Investigating the improvement in surface characteristics following triode plasma oxidation of PVD Al-coated Ti-6Al-4V

Abstract

Despite the wide range of advantageous properties of Ti-6Al-4V, its inadequate tribological performance still inhibits the further extension of its application areas. The practise of surface engineering as a mean to improve the wear properties of titanium alloys is now well established. In this work, aluminium was deposited on the surface of Ti-6Al-4V using electron-beam plasma-assisted physical vapour deposition (EB-PAPVD) and subsequently oxidised using triode plasma oxidation (TPO). The aim of this work was to establish the effect on surface layer structure, composition, hardness and sliding wear performance of varying TPO treatment temperature, duration and substrate negative electrical bias — and to determine whether EB-PAPVD followed by TPO could be a suitable low temperature process able to improve the surface properties of Ti-6Al-4V. Films oxidised at higher temperature and substrate negative bias did indeed exhibit a distinct improvement in performance. Their hardness increased to a maximum of ~11GPa. Film adhesion was found to be satisfactory and ball-on-plate reciprocating-sliding wear tests indicated an improvement in tribological performance.