The aim of the study was to determine the effectiveness of the biodegradable cutting fluid used instead of classical, usually toxic. This paper presents the results of tribological studies of a-C:H coatings formed on HS6-5-2C steel by plasma-assisted chemical vapour deposition. The coating structures were examined using a JSM-7100F SEM. The coating microhardness was measured with a Matsuzawa tester. The surface texture analysis was performed before and after the tribological tests with a Talysurf CCI Lite optical profiler. The tribological properties were investigated using a T-01 M tester and a T-17 tester. The tests were carried out under dry friction conditions and lubricated friction conditions using a lubricant with zinc aspartate. The test results show that the layer formed at the interface prevented the moving surfaces. The investigations discussed in this paper have contributed to the development of non-toxic and environmentally-friendly manufacturing because of the use of biodegradable cutting fluid and thin, hard coatings.
 R. Gałuszka, M. Madej, D. Ozimina, A. Krzyszkowski, G. Gałuszka, The characterisation of the mi-crostructure and mechanical properties of diamond – like carbon (DLC) for endoprosthesis, Metalurgija 5 (1-2), 195-198 (2016).
 M. Folea, A. Roman, N.B. Lupulescu, An overview of DLC coatings on cutting tools performance, Scientific papers, Academic Journal of Manufacturing Engineering 8 (3), 30-36 (2010).
 M. Madej, K. Marczewska-Boczkowska, D. Ozimina, Effect of tungsten on the durability of diamond-like carbon coatings in the chemical industry, Chem. Rev. 93 (4), 505-505 (2014).
 B. Vengudusamy, A. Grafl, K. Preinfalk, Tribological properties of hydrogenated amorphous carbon under dry and lubricated conditions, Diam. Relat. Mater. 41, 53-64 (2014).
 D. Ozimina, M. Madej, J. Kowalczyk, J. Suchanek, F. Taticek, M. Kolarikova, The wear performance of diamond-like carbon coatings in relation to coating composition and friction pair, Tribology 3, 157-166 (2012).
 M. Madej, Properties of tribological systems with diamond-like carbon coatings, Ed. TU, 2013 Kielce.
 D. Ozimina, The exploitation of tribological systems. Tom I. The importance of scientific instrument in operation buildings, M48, Ed. TU, 2013 Kielce.
 T. Roch, D. Benke, S. Milles, A. Roch, T. Kunze, A. Lasagni, Dependence between friction of laser interference patterned carbon and the thin film morphology, Diam. Relat. Mater. 55, 16-21 (2015).
 M.S. Komlenok, V.V. Kononenko, E.V. Zavedeev, V.D. Frolov, N.R. Arutyunyan, A.A. Chouprik, A.S. Baturin, H.J. Scheibe, L. Mikhail, M.L. Shupegin, S.M. Pimenov, Laser surface graphitization to control friction of diamond-like carbon coatings, Appl. Phys. 121 (3), 1031-1038 (2015).
 B. Bhushan, Modern Tribology Handbook, Two Volume Set, Tribology of Diamond, Diamond-Like Carbon, and Related Films, CRC Press, 2000 Florida.
 Ch. Donnet, A. Erdemir, Tribology of Diamond-Like Carbon Films. Fundamentals and Applications, Springer, 2008 New York.
 F. Klocke, Cutting Tool Materials and Tools, in: Manufacturing Processes 1, Springer, 2011 Verlag Berlin Heidelberg.
 E. Miko, Ł. Nowakowski, Measurement of a minimum chip thickness in face milling, Mech. Mies. Nauk. Tech. 7, 521-525 (2013).