Corrosion and Wear Performance of Titanium and Cobalt Chromium Molybdenum Alloys Coated with Dicationic Imidazolium-Based Ionic Liquids

Abstract

The present work investigates the corrosion and wear performance of titanium (Ti6Al4V) and cobalt chromium molybdenum (Co28Cr6Mo) alloys when coated with dicationic imidazolium-based ionic liquids (ILs). As novel, multi-functional compounds, ILs were assessed in terms of coating stability and ability to enhance corrosion resistance and mitigate wear. The IL with the amino acid, phenylalanine, as the anionic moiety was found to maintain stable coatings on both alloy surfaces in phosphate buffered saline (PBS) at 37 °C which lowered corrosion rates in comparison to control specimens. However, ILs with bis(trifluoromethylsulfonyl)imide (NTf2) as the anion were found to form unstable coatings on both alloy surfaces that eventually dissolved into PBS, resulting in corrosion behavior similar to or worse than that exhibited by control specimens. Although all IL-coated alloy surfaces exhibited lower coefficient of friction (COF) values and smaller wear scars relative to control specimens lubricated with PBS, the IL with phenylalanine occasionally underwent coating exhaustion and was slower to reach stable COF values. Overall, the anionic moiety and alkyl chain length of an IL were observed as key properties that influence adsorption onto a given substrate which in turn influence its performance as an anti-corrosive agent and lubricant. This study highlights the need for careful selection of ILs based on their chemical structure and nature of the coating substrate (i.e., surface functional groups) in order to form protective films on biomedical alloys that can improve their corrosion and wear resistance.