Universal Micro-tribotester Research Articles

In-situ surface modified water-soluble Cu nanoparticles as lubrication additives in water-based cutting fluids

Water-based lubricants are essential in the field of tribology, and the application of nanoparticles as additives in water-based lubricants shows promise and significant practical importance. In this study, water-soluble Cu nanoparticles modified with methoxypolyethyleneglycol xanthate long-chain polymers were fabricated by a in-situ surface modification method. The tribological behavior of the Cu nanoparticles synthesized as additives in a water-PEG system was evaluated using a universal micro-tribotester. It was found that the synthesized nanoparticles could be stably dispersed in the water-PEG system and could enhance the tribological properties and load-carrying capacity of the system significantly. For example, the coefficient of friction could be reduced to 0.052, and the PB value increased to 588 N when the Cu nanoparticles were added at a mass fraction of 1.5 %. This was mainly attributed to the formation of a boundary lubrication film consisting of Cu, Fe2O3, Fe2(SO4)3, and FeS throughout the entire friction process. The boundary film effectively prevents direct contact between the friction surfaces, thereby improving the tribological properties. The incorporation of Cu nanoparticles as additives into commercial cutting fluids resulted in a lower coefficient of friction and significantly enhanced the extreme pressure performance of the cutting fluids, demonstrating promising application prospects.

Fabrication of a novel aesthetic orthodontic bracket and evaluation of friction properties between PEEK and stainless steel wires.

Polyetheretherketone (PEEK) is a polyaromatic semi-crystalline thermoplastic polymer with mechanical and lubrication properties favorable for biomedical applications. Despite of its aesthetic appearance, ceramic brackets are unsatisfactory in brittleness and thickness, while PEEK is a potential material for aesthetic orthodontic brackets. To fabricate a novel aesthetic orthodontic bracket and evaluate friction properties of PEEK and stainless steel wires. All polyether ether ketone (PEEK) and ceramic samples disks were made into disks (diameter, 5 mm; thickness, 2mm). The tested surfaces of PEEK were ground with #600, #800 and #1200 SiC papers, followed by polishing with Sof-Lex kit (3M ESPE, USA). The surface roughness was tested using a laser profilometer device (VK-X200, Keyence, Japan). The COFs of the specimens and stainless steel (SS) archwires were tested using a Universal Micro-Tribotester (UMT-3, Bruker, USA). The wear scratches on the materials' surfaces were examined by using a scanning electron microscope (SEM) (Hitachi SU8010). The elastic modulus and hardness of samples were examined with a nano-indenter (XP, Keysight Technologies, USA). The mean surface roughness of PEEK and Ceramic are 0.320 ± 0.028 μm and 0.343 ± 0.044 μm, respectively. PEEK has a lower Friction coefficient than Ceramic and the difference between the two groups was statistically significant (P< 0.05). The abrasive wear of Ceramic was the main wear style and was characterized by the observation of chipping fractures, while PEEK surface looked smooth without obvious scale-like desquamations and granular debris, indicating adhesive wear. Within the limitations of the present study, PEEK shows lower coefficient of friction than ceramic. PEEK has excellent properties such as low friction coefficient, smooth surface and good mechanical properties, and thus meets the requirements for orthodontic brackets. It is considered as a potential bracket material with both low friction and aesthetic performance.

Experimental and theoretical investigations on new organic–inorganic silane/fullerol/α-SiC films with enhanced tribo-corrosion resistance

Steels inevitably suffer friction and corrosion during service, often decreasing durability and functionality. This work presents a novel silane-based composite film that exhibits robust corrosion resistance. When deposited on steels, these films demonstrate exceptional anti-corrosion properties with a high impedance value, even when exposed to highly corrosive media for extended periods (e.g., 240 h). Furthermore, the films show minimal morphological damage after a long-term stability experiment of 25 days in a 3.5 wt % NaCl solution, compared with bare 304 stainless steels (SS). Theoretical studies have been conducted to elucidate the corrosion resistance and sol-gel mechanisms. Upon lubrication, the universal micro-tribotester (UMT) results demonstrate that friction decreases with applied load. The lowest friction coefficient (COF) value of 0.14 is achieved at a regular load of 1 N and a sliding velocity of 0.1 mm/s. The COF performances of these films are explained based on their hydrophobic/hydrophilic nature, uniformity, and Raman spectrum. The Raman spectrum indicates that the excellent friction properties at the sliding interface are attributed to fullerol. This process will inspire a robust, low-cost, and environmentally friendly approach to protecting steel.

Effect of Nanodiamond Concentration and the Current Density of the Electrolyte on the Texture and Mechanical Properties of Ni/Nanodiamond Composite Coatings Produced by Electrodeposition.

An Ni/nanodiamond composite coating was deposited on carbon steel in a traditional Watt’s solution without additives via direct current (DC) electroplating. The effects of the nanodiamond concentration and current density in the plating solution on the morphology, grain size, and texture of the Ni/nanodiamond composite coating were observed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The distribution of the nanodiamond particles in the composite coating was investigated by Raman spectra and SEM. The mechanical properties of the composite coating, such as its elastic modulus and hardness, were examined using a Nano Indenter XP nanometer mechanical test system. The coefficient of friction was tested using a Universal Micro-Tribotester. The results demonstrated that the preferential orientation of the Ni/nanodiamond composite coating varied from the (111) crystal orientation of the pure nickel coating to the (200) crystal orientation. When the nanodiamond concentration in the plating solution was 8.0 g/L and the current density was 3.0 A/dm2, the hardness of the composite coating reached the maximum value of 5.302 GPa and the friction factor was maintained at around 0.1. The average grain size of the composite coating was reduced to 20.4 nm.

Comparison of TiN and CNx coatings on orthodontic stainless steel: Tribological and biological evaluation

Surface modification of orthodontic appliance materials has contributed to the development and popularization of orthodontic treatment. Important characteristics of modified materials include the coefficient of friction, antimicrobial activity, and biocompatibility. To investigate these characteristics, we coated a stainless steel (SS) substrate, which is used to manufacture orthodontic appliances, with a titanium nitride (TiN) or carbon nitride (CNx) film. The coating thickness, elements, and surface morphology were characterized by scanning electron microscopy and energy-dispersive spectrometry. The coefficient of friction was measured using a universal micro-tribotester; the density of Streptococcus mutans was used to assess antimicrobial ability; and the viability of human periodontal ligament fibroblasts implanted on the samples was used to evaluate the biocompatibility of the different films. We found that the CNx film exhibited a lower friction force, effective antimicrobial activity, and favorable biocompatibility compared to the uncoated and TiN-coated SS. In conclusion, a CNx film is promising for modifying archwires to decrease friction and improve antimicrobial activity and biocompatibility.

Synthesis of water-soluble Cu nanoparticles and evaluation of their tribological properties and thermal conductivity as a water-based additive

Efficient and sustainable use of water-based lubricants is essential for energy efficiency. Therefore, the use of water-lubricated mechanical systems instead of conventional oil lubricants is extremely attractive from the viewpoint of resource conservation. In this study, water-soluble Cu nanoparticles of size approximately 3 nm were prepared at room temperature (around 25 °C) via in-situ surface modification. The tribological behavior of the as-synthesized Cu nanoparticles as an additive in distilled water was evaluated using a universal micro-tribotester. The results show that the as-synthesized Cu nanoparticles, as a water-based lubricant additive, can significantly improve the tribological properties of distilled water. In particular, the lowest friction coefficient of 0.06 was obtained via lubrication with a concentration of 0.6 wt% of Cu nanoparticles in distilled water, which is a reduction of 80.6% compared with that obtained via lubrication with distilled water alone. It is considered that some Cu nanoparticles entered the contact area of the friction pairs to form a complex lubricating film and prevent direct contact of the friction pairs. Furthermore, some Cu nanoparticles in the solution accelerate the heat transfer process, which also results in good tribological properties.

Influence of sintering process parameters on corrosion and wear behaviour of SAF 2205 reinforced with nano-sized TiN

The influence of sintering temperature and holding time on microstructure, corrosion and wear of spark plasma sintered duplex stainless steel (SAF 2205) reinforced with nano-sized TiN were investigated. Potentiodynamic polarization measurement was used to study corrosion behaviour in 3.5 wt% NaCl while the wear tests were conducted via universal micro-tribotester. Density and hardness increased with sintering temperature and holding time with maximum densification and hardness achieved at 1150 °C and 15 min respectively. The microstructure shows austenite (γ) and ferrite (α) structure with the austenite phase decreasing as sintering temperature and holding time increases. Optimal corrosion resistance was obtained for composite sintered for 10 min at 1100 °C while that sintered at 1150 °C and 10 min had the highest wear resistance.

Hydrothermal Synthesis of Monodisperse Hard Carbon Spheres and Their Water-Based Lubrication

Monodisperse hard carbon spheres (HCSs) with different size from 300 nm to 1 μm were hydrothermally synthesized and characterized. The tribological performance of green water-based HCSs lubricant systems were studied between glass lens and silicon wafer at various normal loads and concentration on a universal micro-tribotester. The coefficient of friction (COF) increased with the particle size and an average COF of about 0.03 was measured when lubricated by 300 nm HCSs suspensions, whereas for 1-μm-sized carbon sphere, the average COF was 0.059 for the particle concentration of 1 mg/ml. For a given size of particles, the COF first decreases with increasing concentration, but the trend reverses after a critical concentration as adding more particles in the confined space block their movement causing higher COF. The wear life of the 1 μm HCSs lubricant was also evaluated at constant load of 2 N for the total shearing length of 8 m. A very low COF of 0.01 was stably achieved for the lubricant with 4 mg/ml HCSs suspension.

Improvement in the mechanical and friction performance of poly(ether ether ketone) composites by addition of modificatory short carbon fibers and zinc oxide

The composites of poly(ether ether ketone) (PEEK) with zinc oxide (ZnO) nanoparticles and short carbon fibers (SCFs) were produced with twin-screw extruder. ZnO nanoparticles were modified by γ-aminopropyl triethoxyl silane (APTES), and SCFs were wrapped with poly(ether sulfone) (PES). Morphological examination showed that the modified ZnO (m-ZnO) nanoparticles and wrapped SCFs (w-SCFs) were well dispersed in PEEK. The tribological behavior of PEEK composites under dry friction conditions was studied using a universal micro-tribotester. Exhaustive experimental results showed that the tribological behaviors, or the mechanical and thermal properties of the composites after the addition of m-ZnO nanoparticles and w-SCFs, were improved. The tribological properties of PEEK/ZnO/SCFs composites with 5.0 wt% functionalized ZnO and 10.0 wt% w-SCFs are the minimum.

The influence of normal load on the tribological performance of electrophoretic deposition prepared graphene coating on micro-crystalline diamond surface

In the present study, the friction and wear behaviors of a graphene/diamond coating are examined under a variety of normal loads ranging from 4N to 10N, which correspond to contact pressures of 0.77–1.04GPa on the sliding interface. The graphene coating is deposited on the surface of a microcrystalline diamond (MCD) film by electrophoretic deposition (EPD) method. Friction tests are carried out on a ball-on-plate reciprocating Universal Micro-Tribotester (UMT-3, CETR) in ambient air condition (60% RH). Silicon nitride balls (Φ 4mm) are used as the counterpart materials. The results show that a steady-state coefficient of friction is maintained in the range of 0.07–0.09, showing no discernable dependence on the applied normal load. The highly similar equilibrium sliding interfaces formed under varying normal loads are supposed to attribute to this effect largely. Mixtures of graphene flakes and wear particles (Si3N4 or SiO2) produced during the sliding promote the transition from two-body abrasion to three-body abrasion. Meanwhile, the exposed diamond crystallites on the sliding interface are protected from being polished and smoothened thanks to the existence of residual graphene flakes, even though only a portion of the wear track is covered. After the sliding tests, the remaining graphene flakes within the wear track on the Gr/MCD film present no structural damage or degradation, but become thicker sheets by overlapping with each other under the relatively high pressure.

An Experimental Study of Friction and Durability of a Thin PTFE Film on Rough Aluminum Substrates

ABSTRACTFrictional and durability characteristics of 1-µm-thick polytetrafluoroethylene (PTFE) films deposited by hot filament chemical vapor deposition on aluminum substrates were investigated. A universal microtribotester was used to examine the frictional and durability properties using the ball-on-plate and ball-on-disk configurations, respectively. Effects of normal force (2.5, 5, 10, 15 N), sliding speed (0.1, 1, 5 mm/s), and surface roughness of the aluminum substrate (Ra = 0.01, 0.57, 1.28, 2.34 µm) on the coefficient of friction (COF) and the effects of normal force (2.5, 5 N), sliding speed (0.42, 4.19 mm/s), and surface roughness on the durability were investigated. It was shown that the COF of the PTFE-coated interface increases with increasing surface roughness or sliding speed. The COF depends on the normal force to a lesser extent than the other two parameters. The medium-level, O(0.5 µm), roughness of the substrate provides the longest durability, whereas the smoothest or very rough surface provides shorter durability. Analysis of variance (ANOVA) indicates that the surface roughness has the most significant effect on the COF and durability. In the case of a smooth interface, a relationship between COF, sliding speed, and normal force can be predicted. Results indicate an optimal surface roughness for improving durability.

Influence of polishing and glazing on the wear of zirconia and enamel

To investigate the effect of different surface treatment of zirconia and to find the best way to reduce the wear of its antagonist. Twenty-five plates(5 mm×10 mm×15 mm) made of zirconia were divided into five equal groups. Group A was only ground, group B was ground and polished, group C was ground and polished then polished by prophylaxis paste, group D was ground and glazed, group E was ground, polishsed, and then reglazed. Five central incisors were embedded in autopolymerizing acrylic resin with a size of 5 mm×10 mm×15 mm as the control group F. Thirty upper premolars buccal cusps were prepared as the antagonist. Cusps were embedded in autopolymerizing acrylic resin with a shape of circular column whose diameter were 3.1 mm. The wear test was performed in the universal micro-tribotester in artificial saliva. The roughness of each group was measured with rough meter before the wear test. The volume loss of the antagonist was measured using a 3D scanner. The wear surface was observed with scanning electron microscopy to determine the wear characteristics. Data were analyzed using one-way analysis of variance. Each group of surface roughness and mass loss of antagonist showed significant statistical difference (P<0.05). Antagonist of group D showed the maximum volume loss([0.905±0.018] mm3). Antagonist of control group showed the least volume loss([0.235±0.017] mm3). Antagonist of group C showed less volume loss than antagonist of control group did([0.413±0.017] mm3). Wear type of enamel of control group and the antagonist of the groups in which the samples were polished with prophylaxis paste was fatigue wear, and the other groups showed abrasive and adhesive wear. In the surface treatment methods of zirconia, polishing is better than glazing. Ground and polishing and then polishing with prophylaxis paste can decrease the wear of the antagonist.

Structural and friction characteristics of g-C3N4/PVDF composites

This paper introduced the preparation, structural, and friction characteristics of graphite-like carbon nitride (g-C3N4)/poly(vinylidene difluoride) (PVDF) composites. The g-C3N4/PVDF composites with different g-C3N4 contents were prepared via wet mixing and hot press molding technique. The structure, morphology, thermal properties, and friction characteristics were studied by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), thermo-gravimetric analysis (TGA), and universal micro-tribotester under dry sliding conditions. The XRD and FT-IR studies confirmed the incorporation of g-C3N4 into the PVDF matrix. The SEM results showed good dispersion of g-C3N4 in PVDF matrix. The “onset” temperature To of the composites increased with increasing the content of g-C3N4 filler, which confirmed the enhancement of thermal stability of the composites. The friction characteristics results indicated that small amount of g-C3N4 filler was not beneficial to reduce friction coefficient of the composite while large amount of filler had little effect on it. In addition, the g-C3N4 filler was beneficial to reduce wear loss of the composite, and the wear loss decreased with increasing the content of g-C3N4 filler.

Evaluation of Lubrication Properties of Refortified Hydraulic Oils

Used lubricating oil contains more than 90% of good base oil and available additives, providing the potential of energy conservation, environmental protection, and economy, though it loses its useful performance because of contamination by impurities, oxidation, and degradation of additives. Many countries around the world have focused on reclamation and re-refining methods to treat and reuse waste lubricating oils for many years. But the regeneration rate of waste oils is very low in China, less than 20% of the lubricant consumption. Few studies on the performance, especially lubrication properties of recycled lubricating oils, have been considered. In this article, based on differences between used and fresh oils, used oils were reclaimed and replenished with additives (henceforth refortified oils). The physical and chemical properties, including viscosity, total acid number, moisture content, copper corrosion, and water separability from petroleum oil and synthetic fluid as well as the lubrication characteristics of three kinds of refortified hydraulic oils were investigated. The lubrication performance was evaluated using a four-ball tribotester and a Universal Micro-Tribotester (UMT) reciprocating tester. Moreover, the worn surfaces were analyzed using confocal scanning optical microscopy (CSOM), scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), and Raman spectroscopy. The results showed that refortified oils provided good physical and chemical properties, close to those of fresh oils, and produced better tribological characteristics than used and even fresh oils. There were compositional differences between the films of fresh, used, and refortified oils.

Friction and Wear Properties of the Tergum Surface of Mole Cricket, &lt;i&gt;Gryllotalpa orientalis&lt;/i&gt;

Mole cricket is typical insect living under the ground, which tergum is the main component that suffers the wear and tear from the soil particles. In order to adapt this environment, mole crickets have anatomically evolved well-suited tergum with wear-resistance property, which can protect the body from abrasion and damage. In this study, the surface morphology and structure of the tergum of mole cricket were studied and analyzed by stereomicroscope (SM) and Scanning Electron Microscope (SEM). By using a Universal Micro-Tribotester (UMT), the friction-wear properties and the performances of the tergum surface were tested along with the head direction, tail direction and lateral direction of body, respectively. The result shows that the setae have obvious influence on the friction characteristic of mole crickets tergum. By comparing with other direction, the tergum surface has better friction properties on the setae growth direction. This study can be a reference for the design of novel wear resistance surface.

Preparation and micro-tribological property of hydrophilic self-assembled monolayer on single crystal silicon surface

A kind of nano-film was prepared by self-assembling 6-(3-triethoxysilylpropylamino)-1,3,5-triazine-2,4-dithiol monosodium (TES) on the surface of single crystal silicon with hydroxylated pretreatment. The features of the self-assembled monolayer (SAM) were characterized by contact angle meter, spectroscopic ellipsometer, atomic force microscope, X-ray photoelectron spectroscopy and infrared spectroscopy. The experimental results show that the contact angle of distilled water for self-assembled monolayer (SAM) was 35.5° and the film thickness was 3.7nm, and orderly directional nano-clusters were covered on the surface by observation of the topography. Besides, the friction and wear properties of the SAM were investigated under micro-load by universal micro-tribotester. Compared with the substrate, the friction coefficient of the SAM was effectively reduced from 0.494 to 0.102, which was due to the lubricant of the SAM coating. Meanwhile, the film was not destroyed until 130 cycle times of reciprocating gliding under load of 10g. The friction and wear tests show this hydrophilic SAM also has a lubrication effect on the surface while other SAMs often exhibited hydrophobic properties. It is expected that the hydrophilic SAM will be applied in micro electromechanical systems as the solid lubricant coatings.

Friction reducing and anti-wear property of metallic friction pairs under lubrication of aqueous solutions with polyether added

The tribological behaviors of steel–aluminium and steel–steel friction pairs lubricated by aqueous solution with amine-polyoxyethylene-polyoxypropylene-ether, KE-1, as additives are investigated with the help of universal micro-tribotester. The results show that the lubricant has a good effect on the performances of friction reducing and anti-wear. It demonstrates a better performance to steel–steel friction pair than steel–aluminium pairs for the anti-wear property under same conditions.

Preparation and tribological properties of graphene/poly(ether ether ketone) nanocomposites

The tribological behavior of poly(ether ether ketone) (PEEK) composites was investigated using a universal micro-tribotester under dry friction conditions. We studied the effect of addition concentration, applied load, and sliding speed on the friction and wear behavior of composites filled with multi-walled carbon nanotubes (MWNTs), graphene oxide (GO) nanosheets, and γ-aminopropyl trimethoxysilane-modified graphene oxide (GO-Si) nanosheets. The results showed that the friction reduction and anti-wear performance of PEEK composites filled with GO-Si is the most effective, that of the composites filled with GO is the next, while that of the composites filled with MWNTs is the worst. GO-Si-filled PEEK nanocomposites have the best friction reduction and anti-wear properties when the applied load and the sliding speed are 2.94 N and 0.0628 ms−1, respectively. Furthermore, scanning electron microscope (SEM) investigation showed that GO-Si-filled PEEK composites had smooth worn surface under given applied load and sliding speed, and well-dispersed GO-Si in PEEK matrix provided a large surface area available for interaction between polymer molecules and GO-Si, which helped to reduce the wear of PEEK composites.

Anti-friction Behavior of Lead Perrhenate in a Broad Temperature Range

Extensive research efforts have been devoted to develop a new substance which could achieve effective lubrication in a broad temperature range.Pb(ReO4)2,composed of the double oxides of PbO and Re2O7,exists in low shear strength.The anti-friction behavior of Pb(ReO4)2 was tested by Universal Micro-Tribotester(UMT-2M) with ball(Si3N4) on disc(superalloy) at elevated and declined temperature in the range of 22℃ to 600℃.Composi-tion of debris and morphologies of worn tracks were determined by X-ray diffraction(XRD) and scanning electron microscope(SEM),and contact resistance between the worn surface and steel ball was measured by UMT.The re-sults show that Pb(ReO4)2 is a superior lubricant at elevated and declined temperatures,and the friction coefficient is much lower than that without lubricant.The superior lubricating properties should be attributed to the formation of an anti-frictional surface film.And higher temperature could result in the formation of a more complete and du-rable film.For Pb(ReO4)2 melts at 566℃,the fused product is much easier to flow and generate a film which could separate the tribo-pairs perfectly.Subsequently,the lowest friction coefficient is gained at 600℃,and good lubrica-tion can be maintained till to 22℃.

Frictional Characteristics of Ultra–Thin Polytetrafluoroethylene (PTFE) Films Deposited by Hot Filament–Chemical Vapor Deposition (HFCVD)

Frictional characteristics of polytetrafluoroethylene (PTFE) films deposited by a hot filament chemical vapor deposition (HFCVD) method on glass substrates was investigated. A universal micro-tribotester (UMT) was used in the ball-on-flat configuration to examine the effect of coefficient of friction (COF). The effects of normal force (2.5–15 N), sliding speed (1.4 × 10−3 to 14 mm/s) and film thickness (0.3, 1, 5, 10 μm) on the frictional behavior of the PTFE film were tested. Optical microscopy was used to examine the wear tracks of the PTFE films. In addition, durability of the PTFE films was examined by monitoring the change of COF in ball-on-disk tests. The COF values of the tested PTFE films were found to be in the range 0.03–0.18 depending on the measurement conditions. In particular, PTFE exhibits a low COF at slow speeds and high normal forces compared to a high COF at high speeds and small normal forces. Modified Hertzian contact equations and finite element analysis were used to analyze the indentation process. Comparison with the width of the experimental wear tracks indicates that the PTFE layer has a small contribution in carrying the normal load yet provides good protection against tangential forces.