Effects of substrate roughness on the vacuum tribological properties of duplex PEO/bonded-MoS2 coatings on Ti6Al4V

The present study focuses on the influence of substrate roughness on the vacuum tribological properties of PEO/Bonded-MoS2 coatings on Ti-6Al-4V. Four different surface conditions of Ti-6Al-4V coupons, namely Ra being 0.8, 1.6, 3.2 in as-machined conditions, and Ra 1.6 post-treated by sandblasting, were used as substrates. A ball-on-disk tribometer was used to evaluate the vacuum tribological performances of the coated samples. Results showed that the Ra 1.6 sample exhibited the longest anti-wear life, which were attributed to two causes: a hard PEO coating and a special PEO topography with grooves and ridges. The grooves provided 'reservoirs' of MoS2, and the ridges acted as hard anti-wear “phases”. The particular wear mechanism and the effects of roughness were proposed and discussed in this study.