Bulk metal matrix composites of nanocrystalline Inconel 718 (IN718) reinforced with various solid lubricant (SL) particles were fabricated from powder blends using a combination of colloidal mixing and high-pressure torsion (HPT). Conventional (MoS2, WS2, graphite) and modern SL (graphene nanoplatelets and functionalized carbon nanotubes) were incorporated at varying concentrations. Tribological performance was investigated under ambient conditions with a focus on running-in behavior. Linear reciprocating ball-on-disc tests were conducted against spherical Si3N4 and 100Cr6 counterbodies, with wear characterized by confocal laser microscopy and scanning electron microscopy, including qualitative chemical analysis. The friction evolution of HPT-deformed IN718 exhibited strain-dependent behavior, as evidenced by microhardness measurements. Conventional SL and graphene provided predominantly limited improvements in friction and wear. Only carbon nanotube reinforcements consistently improved tribological performance across all concentrations and counterbody materials. Best results were achieved at a content of 5 wt
This study comparatively investigates the friction and wear behavior of three commercially available resin-based composites with different curing modes—light-cured (3M Filtek One Bulk Fill), self-cured (STELA), and dual-cured (ACTIVA Bioactive)—under simulated oral conditions of artificial saliva, artificial saliva containing PMMA slurry, and citric acid solution. Reciprocating ball-on-flat wear tests were conducted in accordance with ASTM G133 at 37 °C. Quantitative wear assessment was performed via 2D/3D volumetric material loss measurements, complemented by microhardness and detailed worn-surface analyses using optical profilometry and scanning electron microscopy (SEM). The results revealed pronounced environment- and material-dependent tribological responses. ACTIVA dual-cured composite exhibited the lowest and most stable friction coefficients and superior wear resistance in saliva and saliva containing PMMA slurry conditions, whereas STELA self-cured composite showed intermediate performance and the highest wear resistance under acidic exposure. Despite its higher hardness, 3M Filtek demonstrated the greatest volumetric wear across in all environments. SEM observations confirmed distinct wear mechanisms ranging from mild adhesive wear to severe micro-ploughing and filler pull-out, in strong agreement with quantitative wear data. Overall, the findings highlight the decisive role of polymerization pathways and environmental chemistry on wear evolution and provide clinically relevant insights for the selection of restorative composites under mechanically and chemically challenging oral conditions.
To address excessive frictional resistance between some components of engineering equipment and sandy soil, this study proposes a reptile epidermal structure-inspired bionic hexagonal prism surface. Single-factor plate-soil friction tests are performed under dry sand and slurry-coated conditions to explore effects of structural parameters on friction reduction. Experimental results show that in dry sand conditions, the structure confined local particle migration and promoted particle rotation and rearrangement, thereby reducing direct plate-sand sliding. The optimal sample (2.5 mm length, 1.5 mm spacing, 1 mm thickness, 90°azimuth angle) yields a 10.65
Due to its specially layered structure and excellent chemical properties, Ti3C2TX is widely used in the field of tribology. Ti3C2TX is prepared by etching Ti3AlC2 with NH4HF2, and MoS2 is prepared by hydrothermal method. Then Ti3C2TX and MoS2 are sprayed onto the surface of PI precursor, and PI/Ti3C2TX, PI/MoS2, PI/Ti3C2TX-MoS2 gradient nanocomposite coatings are prepared under the action of gravity, hydrogen bond, and van der Waals force. The morphologies of Ti3C2TX, MoS2, and coatings are characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and atomic force microscopy (AFM). The thermal stability, mechanical properties, adhesion, and excellent tribological properties of the PI, PI/Ti3C2TX, PI/MoS2, PI/Ti3C2TX-MoS2 coatings are fully evaluated by thermogravimetric analysis, tensile test, adhesion test, and tribological performance test. Compared to the pure PI coating, gradient self-assembled coatings gradually shift the wear mechanism from fatigue wear of pure PI coatings to a mixed wear of abrasive wear and fatigue wear, resulting in better tribological properties of the PI/Ti3C2TX, PI/MoS2, and PI/Ti3C2TX-MoS2 nanocomposite coatings. The friction coefficient (0.04) and wear rate (5.2 × 10–6 mm3/N·m) of the PI/Ti3C2TX-MoS2 coating are 89.2
A laboratory methodology was developed to measure ice friction under controlled conditions while ensuring sliding contact with fresh ice and avoiding hysteresis effects associated with repeated sliding over the same track. Metallic sleds were pulled at constant low speeds over fresh polycrystalline ice, enabling systematic comparison of frictional behavior across surfaces with varied roughness, texture, and coatings. Twelve 6061-T6 aluminum sled variants, including ground, milled, and polished surfaces with and without chromium nitride (CrN) coatings, were tested at sliding speeds of 0.003 and 0.01 m/s and compared against stainless steel. Surface roughness, texture anisotropy, wettability, and coating properties were characterized using profilometry, contact angle measurements, electron microscopy, and nanoindentation. Coefficient of friction measurements exhibited limited dependence on sliding speed, water contact angle, and the presence of CrN coatings. Instead, friction increased with surface roughness once asperity heights exceeded threshold values, consistent with plowing-dominated friction. Accounting for surface texture direction further revealed that friction was reduced with anisotropic textures aligned with the sliding direction. These results demonstrate that surface roughness magnitude and texture orientation dominate ice friction in this regime and provide guidance for minimizing friction through surface smoothing and controlled surface texturing.
Lubricated gears and bearings are increasingly operating in starved conditions due to downsized units, low-viscosity lubricants and increased speeds and loads. Under such conditions where a full hydrodynamic film is not formed, scuffing becomes increasingly prevalent as a critical failure mode. This study investigates how oil film thickness and ZDDP tribofilm development influence scuffing resistance when lubricant supply is limited. Step-sliding speed tests in a ball-on-disk tribometer are used to evaluate scuffing protection of base oils and ZDDP solution under controlled oil volumes. The results show that reduced oil volume accelerates scuffing, particularly for high-viscosity oils, due to rapid transition from EHL to mixed and boundary lubrication. ZDDP significantly improves scuffing protection by forming tribofilms under oil-starved conditions. Its effectiveness depends on additive concentration and chemical reactivity. Higher ZDDP concentrations and reactive structures enable rapid tribofilm growth before critical sliding speeds are reached where scuffing would occur, preventing scuffing. The findings provide insights into the design of lubricant formulation for mechanical systems under oil-starved conditions.
Fractal theory is widely used in multiscale contact analysis of rough surfaces. However, it typically extends single-asperity contact behavior to the entire surface via the area distribution law, assuming that all asperities are fully deformed. This simplification fails to adequately describe the actual contact state. To overcome this limitation, this paper introduces a contact ratio and develops a multiscale contact model that can appropriately capture the asperity contact condition. First, a single-asperity elastoplastic constitutive model is constructed with the mean absolute slope (MAS), and the contact ratio is introduced to characterize the contact state. Based on this single-asperity model, statistical extension to the whole surface is realized through the area distribution function. Subsequently, a method for calculating the contact ratio of rough surfaces and an MAS-based truncation contact model are presented. Using the proposed model, the variation of the contact ratio with fractal parameters is revealed, and the effective computational range of the truncation contact model is discussed. Finally, the accuracy and applicability of the model are validated through finite element simulations, comparisons with classical experimental data, and independent compression experiments on scraped surfaces. This study offers a new perspective for advancing rough surface contact theory.
The scientific research community stands at a critical juncture in its approach to data management. While we have successfully transitioned from manual to computer-controlled experiments across diverse fields (from tribology to materials science, from chemistry to bioengineering), our data practices have not kept pace with the exponential growth in data generation and the emergence of artificial intelligence. This paper explores why investing time in understanding modern data architectures is essential, not just as another publication requirement, but also as the foundation for accelerated collaborative discovery within our organizations and across the community. We examine the current landscape through recent survey data, explain the fundamental concepts behind FAIR (Findable, Accessible, Interoperable, and Reusable) data principles with the technical depth needed to assess true FAIR-ness, and present FAIR digital twins of scientific work as one concrete implementation that can transform isolated data into interconnected knowledge networks. Just as computer-controlled instruments revolutionized our experimental capabilities, modern data architectures promise to be the next enabling technology that amplifies our collective scientific output. While we use tribology as our primary field of interest, the principles apply equally to any experimental science dealing with multi-dimensional, context-dependent data.
Frictional losses account for nearly a quarter of global energy consumption, underscoring the urgent need for advanced self-lubricating materials that enhance energy efficiency throughout their entire life cycle, from manufacturing to end use. Solid lubricant films are limited by wear, whereas vacuum impregnation of sintered components provides sustained lubrication and tunable tribological properties. Here, a novel strategy for engineering low-alloy sintered steels with superior dry sliding performance via vacuum impregnation with MoS2 and graphite is reported. While each lubricant is widely used, its combined impregnation into porous steels has not been previously explored. Tribological testing revealed a synergistic effect: samples impregnated with both lubricants achieved an exceptionally low coefficient of friction (0.056 ± 0.0052) under dry sliding conditions and wear rates on the order of 10−6 mm3/N m, outperforming single-lubricant systems. Microstructural and Raman spectroscopy analyses demonstrated that the lamellar overlap of MoS2 and graphite suppresses the formation of abrasive debris and MoO3 oxidation, shifting the wear mechanisms from mild oxidative and abrasive wear toward stable plastic flow. Regarding the behavior of the solid lubricants, MoS2 retained its bulk-like lubricity, while graphite experienced limited degradation (< 20
The field of elastohydrodynamic lubrication (EHL) has gleaned little benefit from one-hundred years of high-pressure viscometers. Tribologists have sought substitutes for difficult viscometry [1], and a recent substitute is non-equilibrium molecular dynamics (NEMD) simulation. Attempts to predict film thickness and friction with the Eyring sinh-law for shear dependence have used alterations of the temperature and pressure dependences [1]. Unfortunately, the same errors are being made with NEMD. The shear stress capability of pressurized thin-film Couette viscometers has been significantly expanded. Film thickness and friction can be predicted from viscometry [1], and NEMD simulations do not provide the same constitutive behavior as viscometers except for very low-viscosity cases.
These data were collected to systematically characterize the relationship between 3D surface topography and dry sliding friction behavior for 32 distinct micro-milled textures on hardened X153CrMoV12 tool steel. The dataset was designed to provide a comprehensive experimental basis for understanding running-in behavior and orientation-dependent friction. It is intended to support the development of advanced numerical simulations in lubricant-free forming applications. The dataset includes 96 high-resolution confocal laser scanning microscopy images that are presented along with their milling parameters and selected ISO 25178 areal roughness parameters. These are linked to tribological data from unidirectional linear scratch tests (1 N load, 50 cycles) conducted at perpendicular sliding orientations. The records contain raw friction logs, a processed steady-state friction table, a representative validation plot, and the Python code used for data extraction. All files, including a detailed methodology document, are openly available on the Zenodo repository. By providing an entire characterization parameter sequence (from milling to friction results), this dataset provides a comprehensive view.
Future space missions, such as lunar exploration, will require lubricants with enhanced antiwear performance and extended operational lifetimes compared with currently available space lubricants. To address this challenge, this study investigates the applicability of widely used phosphorus- and sulfur-containing antiwear additives under high-vacuum conditions for space lubricants. However, the performance and tribochemical behavior of such additives under vacuum conditions lacking oxygen and moisture remain insufficiently understood. In this work, nine antiwear additives containing phosphorus and/or sulfur were dissolved in poly-α-olefin (PAO) base oil, and sliding tests were performed under oil-immersed conditions in both air and high-vacuum conditions. Although most additives exhibited increased wear under vacuum, some additives maintained stable antiwear performance despite the absence of atmospheric oxygen and moisture. The tribochemical behavior on the sliding surfaces was analyzed by energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) to elucidate the underlying tribochemical mechanisms. The results suggest that, under the present test conditions, the acidic phosphate ester with saturated alkyl chains maintained antiwear performance under vacuum, and sulfur-containing species may contribute to the protection of fresh surfaces in oxygen-deficient environments. Furthermore, the tribofilm compositions were found to differ between air and vacuum conditions. These findings provide useful implications for further studies on the molecular design of lubricants for future space missions.
Ag exhibits excellent lubricating properties owing to its low shear modulus and is therefore widely employed as a solid lubricant in high-temperature wear-resistant coatings. However, rapid Ag diffusion at elevated temperatures can severely compromise coating integrity through microstructural degradation—a critical limitation that must be addressed. In this work, MoN-Ag/WN multilayer coatings were fabricated via magnetron sputtering. Results demonstrate that the WN interlayer suppresses columnar grain growth in the MoN-Ag layer, yielding a fine-grained strengthening effect that enhances both nanohardness and wear resistance. Crucially, at 500 °C and 650 °C, the WN interlayer can effectively prevent the diffusion of silver, thereby reducing the formation of internal voids and the generation of microcracks due to the depletion of silver. Furthermore, this WN interlayer did not exhibit significant adverse effect on the friction and wear properties of the coating. Consequently, the MoN-Ag/WN multilayer coating exhibits outstanding high-temperature wear resistance. These findings provide both a mechanistic foundation and a rational structural design strategy for next-generation high-temperature wear-resistant coatings.
To investigate the wear behavior of work rolls under hot rolling conditions, an experimental wear-testing apparatus capable of controlling load, slip ratio, cyclic temperature variation, and cooling was developed. The evolution of the friction coefficient and surface damage during rolling was systematically examined, while fractal theory was employed to characterize the evolution of surface morphology. The results reveal that abrasive wear and surface mechanical damage dominate during the initial stage, whereas oxidation-assisted and adhesive wear gradually become more significant with increasing rolling time because of the repeated formation and fracture of oxide layers. The formation of the oxide film may help reduce direct metal-to-metal contact and alleviate material removal. However, repeated cracking and spallation under coupled thermal and mechanical loading progressively weaken its protective effect. Under intensified thermo-mechanical loading, unstable oxide layers tend to undergo severe spallation, which is associated with accelerated surface degradation. A coupled wear model incorporating thermal, mechanical, and oxidation effects was established to describe the wear evolution, and the predicted results show reasonable agreement with the experimental observations. Sensitivity analysis further indicates that the fractal parameters D and G play important roles in wear evolution, while thermal and oxidation-related parameters also affect the wear process through coupled interactions. These findings provide useful insights into the wear evolution of work rolls under hot rolling conditions.
High-velocity particle impact is a fundamental process in contact mechanics, underlying techniques such as cold spray and surface peening. This study investigates particle impact on randomly rough surfaces using finite element simulation. Results show that surface roughness intensifies plastic deformation, reduces bonding threshold, and increases substrate residual stress by up to 21 σ_r∝V_i^1 below and σ_r∝V_i^-1 above the critical velocity. This model provides a practical tool for residual stress control in tribological applications involving high-velocity contact and interfacial adhesion.
Finite element simulations were performed to investigate elastoplastic contact of self-affine fractal rough surfaces. The effects of yield strain, hardening exponent, and Hurst exponent on pressure distribution, separation distribution, mean separation, and interfacial stiffness were examined. The load-separation relation is well described by a piecewise function, including a complementary error function branch at light loads and an exponential branch at intermediate loads. More importantly, after normalization by a reference load scale, both the load-separation and stiffness-load relations collapse onto nearly unified curves, indicating that material hardening and surface morphology mainly rescale the load level rather than changing the basic contact response. Stronger hardening enhances near-contact elastic coupling, increases the probability of small positive separations, and reduces the mean separation. These results provide a unified scaling picture for interpreting separation and stiffness in elastoplastic rough contact.
Due to their intrinsically incommensurate interfaces, two-dimensional van der Waals heterostructures are promising candidates for achieving stable structural superlubricity. However, substantial differences in interlayer friction are still observed among different heterostructures. In this study, nonequilibrium molecular dynamics simulations were employed to investigate, at the atomic scale, how phonon-mediated dissipation governs frictional behavior. The results show that in the MoS2/PdSe2 heterostructure, stronger interlayer interactions and larger substrate potential corrugation make the friction process more strongly dominated by the substrate potential, resulting in a higher friction force and friction coefficient. In contrast, the graphene/MoS2 and graphene/PdSe2 heterostructures exhibit smoother potential energy surfaces, and their frictional behavior is governed mainly by the resonant vibration of the cantilever-probe system. Increasing the normal load enhances friction by increasing the interfacial potential corrugation and the associated mechanical work, which is dissipated through amplified excitation of substrate phonons at the washboard frequency. Among the three systems, MoS2/PdSe2 exhibits the most pronounced increase in the phonon population at this frequency, corresponding to a higher friction coefficient and a more pronounced linear load dependence. Increasing the sliding velocity enhances energy dissipation by increasing both the frequency and the population of low-frequency phonons. When a harmonic of the washboard frequency approaches the natural frequency of the cantilever-probe system, resonance is triggered, leading to a peak in friction force. This work clarifies the phonon-mediated dissipation mechanisms in different two-dimensional van der Waals heterostructures and provides new insights into the understanding and regulation of interfacial friction.
The control of frictional losses in the drivetrains of electrified vehicles is a key factor in ensuring their long-term reliability and improving their efficiency, thereby contributing to the reduction of carbon emissions. To achieve this, friction modifiers are added to transmission lubricants to control friction between moving parts. However, their behavior under electrical stress, which may be induced by stray currents in electric powertrains, remains poorly understood. In this work, a ball-on-disc tribometer equipped to apply a controlled direct current was used to compare the performance of an organic amide-ester ashless friction modifier and molybdenum dialkyldithiocarbamate (MoDTC) under electrified and non-electrified conditions. The influence of current intensity on the coefficient of friction (CoF) and wear at the ball–disk interface was systematically assessed. The results show that, compared with MoDTC, the amide-ester OFM is more sensitive to the presence of electrical current. From an applied current of 0.05 A, an increase in both friction and wear is observed. By contrast, MoDTC maintains a CoF close to that obtained under zero-current conditions up to 0.4 A, with only slight wear detected. At 0.5 A, MoDTC initially fails to provide low friction; however, after a running-in period, the CoF drops sharply and returns to the level measured in non-electrified tests. SEM–EDX and XPS analyses suggest that this transient increase in CoF arises from the oxidation of MoS₂ under high current, whereas a pre-formed MoS2 tribofilm can withstand electrical stress, maintaining stable low friction and significantly limiting wear.
Non-equilibrium molecular dynamics (NEMD) simulations were carried out to investigate the lubrication of two amorphous carbon surfaces by a confined fluid of n-hexadecane molecules. Interatomic interactions were described by the AIREBO-M potential. An external pressure of 1 GPa and shear rates in the range of 10^9 – 10^10 s ^-1 were applied to the system. Subjected to this high shear rates, above the critical shear rate, the n-hexadecane fluid behaved as a non-Newtonian fluid. Slip-boundary behavior was not observed, but the system demonstrated shear localization. Due to stronger interactions at the solid–lubricant interface, where some n-hexadecane molecules were adsorbed, the corresponding sublayers of lubricant molecules moved with the same velocity of the sliding surfaces. Away from the interfaces, a linear velocity profile, consistent with Couette flow, developed towards the center of the fluid channel. The friction coefficients calculated from the mean shear stresses were in the ultra-low friction region, which is compatible with experimental data for similar tribosystems.
