Abstract:The study deals with tribological properties of diamond films that were tested under reciprocal sliding conditions against Si 3 N 4 balls. Adhesive and abrasive wear are explained in terms of nonequilibrium thermodynamic model of friction and wear. Surface roughness alteration and film deformation induce instabilities in the tribological system, therefore self-organization can occur. Instabilities can lead to an increase of the real contact area between the ball and film, resulting in the seizure between the sliding counterparts (degenerative case of self-organization). However, the material cannot withstand the stress and collapses due to high friction forces, thus this regime of sliding corresponds to the adhesive wear. In contrast, a decrease of the real contact area leads to the decrease of the coefficient of friction (constructive self-organization). However, it results in a contact pressure increase on the top of asperities within the contact zone, followed by material collapse, i.e., abrasive wear. Mentioned wear mechanisms should be distinguished from the self-lubricating properties of diamond due to the formation of a carbonaceous layer.

The study investigates the wear of microcrystalline diamond (MCD) and diamond-like carbon (DLC) coatings. The MCD and DLC coatings were grown by plasma enhanced chemical vapor deposition (PECVD) method on WC-Co substrates. The sliding wear tests were performed on the ball-on-plate type of tribometer in reciprocating mode. The ball-cratering wear tests were carried out using Calo tester. The mechanical profilometer, optical and scanning electron microscopes (SEM) were used for investigation of the surface morphology of the wear scars. The wear of DLC coating is more intense in comparison to the MCD coating. In contrast to the MCD coating, no evidence of the DLC coating deflection was found.

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Comparative analysis of dry sliding wear behavior of nanocrystalline diamond (NCD) films and NCD films coated with a thin Al 2 O 3 layer (Al 2 O 3 /NCD) is the main goal of the present study. Plasma-enhanced chemical vapor deposition (PECVD) and atomic layer deposition (ALD) methods were used to prepare the NCD and alumina films, respectively. Sliding wear tests were conducted at room temperature (RT), 300 and 450 • C in air. Independent of type of specimen, superlubricating behavior with the coefficient of friction (COF) in the range of 0.004-0.04 was found for the tests at 300 • C. However, the COF value measured on the Al 2 O 3 /NCD films in the tests at 450 • C is lower than that for the NCD film. A relatively short run-in period and a stable COF value of about 0.15 were observed at this temperature for the Al 2 O 3 /NCD films. The width of the wear scars measured on the Al 2 O 3 /NCD films after the tests at 450 • C is significantly smaller in comparison with the NCD film. The apparent wear volume of the wear scar on the NCD film tested at 450 • C was noticeably higher than that on the Al 2 O 3 /NCD films.

Mechanical and tribological properties of the hard-multilayer TiN-AlTiN/nACo-CrN/AlCrN-AlCrO-AlTiCrN coating deposited on WC-Co substrate were investigated. The sliding tests were carried out using ball-on-disc tribometer at room (25 °C) and high temperatures (600 and 800 °C) with Al2O3 balls as counterpart. Nano-scratch tests were performed at room temperature with a sphero-conical diamond indenter. The surface morphology and chemical composition were investigated with scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS) and in-situ high-temperature X-ray diffraction (HT-XRD). The phase transition from fcc-(Al,Cr)2O3 into α-(Al,Cr)2O3 was observed at about 800 °C. The results of the tribological tests depends on the temperature, the lowest apparent and real wear volumes were observed on the coating after the test at 800 °C along with the smallest coefficient of friction (COF). The plastic deformation of the coating was confirmed in sliding and nano-scratch tests. The nano-scratch tests revealed the dependence of COF value on the temperature of the sliding tests.