Surface interactions in lubrication of titanium, aluminium, and titanium–aluminium alloys with the ionic liquid [C2mim]Tf2N under increasing temperature

Abstract

The tribological behaviour and surface interactions of Al2011/AISI 52100 steel at 25°C, 100°C, and 200°C, using the room-temperature ionic liquid (IL) 1-ethyl-3-methylimidazolium bis(trifluoromethanesulphonyl)imide ([C2mim][Tf2N]) as lubricant have been studied and compared with that of Ti6Al4V and Ti Grade 3. The best tribological performance at room temperature is that of Ti6Al4V, while Ti Grade 3 shows the lowest friction coefficients and wear rates at high temperature. Al2011 shows constant friction coefficients with no running-in periods. The tribochemical interactions between [C2mim][Tf2N] and Al2011 produce a tribolayer on the steel ball containing sulphur from the IL anion combined with Cu from the Al2011 alloy, while wear debris are mainly composed of aluminium oxide and fluoride. Al2011 wear debris morphology evolves from powder at 25°C, to adhesion flat flakes at 100°C, to abrasion chips at 200°C. The titanium alloys show high running-in friction values, with running-in distances that increase with increasing temperature. Titanium Grade 3 shows an adhesive wear mechanism, with material transference to the steel ball and formation of a tribolayer on the wear track as a result of the tribochemical interactions with the IL anion. At 200°C, Ti6Al4V shows a more abrasive wear mechanism than Ti Grade 3, due to severe corrosion of the steel ball.