Surface modification of Ti–6Al–4V alloys using triode plasma oxidation treatments

In this study, triode plasma oxidation (TPO) has been used to improve the tribological characteristics of Ti–6Al–4V. The effect of TPO on ball-on-plate reciprocating-sliding, impact, and micro-abrasion wear resistance of this alloy is investigated. Surface micro-profilometry, nano-/micro-indentation hardness testing, scratch-adhesion testing, scanning electron microscopy (SEM), atomic force microscopy (AFM), glancing-angle X-ray diffraction (GAXRD), and glow-discharge optical emission spectroscopy (GDOES) data is presented to corroborate the effects of the oxidation process. ‘Traditional’ thermal oxidation processes were used to benchmark this novel treatment. Following TPO treatment at 700 °C for only 4 h, a hard (exceeding 11 GPa) and well-adhered oxide layer, composed of mixtures of the anatase and rutile polymorphs of TiO2, was formed at the surface of the Ti-alloy. This layer is accompanied by a much larger oxygen-solution strengthened zone which creates a gradual chemical and mechanical gradient from the hard oxide ‘compound layer’ into the ductile substrate core. The various wear testing methods employed revealed excellent wear resistance of the TPO-treated alloy—compared both to the untreated alloy and to conventional, thermally oxidised samples.