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B. Kohlhauser, M. Ripoll Rodríguez, H. Riedl, C.M. Koller, N. Koutná, A. Amsüss, H. Hutter, G Ramirez, C. Gachot, A. Erdemir, P.H. Mayrhofer:
"How to get noWear? - A new take on the design of in-situ formed high performing low-friction tribofilms";
Materials & Design, 190 (2020), 108519; 1 - 8.

Despite growing environmental concern, combustion engines are projected to stay the main technology of transportation for many years, so will unpopular S- and P- containing additives in lubricating oils. Therefore, it is essential to maximize efficiency and minimize the harmful impacts of these additives in the meantime. Coatings based on Mo and W hold great promise as they can chemically interact with S-bearing additives and form low friction tribofilms like MoS2 and in particular WS2. Here we highlight the reaction pathways involving first the formation of oxide intermediates, followed by the generation of a highly protective and low-shear transition metal disulfide tribofilm on a tailored WN-based coating, affording coefficients of friction as low as 0.05 combined with an extraordinary wear protection (i.e., no measurable wear on sliding surfaces even after 100 h of testing). High resolution TEM and Raman spectroscopy confirm the formation of WS2 sheets and hence the huge potential of these coatings for lubricated surfaces.

In-situ WS; Coating-lubricant interaction; Tungsten nitride; Thin film; Tribofilm

http://dx.doi.org/10.1016/j.matdes.2020.108519

https://publik.tuwien.ac.at/files/publik_292781.pdf