Self-lubricated nanoporous TiO2-TiN films fabricated on nanocrystalline layer of titanium with enhanced tribological properties

Abstract Nanoporous TiO 2 -TiN composite films with enhanced tribological properties were fabricated on commercial pure titanium by combining a mechanical surface modification process, i.e., electropulsing assisted ultrasonic surface rolling process (EP-USRP), and an electrochemical process, i.e. sparking anodization (SA) in an aqueous ammonia sulfate electrolyte. The EP-USRP endowed a gradient nanocrystalline layer with high surface hardness of ~295 HV (strengthened by ~41.1% to untreated sample) and deep hardening depth (>600 μm). In addition, TiO 2 -TiN composite films fabricated on EP-USRP treated surface exhibited smoother morphology and more uniform pores than that of anodization without EP-USRP. The SA produced a sponge-like nanoporous TiO 2 -TiN composite film with anatase and rutile-TiO 2 phases. Moreover, the surface wettability was remarkably improved compared to EP-USRP. The combinatorial technique led to lower friction coefficient and effectively inhibited the adhesion during wear test compared with turning, EP-USRP and anodization without EP-USRP, which could be attributed to the synergetic effects of the self-lubrication nature of nanoporous TiO 2 -TiN films by SA and the ultra-smooth and hardening nanocrystalline layer by EP-USRP. The promoted elastic deformation and the reduced adhesion wear rate by rutile-TiO 2 phase as well as the lubricating and wettable grinding powder should be the primary intrinsic reasons for the improvements.