Development of hydrophobic PTFE coatings by electrophoretic deposition and heat treatment for low-friction applications

This study investigated the possibility of producing polytetrafluoroethylene (PTFE) coatings on Ti-6Al-4V titanium alloy substrates using electrophoretic deposition (EPD) and heat treatment. Three different size of PTFE particles and three different surfactants, namely chitosan (CS), sodium alginate (SA), and PAZO, were used to facilitate the deposition process. All polyelectrolytes were effective and enabled coating deposition regardless of the size of the PTFE particles. As a result of heat treatment, PTFE changed its morphology from particles to a continuous coating. All coatings showed high open porosity, and in some of them a network of microcracks was observed, which excluded them from further tests. PTFE coatings including a mixture of nanoparticles and submicroparticles deposited without mixing with CS or SA showed very high adhesion to the substrate and relatively high scratch resistance. The coating deposited with CS had a higher roughness compared to that of the coating deposited with SA. The coatings were characterized by a high contact angle, i.e. 145.4±1.1° and 133.4±4.0° for the coatings deposited with CS and SA, respectively, indicating their high hydrophobicity. The coatings showed very good sliding properties until the continuity of the coating was ensured in the friction contact. The friction coefficient with the Al2O3 ball was 0.09 and 0.11 for the coatings obtained with CS and SA, respectively. A thin tribofilm was formed on the surface of the ball at the point of contact, which ensured sliding. However, the wear resistance of the coatings was low and they were subject to significant deformation and intense abrasion. This work contributes to understanding of the PTFE coating production processes and their resulting properties, with implications for various applications.