Tribocorrosion behaviour of Ti6Al4V under various normal loads in phosphate buffered saline solution
(1. School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, Tehran, Iran;
2. Department of Metallurgy and Materials Engineering, Faculty of Engineering, University of Kashan, Kashan, Iran;
3. Institute of Functional Surfaces, School of Mechanical Engineering, University of Leeds, Leeds, LS2 9JT, UK)
2. Department of Metallurgy and Materials Engineering, Faculty of Engineering, University of Kashan, Kashan, Iran;
3. Institute of Functional Surfaces, School of Mechanical Engineering, University of Leeds, Leeds, LS2 9JT, UK)
Abstract: Tribocorrosion tests were conducted on Ti6Al4V against alumina in phosphate buffered saline solution under normal loads of 3-30 N (corresponding to the maximum Hertzian contact pressures of 816-1758 MPa) using a ball？on？disk tribometer. Nano-hardness measurements revealed the formation of work-hardened layers on the pure wear and tribocorrosion surfaces. As the normal load increased from 15 to 30 N during the pure wear, the surface hardness was increased by about 100%. However, a lower generation of wear debris resulted in a lower wear rate under a normal load of 30 N. The presence of corrosion caused an increase in the wear rates by 28%-245% under various normal loads. The corrosion current density acquired from polarization curves was increased by three orders of magnitude and the open circuit potential (OCP) shifted to more negative potentials during tribocorrosion compared with the stagnant condition. The successive formation and removal of tribofilms, which consisted of oxygen and phosphorous compounds, resulted in peaks in the OCP trend and lower fluctuations in coefficient of friction under normal loads higher than 3 N.
Key words: Ti6Al4V alloy; tribocorrosion; nano-hardness; wear; corrosion