Fretting-corrosion behavior of β titanium alloys in simulated synovial fluid

Fretting-corrosion is a material degradation process resulting from the combined action of a corrosive environment and small displacement fretting wear. In this work, the fretting-corrosion behavior of Ti–12.5Mo, Ti–13Nb–13Zr, and Ti–29Nb–13Ta–4.6Zr, β titanium alloys which are candidate biomaterials for joint prostheses was studied in Hankʹs balanced salt solution. Ti–6Al–4Fe α + β titanium alloy was also tested for comparison. The open circuit potential, anodic current and friction coefficient were measured in situ, while the microstructure and volume of the wear track were characterized after testing. Ti–13Nb–13Zr and Ti–29Nb–13Ta–4.6Zr exhibited the ability to regain their passive state during fretting, while Ti–6Al–4Fe exhibited large dissolution pits around the wear track indicative of a widespread depassivation activated by fretting. The ability of these β alloys to recover their passive state during fretting was related to the mechanical properties of the superficial passive layers and the evolution of the contact pressure defined by the wear of the alloy. The effects of the addition of synovial constituents, namely bovine serum albumin, hyaluronic acid and dipalmitoyphosphatidycholine on the fretting-corrosion of Ti–12.5Mo alloy were also studied. The addition of synovial constituents induced a decrease of the friction coefficient, the amount of elastic accommodation of the displacement and the wear rate of the alloy.