Roughness and mechanical properties of electron-beam surface modified and TiN/TiO₂-coated Ti6Al4V alloy

In this study, we used PVD deposition of TiN/TiO₂ coatings on polished and electron-beam-treated Ti6Al4V alloy to explore the changes in the surface roughness and mechanical properties of the coated systems. After the electron-beam treatment (EBT), the average surface hardness and roughness (R_a) increased from 323±5.62 HV_0.2 and 0.14±0.004 μm up to 387.5±9.33 HV_0.2 and 1.58±0.05 μm, respectively. After coating with 3.7-μm thick TiN/TiO₂, the average S_a roughness and nanohardness of the film on the polished substrate reached 0.87±0.1 μm and 13.05±2.07 GPa while that on the EBT was equal to 1.57±0.2 μm and 9.02±2.15 GPa, respectively. However, the comparison of the coefficient of friction (COF) evolution of the substrates and the coated specimens indicated a COF decrease by about 0.18±0.03 for the coated EBT alloy as compared with the polished and EBT substrates, whose average COF were 0.45±0.04 and 0.38±0.06, respectively. A high average COF (0.68±0.16) was registered for the coated as-received alloy because of the gradual and complete wearing off of the film during the test. These results indicate that the combination of initial EBT of the Ti6Al4V alloy with PVD deposition of a TiN/TiO₂ coating could substantially improve the roughness and tribological properties of the coated systems.