Ionic-liquid lubrication of a nickel-based coating reinforced with tungsten carbide particles

Trihexyltetradecylphosphonium bis(2-ethylhexyl)phosphate ([P6,6,6,14][BEHP]) and trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide ([P6,6,6,14][NTf2]) ionic liquids were used as neat lubricants in nickel-based coatings reinforced with spherical WC particles (sizes: −106 + 45 μm). Three different coatings with 0, 3.3, and 12.4 wt% of WC on the surfaces were tested. Reciprocating tribological tests were performed (load: 100 N, frequency: 25 Hz, stroke length: 4 mm, for 60 min at room temperature). The wear was not related to the WC content for [P6,6,6,14][BEHP]. However, the wear decreased with the increase in WC content when [P6,6,6,14][NTf2] was used. [P6,6,6,14][BEHP] exhibited a better tribological behaviour than [P6,6,6,14][NTf2], particularly in the coating without WC, owing to the formation of a CrO3 protective layer. Compared with [P6,6,6,14][NTf2], [P6,6,6,14][BEHP] slightly worsened the antifriction and antiwear behaviour of the coatings with the decrease in WC content.