Improvement of wear resistance of Ti-6Al-4V alloy by means of thermal oxidation

Thermal oxidising treatment is an easy and environmental friendly technique that can be used to harden the surface of titanium alloys, and hence improve the poor tribological properties of these materials. The aim of the present research was to evaluate the tribological behaviour of thermally oxidised titanium alloy samples as both counterparts. With this purpose, Ti–6Al–4V alloy disks were treated in an air circulating furnace at 1173 K for 2 h at 10^5 Pa, and then quenched using compressed air, in order to remove the poorly adherent part of the oxide scale. The modified surface layer shows decreasing hardness values, from ~970 HK0.025 to matrix values; the case depth of the hardened layer is ~35 µm. Wear tests, carried out on both untreated and oxidised samples in block-on-ring configuration, in dry sliding conditions, with sliding velocity in the range 0.4–1.6 m s^-1, 50 N coupling load and 3000 m sliding distance, show that the thermal oxidation treatment is able to substantially improve the wear resistance of Ti–6Al–4V samples, reducing the wear volumes from about 4 to 6 times in respect of the untreated alloy. Moreover, further wear tests (sliding velocity: 0.8 m s^-1; coupling load: 50 N; sliding distance: 1700 m), performed on untreated, glow-discharge nitrided and thermally oxidised samples, point out that, with the used test conditions, a marked improvement of the wear resistance is obtained for the oxidised samples in respect of both untreated and nitrided ones.