation

In the present paper, coatings obtained on CP Titanium Grade 2 samples by Plasma Electrolytic Oxidation (PEO) in electrolyte containing concentrated phosphoric acid H3PO4 with copper nitrate Cu(NO3)2∙3H2O, are studied with Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDS), X-Ray Photoelectron Spectroscopy (XPS) and Glow Discharge Optical Emission Spectroscopy (GDOES). A three-layer model is proposed on the basis of GDOES depth profile signals and their first and second derivatives. It was found that the time of Plasma Electrolytic Oxidation process has an influence on the chemical composition and the thickness of the obtained porous coatings. The longer time the PEO treatment is applied, the thinner porous coatings are obtained and the lowest amounts of copper, phosphorus and oxygen inside them are found. The proposed model of PEO coatings consists of three layers, i.e. the top one "A", having a thickness corresponding to the sputtering time in GDOES of about 100 s; the operating conditions applied provide very porous and contaminated by organic substances layer down to about 50 s by sputtering time; the semi-porous sub-layer named "B" has a thickness that depends on the PEO treatment time. The sub-layer "B" of PEO coating is the thickest after one-minute PEO treatment and it decreases with increasing the treatment time. The PEO coating thickness also decreases after each successive PEO processing. The last layer (from the top surface), is the transition sub-layer named "C", and it has a thickness corresponding to a sputtering time equaling 450 s