Applied Surface Science, Vol.368, 177-190, 2016
Corrosion and wear behaviours of a reactive-sputter-deposited Ta2O5 nanoceramic coating
In order to improve the wear and corrosion resistance of Ti-6Al-4V, a novel beta-Ta2O5 nanoceramic coating was synthesised using reactive sputter deposition enabled by double glow discharge plasma technique. The surface topography, chemical composition, and microstructure of the newly developed coating were characterised by a variety of surface analytical techniques. The coating microstructure was found to exhibit a compact striated pattern extending in a direction perpendicular to coating surface, which is composed of equiaxed beta-Ta2O5 grains with an average grain size of similar to 20 nm, well adhered to the Ti-6A1-4V substrate. The hardness and the Young's modulus of the as-deposited coating were obtained by nanoindentation, and the adhesion strength between the coating and substrate was determined by a scratch tester. The dry sliding wear behaviours of the coating were investigated at room temperature against Si3N4 ceramic balls at room temperature under applied loads ranging from 2.3 N to 5.3 N using a ball-on-disc tribometer. The specific wear rates of the coating exhibited only a slight increase with applied normal load, and were shown to be two orders of magnitude lower than that for Ti-6Al-4V under the same loading condition. Furthermore, the electrochemical behaviour of the coating immersed in 3.5 wt.% NaCl solution was systematically examined by using a range of complementary electrochemical techniques including potentiodynamic polarisation, electrochemical impedance spectroscopy (EIS), MottSchottky analysis as well as potential of zero charge (PZC). The results showed that the corrosion resistance of the beta-Ta2O5 nanoceramic coating was better than that of Ti-6Al-4V alloy in 3.5 wt.% NaCl solution. Hence, by possessing higher mechanical properties and good wear and corrosion resistance, the beta-Ta2O5 nanoceramic coating is considered to be a promising candidate for protection of engineering components operating under harsh conditions. (C) 2016 Elsevier B.V. All rights reserved.
Keywords:beta-Ta2O5 coating;Friction and wear;Corrosion resistance;Electrochemical impedance spectroscopy (EIS)