Low Friction Properties Research Articles

New Optimized Lubricating Blend of Peanut Oil and Naphthenic Oil Additivated with Graphene Nanoparticles and MoS2: Stability Time and Thermal Conductivity

Lubricants are essential to machinery life, as they play a crucial role in controlling and diminishing the friction and wear between moving parts when operated under extreme conditions. To this end, due to tight environmental conditions, manufacturers are looking for alternative solid lubricants to be dispersed in base liquid lubricants. MoS2 and graphene are solid lubricants that provide low frictional properties and high thermal stability in both oxidizing and non-oxidizing environments. This research offers a new lubricant with improved thermal conductivity that combines the synergistic effect of graphene and MoS2 in a blend of vegetable oil (peanut) and naphthenic oil. The ratio of peanut oil and naphthenic oil varies from 1:3–3:1. A fixed composition of 4.34 wt.% palm oil methyl ester (POME) is added to enhance the anti-wear property further. Graphene and MoS2 concentrations varied between 1:2–5:2, respectively. This nanoparticle additive oil blend is physically mixed using a water bath sonication for 4 h. The stability of the blend lubricant dispersed with MoS2 and graphene is studied using a UV-Vis spectrophotometer for 25 days. The effect of various concentrations of graphene, MoS2, peanut oil, and naphthenic oil on the thermal conductivity of the nanolubricant is also studied as a function of temperature (25 °C–55 °C). Artificial neural network models were used for the parametric investigation of the nanolubricant. It is found that the stability of the formulated nanolubricant increased with peanut oil composition above 25 wt.%. The results show that the 3:1 blend ratio showed higher stability for hybrid MoS2-based lubricants. Similarly, the highest thermal conductivity is observed for 100 wt.% naphthenic oil with a 1:2 ratio of graphene–MoS2 at 55 °C.

Cationic Modified PVA Hydrogels Provide Low Friction and Excellent Mechanical Properties for Potential Cartilage and Orthopedic Applications

Front Cover: This image is an analogy between the structure and potential application of the hydrogel in current work and a Chinese mythology “Carp Leaping Over the Dragon's Gate”. The leaping of carps also indicates a potential increase in the cartilage repair field achieved by this cationic polymer modified PVA hydrogel with satisfying mechanical properties. This is reported by Yuru Chen, Jian Song, Song Wang, and Weiqiang Liu in article number 2200275.

Mechanical and Three Body Abrasive Wear Behaviour of Nano-Filler Filled, Chopped Glass Fiber Filled Hybrid Composites

Polymer matrix composites are developed for tribological applications due to the possibility of optimizing the properties with the addition of special filler materials as reinforcement. Filler filled polymer matrix composite systems are used in many automotive parts and components like brake pads or clutches which require high coefficient of friction coupled with low wear. However, in most cases it is the primary concern to develop polymer composites that posses low friction and low wear properties under dry sliding conditions against smooth metallic counterparts e.g., gears or bearings, chute liners and coal handling equipments in power plants, gear pumps handling industrial fluids, agricultural machine components. Polymer composites operate in applications where fluid and grease lubricants fail, and have superior tribological performance to traditional polymer composites. Particulate fillers or fibres or solid lubricants have been a part of notable reductions in the wear rate of the polymer matrix at very low loading, and there exists a wide scope on the development of polymer composites on the tribological behaviour. The incorporation of fillers in polymer could provide a synergism in terms of improving mechanical properties and wear performance, which has not been adequately explored so far. The research on nano fillers such as nano clay, Glass fiber and Titanium di-oxide (TiO2) in epoxy system is scarcely reported and further they focus on a few specific issues only. The present study was focused on investigating Mechanical - Tensile, Hardness, and three body abrasive wear characteristics of thermosetting based Epoxy composites and the effect of incorporation of nano clay, TiO2 nanoparticles and chopped glass fiber on microstructure, hardness, friction and abrasive wear are determined and analyzed. The main aim was to investigate the effect of applied load, sliding distance /abrading distance, sliding speed and percentage of filler. The surface morphology of the worn out surfaces were examined using SEM, to get a better understanding of the wear mechanisms.

Cationic Modified PVA Hydrogels Provide Low Friction and Excellent Mechanical Properties for Potential Cartilage and Orthopedic Applications.

Poly(vinyl alcohol) (PVA) hydrogel is a promising candidate for articular cartilage repair yet restrained by its mechanical strength and tribological property. Current work reports a newly designed PVA-based hydrogel modified by glycerol (g), bacterial cellulose (BC), and a cationic polymer poly (diallyl dimethylammonium chloride) (PDMDAAC), which is a novel cationic strengthening choice. The resultant PVA-g-BC-PDMDAAC hydrogel proves the effectiveness of this modification scheme, with a confined compressive modulus of 19.56MPa and a friction coefficient of 0.057 at a joint-equivalent load and low sliding speed. The water content, swelling property, and creep behavior of this hydrogel are also within a cartilage-mimetic range. The properties of PVA-based hydrogels before PDMDAAC addition are likewise studied as a cross-reference. Besides, PDMDAAC-modified PVA hydrogel realizes ideal mechanical and lubrication properties with a relatively low PVA concentration (10wt.%) and facile fabrication process, which lays a foundation for mass production and marketization in the future.

Low-friction, wear-protecting coatings on polymers by atmospheric pressure plasma spraying

Deposition strategies to obtain low-friction and wear resistant coatings on 3D-printed rough polyamide 12 (PA12, nylon) surfaces were developed via atmospheric pressure plasma deposition. The feedstock materials for the DC plasma torch InoCoat 3 produced by INOCON Technologie GmbH were dry lubricants such as MoS2 and graphite. In addition, parameter sets that would not thermally damage the heat sensitive polymers were applied. Generally, microtribological characterisation indicates that coating composition and thickness particularly influence the coating performance significantly. Pure MoS2 coatings wear rapidly, particularly on the roughness tips (mean substrate roughness Ra up to 20 μm); this exposes the substrate and leads to friction coefficients similar to those of PA12 and rather limited potential for protection against wear. Composite coatings with graphite in a MoS2 matrix provide huge potential for wear protection (i.e. >20 times less penetration depth) even for exposed PA12 roughness tips, owing to the transfer of lubricating carbon into these exposed areas. If the thickness is sufficiently high, preventing the wear of tips results in low-friction properties (friction coefficients < 0.1, i.e. four times lower than those for uncoated PA12).

Articular Cartilage-Inspired Hybrid Double-Network Hydrogels with a Layered Structure and Low Friction Properties

Articular Cartilage-Inspired Hybrid Double-Network Hydrogels with a Layered Structure and Low Friction Properties

Alginate Fiber-Enhanced Poly(vinyl alcohol) Hydrogels with Superior Lubricating Property and Biocompatibility.

The design of a novel interpenetrating network hydrogel inspired by the microscopic architecture of natural cartilage based on a supramolecular sodium alginate (SA) nanofibril network is reported in this paper. The mechanical strength and toughness of the poly(vinyl alcohol) (PVA) hydrogel were significantly improved after being incorporated with the alginate nanofibril network. The multiple hydrogen bonds between PVA chains and alginate fibers provided an efficient energy dissipation, thus leading to a significant increase in the mechanical strength of the PVA/SA/NaCl hydrogel. The PVA/SA/NaCl hydrogel demonstrated superior water-lubrication and load-bearing performance due to noncovalent interactions compared with pure PVA hydrogels. Moreover, the bioactivity of the PVA/SA/NaCl hydrogel was proved by the MC3T3 cell proliferation and viability assays over 7 days. Therefore, alginate fiber-enhanced hydrogels with high strength and low friction properties are expected to be used as novel biomimetic lubrication materials.

Facile preparation and characterization of tough poly(vinyl alcohol) organohydrogels with low friction and self-cleaning properties

Although many hydrogels have been applied to wearable sensors, it is still challenging to simultaneously realize hydrogels with optical transparency, superior mechanical properties, excellent sensing performance, and anti-freezing by using inexpensive raw materials and an easy preparation process. Herein, using ethylene glycol/H2O (EG/ H2O) as a solvent, poly(vinyl alcohol)/EG organohydrogel (PVA/EG OHG) was prepared by a simple heating and frozen-thawing method. Owing to the multifunctionality of EG (i.e., physical cross-linker, anti-freezer and co-solvent), PVA/EG OHG demonstrated excellent integrated properties, including high strength, high toughness, and anti-freezing performances. Besides, PVA/EG OHG also showed low friction, self-cleaning, and frost resistance properties. After the introduction of LiCl, ionically conductive PVA/EG @LiCl organohydrogel was served as a self-cleaning strain sensor, which could be long-term stable to detect the motions of human under room and low temperatures. The study provides to further understanding of the organohydrogel, which will help us design next-generation high-performance organohydrogels.

Physical, Mechanical, and Biological Properties of Fibrin Scaffolds for Cartilage Repair.

Articular cartilage is a highly organized tissue that provides remarkable load-bearing and low friction properties, allowing for smooth movement of diarthrodial joints; however, due to the avascular, aneural, and non-lymphatic characteristics of cartilage, joint cartilage has self-regeneration and repair limitations. Cartilage tissue engineering is a promising alternative for chondral defect repair. It proposes models that mimic natural tissue structure through the use of cells, scaffolds, and signaling factors to repair, replace, maintain, or improve the specific function of the tissue. In chondral tissue engineering, fibrin is a biocompatible biomaterial suitable for cell growth and differentiation with adequate properties to regenerate damaged cartilage. Additionally, its mechanical, biological, and physical properties can be enhanced by combining it with other materials or biological components. This review addresses the biological, physical, and mechanical properties of fibrin as a biomaterial for cartilage tissue engineering and as an element to enhance the regeneration or repair of chondral lesions.

Friction-reducing and vibration-absorbing performances on a novel thermoplastic bearing material reinforced by nano-WS2 and UHMWPE

High performance materials with low friction and high vibration-absorbing properties play a vital role in stable operation of water-lubricated ship stern bearings. Therefore, a TPU composite material reinforced by WS2 and UHMWPE was prepared. After friction and vibration tests, it was found that WS2 reduced the coefficient of friction of TPU matrix with its excellent lubricating properties, and after adding UHMWPE, the coefficient of friction continued to drop to 0.07 and became more stable during the whole friction process. The synergistic effect of WS2 and UHMWPE effectively reduced the friction and amplitude of the composite and made the composite present the best tribological and vibration-absorbing performance. This research provided a basis for the design of new water-lubricated ship bearing materials.

Effect of roughness on the running-in behavior and tribofilm formation of carbon fiber reinforced PTFE composite in trace moisture environment

Counterface roughness is known to affect the tribological behavior of carbon fiber reinforced PTFE. However, the effect of roughness in trace moisture environments has not yet been extensively investigated. In this study, the tribological behavior and tribofilm formation were evaluated for a carbon fiber reinforced PTFE composite sliding in a trace moisture environment against 34CrNiMo6 steel counterfaces with different roughness. Tribotests were conducted with a three-pin-on-disc tribometer at a sliding velocity of 2.2 m/s and in a nitrogen environment with moisture content controlled to 11 ppm. Generally, smoother counterfaces gave lower wear, both during running-in and steady-state. Contrarily, the coefficient of friction was only affected by roughness during running-in. Surface analysis from different stages of running-in were done to elucidate the formation of tribofilms and their different characteristics. For the rough countersurface, a loosely adhered transfer film is transitionally formed at the beginning of sliding to enable the formation of a persistent transfer film. Contrarily, for the case of a smooth countersurface, the formation of a persistent transfer film is initiated from the start. Similarly for the rough and smooth countersurface, a micrometer thick tribofilm with excellent low friction properties is observed on the PTFE composite after running-in.

Interlayer Friction in Graphene/MoS2, Graphene/NbSe2, Tellurene/MoS2 and Tellurene/NbSe2 van der Waals Heterostructures

Two-dimensional (2D) materials have a wide range of applications in the field of molecular-level solid lubrication due to their ultrahigh mechanical strength and extremely low friction properties at the nanoscale. In this work, we investigated the interlayer friction properties of four different heterostructures, namely, graphene/MoS2, graphene/NbSe2, α-tellurene/MoS2 and α-tellurene/NbSe2, using a molecular dynamics (MD) method. The effects of a series of influencing factors on the interlayer friction were investigated. The results show that for the four heterostructures, the influence laws of layer number, temperature, and normal load on interlayer friction show consistency. The twist angle can effectively regulate the interlayer friction of these 2D materials, but the superlubricity phenomenon cannot occur for α-Te/MoS2 and α-Te/NbSe2 systems. Furthermore, we address the origin of friction in detail, emphasizing the contribution of edge pinning and interface sliding resistance to the frictional force of the heterostructure. The friction decreases with increasing temperature and sliding speed due to the reduction in the interlayer adhesion force. The present findings provide a deep understanding of friction control and contribute much to the design of robust 2D superlubricity systems.

Structural reorientation and compaction of porous MoS2 coatings during wear testing

Industrial upscaling frequently results in a different coating microstructure than the laboratory prototypes presented in the literature. Here, we investigate the wear behavior of physical vapor deposited (PVD) MoS2 coatings: A dense, nanocrystalline MoS2 coating, and a porous, prismatic-textured MoS2 coating. Transmission electron microscopy (TEM) investigations before and after wear testing evidence a crystallographic reorientation towards a basal texture in both samples. A basal texture is usually desirable due to its low-friction properties. This favorable reorientation is associated to a tribological compaction of the porous specimens. Following running-in, sliding under high contact pressure ultimately leads to a wear rate as small as for an ideal grown bulk MoS2 single crystal grown by chemical vapor deposition (CVD). This suggests that the imperfections of industrial grade MoS2 coatings can be remediated by a suitable pretreatment.

Polysaccharide-derivative coated intravascular catheters with superior multifunctional performance via simple and biocompatible method

• An intravascular catheter was coated with CMC layer exhibiting antimicrobial, antithrombotic, and low friction properties. • Whole manufacturing process was water-based, hence eco-friendly and biocompatible. • Functionalities of CMC layer were enhanced by engineering the porous structure. • Sufficient lubricity of porous CMC coated catheter was verified via trackability test. Antimicrobial, antithrombotic activity and low-friction functions are essential for the surface of intravascular catheters (ICs). However, the multifunctional surface, encompassing all of the above properties has not yet been realized. Here, we report a novel strategy for biocompatible and eco-friendly surface modification of the ICs with multifunctional polysaccharide, O-carboxymethyl chitosan (CMC). Micro- and nanoscale porous CMC (p-CMC) layer was simply fabricated via a selective elimination of the water-soluble polyethylene glycol (PEG) from heterogeneous CMC/PEG composite. The p-CMC structure exhibited a significantly enhanced hydration rate and superhydrophilic property. In particular, the antifouling property of superhydrophilic surface showed excellent anti-adhesion of Escherichia coli and platelets along with the intrinsic multifunctionality of CMC, indicating a dual effect of our p-CMC layer: (1) intrinsic antibacterial and antithrombotic properties of CMC and (2) anti-adhesion of substances on superhydrophilic surface. Meanwhile, despite the rough surface of the p-CMC layer, it showed high lubricity and durability under continuous wet friction conditions. Furthermore, we demonstrated that the actual p-CMC coated intravascular catheter (IC) provides superior trackability in a curved artificial blood vessel. The potential of the proposed coating strategy can be offered not only ICs, but also wide range of polymer-based applications including vascular filters, grafts, pacemakers and soft robots.

Ice-based triboelectric nanogenerator with low friction and self-healing properties for energy harvesting and ice broken warning

In this paper, a new type of ice-based triboelectric nanogenerator (ICE-TENG) has been fabricated to harvest energy in cold weather. Ice is a preferred material for designing TENGs in cold winter, alpine or snowy mountain regions because of its cleanness, environmental protection, abundant reserves, low friction, and self-healing properties. The short-circuit current and voltage can achieve 2.4 µA and 48 V with 4 mm thickness of ice layer, 30 N loadings, and 5 Hz contact frequency, which can be useful in some practical applications such as lighting LEDs and charging capacitors. The ICE-TENG possesses excellent stability and can reach an output power of 35 µW under 20 MΩ loading resistance. The coefficient of friction between ice and other friction pairs is negligible, and it can even become super-slippery with the coefficient of friction below 0.008. Thus, the wear of the friction pairs is small, which can help TENG to have a long working life. Besides, due to the rapid phase change of ice, the ICE-TENG exhibits a commendable self-healing ability and maintains the original output performance after several damage and repair processes. To simulate the practical applications, a single electrode ICE-TENG driven by walking has been designed for harvesting energy on the ice surface. Because of the difference in electric output before and after the ice fragmentation, the ICE-TENGs are designed to construct a warning system to remind the danger when the ice surface suddenly shatters. Moreover, such ICE-TENGs are capable of lighting “ICE” LEDs and powering an electric watch with footsteps. This illustrates a promising potential in self-powered systems such as danger warning, charge shortage, and energy harvesting.

Study on galling behaviour of HiPIMS deposited Mo/DLC multilayer coatings at ambient and elevated temperature

Galling has been a severe concern in oil – gas, automotive, and nuclear sectors. SS 304 steel is used in these industries despite its low galling resistance because it possesses good corrosion resistance properties. The threads of bolt, nut or a tapped hole and fasteners made of SS 304 experience severe damage due to galling or cold working. Therefore, the galling characteristics of the coated SS 304 samples were studied against the uncoated counterpart. A multilayer coating of molybdenum (Mo) and diamond like carbon (DLC) was deposited through dual sputtering using a high power impulse magnetron sputtering (HiPIMS) power source for graphite target and pulsed DC power source for Mo target. The Mo/DLC multilayer coating was optimized for antiwear and low friction properties. The evaluation of friction properties was done through a nanotribometer. The galling samples of SS 304 steel were prepared following the ASTM G196 standard, and the optimized coating was deposited on the galling samples. The adhesion strength of the coating was analyzed with the help of a nanoscratch tester. The galling behavior of coated and uncoated samples was investigated at room temperature (RT) and 300 °C. Galling damage was quantified by calculating the galling area on the galled sample. Image processing and computer vision tools were used to calculate the galled area. The tribopair having coated (Mo/DLC multilayer coating on SS 304) and the uncoated sample (SS 304) showed lower galled area than the tribopair containing both uncoated samples in every test conditions. At RT the coated sample failed at 15 MPa, whereas the uncoated samples failed at 5 MPa. Similar type of results were obtained when the samples were tested at 300 °C. The characterization of the coating and the mechanism of galling were studied in detail with the help of Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), nanoindentation, stereo-zoom optical microscopy, and scanning electron microscopy (SEM).

Frictional Properties of Element- and Compound-Doped Diamond-Like Carbon Films under Boundary Lubrication with Synthetic Base Oil

The frictional properties of diamond-like carbon (DLC) films under boundary lubrication with a synthetic base oil were investigated. The specimens tested were a-C:H, Cr-a-C:H, Ti-a-C:H, W-a-C:H, WC-a-C:H, Mo-a-C:H, MoS2-a-C:H, and Sn-a-C:H films. The tribological properties of DLC/steel contacts were evaluated using a reciprocating-type cylinder-on-disk tribotester. The DLC films exhibited different frictional properties depending on the type of doping elements and compounds used. Notably, the Sn-a-C film gave the lowest friction. The friction tests and static contact angle analyses revealed that the average friction coefficient decreased with a decrease in the static contact angle of the worn DLC film surface, demonstrating that the DLC films with relatively high surface wettabilities exhibited relatively low friction properties. Therefore, surface wettability plays an important role in determining the frictional properties of DLC films under boundary lubrication with synthetic base oil..

Effect of Steel Hardness and Composition on the Boundary Lubricating Behavior of Low-Viscosity PAO Formulated with Dodecanoic Acid and Ionic Liquid Additives.

Two ionic liquids, tributylmethylphosphonium dimethylphosphate (PP) and 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate (BMP), as lubricant additives in polyalphaolefin (PAO8) were studied under boundary lubricating conditions on two types of steel (AISI 52100 bearing steel and AISI 316L stainless steel). The tribological behavior of these ILs was compared with dodecanoic acid, a well-known organic friction modifier. This study employs a ball-on-disk tribometer with an alumina ball as a counterpart. A range of advanced analytical tools are used to analyze the tribofilms, including scanning electron microscopy equipped with a focused ion beam, scanning transmission electron microscopy equipped with X-ray energy-dispersive spectroscopy, and X-ray photoelectron spectroscopy. A quartz crystal microbalance with dissipation was used to study the surface adsorption of the additives on iron- and stainless steel-coated sensors to reveal the adsorption kinetics, adsorbed layer mass, and bonding strength of the adsorbed layer on the metallic surfaces. The most important factors controlling friction and wear are the thickness and viscoelastic properties of the adsorbed layer, the thickness and chemical composition of the tribofilm, and the hardness and chemical composition of steel. Among all additives studied, BMP on stainless steel gives a strongly adsorbed layer and a durable tribofilm, resulting in low friction and excellent antiwear properties.

Ice-Based Triboelectric Nanogenerator with Low Friction and Self-Healing Properties for Energy Harvesting and Ice Broken Warning

Ice-Based Triboelectric Nanogenerator with Low Friction and Self-Healing Properties for Energy Harvesting and Ice Broken Warning

Effect of nitrogen gas supply to graphite target on properties of ta-CNx films deposited by FCVA method

It has been reported that ta-CNx coatings deposited by the IBA-FAD method show excellent low friction and wear properties, however the hardness decreases with the N/C ratio in the coating. Although, using an ion gun to mix nitrogen in the coating gives several pros to the coating, however, it rises initial cost of equipment. To overcome this situation, nitrogen ion generation by just supplying nitrogen gas close to an arc discharge area which is used in the FAD carbon ion generation was suggested by authors. The supplied nitrogen gas is ionized by the high voltage arc which is supplied to a graphite target. The effects on the N/C ratio was measured by AES, hardness was measured by nano-indentation tester, and tribological properties of the deposited ta-CNx coatings were examined. The results showed that ta-CNx coatings deposited by nitrogen gas supply method showed higher hardness than ordinally nitrogen ion beam deposition method.