formation of nano-structured tribolayer on ti 6al 4v during sliding in a phosphate buffer saline solution

Various parameters such as applied normal load, sliding speed, environment, mating materials, etc. can affect the tribolayer characteristics that may form on the wear surface of a tribopair. the formation of tribolayer can then have impact on the friction and wear corrosion behavior of the mating surfaces. this study aimed to investigate the characteristics of tribolayer formed on the wear surface of ti 6al 4v alloy. the tribocorrosion tests were conducted under a reciprocating condition with a frequency of 1 hz under applied normal loads of 1 n and 15 n against an alumina ball in a phosphate buffer saline (pbs) solution for 3600 cycles of sliding. scanning electron microscopy (sem) images indicated that an increase in the normal load resulted in a more coverage of a tribolayer. an energy dispersive spectroscopy (eds) analysis showed that this layer was rich in oxygen. x-ray photoelectron spectroscopy (xps) analysis conducted on the wear surfaces indicated that the tribolayer contained tio2, phosphate compounds, and unstable tio, and ti2o3 oxides, which were a result of the tribocorrosion process. a transmission electron microscopy (tem) specimen was prepared using focused ion beam (fib) method. in this method, a cross-sectional specimen was obtained from the wear surface parallel to the sliding direction under the normal load of 15 n. the tem images showed that the thickness of the tribolayer varied between 600 nm to 1000 nm. elemental distribution maps obtained from the tem sample confirmed that the tribolayer was rich in oxygen; however, titanium and aluminum were also found in the tribolayer. ring diffraction patterns were observed in the selected area electron diffraction (saed) indicating that the tribolayer had a nanocrystalline structure. the formation of nanograins in the tribofilm was due to a very high strain and strain rate that existed at contact points during the sliding process. the data from the international centre for diffraction data (icdd), the d spacing obtained from the diffraction pattern, the xps and eds analyses revealed that the tribolayer consisted of tio2 (rutile), ti2o3, α-ti, and β-ti phases. the presence of the oxygen rich tribolayer, which had a greater coverage of the wear surface under a normal load of 15 n, led to a decrease in a coefficient of friction (cof). in addition, the results indicated that the oscillation of cof significantly reduced at the higher normal load due to a lower adhesion between titanium alloy and alumina. the durability of the tribolayer under the applied normal load of 15 n also resulted in a lower specific tribocorrosion rate (str).