Lubricated rolling–sliding behaviour of ion nitrided and untreated Ti–6Al–4V

The lubricated rolling–sliding wear of an untreated and ion nitrided Ti–6Al–4V alloy has been investigated. All the tests were carried out under boundary lubrication using commercial SAE 14-W oil. The results show that nitriding improved wear resistance of the Ti–6Al–4V alloy. In particular the material nitrided for 24 h displayed the best wear resistance because the compound layer was effectively sustained by the hardened diffusion layer at the contact loads here investigated. Friction coefficient, on the other hand, was found to be higher in the nitrided materials, although the λ-factors were similar in all the tribological couplings. This was attributed to the lower wettability of the lubricant versus the nitrided layer than the passivated surface of the untreated alloy.