Corrosion-wear behaviour of novel surface coatings developed by means of advanced techniques

Résumé

This work deals with Tribocorrosion behaviour of different surface treatments destined to improve material properties for different industrial applications. Among the wide variety of surface treatments able to functionalize metal surfaces, Physical Vapour Deposition coatings (PVD) and Plasma Electrolytic Oxidation treatment were selected and studied in this work PVD processes consist of the evaporation of a solid in the form of atoms or molecules transported under vacuum conditions and deposited on a specific substrate where they condense generating a thin film with specific physic and chemical properties. Plasma Electrolytic Oxidation is a high voltage electrochemical process where a plasma discharge is induced in the surface/electrolyte interface promoting the growth of an oxide film on the substrate surface with excellent corrosion and wear resistance. Both treatments studied in this work were focused on the improvement of the tribocorrosion behaviour of different substrates. Additional characterization results such as electrochemical corrosion tests, surfaces analysis and tribological simulations were also included to complete the information provided by the tribocorrosion analysis. PVD multilayer films were selected to be applied on a typical gear ferrous steel named F1272 (40CrNiMo7). The main cause of failure observed since many years ago in these components is due to the wear they suffer during their working life despite they usually work under lubricated conditions. Then, the application of thin and hard PVD coating mono or multilayer was found to increase the tribological performance of these components by reducing friction and wear. But nowadays, the off-shore wind turbine application and the continuous advances in the development of novel biolubricants containing water or ionic additives make these components also susceptible to suffer tribocorrosion degradation by the simultaneous effect of electrochemical and mechanical solicitations. Because of that, tribocorrosion study of novel multilayer PVD coatings deposited on F1272 gear steel was selected as a topic of this thesis. In the field of artificial joints, Ti-DLC PVD coatings were applied on three different biomedical alloys named AISI 316, CoCrMo and Ti6Al4V with the aim of protecting them when they have to work under certain conditions suffering the simultaneous effect of corrosion and wear phenomena. Different deposition processes were developed by varying the adhesion layers, carbon and nitrogen contents, hardness, microstructure, etc. The ability of all these Ti-DLC coatings to protect against tribocorrosion in simulated body fluids is analyzed in this work. Plasma Electrolytic oxidation coatings are proposed for improving tribological and tribocorrosion properties of low pressure diecasting aluminium-silicon alloys used in the manufacturing of cylinder liners for automobile engine blocks. Different oxides were grown on this alloy and their performance under several testing conditions was evaluated and compared with different coatings available in the automotive industry for the same application such as High Velocity Oxy-Fuel (HVOF) coatings.