Interplay between mechanical wear and electrochemical corrosion during tribocorrosion of oxygen diffusion layer on Ti–6Al–4V in PBS solution

Abstract

Oxygen diffusion layers were formed on Ti–6Al–4V by thermal oxidation at a temperature of 850 °C for three and six hours. The presence of interstitial oxygen led to a partial transformation of β-Ti to α-Ti and increased “c/a” ratio of hcp structure from 1.597 for Ti–6Al–4V to 1.610 and 1.611 for three- and six-hour oxidation processes, respectively. Tribocorrosion experiments in phosphate buffered saline (PBS) solution were conducted on the samples under various normal loads of 7.5, 15 and 30 N against an alumina ball as the counterpart. The wear surfaces and subsurfaces of the ODLs showed limited plastic deformation during tribocorrosion; due to obstacles provided by oxygen diffusion against dislocation slip. This was attributed to a higher hardness and c/a ratio of α-Ti hcp and a lower work of plastic deformation. SEM, TEM and SAED patterns of the ODL wear regions in conjunction with electrochemical measurements showed different plastic deformation modes and tribo-electrochemical responses during tribocorrosion compared with Ti-6Al-4V, which led to a decrease in tribocorrosion rate by up to 25 times.