This paper presents methods of modifying the anode surface layers of Al2O3 by introducing carbon to their microstructure. Composite coatings were prepared using two different methods. In the first, coatings were formed by means of oxidation under constant current conditions. Anodic oxidation of aluminium was conducted in a multicomponent electrolyte with the addition of organic acids and graphite. The second method was based on the formation of oxide coatings in an electrolyte without the addition of graphite or heat treatment of the layers of succinic acid. The obtained coatings were tested using SEM, TEM, and GDOES (glow discharge optical emission spectrometry) and their tribological and stereometric properties were measured. The study demonstrated the beneficial effects of the methods when used to improve the tribological properties of sliding couples.
The paper presents the properties of surface oxide layers with an increased content of carbon for tribological applications. The composite surface oxide layers were produced using a two-step technology through hard anodising of the surface of an aluminium alloy, followed by thermochemical treatment of anodic oxide coatings. The surface oxide layers were subjected to tribological tests in an oil-less sliding couple with T5W plastic. The presented test results confirm the usefulness of the proposed modifications of surface oxide layers for the purpose of enhancing the operational durability of oil-less sliding couples in a reciprocating motion.
The paper presents the microstructure and mechanical and tribological properties of polymer composites based on polytetrafluoroethylene (PTFE) intended for use in friction couples where reciprocating motion is performed, e.g., in compressors or actuators. Micromechanical tests carried out using the Oliver-Pharr method showed that the PTFE composite with a 40% bronze content (T8B) had the most advantageous mechanical properties (hardness H, Young’s modulus E). In turn, tribological tests that were conducted using a ballon- disc tester in the linear (reciprocating) motion showed that the polytetrafluoroethylene composite with a mixture of 25% bronze powder and 15% graphite (T4GM) had the lowest tribological wear. The tribological properties of composite T5W with 25% graphite content were not much worse. Despite the most favourable mechanical parameters, the tribological wear of composites T8B and PTFE with glassy carbon (T3Ws) was nearly twice higher due to the absence of grease formed by a graphite filling. The results show that the use of composites containing a bronze-graphite filling improves the service life of lubricant-free friction couples that perform reciprocating motion.
Dry friction tests were performed using a pin-on-plate tribological tester. In this study, Al 2 O 3 and Al 2 O 3 with MoS 2 admixture plate with PEEK/BG pin. Plate surfaces were created using the constant current method and the non-periodic alternating current method. The dimension of Al 2 O 3 fibers walls were calculate based on SEM micrographs. SGP measurements of the oxide layers were made by a Taylor Hobson Talysurf 2D pin profilometer. It was found that the gradient structure favors the reduction of the friction coefficient and weight loss of PEEK/BG in the tested friction pairs, and the method of gradually reducing non-periodic alternating current allowed to obtain a more homogeneous microstructure of aluminum oxide. The use of high current densities at the beginning of the process leads to the production of non-gradient coatings characterized by higher SGP amplitude parameters. This property translates directly into higher wear of the sliding PEEK/BG material and higher values of the friction coefficients of the tribological pairs thus obtained. The research also identified a strong correlation between the friction coefficient µ and surface topography parameters before the tribological cooperation of PEEK/BG pairs -Al 2 O 3 oxide coating.
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