Friction Tests Research Articles

Influence of cartilage defects and a collagen gel on integrity of corresponding intact cartilage: a biomechanical in-vitro study.

Numerous cartilage repair procedures have been developed for focal lesions to minimize suffering and possibly prevent the development of osteoarthritis with a focus on so-called one-step procedures. The aim of this work was to investigate the effects of both focal cartilage defects and a biomaterial (ChondroFiller) on the corresponding articular cartilage. On a friction test stand, 18 porcine osteochondral cylinders were tested in six experimental setups under cyclic loading (33 N) against a friction partner in saline solution. The friction partner (cartilage, bone, cartilage defect, cartilage defect with ChondroFiller) and the running times (1 hour and 6 hours) were varied. The damage to the osteochondral cylinders was assessed histologically using a visual damage classification. The cartilage versus bone group showed severe cartilage damage in both the one-hour and six-hour experiments, with an average damage score of 3.5. Damage in the cartilage versus cartilage defect group was moderate, with damage values of 2.5 (1 h) and 2.67 (6 h). The cartilage versus cartilage defect with ChondroFiller group showed a damage value of 2.67 for the one-hour and 2.5 for the six-hour trials. Even focal grade IV cartilage lesions can lead to significant damage to the corresponding cartilage in vitro. The damage could not be reduced by the use of ChondroFiller, likely because of the initial instability of this biomaterial. Therefore, a biomaterial must be stable in the beginning with regard to full weight-bearing, or joint loading should be delayed until stable filling of the defect is achieved.

Using Thin Ultra-High-Molecular-Weight Polyethylene Coatings to Reduce Friction in Frost-Resistant Rubbers.

Frost-resistant rubbers retain their highly elastic properties over a wide temperature range. They are used in various friction units (e.g., seals), but their high friction coefficient and low wear resistance lead to the need for frequent replacement. In this paper, we propose applying thin (several hundred microns) UHMWPE coatings to formed rubber rings. The application technology depends on the required coating thickness. Friction tests of the coatings and pure UHMWPE were performed using the ball-on-disk (unidirectional sliding) scheme for various loads and velocities. In the experiments, the friction coefficients and temperatures near the contact area were determined. Friction tracks were studied using microscopy methods. The sliding contact of the ball and the two-layer material was modeled to obtain the dependences of the deformation component of friction on the sliding velocity for coatings of different thicknesses. UHMWPE is sensitive to frictional heating, so the thermal problem of determining the temperature in the contact area was also solved. It is shown that the minimum friction coefficient occurs for coatings with a thickness of 600 μm. At the same time, in the case of the 300 μm coating, the surface of the friction track is practically no different from the initial one. Thus, the studied combination of polymers provides antifrictional properties and wear resistance to the surface layer while maintaining the damping properties of rubber.

Effect of current on the tribological behavior of Cu-Fe-P immiscible alloy produced by laser powder bed fusion

Cu-based immiscible alloys have significant potential application value in the field of electrical contacts. This study investigated the tribological behavior of Cu-Fe-P immiscible alloys produced via laser powder bed fusion (LPBF) under current-carrying conditions. The alloys consist of softer ε-Cu phase and harder Fe-rich phases. The Fe-rich phase acts as a protective reinforcement during current-carrying friction and wear tests, improving the wear resistance of the alloy. With the increasing current, the coefficient of friction initially rose and then decreased, whereas the wear rate showed a gradual increase. At low currents (0, 2, 3 and 5 A), mechanical wear predominantly governs the wear mechanism. As the current increases, the mechanical wear gradually transitions from adhesive wear to abrasive wear, accompanied by weak oxidative wear. At higher currents (7 A and 10 A), the wear mechanism is dominated by arc erosion wear and oxidative wear. Notably, when the current exceeded 2 A, an oxide film consisting of CuO, Fe2O3, and Fe3O4 formed, enhancing the frictional properties of the alloy. Once the current surpassed 5 A, the arc discharge occurred at high currents, forming molten phases and arc erosion pits on the worn surface of the Cu-Fe-P immiscible alloy.

Relationship between friction reduction effect and solubility in base oil of organic friction modifiers

This study explored the relationship between the solubility of additives in base oils and their friction-reduction efficacy using cetyl alcohol as a model additive. Atomic force microscope friction tests demonstrated that the friction-reduction effect of cetyl alcohol varied significantly across the base oils. The solvation free energy was computed to evaluate the solubility of cetyl alcohol. A direct proportional relationship between friction-reduction and solvation free energy was observed, indicating additives with lower solubility have better friction-reduction performance. Neutron reflectometry experiments and molecular dynamics simulations revealed that lower solubility correlates with stronger adsorption. This study quantitatively clarified the relationship between solubility, adsorption, and friction reduction, providing insights into optimizing lubricant formulations and contributing to a deeper understanding of boundary lubrication mechanisms.

Effects of chemical etching on surface structure and tribological behavior of silicate substrates

Abstract This study investigated the effect of chemical etching on the surface structure and tribological behavior of silicate substrates. Silicate surfaces were etched using a mixture of nitric acid (HNO3) and ammonium bifluoride (NH4HF2) for durations ranging from 1 to 60 min. The etched surfaces were characterized using optical microscopy, scanning electron microscopy, surface profilometry, water contact angle measurements, and UV–vis spectroscopy to evaluate the changes in surface morphology, roughness, wettability, and optical properties. Tribological performance was assessed using reciprocating ball-on-plate friction tests. The results showed that increasing the etching time resulted in the formation of microscale surface features, increased surface roughness, enhanced hydrophilicity, and reduced optical transmittance. The average friction coefficient decreased with an increase in the etching time up to 30 min, beyond which a slight increase was observed. The 1-minute etched specimen exhibited the best wear resistance with the narrowest wear track and the least material removal. The improved tribological performance was attributed to the formation of a stable transfer film, reduced real contact area, and entrapment of wear debris. This study highlights the potential of chemical etching as a technique to tailor the surface structure and tribological properties of silicate materials for various applications.

Synthesis and Performance Evaluation of Metallocene Polyalphaolefins (mPAO) Base Oil with Anti-Friction and Anti-Wear Properties

Anti-wear and anti-oxidation abilities are two key properties of lubricants that play a crucial role in ensuring long-term stable equipment operation. In this study, we aimed to develop a base oil with good anti-oxidation and anti-wear properties for use under extreme pressure. The as-prepared metallocene polyalphaolefin (mPAO) was chemically modified using the trifluoromethanesulfonic acid (TfOH) catalysis through an alkylating reaction with triphenyl phosphorothioate (TPPT). During the experiments, when the reaction temperature exceeded 70 °C or the concentration of TfOH exceeded 2.67%, the β-scission reaction in the alkylation process became significantly more pronounced. The physical and chemical properties of TPPT-modified mPAO (T-mPAO) were evaluated by nuclear magnetic resonance spectroscopy, Fourier trans-form infrared spectroscopy, gel–permeation chromatography, and ASTM standards. T-mPAO showed significantly improved antioxidant capacity, with the initial oxidation temperature increasing by 32 °C compared to the base oil, and it exhibited the slowest increase in acid number in the 96-h oven oxidation test. The tribological tests showed that T-mPAO had the lowest friction coefficient, wear track, and wear rate (72.7% lower than that of mPAO) as well as the highest PB (238 kg) and PD (250 kg) among all tested samples. Compared to mPAO, the average friction coefficient of TPPT-modified mPAO in the four-ball friction test was reduced by 30.5%, and by 16.4% in the TE77 reciprocating friction test. Based on the experimental results, T-mPAO had strong anti-oxidation ability and excellent lubricating performance.The successful synthesis of multifunctional mPAO has enabled lubricant base oil additization, making it possible to use it in more demanding work scenarios, greatly broadening its application scope and making lubricant formulation blending more flexible.

Microstructure and Wear Resistance of FeCrV15 Coatings by Laser Cladding

Improving the surface performance and service life of 60Si2Mn steel is an important issue in agricultural machinery. A FeCrV15 coating layer may exhibit excellent performance in wear resistance. This research focuses on studying the microstructure and wear resistance of the FeCrV15 coating layer at various scanning speeds through laser cladding. Microstructure, phase distribution, surface hardness, and wear resistance of the coating layers are analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), a microhardness tester, and laser confocal microscopy. The results indicate that the FeCrV15 alloy coating consists of γ-Fe, V8C7, and Cr7C3. The microhardness of the FeCrV15 coatings increases with the increase in the scanning speed. At a scanning speed of 8 mm/s, the highest microhardness reaches 727.5 ± 27 HV, approximately 2.5 times higher than the substrate. The friction and wear test of the coating is conducted using a 4 mm diameter Si3N4 ball grinding pair. The coatings prepared at different scanning speeds exhibit lower average coefficients of friction and wear rates compared to the substrate. Both the average coefficient of friction and wear rate decrease with increasing scanning speed. At a scanning speed of 8 mm/s, the lowest average coefficient of friction and the lowest wear rate were observed. The main wear mechanisms of the coating are oxidative wear and adhesive wear, with a small amount of abrasive wear.

Fabrication and tribological properties of WC-reinforced Inconel X-750 alloy at elevated temperature

The nickel-based superalloy Inconel X-750, valued for its exceptional mechanical properties, is used in gas-lubricated foil bearings. However, prolonged exposure to high temperatures can lead to wear failure, affecting their service life. Here, we propose a novel method named ultrasonic strengthening grinding (USG) that applies a WC coating on Inconel X-750. Friction tests reveal that at 600 °C, the friction coefficient and wear rate of the USG-treated samples were reduced by 30.2 % and 79.7 %, respectively. Detailed experiments and analysis demonstrate that the surface grain refinement and the WC-rich coating cooperate to improve the high-temperature tribological properties. These findings offer new insights into the design of wear-resistant coatings for enhancing the high-temperature tribological performance of Inconel X-750 Alloy.

Tribological properties of graphene oxide reinforced aramid paper-based composites

Self-lubricating paper-based composites can provide technological solutions such as low friction and extended service life for the aerospace airframe kinematic mechanical components. To improve the tribological properties of aramid short fibers, this study chemically combined graphene oxide (GO) with aramid nanofibers (ANF) through intermolecular forces, creating a self-lubricating GO-reinforced aramid paper-based composite GO/ANF. Mechanical performance tests have shown that the introduction of GO can significantly improve the fracture strength, Young's modulus, and toughness of paper-based composites. The frictional performance test results show that compared with ANF, the GO/ANF paper-based composites can maintain the lowest coefficient of friction (COF) and wear under high load and high sliding rate conditions. When the amount of GO added is 1 wt%, the COF and volume wear rate of GO/ANF paper-based composites are reduced by 23 % and 89 %, respectively. Mechanism analysis indicates that synergistic effects and friction transfer films are important factors contributing to the excellent performance of paper-based composites. This GO/ANF paper-based composite has good application prospects as a good anti-wear liner material in self-lubricating sliding bearing.

Preparation of zirconium hydrogen phosphate coatings on alkali thermal titanium via a one-step sol–gel method to improve the friction resistance, bioactivity, and osteogenic potential

Titanium implants are widely used in dental restorations for patients suffering from dentition defects. However, the biologically inert of Ti, poor osteoinduction properties and the release of Ti particles due to friction between the bone and the implants can inhibit osseointegration and adversely affect the success rate of implantation. In this study, a zirconium phosphate (ZrP) coating was constructed on the surface of alkali thermal titanium (AT-Ti) via a one-step sol–gel approach. Subsequently, the friction resistance, bioactivity, and osteogenesis properties of the prepared coating were studied. The surface characterization results confirmed that AT-Ti was successfully coated with amorphous ZrP, and ZrP modification was found to effectively reduce the friction rate. In addition, the surface morphology after friction test was smoother. In terms of the bioactivity, the presence of a phosphate group in the ZrP coating led to the effective enrichment of Ca2+ to promote the formation of hydroxyapatite (HAp). It was also discovered that ZrP exhibited an excellent performance in cell viability and mineralization experiments, in addition to up-regulating the expression of osteogenesis related genes. Overall, ZrP modification of AT-Ti leads to an excellent friction resistance, bioactivity, and osteoinductive properties, thereby indicating its broad application prospects in implant therapy.

Investigating on the Tribological Behavior of Binderless WC Matrix Composite

The purpose of this study was to investigate the dry friction and wear behavior of WC-4.3wt.%MgO-2wt.%ZrO2 (WM2Z) composite. WM2Z composite prepared by high-energy ball milling and spark plasma sintering (SPS) technology exhibited excellent comprehensive mechanical properties and dense microstructure. Dry friction test results indicated that the increase of sliding speed will lead to the decrease of friction coefficient, while at the same sliding speed, the extension of sliding time has no significant effect on the friction coefficient. The wear volume increased proportionally with the sliding time, while the wear rate stabilized after reaching a certain duration. The wear mechanism was mainly slight abrasive wear. Additionally, some oxidation occurred on both the WM2Z composite and the Si3N4 ball during friction, forming an oxide film that contributed to the reduction of the friction coefficient. The novelty of this study lies in the first systematic investigation of the effects of sliding speed and time on the wear performance of WM2Z composite, and the revelation that in high-speed sliding environments, even with shorter sliding times, the material experiences faster wear. This discovery emphasizes the important role of sliding speed in the wear process and provides new insights into understanding the wear mechanism of materials in practical applications. This study not only enriches the friction and wear theory of binderless WC matrix composites, but also provides important experimental data and theoretical support for the design and application of related materials, laying a solid foundation for wear resistance optimization and industrial applications.

Tribological Analysis of Surface Textures in Porcelain Tiles for Enhancing Pedestrian Walkway Safety

Due to their durability and aesthetic appeal, porcelain tiles have become a staple in modern construction and interior design. However, the persistent challenge of mitigating slip hazards, particularly in moist conditions, remains a critical concern for pedestrian safety. This study investigates the slip resistance performance of porcelain tiles, focusing on the influence of varying surface textures. The study clarifies the intricate relationship between surface texture and slip resistance through comprehensive dynamic friction tests involving four distinct porcelain tile samples and three different shoe samples conducted under arid, damp, and lathered conditions. While dry conditions showcase robust traction, moist environments underscore the significance of surface textures in enhancing grip. Moreover, the study introduces an operational scale of surface roughness, delineating optimal texture boundaries for maximal slip resistance. The implications of these findings extend beyond mere material characterisation, offering actionable insights for architects, designers, and safety professionals to enhance pedestrian safety in diverse settings. By bridging the gap between material science and real-world safety concerns, this research paves the way for innovative porcelain tile designs that prioritise safety without compromising aesthetic appeal.

Characterization and Growth Kinetics of Borides Layers on Near-Alpha Titanium Alloys.

Pack boriding with CeO2 was performed on the powder metallurgical (PM) near-α type titanium alloy at a temperature of 1273-1373 K for 5-15 h followed by air cooling. The microstructure analysis showed that the boride layer on the surface of the alloy was mainly composed of a monolithic TiB2 outer layer, inner whisker TiB and sub-micron sized flake-like TiB layer. The growth kinetics of the TiB2 and TiB layers obeyed the parabolic diffusion model. The diffusion coefficient of boron in the boride layers obtained in the present study was well within the ranges reported in the literature. The activation energies of boron in the TiB2 and TiB layers during the pack boriding were estimated to be 166.4 kJ/mol and 122.8 kJ/mol, respectively. Friction tests showed that alloys borided at moderate temperatures and times had lower friction coefficients, which may have been due to the fine grain strengthening effect of TiB whiskers. The alloy borided at 1273 K for 10 h had a minimum friction coefficient of 0.73.

Effect of HVOF method spraying parameters on phase composition and mechanical and tribological properties of 86WC-10Co-4Cr coating

Valve components used in the petroleum industry are subjected to intense wear during operation, which leads to a sharp decrease in their durability. Usually, the often subjected to the wear process surface of the valves is treated by tungsten carbide cladding to improve its durability. Because of the difficulty in applying tungsten carbide using conventional surfacing techniques, high velocity oxyfuel (HVOF) spraying technology is rec- ommended. In this work, the mechanical, tribological properties and phase composition of 86WC-10Co-4Cr composition coatings obtained by HVOF Termika-3 high-velocity gas-fuel spraying were investigated. Vary- ing the technological parameters of spraying was carried out by changing the spraying distance, which led to differences in the thickness of the coatings. The phase composition, microstructure and distribution of ele- ments were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM) methods. The hardness of the samples was measured on a microhardness tester using the Vickers method, the friction coef- ficient and the wear rate were investigated using a friction and wear tester. It was determined that the surface of the coatings had developed character and high roughness. The results of X-ray phase analysis showed the predominance of hexagonal WC as the major phase, with a small amount of hexagonal tungsten carbide W2C as the minor phase, and the minor presence of cobalt oxide CoO. It was found that the increased wear re- sistance and low friction coefficient of 86WC-10Co-4Cr coatings are explained by the high volume fraction of hard and stable WC grains with high resistance to wear.

Numerical Simulation on Lubrication and Experiment Study on Tribology Improvement of Slipper Pair at Low speeds

A mixed lubrication model for the slipper pair of an electric piston pump is proposed to solve problems such as inadequate lubrication, extreme friction, and wear at near-zero and low speeds. The lubrication characteristics of the slipper pair were numerically calculated and simulated, and the frictional characteristics in the low-speed range were analyzed. A self-lubricating and anti-wear slipper pair was developed to mitigate severe friction and wear at near-zero and low speeds. To improve the tribological properties of slippers, various concentrations of molybdenum disulfide (MoS2) powder mixed with epoxy resin (EP) were used as self-lubricating materials. The content of MoS2 ranged from 1 and 20 wt%. The optimal content of MoS2 was obtained by conducting frictional tests on the slipper pair samples as well as material examination and analysis of the slipper sample surfaces before and after the surface characterization tests. The lubrication mechanisms of the self-lubricating and antiwear slippers were determined. The EP/MoS2 composite lubricating materials exhibited excellent self-lubricating and anti-wear properties, providing a new direction for the optimized design of slipper pairs and other important friction pairs in piston pumps and promising research prospects.

Plasma Spraying NiCoCrAlY-Cr2O3-AgMo Coatings: Fabrication and Tribological Mechanisms

The increasing demand for high-performance aircraft engines has led to a greater emphasis being placed on advanced sealing coating technologies. Developing long-life, self-lubricating, and wear-resistant coatings is of significant research value. This study focuses on the fabrication of a novel self-lubricating and wear-resistant NiCoCrAlY-Cr2O3-AgMo composite coating. This coating was deposited onto a GH4169 substrate utilizing plasma spraying. Scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) and X-ray diffraction (XRD) methods were employed to characterize the elemental composition and microstructure of the fabricated NiCoCrAlY-Cr2O3-AgMo composite coating. Microhardness measurements across the coating cross-section indicated a gradual increase in hardness from the GH4169 substrate to the NiCoCrAlY-Cr2O3-AgMo coating. The average hardness of the GH4169 substrate was 413.92 HV0.2, while the CoNiCrAlY bonding layer region exhibited an average hardness of 467.60 HV0.2. The NiCoCrAlY-Cr2O3-AgMo coating itself demonstrated an average microhardness of 643.22 HV0.2. Room temperature friction tests indicated that the average coefficient of friction (COF) of the GH4169 substrate was 0.665. In contrast, the NiCoCrAlY-Cr2O3-AgMo coating exhibited a significantly lower average COF of 0.16, representing a 75.94% reduction compared to the uncoated GH4169 substrate. High-temperature friction tests were conducted at 400 °C, 500 °C, and 600 °C, indicating average COF values of 0.438, 0.410, and 0.268, respectively, for the NiCoCrAlY-Cr2O3-AgMo coating. Specifically, at 600 °C, the formation of a lubricious NiMoO4 tribofilm on the coating surface was observed. This tribofilm effectively reduced the wear rate of the GH605 pin to 2.78 × 10−6 mm3/N·m, highlighting the potential of the NiCoCrAlY-Cr2O3-AgMo coating to reduce wear in high-temperature sliding contact applications.

Tribological Properties of MoN (Ag‐W)‐MoS2 (W) Multilayer Films in Wide Temperature Range

In nitride films, an enhanced lubrication effect has been achieved through the incorporation of a soft metal element such as Ag. However, at medium and high temperatures, the favorable tribological properties cannot be sustained for an extended period due to the rapid depletion of Ag. To address this issue, a multilayer film design with W element doping is conceived to impede Ag depletion. MoN (Ag‐W)‐MoS2 (W) multilayer films with 4 different layers are prepared, and their tribological properties are systematically characterized across temperatures ranging from 25 to 800 °C. The results indicate that the tribological properties of four different multilayer films vary considerably at different temperatures. The 8‐layer multilayer film exhibits a relatively low friction coefficient that can be maintained at wide‐range temperatures. X‐ray diffractometer patterns are obtained before and after the friction test to elucidate the lubrication phases of different layers within the multilayer films at various temperatures. Additionally, 3D profiles of wear trajectory surfaces are generated, revealing enhanced wear resistance achieved by effectively inhibiting the migration of Ag. The low friction coefficient in multilayer films can be attributed to the oxidation of MoS2 and the generation of new lubrication phases, as confirmed by Raman spectra analysis.

Experimental Study of Surface Microtexture Formed by Laser-Induced Cavitation Bubble on 7050 Aluminum Alloy

In order to study the feasibility of forming microtexture at the surface of 7050 aluminum alloy by laser-induced cavitation bubble, and how the density of microtexture influences its tribological properties, the evolution of the cavitation bubble was captured by a high-speed camera, and the underwater acoustic signal of evolution was collected by a fiber optic hydrophone system. This combined approach was used to study the effect of the cavitation bubble on 7050 aluminum alloy. The surface morphology of the microtexture was analyzed by a confocal microscope, and the tribological properties of the microtexture were analyzed by a friction testing machine. Then the feasibility of the preparation process was verified and the optimal density was obtained. The study shows that the microtexture on the surface of a sample is formed by the combined results of the plasma shock wave and the collapse shock wave. When the density of microtexture is less than or equal to 19.63%, the diameters of the micropits range from 478 μm to 578 μm, and the depths of the micropits range from 13.56 μm to 18.25 μm. This shows that the laser-induced cavitation bubble is able to form repeatable microtexture. The friction coefficient of the sample with microtexture is lower than that of the untextured sample, with an average friction coefficient of 0.16. This indicates that the microtexture formed by laser-induced cavitation bubble has a good lubrication effect. The sample with a density of 19.63% is uniform and smooth, having the minimum friction coefficient, with an average friction coefficient of 0.14. This paper provides a new approach for microtexture processing of metal materials.

Magnetic-Manipulation of tribofilm for Si3N4/1045 steel contact toward sustainable reduction in friction and wear

Conventional anti-wear approaches lead to energy inefficiency and excessive waste, posing significant challenges to sustainability and cleaner production. Herein, we investigate the influence of eco-friendly magnetic fields on the tribological behavior of interfaces, with an emphasis on the formation and characteristics of the protective tribofilm. The experimental design combined finite element analysis and friction tests to systematically reveal the relationship between magnetic field strength, oxidation of wear debris, and tribological properties. The results demonstrated that the introduction of a magnetic field led to a 22% reduction in the friction coefficient and a 28% decrease in wear volume. High-intensity magnetic fields refined the wear debris by up to 42.6% and also promoted the oxidation of wear debris, leading to a predominance of Fe3O4 in the tribofilm. The structured arrangement and reorganization of Fe3O4 particles within the tribofilm enhance its density and thickness (from 2 μm to 3 μm). Simultaneously, the rotational motion of Fe2O3 particles at the interface modifies the friction contact state, thereby refining friction performance. The findings underscore the significance of considering magnetic fields in the design of tribological systems for enhanced performance and sustainability.

The mechanism of small wear particles entrainment in friction under boundary lubrication

When the lubricating oil flowing between the contact surfaces contains simulated wear particles, it is considered that there is a high possibility for the particles to enter between the contact surfaces if the particles are present on the disk side in a friction test between a fixed ball and a rotating disk. For particles with a diameter of 0.8 μm, it has been previously shown that the entrainment frequency changes with the outside oil film thickness, but the effect of the disk material on the amount of particle deposition and the visualization of particle movement direction due to vortices generated between the contact surfaces had not been performed. In this study, by using SiO2 disks and sapphire disks with different Hamaker constants, the effect on the amount of particle deposition in front of the contact surfaces was experimentally clarified by changing the van der Waals forces acting between the particles and the disks. Additionally, assuming that vortices generated in the oil film between the contact surfaces move the particles to the disk surface side, the flow direction of the lubricating oil was visualized using Navier-Stokes simulation.