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The transmissions of mining conveyors are exposed to very harsh conditions. These are primarily related to the contamination of the gear oil with hard particles coming from coal and lignite, which can cause intensive abrasive wear, scuffing, and even pitting, limiting the life of gears. One of the ways to prevent this problem is the deposition of a wear-resistant coating onto gear teeth. However, a proper choice of gear oil is an important issue. The abrasion, scuffing, and pitting tests were performed using simple, model specimens. A pin and vee block tester was employed for research on abrasion and scuffing. To test pitting, a modified four-ball pitting tester was used, where the top ball was replaced with a cone. The test pins, vee blocks, and cones were made of 18CrNiMo7-6 case-hardened steel. A new W-DLC/CrN coating was tested. It was deposited on the vee blocks and cones. For lubrication, three commercial industrial gear oils were used: A mineral oil, and two synthetic ones with polyalphaolefin (PAO) or polyalkylene glycol (PAG) bases. The results show that, to minimize the tendency forabrasion, scuffing, and pitting, the (W-DLC/CrN)-8CrNiMo7-6 tribosystems should be lubricated by the PAO gear oil. MoS 2 /Ti, C/Cr [4], TiN, and CrN [15]. Concerning DLC coatings, they are either doped coatings: W-DLC [2,15-17], Cr-DLC [18], and Si-DLC [19]; or non-doped coatings: a-C:H [ [18][19][20] or ta-C [19]. The review of the literature allows one to state that it is the DLC coating that is currently used in the majority of tribological research works.Apart from testing thin coatings, it is also important to select a proper oil to lubricate the coated parts [15]. For decades, a lot of research works have been devoted to investigating the interaction between the lubricating additives in the oil with the steel surface [21][22][23][24][25][26][27][28][29][30][31][32], and the mechanisms of the interaction between steel surfaces and lubricants are well recognized.Concerning the interaction between the oil and the thin coating, the publications are less frequent [15,18,[33][34][35][36][37][38] and have been mostly issued in the last 20 years. Unlike the oil-steel interactions, when testing coatings, one can find different statements and observations in the literature. Some authors point out an effect of the coating's elemental composition, occurrence of the transfer of material between the samples, forming of protective films on the surface, or even chemical reactions of the coating with the lubricating additives in the oil.In a review paper, Kalin et al.[33] compared oil-coating interactions when lubricating with oils with a mineral, synthetic ester, and polyalphaolefin (PAO) base using various tribosystems. They stated that non-doped DLC coatings can react with different types of additives (e.g., a friction modifier (FM), antiwear (AW), and extreme-pressure (EP) additives), and that the hydrogen content in DLC coatings plays a crucial role in the tribological performance under lubricated conditions.Michalczewski et al.[15...

In the present study, the influence of the volume fraction of graphene on the tribological properties of copper matrix composites was examined. The composites were obtained by the spark plasma sintering technique in a vacuum. The designed sintering conditions (temperature 950°C, pressing pressure 50 MPa, time 15 min) allowed obtaining almost fully dense materials. The tribological behaviour of copper-graphene composite materials was analysed. The tests were conducted using a CSM Nano Tribometer employing ball-on-plate tribosystem. The friction and wear behaviour of copper-graphene composite materials were investigated. An optical microscope, interferometer, and scanning electron microscope were used to analyse the worn surfaces. In friction zone, the graphene acts as a solid lubricant, which results in the increase in the content in the composites positively influencing the tribological characteristics of the steel- Cu-graphene composite.