Tribocorrosion of selective laser melted (SLM) Ti–6Al–4V: effect of an oxygen diffusion layer formed by thermal oxidation

The present study investigates the effect of forming an oxygen diffusion layer (ODL) via thermal oxidation at 850 °C for 6 h on enhancing the tribocorrosion resistance of additively manufactured Ti-6Al-4V fabricated by selective laser melting (SLM). The presence of the ODL significantly increased the surface hardness from 422 ± 9 HV 0 . 025 for the untreated SLMed Ti-6Al-4V to 1008 ± 7 HV 0 . 025 . The tribocorrosion behavior of the materials before and after thermal oxidation were investigated using a reciprocating ball-on-flat tribometer under normal loads of 1, 5, and 15 N in phosphate-buffered saline (PBS) solution against zirconia balls. The higher surface hardness, together with the formation of oxidative tribolayers on the worn surfaces of the ODL specimens, reduced the tribocorrosion rates compared to those of the untreated Ti-6Al-4V under the normal loads. The results showed that no wear occurred on the ODL samples up to 72000 cycles (20 h) of sliding under a normal load of 1 N. Furthermore, after 36000 cycles (10 h) of sliding under higher normal loads of 5 and 15 N, the tribocorrosion rates of the ODL-treated specimens were respectively 4.2% and 15.4% of those observed in untreated materials after 3600 cycles (1 h) of sliding, demonstrating a substantial enhancement in durability against combined wear and corrosive effects.