Effect of Low-Friction Composite Polymer Coatings Fabricated by Electrophoretic Deposition and Heat Treatment on the Ti-6Al-4V Titanium Alloy’s Tribological Properties

In this work, polytetrafluoroethylene/polyetheretherketone (PTFE/PEEK 708) coatings were fabricated by electrophoretic deposition (EPD) and heat treatment to improve the tribological properties of the Ti-6Al-4V alloy. A stable suspension containing chitosan polyelectrolyte allowed the co-deposition of both polymer types. The effect of soaking temperature and cooling rate on the coating microstructure was determined. The homogeneous coatings were obtained by heating at 450 °C and cooling with a furnace or in water. The crystalline PTFE separate particles and their agglomerates were homogeneously distributed in a PEEK matrix. Interestingly, the PEEK structure was amorphous regardless of the cooling rate after heating. This new phenomenon is associated with the fluorination process. The coatings exhibited moderate scratch resistance but significantly decreased the coefficient of friction (COF) and enhanced the wear resistance of the alloy during the dry friction process in sliding contact with an Al2O3 ball. The COF of the PTFE/PEEK 708 coating equaled 0.10 at room temperature (RT) and was lower than that of the alloy and pure PEEK 708 coating investigated in the same conditions, which reached 0.70 and 0.27, respectively. The wear rate of the coated alloy at RT was lower than that of the uncoated and PEEK 708 coated alloy, around 1900 and 10 times, respectively. Both the COF and wear increased slightly during friction at 150 °C. The coating was not effective in improving the alloy’s tribological properties during friction at 260 °C.