Longer Wear Life Research Articles

Sustainable Denim Design Using Giza Cotton

Designing denim fabrics that will have a longer wear life by combining Giza cotton, one of the best cottons in the world, with yarn technology, without using any reinforced synthetic fibers. Giza cotton will be used in the products to be developed specifically for the project. High strength yarns will be obtained with the fiber length of Giza cotton and the appropriate twist value to be applied. It is aimed that the fabrics produced from these threads will have a longer lifespan than normal cotton threads. One of the most important steps for the continuity of sustainable production will be that the produced product is recyclable and can be used for a longer time. In this way, a significant decrease in the carbon and water footprint resulting from production will be achieved. The environmental impact of production will be minimized.

Combining Carbon Nanoparticle Coatings and Laser Surface Texturing for Enhanced Lubricity Under High Loads

Developing new lubrication concepts greatly contributes to improving the energy efficiency of mechanical systems. Nanoparticles such as those based on carbon allotropes or 2D materials have received widespread attention due to their outstanding mechanical and tribological performance. However, these systems are limited by a short wear life. Combining nanoparticle coatings with laser surface texturing has been demonstrated to substantially improve their durability due to the reservoir effect which prevents immediate particle removal from the contact. In this study, we investigate the high-load (20 N) tribological performance of AISI 304 austenitic stainless-steel substrates, which are line-patterned by laser interference patterning and subsequently coated with different carbon nanoparticle coatings (carbon nanotubes, carbon onions, carbon nanohorns) against alumina and 100Cr6 counter bodies. In addition to that, benchmark testing is performed with conventional solid lubricant coatings (graphite, MoS2, WS2). Electrophoretic deposition is used as the main coating technique along with air spraying (for WS2). All coatings substantially improve friction compared to the purely laser-patterned reference. Among all coating materials, carbon nanotubes demonstrate superior lubricity and the longest wear life against 100Cr6 and alumina counter bodies. Detailed characterization of the resulting wear tracks by energy-dispersive X-ray spectroscopy, scanning electron microscopy, and confocal laser scanning microscopy provides insights into the friction mechanisms of the various solid lubricant particles. Further, material transfer is identified as an important aspect for effective and long-lasting lubrication.

Two-step mask in-situ forming (CFx)n-TiO2/ZrO2 alternate coatings with different width ratios by electrohydrodynamic atomization

This paper utilizes a two-step mask process to prepare the crosswise lubricant-hard alternating coatings of (CFx)n-TiO2/ZrO2 with different width ratios, based on the electro-fluid in-situ forming technique. The research explored the micro morphologies, mechanical performance, sliding friction against 304 balls and wear properties of the coatings. A comparison was made with the (CFx)n-TiO2/ZrO2 composite laminate coating. X-ray diffraction and X-ray photoelectron spectroscopy results indicated the presence of Ti-O-Zr chemical bonds within the sintered TiO2/ZrO2 composite coatings. Dry friction tests revealed that the sample with a lubricant-hard coating width ratio of 2:1 (AT-D), exhibited the highest interfacial bonding performance (∼53.2 N) and the longest wear life (∼10658 s). The sample featuring a lubricant-hard coating width ratio of 1:1 (AT-C), displayed the lowest friction coefficient (∼0.13) and the smallest coating wear rate of 2.04×10−7 mm3 N−1 mm−1. These disparities could be attributed to the varying continuity of the self-lubricating film and the actual contact area between the mating components induced by different lubricant-hard coating width ratios.

Tailoring the tribological properties of nanostructured carbon films under water lubrication

Carbon films have been considered suitable to be applied in water lubrication since they exhibit excellent friction-reducing and wear resistance, chemical inertness, etc. However, the basic understanding of tribological behaviors of carbon-based films under water lubrication still needs to be explored. In the present work, carbon films with different nanostructures were prepared by the electron cyclotron resonance (ECR) plasma nano-surface manufacturing system, and micro-textures with different sizes were prepared on the surface of carbon films by plasma etching. The influence of nanostructure and surface texture on the tribological properties of carbon films was investigated. The results show that different nanostructured carbon films can obtain lower friction coefficients and longer wear life under water lubrication than under dry condition. Due to low surface roughness, high hardness, and compact structure, the tribological properties of amorphous carbon (a-C) films under water lubrication are much better than those of graphene sheet-embedded carbon (GSEC) films. The prepared surface texture has a negative effect on the hard a-C film, but it can make the soft GSEC film generate soft wear debris at the initial stage. With the action of water, the soft wear debris is bonded on the surface of the contacting ball to form a silt-like transfer film, which increases the wear life by nearly three orders of magnitude. These results extend the basic understanding of the tribological behavior of carbon film under water lubrication, which is crucial in both fundamental and applied science.

Tribological behaviors of oxygen-doped carbon coatings deposited by ion-irradiation-assisted growth

Oxygen-doped carbon coatings were deposited by ion-irradiation-assisted growth using an electron cyclotron resonance plasma processing system, and the effects of the O 2 content on the coating's structure and tribological behavior were studied. During the coating deposition, O + , O 2 + , and Ar + ions in the oxygen plasma were attracted to irradiate the growing coating surface , realizing oxygen plasma during-etching. X-ray photoelectron spectroscopy characterization showed that the O 2 addition incorporated some oxygen atoms into the carbon coating, and the sp 3 / sp 2 ratio of the entire coating increased. Such structural changes made the carbon coating present higher nanoscratch resistance and longer wear life that increased from 990 cycles to more than 5000 cycles. Finally, the reason why the oxygen doping can induce the sp 3 / sp 2 ratio to increase was suggested to be ion-irradiation-induced chemical recombination energy release, which could only occur when the O 2 introduction reduced the atom displacement threshold energy. • Oxygen-doped carbon coatings were deposited by ion-irradiation-assisted growth. • Plasma during-etching was realized by attracting O + , O 2 + , and Ar + ions to irradiate the growing coating. • After doping, the wear life increased due to the increase in sp 3 / sp 2 of the entire coating. • The increase in sp 3 / sp 2 was caused by ion-irradiation-induced chemical recombination energy release.

The effect of coating thickness on the tribological properties of polydopamine/PTFE + graphite particle coatings on 60NiTi

Polydopamine (PDA)/polytetrafluoroethylene (PTFE) + 0.25 wt% graphite particle (GrP) coatings of three different thicknesses were deposited on roughened 60NiTi substrates. Their tribological properties were evaluated by coating durability, wear progression, and scratch tests. It was found that the thicker coatings have longer wear life, but the wear life was not proportional to the coating thickness. The coating thickness affected the transfer film and contact pressure and thus the coating durability. The coating wore rapidly to the coating-substrate interface and then wore at a very low wear rate. The thicker coatings had lower critical loads at which gross coating failure occurred.

Wear Behavior of Ductile Iron Wheel Material Used for Rail-Transit Vehicles under Dry Sliding Conditions.

A ductile iron wheel used for a rail-transit vehicle was treated with a recommended heat-treatment process. The ductile iron wheel after heat treatment was composed of graphite nodules and tempered sorbite with an area fraction of 98%. A friction test of the ductile iron and carbon steel wheel materials was systematically performed under different normal loads and sliding velocities. The results indicated that the wear mechanism of the ductile iron wheel changed from adhesion to abrasion with an increase in the normal load level. Adhesion was the main wear mechanism at different sliding velocities and normal load level. The impact of the normal load on the wear mechanism was greater than that of the sliding velocity. Since the ductile iron wheel material had excellent thermal property and higher carbon content, it exhibited a lower wear rate, a smaller difference value of the friction coefficient, and plastic deformation on the worn surface than those of the carbon steel wheel material. This indicates that ductile iron wheels may have a longer wear life, greater traction, and higher stability during operation than carbon steel wheels. The iron wheels have the potential for being applied in rail-transit vehicles.

Integration of MoST and Graphit-iC coatings for the enhancement of tribological and corrosive properties

MoS2-based coatings present low friction coefficients in vacuum or inert environments, but they also present high wear rates in air environments, which is difficult to serve in complicate environments and extreme conditions. It is becoming more important to improve tribological properties in various environments for widely use. Conversely, carbon-based coatings exhibit good anti-wear properties in air environments, especially humid environments. In this study, we introduced the hydrogen-free carbon-chromium coating(Graphit-iC™) into the MoS2 coating doped with titanium(MoST™) by layer-by-layer deposition techniques, and we built a series of MoST/Graphit-iC multilayer coatings with different numbers of layers. The results show that multilayer coatings are composed of denser structure compared with the MoST coating. Furthermore, the tribological performance in various environments are significantly improved by building the multilayer structure. The lowest wear rate and longest wear life in ambient environment are obtained with 8 layers and the friction coefficient decreases to around 0.02 in vacuum environment. In addition, interfaces between MoST layers and Graphit-iC layers can inhibit the permeation of the corrosive mediums. Overall, the improvement of the tribological performance and corrosion resistance are attributed to the heterogeneous interfaces in multilayer coatings, and multilayer coatings exhibit great potential in widely use.

Precise control of surface texture on carbon film by ion etching through filter: Optimization of texture size for improving tribological behavior

Surface texture is a potential way to promote the tribological behavior of films with a range of tens to hundreds nanometers, but how to precisely control the texture size and find an optimal size for improving the tribological behavior is still challenging. In this paper, we proposed a method to fabricate pit texture with tunable size on the surface of carbon film by ion etching through a filter. The pit depth (10, 30 and 60 nm) was decided by the etching time and the pit diameter (10, 60 and 120 μm) was equal to the through-hole on the filter. The tribological properties of these carbon films were tested using a pin-on-disk tribometer. The results demonstrated that the friction coefficient and wear life were strongly affected by the texture parameter and there were an optimal pit depth and diameter under which the film exhibited the lowest friction coefficient and the longest wear life. The mechanism of the tribological property promotion was further discussed based on the variation of the transfer film structure and contact condition induced by the texture. These results provided an effective way to choose proper texture parameters for better tribological performance of the surface, which can be expected for expanding the texture techniques.

Synthesis of fullerene-like hydrogenated carbon films containing iron nanoparticles

Fullerene-like hydrogenated carbon films deposited by plasma enhanced chemical vapor deposition (PECVD) as compared with other methods can attain super-low friction and wear. But they often have bad adhesion to steel substrate and their structures are tailored by non-metal elements as F, N etc. In this work, we have prepared the films on steel balls by the combination of PECVD and plasma nitriding, among which iron nitride particles are sputtered and introduced in the films. The films have longer wear life and better adhesion to the steel substrate due to the N diffusion from iron nitride particles to the atom matrix of the ball.

Performance Analysis of Polytetrafluoroethylene as Journal Bearing Material

In this study, the friction and wear behaviour of solid lubricant polytetrafluoroethylene (PTFE) reinforced with carbon, MoS2, glass fiber, polyether ether ketone (PEEK) particles are tested as journal bearing material with respect to varying high loads, under dry and wet condition against AISI SS 304 stainless steel using a pin-on-disc arrangement. Compared with pure PTFE, introduction of the fillers made composites have longer wear life. Among the all PTFE composites under experimental investigation due to friction and wear mechanism the lowest wear loss is observed for the composite of PTFE composite reinforced with 15 % Glass fiber + 5% MoS2 particles by weight for the values of loads and sliding velocity.

Tribological behavior of polyimide/epoxy resin-polytetrafluoroethylene bonded solid lubricant coatings filled with in situ-synthesized silver nanoparticles

Abstract Polyimide/epoxy resin-polytetrafluoroethylene (denoted as PI/EP-PTFE) bonded solid lubricant coatings filled with silver nanoparticles synthesized in situ were prepared. The phase composition and grain size of the Ag nanoparticles were analyzed by X-ray diffraction and field-emission scanning electron microscopy, respectively. A micro-hardness tester was employed to determine the micro-hardness of the as-fabricated PI/EP-PTFE lubricant coatings, and a ring-on-block test rig was selected to evaluate the tribological behavior of the lubricant coatings under dry friction and RP-3 aviation kerosene lubrication conditions. The worn surfaces of the lubricant coatings were observed with a scanning electron microscope. Results indicate that the silver citrate precursor was decomposed to generate Ag nanoparticles during the curing process of PI/EP-PTFE lubricant coatings. Resultant in situ-synthesized Ag nanoparticles with a size of about 100 nm were homogeneously dispersed in the lubricant coatings, thereby significantly increasing the micro-hardness, reducing the friction coefficient and enhancing the wear life of the lubricant coatings. Particularly, the lubricant coating filled with 5% Ag nanoparticles exhibited the lowest friction coefficient and the longest wear life. Moreover, due to the excellent lubrication and cooling effect of RP-3 aviation kerosene, the lubricant coating achieved better friction-reducing and anti-wear abilities under RP-3 aviation kerosene lubrication than that under dry friction.

Oleylamine/graphene-modified hydrotalcite-based film on titanium alloys and its lubricating properties

A novel structured hydrotalcite-based film was synthesized on TC4 titanium alloy by facile hydrothermal method, and then modified with graphene and oleylamine. The structure, morphology, composition, wetting and lubricating properties of the as-prepared films were investigated. The oleylamine/graphene-modified hydrotalcite-based film (HT-OAm/GN) exhibited lower friction coefficient and longer wear life. The enhancement of wear properties was attributed to the synergistic effects of the hard and lubricating graphene layer and oleylamine molecules.

A direct atomic layer deposition method for growth of ultra-thin lubricant tungsten disulfide films

We describe a direct atomic layer deposition method to grow lubricant tungsten disulfide (WS2) films. The WS2 films were deposited on a Si (100) substrate and a zinc sulfide (ZnS) film coated the Si (100) substrate using tungsten hexacarbonyl and hydrogen sulfide as precursors. The ZnS film served as an intermediate layer to facilitate the nucleation and growth of the WS2 films. The thickness of the WS2 films was measured via scanning electron microscope, the microstructure was probed with an X-ray diffractometer and a transmission electron microscope. The friction coefficient was measured with a ball-on-disk tester under dry nitrogen. The results reveal that the WS2 films deposited on both substrates are ~175 nm and have (002) and (101) crystal orientations. The WS2 film deposited on the ZnS coated Si substrate exhibits a stronger (002) orientation and a denser crystal structure than that deposited on the Si substrate. The WS2 films on both substrates have low friction coefficients. However, due to the stronger (002) orientation and denser crystal structure, the friction coefficient of the WS2 film deposited on ZnS coated Si substrate is smaller with longer wear life.

Preparation and characterization of MoS2-TiL/MoS2-TiH nano multilayer coating with excellent wear properties

MoS2-TiL/MoS2-TiH nano multilayer coating was deposited by magnetron sputtering technology with the power of Ti target varying from 50W to 100W alternatively. The microstructure, composition, mechanical and tribological behaviors of coatings were investigated. The results showed the multilayer coating had a structure with nanolayer alternately and displayed denser and more compact. The coating was composited of Ti, S, Mo and O with a broad amorphous peak around 2θ range from 10° to 20°. The nanoindentation test illustrated the coating had nanohardness of 6.4GPa. In contrast to MoS2-TiL monolayer coating, coating hardness didn’t get increased, while wear properties got enhanced obviously. The multilayer coating with novel structure possessed lower friction coefficient, longer wear life and narrower wear trace. Overall, the enhancement of wear properties was attributed to the advantages of nano multilayer structure.

Microstructure Evolution and Enhanced Tribological Properties of Cu-Doped WS2 Films

To improve the tribological properties of WS2 film both in vacuum and in humid air conditions, its microstructure was optimized by doping different concentrations of Cu via radio frequency co-sputtering method. The film microstructure and composition were investigated by field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, grazing incidence X-ray diffraction and high-resolution transmission electron microscopy. It was verified that Cu was presented in amorphous phase in the WS2 matrix and could also induce amorphization and densification of the composite films gradually. The film microstructure changed from coarse columnar platelet structure at low Cu content (0–5.8 at.%) to transition structure with two separate layers at increased Cu content (11.5–16.2 at.%) and to a featureless structure at high Cu content (above 24.4 at.%). The mechanical and tribological properties of films were evaluated using the scratch tester and ball-on-disk tribometer, respectively. It was found that the incorporation of a suitable content of Cu dopant could significantly improve the film toughness, but excess amount of Cu dopant lead to high brittleness. All the composite films exhibited much lower wear rate and longer wear life than those of pure WS2 film both in vacuum and in humid air conditions. The wear mechanisms were proposed after correlating the mechanical performance with film microstructure.

The influence of nitrogen concentration on microstructure and ultra-low friction behaviour of Fe–N thin films

The influence of nitrogen concentration on the microstructure, chemical and electronic properties of Fe–N thin films and their tribological behaviour are studied. Increasing the nitrogen concentration from 5% to 12%, results in the decrease in friction coefficient from 0.14 to 0.04, while wear life increases significantly. However, increase in nitrogen concentration to 32% results in the increase in friction coefficient to 0.1 and decrease in wear life. Therefore, lowest friction and longest wear life is observed in the film with 12% nitrogen, which is due to the formation of ε-Fe2N phase having high bond strength and chemically passive surface.

Wear Process and Analysis of Lubrication Failure about Sputtering MoS<sub>2</sub> Composite Solid Films Applied to Spacecraft

The solid MoS2composite films which were doped with Sb2O3were investigated by means of UMT-2 tribometer. The worn surface morphology of balls and discs during different worn phases were measured on a high resolution microscope. The main chemical elements S,Mo in the worn surface were analyzed with PHI-5720 XPS. The worn areas of discs during different worn phases were measured with the aid of a nano scratch meter(CSM,Switzerland) .The results showed that the MoS2/Sb2O3composite films had better oxidation resistance properties and longer wear-life(6.5×105r).The model of contact between the ball and its counterpart (steel disc) was converted into flat contact during the wear test. The MoS2transferred from discs to the surface of the balls helped to contribute their longer wear-life. Continually accumulated wear at the interface between balls and their respective counterpart discs resulted in their lubrication failure, and the accompanying oxidation of MoS2occurring partially accelerated lubrication failure of the solid MoS2composite lubrication films.

Tribological Behaviors of Lubricants Modified Nanoporous Anodic Alumina Film

A uniform closely packed hexagonal array of porous anodic alumina (PAA) film with an average pore diameter of ~100 nm and a pore height of ~330 nm was obtained by anodizing in oxalic acid solution. Low surface energy molecules of perfluoropolyether (PFPE) and octadecyltrichlorosilane (OTS) were used to enhance the hydrophobicity of the PAA and aluminum (Al) surface. The tribological performances were investigated in detail. The results showed that the static friction coefficient of PAA was much lower than that of smooth Al, which could be due to the higher hardness of the PAA than that of Al. PAA modified with PFPE was characterized by lower friction coefficient and longer wear life as compared with bare Al, PAA, and PAA modified with OTS. This is caused by the combined effects of flexibility, mobility, and inherent lubricity of PFPE molecules and the nanoporous structure of PAA as a reservoir for lubricants and wear particles.

Characterization of DLC films prepared by plasma-based ion implantation on AISI 321 steel

DLC films were prepared by plasma-based ion implantation (PBII) using acetylene as carbon source on AISI 321 steel substrate. The effect of implanting voltage on the characteristics of these films was investigated. The structures of the films were analyzed by Raman spectroscopy. The morphologies of the films were observed by atomic force microcopy (AFM), and the hardness of the films was measured with mechanical property microprobe. The results indicated that the characteristics of these films are strongly depended on the implanting voltage. The DLC films with lowest friction coefficient, longest wear life, and lowest surface roughness was achieved around −30 keV, which was thought to be the optimum implanting voltage in this study.