Effect of EDTA addition on the biotribological properties of coatings obtained from PEO on the Ti6Al4V alloy in a phosphate-based solution

Abstract

Coatings were obtained on the Ti6Al4V alloy by Plasma Electrolytic Oxidation (PEO) in a phosphate-based electrolyte with different Ethylenediaminetetraacetic acid (EDTA) concentrations. TiO2 was detected in the coatings in both anatase and rutile phases, with the incorporation of P and Ca into the coating from the electrolyte. A significant change was evidenced for samples anodized with EDTA addition, compared to the sample anodized without EDTA. The thickness was higher for coating obtained with an increased amount of EDTA sample (20.24 μm), compared to the coating anodized without EDTA (13.12 μm). All samples were anodized at galvanostatic conditions, applying a current density of 50 mA cm−2 during 1000s. A higher coating thickness leads to the formation of higher intensity micro-discharges, which promotes the formation of a higher amount of rutile phase, in the coatings with higher EDTA content in the anodizing electrolyte. The friction and wear properties of coatings were analyzed in a ball-on-disk tribometer, under lubricated conditions in simulated body fluid (SBF). The coatings substantially improved the wear behavior of the Ti6Al4V alloy. The coating with a higher amount of EDTA exhibits better tribological performance (6 times better than the substrate (Wear rate: 22.077 × 10−10 Kg/N.m)), due to the higher amount of rutile into the coating, which reduces the wear rate as well as the friction coefficient.