Regulation on tribological performance of tungsten-doped DLC coatings by Choline Chloride-Urea and -Thiourea Deep Eutectic Solvents

Solid-liquid composite lubrication system has attracted an increased interest for low friction and wear. Nevertheless, the effect of mechanical and surface properties of the solid materials, especially the mechanical and surface properties governed by doping elements, on the tribological performance solid-liquid composite lubrication system is still not well comprehended. Here, we reported the effect of W content on the mechanical and surface properties of W-DLC coatings as well as the tribological properties of W-DLC coatings under (choline chloride-urea and choline chloride-thiourea) deep eutectic solvents lubrication. Although the wear of W-DLC coatings under dry friction increases with W content, the wear under DESs is slight when coatings show excellent wettability to DESs or a DES-derived tribochemical film is formed. We demonstrate that the tribological behavior of W-DLC and DESs composite lubrication system is related to the mechanical properties of W-DLC coatings together with the contact angle and tribochemical interaction between DESs and W-DLC coatings.

Enhancement of sp3 C Fraction in Diamond-like Carbon Coatings by Cryogenic Treatment

Diamond-like carbon (DLC) coatings deposited onto high-speed-steel surfaces were subjected to deep cryogenic treatment (DCT) at temperatures of −120 to −196 °C to investigate the evolution of microstructure, bonding structure, and mechanical properties. The surface morphology and the bonding structure of the DLC coatings were studied using scanning electron microscopy, transmission electron microscopy, micro-Raman spectroscopy, and X-ray photoelectron spectroscopy. It is found that DCT affects the surface morphology, especially the size and the height of the aggregates. For those DLCs with more than 50% sp3 C fraction, the sp2 C → sp3 C transformation occurred in coatings treated at a temperature of −120 to −160 °C; and the maximum fraction of sp3 C was obtained after treatment at −140 °C. Almost keeping the wear resistance of DLCs, DCT can improve the adhesion strength, and surface hardness. The findings of this study indicate that DCT will be a potential post-treatment method to tune the microstructure and mechanical performance of DLC coatings.

Thick Si-doped DLC coatings with high load bearing capacity on cold working tool steels by PECVD

For improving the wear resistance, thick silicon doped hydrogenated amorphous carbon (a-SiC:H) coatings were deposited on cold working tool steels by Plasma Enhanced Chemical Vapor Deposition (PECVD) technology. The increase of the acetylene (C2H2) flow rate distinctly tuned the microstructure of a-SiC:H coatings, including an increase in the coating thickness (>15 μm), a decrease in the silicon content, a greater sp2/sp3 ratio and higher degree of graphitization. The highest hardness of 19.61 GPa and the greatest critical load of 50.7 N were obtained. The coating showed low wear rates against different friction pairs and presented excellent abrasive wear resistance at high applied load and the wear rates decreased with increasing loads, which exhibited an outstanding application prospect in cold working tool steels.

Investigation of changes in the properties of diamond-like films under friction by the XPS method

The combination of unique physicochemical, mechanical and tribological properties of diamond-like coatings determines the prospects for their use in critical friction units, including those operating in a rarefied atmosphere and vacuum. The properties of diamond-like carbon (DLC) coatings depend on the contribution of the sp2 and sp3 fractions of the carbon hybrid atomic electron orbitals. Modern methods of determining the graphite and diamond proportion in coatings are time-consuming and insufficiently accurate. In addition, the determination of the sp3/sp2 ratio is often difficult due to the displacement of the energy position of the C1s electron line. In this paper, the change in the chemical state of carbon over the thickness of a diamond-like coating is studied by X-ray photoelectron spectroscopy. Analysis of the carbon line fine structure of the differential graphite spectra (sp2 bonds) and diamond (sp3 bonds) allowed us to establish the parameter δ, which determines the ratio of the graphite and diamond components in the DLC coating. Profiling with Ar+ ions of the diamondlike coating surface showed that with an increase in the etching time, the proportion of amorphized carbon increases, which means that the antifriction properties increase with the abrasion of the coating. The obtained regularities allow us to predict changes in the tribological properties of DLC coatings during operation. Ion profiling also allows to determine the thickness of coatings with high accuracy.

The performance evaluation of heavy loaded tribosystems with vacuum ion-plasma PVD and DLC coatings

The results of studies of the physical, mechanical and tribological characteristics of PVD and DLC coatings are presented. The complex of basic mechanical properties (hardness H and elastic modulus E), as well as derivatives of mechanical characteristics H/E and Н3/Е2 , were investigated by the method of continuous indentation at various loads. The friction coefficient, the wear rate of the sample and the counterbody were determined as tribological indicators. The applied purpose of the work was to determine the friction unit for applying the developed coatings, materials and modes of applying PVD and DLC coatings. To solve this problem, a test bench was designed and built that simulates the operation of the selected friction unit. As a result of the research carried out, the results of laboratory and bench tests were compared. The performance of the coatings was determined by the volume of the tooth wear of the sleeve and the tip with the help of the method of micrometric measurements. As a result of the study of the surface morphology, the volumes of wear of rubbing conjugations and the intensity of their wear were determined. It has been established that the results of bench tests confirm laboratory studies and suggest that such an installation can be used for researching other heavily loaded spline conjugations.

Friction and Wear Performance Evaluation of Bio-Lubricants and DLC Coatings on Cam/Tappet Interface of Internal Combustion Engines

The environmental concerns associated with artificially formulated engine oils have forced a shift towards bio-based lubricants. The deposition of hard coatings on engine components and migrating to environmentally friendly green lubricants can help in this regard. Chemically modified forms of vegetable oils, with better low-temperature characteristics and enhanced thermo-oxidative stability, are suitable substitutes to conventional lubricant base oils. The research presented in this manuscript was undertaken to experimentally investigate the wear and friction performance of a possible future generation of an environmentally friendly bio-based lubricant as a potential replacement for conventional engine lubricants. In order to quantify the tribological benefits which can be gained by the deposition of DLC coatings, (an (a-C:H) hydrogenated DLC coating and an (a-C:H:W) tungsten-doped DLC coating) were applied on the cam/tappet interface of a direct acting valve train assembly of an internal combustion engine. The tribological correlation between DLC-coated engine components, lubricant base oils and lubricant additives have been thoroughly investigated in this study using actual engine operating conditions. Two additive-free base oils (polyalphaolefines (PAO) and chemically-modified palm oil (TMP)) and two multi-additive-containing lubricants were used in this investigation. Real-time drive torque was measured to determine the friction force, detailed post-test analysis was performed, which involved the use of a specialized jig to measure camlobe wear. An optical profilometer was used to measure the wear on the tappet, high-resolution scanning electron microscopy was employed to study the wear mechanism and energy-dispersive X-ray spectroscopy was performed on the tested samples to qualitatively access the degradation of the coating. When using additive-free TMP, a low friction coefficient was observed for the cam/tappet interface. The presence of additives further improved the friction characteristics of TMP, resulting in reduced average friction torque values. A tremendous enhancement in wear performance was recorded with a-C:H-coated parts and the coating was able to withstand the test conditions with little or no delamination.

Evaluation of the tribological properties of two PEEKs sliding against Al2O3, WC and DLC coatings under dry friction and water lubrication

The tribology performance of two carbon fibre-reinforced polyether-ether-ketones (450FC30 and WG101) sliding against stainless steel 3Cr13 and 3Cr13 coated with aluminium oxide (Al2O3), tungsten carbide (WC) and diamond-like carbon (DLC) under dry friction and water lubrication were studied to reduce the coefficient of friction and improve the wear resistance of water-lubricated bearings. The friction and wear mechanism of different tribopairs were determined via pin-on-disc sliding tests. Experimental results showed that the WG101/Al2O3 tribopair exhibited excellent wear resistance under dry friction and water lubrication. Carbon fibres were exposed on the friction surface of WG101 when WG101 slid against Al2O3. These carbon fibres bore most of the load to reduce wear. This work provides a practical basis for selecting the optimal tribopair for water-lubricated bearings.

Carbon-Based Coatings in Medical Textiles Surface Functionalisation: An Overview

The COVID-19 pandemic has further highlighted the need for antimicrobial surfaces, especially those used in a healthcare environment. Textiles are the most difficult surfaces to modify since their typical use is in direct human body contact and, consequently, some aspects need to be improved, such as wear time and filtration efficiency, antibacterial and anti-viral capacity, or hydrophobicity. To this end, several techniques can be used for the surface modification of tissues, being magnetron sputtering (MS) one of [hose that have been growing in the last years to meet the antimicrobial objective. The current state of the art available on textile functionalisation techniques, the improvements obtained by using MS, and the potential of diamond-like-carbon (DLC) coatings on fabrics for medical applications will be discussed in this review in order to contribute to a higher knowledge of functionalized textiles themes.

Evaluating the Mechanical and Tribological Properties of DLC Nanocoated Aluminium 5051 Using RF Sputtering

The diamond-like carbon- (DLC-) coating technique is used in the sliding parts of automotive engines, among other applications, to reduce friction and wear. In this work, DLC has been coated on the Aluminium 5051 sample to assess the mechanical and tribological properties. A sputtering deposition mechanism is used, and the DLC is coated using a graphite target. The developed DLC coatings are tested for adhesion strength, hardness, chemical composition using XRD, and wear behaviour. The developed DLC thin films have considerably increased the wear behaviour of the Aluminium 5051 sample and have fulfilled the objective of this study. The XRD data indicated the presence of amorphous carbon in the coating with a threefold increase to the hardness of the naked aluminium. This study provides insight into improving the aluminium wear resistance by developing a considerably hard coating.

Advanced Tribological Characterization of DLC Coatings Produced by Ne-HiPIMS for the Application on the Piston Rings of Internal Combustion Engines

Piston rings (PR) are known for almost a quarter of the friction losses in internal combustion engines. This research work aims to improve the tribological performance of PR by a recently developed variant of Diamond-like Carbon (DLC) coatings deposited in a mixture of Ar and Ne plasma atmosphere (Ne-DLC) by high-power impulse magnetron sputtering (HiPIMS). For the benchmark, the widely used Chromium Nitride (CrN) and DLCs deposited in pure Ar plasma atmosphere (Ar-DLC) were used. The tribological tests were performed on a block-on-ring configuration under different lubrication regimes by varying temperatures and sliding speeds. The analysis of the results was performed by Stribeck curves corresponding to each sample. An improvement of the tribological performance was observed for Ne-DLC films by up to 22.8% reduction in COF compared to CrN in the boundary lubrication regime, whereas, for the Ar-DLC film, this reduction was only 9.5%. Moreover, the Ne-DLC films achieved ultralow friction of less than 0.001 during the transition to a hydrodynamic lubrication regime due to better wettability (lower contact angle) and higher surface free energy. Increasing the Ne up to 50% in the discharge gas also leads to an increase of hardness of DLC films from 19 to 24 GPa.