Friction最新文献

This study focused on producing metal matrix composite (MMC) coatings on Ti–6Al–4V alloy through laser surface alloying using a novel combination of Inconel 625 and SiC precursor materials. Various ratios of alloying powders were examined to evaluate surface properties such as microhardness, wear resistance, and friction coefficient, along with analyzing the phase composition and microstructure of the coatings. The in situ synthesized MMC coatings exhibited the presence of α-Ti, NiTi, NiTi₂, and TiC phases. Additionally, Ti₅Si₃ and α-Ti/Ti₅Si₃ eutectic structures were observed when the SiC content exceeded 20%. In comparison to the titanium substrate, the MMC coating significantly enhanced microhardness by over threefold and reduced wear by 95%. However, it was crucial to carefully select the appropriate combination of alloying powders to avoid a substantial decrease in friction performance and excessive formation of cracks. Through a comparative analysis of experimental results, the optimal precursor material composition was identified as 85% Inconel 625 and 15% SiC. This study demonstrated the effective utilization of Inconel 625 and SiC alloying materials to enhance the surface properties of titanium alloys, thereby expanding their application in challenging environments.

Friction remains as the primary mode of energy dissipation and components wear, and achieving superlubricity shows high promise in energy conservation and lifetime wear protection. The results in this work demonstrate that direct superlubricity combined with superlow wear can be realized for steel/Si₃N₄ contacts on engineering scale when polyhydroxy alcohol solution was selectively modified by amino group. Macroscopic direct superlubricity occurs because 3-amino-1,2-propanediol molecules at the friction interface could be induced to rotate and adsorb vertically on the friction surface, forming in-situ thick and dense molecular films to passivate the asperity contacts. Furthermore, amino modification is also conducive to improving the lubrication state from boundary to mixed lubrication regime by strengthening the intermolecular hydrogen bonding interaction, presenting enhanced load-bearing capability and reduced direct solid asperity contacts. Thus, direct superlow average friction of 0.01 combined with superlow wear are achieved simultaneously. The design principle of direct superlubricity and superlow wear in this work indeed offers an effective strategy to fundamentally improve energy efficiency and provide lifetime wear protection for moving mechanical assemblies.

Two-dimensional (2D) materials are potential candidates for electronic devices due to their unique structures and exceptional physical properties, making them a focal point in nanotechnology research. Accurate assessment of the mechanical and tribological properties of 2D materials is imperative to fully exploit their potential across diverse applications. However, their nanoscale thickness and planar nature pose significant challenges in testing and characterizing their mechanical properties. Among the in situ characterization techniques, atomic force microscopy (AFM) has gained widespread applications in exploring the mechanical behaviour of nanomaterials, because of the easy measurement capability of nano force and displacement from the AFM tips. Specifically, AFM-based force spectroscopy is a common approach for studying the mechanical and tribological properties of 2D materials. This review comprehensively details the methods based on normal force spectroscopy, which are utilized to test and characterize the elastic and fracture properties, adhesion, and fatigue of 2D materials. Additionally, the methods using lateral force spectroscopy can characterize the interfacial properties of 2D materials, including surface friction of 2D materials, shear behaviour of interlayers as well as nanoflake-substrate interfaces. The influence of various factors, such as testing methods, external environments, and the properties of test samples, on the measured mechanical properties is also addressed. In the end, the current challenges and issues in AFM-based measurements of mechanical and tribological properties of 2D materials are discussed, which identifies the trend in the combination of multiple methods concerning the future development of the in situ testing techniques.

The bonded MoS₂ solid lubricant coating is an effective measure to mitigate the fretting wear of AISI 1045 steel. In this work, the amino functionalized MoS₂ was protonated with acetic acid to make the MoS₂ positively charged. The directional arrangement of protonated MoS₂ in the coating was achieved by electrophoretic deposition under the electric field force. The bonded directionally aligned MoS₂ solid lubricant coating showed high adaptability to various loads and excellent lubrication performance under all three working conditions. At a load of 10 N, the friction coefficient and wear volume of the coating with 5 wt% protonated MoS₂ decreased by 20.0% and 37.2% compared to the pure epoxy coating, respectively, and by 0.07% and 16.8% than the randomly arranged MoS₂ sample, respectively. The remarkable lubricating properties of MoS₂ with directional alignment were attributed to its effective load-bearing and mechanical support, barrier effect on longitudinal extension of cracks, and the formation of a continuous and uniform transfer film.

Friction has been considered to mediate physiological activities of cells, however, the biological friction between a single cell and its ligand-bound surface has not been thoroughly explored. Herein, we established a friction model for single cells based on an atomic force microscopy (AFM) combined with an inverted fluorescence microscopy (IFM) to study the friction between a highly sensitive platelet and fibrinogen-coated surface. The study revealed that the friction between the platelet and fibrinogen-coated tip is mainly influenced by specific ligand–receptor interaction. Further, we modeled the biological friction, which consists of specific interaction, non-specific interaction, and mechanical effect. Besides, the results suggested that the velocity can also affect specific ligand–receptor interactions, resulting in the friction change and platelet adhesion to fibrinogen surfaces. The study built a friction model between a single cell and its ligand-bound surface and provided a potential method to study the biological friction by the combination of AFM and IFM.

Ethanol has emerged as a promising alternative to fossil fuels, but its use can lead to significant dilution in lubricants, particularly during cold start or heavy traffic. This dilution can affect the performance of additives, including friction modifiers like molybdenum dithiocarbamate (MoDTC), which are designed to reduce friction under extreme contact conditions. Prior research suggests that ethanol may impact the performance of MoDTC, prompting this study’s goal to investigate the effects of ethanol on MoDTC tribofilms and their friction response under boundary lubrication conditions. Therefore, reciprocating tribological tests were performed with fully formulated lubricants containing MoDTC with varying ethanol concentrations. The results indicate that a critical ethanol dilution level inhibits friction reduction by MoDTC activation, resulting in friction coefficients (COFs) similar to the base oil. Surfaces tested with simple mixtures of polyalphaolefin (PAO) + MoDTC showed increased COFs with added ethanol. Analysis of tested surfaces using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy near the edge structure (XANES) revealed the presence of sulfates, MoO₃, MoS₂, and MoS_xO_y compounds in the tribofilms formed on the surfaces, with and without ethanol diluted in the lubricant. However, the addition of ethanol increased the sulfates and MoO₃ content of the tribofilms at the expense of friction-reducing compounds such as MoS₂ and MoS_xO_y. These findings suggest that ethanol dilution in lubricants containing MoDTC creates an oxygen-rich interfacial medium that favors the formation of compounds with insufficient friction-reducing capabilities.

The pronounced brittleness of hard Laves phase intermetallics is detrimental to their tribological properties at room temperature. In this study, we utilized a heterogeneous structure to engineer an ultrastrong dual-phase (Laves + B2) AlCoFeNiNb high-entropy alloy that exhibits a low wear rate (3.82×10⁻⁶ mm³/(N·m)) at room temperature. This wear resistance in the ball-on-disc sliding friction test with the counterpart of Al₂O₃ balls stems from the activated deformation ability in the ultrafine Laves lamellae under heterogeneous interface constraints. Furthermore, as tribological stress intensifies, the surface deformation mechanism transitions from dislocation slip on the basal and pyramidal planes to a unique combination of local shear and grain rotation within the Laves phase. Our study illuminates fresh perspectives for mitigating the embrittling effect of Laves phase intermetallics under tribological loading and for the development of wear-resistant materials.

The coefficient of friction (CoF) between the deflection pulley and rope in a lift strongly affects the life span of the rope. Although surface roughness is a key factor affecting the metallic pulley–rope CoF, its effect on polymeric pulleys is unknown. The present study analyses the effect of roughness and working conditions on cast polyamide 6 (PA6G) deflection pulley–thermoplastic polyurethane (TPU)-coated rope contacts. The statistical analysis revealed that the effect of surface roughness on the CoF for low-load tests was significant. The present study contributes significantly to parameter selection in deflection pulley machining to minimise friction between the pulley and rope.

Fused filament fabrication (FFF) is one of the additive manufacturing processes which has gained more interest because of its simplicity and low-cost. This technology is similar to the conventional metal injection moulding (MIM) process, consisting of the feedstock preparation of metal powder and polymer binders, followed by layer-by-layer 3D printing (FFF) or injection (MIM) to create green parts and, finally, debinding and sintering. Moreover, both technologies provide near-dense parts. This work presents an in-depth study of the processing method’s influence. The porosity, microstructure, hardness, corrosion, and tribocorrosion behaviour are compared for 17-4 PH SS samples processed from powder by additive manufacturing using FFF and MIM, as well as conventional powder metallurgy (PM) samples. MIM samples exhibited the highest macro and microhardness, while corrosion behaviour was similar for both MIM and FFF samples, but superior in comparison to conventional PM samples. However, the FFF-as fabricated samples displayed a significant improvement in tribocorrosion resistance that could be explained by the higher proportion of delta ferrite and retained austenite in their microstructure.

Fretting wear damage of high-strength titanium fasteners has caused a large number of disastrous accidents. Traditionally, it is believed that both high strength and excellent ductility can reduce fretting wear damage. However, whether strength and ductility are contradictory or not and their appropriate matching strategy under the external applied normal stress (F_w) are still confusing problems. Here, by analyzing the subsurface-microstructure deformation mechanism of several samples containing various α precipitate features, for the first time, we design strategies to improve fretting damage resistance under different matching relation between F_w and the tensile strength of materials (R_m). It is found that when F_w is greater than R_m or F_w is nearly equivalent to R_m, the deformation mechanism mainly manifests as serious grain fragmentation of β and α_GB constituents. Homogeneous deformation in large areas only reduces damage to a limited extent. It is crucial to improve the strength to resist cracking and wear, but it is of little significance to improve the ductility. However, when F_w is far less than R_m, coordinated deformation ability reflected by ductility plays a more important role. The deformation mechanism mainly manifests as localized deformation of β and α_GB constituents (kinking induced by twinning and spheroidizing). A unique composite structure of nano-grained/lamellar layer and localized deformation transition layer reduces fretting damage by five times compared with a single nano-grained layer. Only when the strength is great enough, improving the plasticity can reduce wear. This study can provide a principle for designing fretting damage resistant alloys.