The Effect of the Polymer Structure in Composite Alumina/Polyetheretherketone Coatings on Corrosion Resistance, Micro-mechanical and Tribological Properties of the Ti-6Al-4V Alloy

This paper describes ways of improving the tribological properties of the Ti-6Al-4V titanium alloy at room and elevated temperatures by electrophoretic deposition of Al2O3/PEEK708 composite coatings and post-heat treatment. The microstructure of the coating components and the coatings was examined by scanning and transmission electron microscopy as well as x-ray diffractometry. The influence of cooling rate after heating of the coated alloy on the PEEK structure and coating surface topography was investigated. It was found that slow cooling with a furnace produced a semi-crystalline structure, whereas fast cooling in water generated an amorphous polymer structure. The semi-crystalline coatings exhibited a more developed surface topography than the amorphous ones. The coatings with a semi-crystalline structure revealed higher scratch resistance than the amorphous ones. The corrosion resistance of the uncoated and coated specimens was examined using electrochemical techniques in a 3.5 wt.% NaCl aqueous solution. Both coatings increased the corrosion resistance of the alloy. The friction and wear properties of the coated specimens against an alumina ball in dry sliding contact at room temperature and elevated temperatures of 150 and 260 °C at ball-on-disk were examined. Both amorphous and semi-crystalline coatings increased the wear resistance and decreased the friction coefficient of the titanium alloy at room temperature. In addition, the semi-crystalline coating was also very effective in improving the titanium alloy’s tribological properties at elevated temperatures. The obtained results clearly show that the composite alumina/PEEK coatings are promising for tribological applications in mechanical engineering.