Tribo active and tribo catalytic (Cr,Al)N coatings (CrAlN+X II)

• Applicant: Professorin Dr.-Ing. Kirsten Bobzin
• Subject Area: Coating and Surface Technology
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 406952973

Tribological components such as gears, bearings and piston rings are usually operated lubricated, whereby lubrication is crucial for protection against wear and for friction reduction. To achieve an appropriate effect, lubricants are formulated with additives specifically designed to interact with steels. Due to increasing demands on performance and energy efficiency, the use of physical vapour deposition (PVD) coatings on tribologically highly loaded components is established, while conventional lubricant formulation has been largely retained, so that the formation of friction and wear reducing reaction layer initiated by the interaction of steel surfaces and additives does not take place. In the previous project, three approaches were investigated for the formation of reaction layers due to the interaction of PVD coatings and lubricants. Thereby, Fe-modified (Cr,Al)N coatings showed the greatest potential for effective friction reduction as a result of the transfer of conventional steel/lubricant interactions to the contact between PVD coatings and lubricants. In combination with Fe, modification of the (Cr,Al)N matrix by Mo also showed synergistic effects, so that in situ formation of MoS2 can contribute to wear and friction reduction. However, it also became clear that friction reduction does not necessarily accompany the formation of FeS2 and MoS2. The Fe content and ist bonding character in the coatings as well as the type of lubricant and ist additives were identified as factors influencing a friction-reducing effect. However, a detailed investigation of the relationships has not been possible so far.The aim of the proposed project is therefore to gain a more comprehensive understanding of the processes that occur in tribological contact when Fe-modified PVD coatings interact with lubricating oils, so that the design of the Fe-containing PVD coatings can ultimately be used to reliably reduce friction and wear. For this purpose, it is planned to adapt the coatings on the basis of findings from tribological investigations, focusing in particular on the bonding character and the content of Fe and Mo in the (Cr,Al)N matrix. For a specific design of the coatings with regard to a friction-reducing effect, tribological tests are planned. In addition, the structure of the reaction layers formed by the interaction of Fe-modified PVD coatings and lubricating oils, as well as the adhesion of the reaction products to the surface, will be investigated in more detail in order to be able to adapt them to the reaction products conventionally formed between steel surfaces and lubricants. The planed investigations promise new and significant findings regarding the function and mode of action of Fe-modified triboactive coatings, which extend the knowledge gained to date.

• DFG Programme: Research Grants