Excellent Tribological Performance Research Articles

Evaluation of Fine Wear Particles Emission from Styrene-Butadiene Rubber Reinforced with Aligned Carbon Nanotubes: A Study Based on Unit Wear Mass Analysis

Rubber filled with carbon nanotubes (CNTs) oriented along a specific direction exhibits excellent tribological performance owing to the unique directional structure of the CNTs, and offers significant application potential. However, when CNT-reinforced rubbers are worn, fine wear particles (WPs), including CNTs, are emitted, creating a potential respiratory health risk. This study explores the relationship between the emission of fine WPs (with sizes ) against a frosted glass disc under sliding conditions and the tribological performance of styrene-butadiene rubber (SBR) reinforced by aligned CNTs. The number of WPs per unit worn mass (QwpS/uwm, where S is the upper limit to the particle size in μm), was defined to quantify the emissions after a unit mass was worn. Using a pin-on-disc test rig developed for this study, the results showed that SBR with CNTs oriented perpendicular to the wear surface (denoted as CNTs-z-SBR) exhibited higher Qwp3.0/uwm and Qwp5.0/uwm values owing to its superior wear resistance. A greater worn mass resulted in larger amounts of WPs, but smaller Qwp3.0/uwm and Qwp5.0/uwm. Furthermore, both water lubrication and lower coefficients of friction (COF) increased the value of Qwp3.0/uwm, whereas a larger load and velocity decreased the values of Qwp3.0/uwm and Qwp5.0/uwm.

Improve wear resistance of C/C composites as artificial bone using diamond-like carbon coatings

In this study, diamond-like carbon (DLC) coatings and silicon-doped diamond-like (Si-DLC) coatings were prepared on the surface of C/C composites by a combination of plasma-enhanced chemical vapor deposition (PECVD) and magnetron sputtering processes. The film composition, microstructure and atomic bond structure were characterized using X-ray photoelectron spectroscopy, field-emission scanning electron microscopy and Raman spectroscopy. The mechanical properties and friction behavior related to the Si element were investigated using nanoindentation and HT-1000 high temperature friction and wear tester. The biocompatibility of the materials was also evaluated by the MG-63 proliferation test. The results indicate that Si elements were successfully incorporated into the DLC films, bonding with C and O atoms, which altered the thermal stability and microstructure of the coatings, reduced the internal stress of the films, and increased disorder. Compared to C/C composites, all coated layers exhibited lower coefficients of friction, with the formation of transfer layers and graphitization induced by friction contributing to the excellent tribological performance. Both coatings showed no cytotoxicity and demonstrated good biocompatibility. Both coatings are effective in reducing wear and chip losses in C/C composites when used as artificial bones. This work suggests that diamond-like carbon coated C/C composites can be excellent structural materials for human body in biomedical science.

Mechanical, tribological and modal characteristics of eco-friendly coir/sugarcane fillers reinforced polymer composites

Abstract Polymer-based composites have been drawing the attention of the research community for many decades, not only in academia but also in industry. However, continuously increasing environmental concerns have led the researchers to focus on natural composite materials. This is a challenge for researchers to develop a natural composite without compromising the composites’ excellent mechanical properties and tribological performance. In this research, coir and sugarcane are selected as the natural fillers, and epoxy resin has been chosen for matrix material. To look into the crystallinity of composites, XRD analysis was done. In addition, a mechanical study was done to look at the manufactured composites’ tensile and flexural characteristics. The tribological performance (i.e., wear rate and friction coefficient) of the composite samples is investigated by using a pin-on-disc setup. The parameters such as filler loading and normal load affecting the tribological performance of epoxy-based natural composites are studied. The results show that the wear and friction characteristics of the composite reinforced with sugarcane and coir were 10.78% and 57.80% lower than those of the neat composite, respectively.

Facile construction of CeO2@MoS2 nanohybrid for enhancing tribological performance of electroplated Co-based composite coatings

Developing and manufacturing novel coatings with excellent tribological performance using environmentally friendly and simple methods hold significant potential and challenge for reducing energy consumption and carbon emissions. Here, we use a gentle method to synthesize the MoS2-load CeO2 nanohybrid (CeO2@MoS2) as an additive to construct a Co-CeO2@MoS2 composite coating with friction reduction and wear resistance through a low-cost electrodeposition technique. The friction measurement results show that CeO2@MoS2 nanohybrid effectively reduces the friction coefficient and increases the wear resistance compared to single CeO2 or MoS2. The synergistic effect of hard CeO2 and soft MoS2 gives the Co-CeO2@MoS2 coating with an extremely low coefficient of friction of about 0.05 and a wear rate of about 3.53×10−6 mm3(N·mm)−1. In addition, the Co-CeO2@MoS2 coating can maintain an extremely low coefficient of friction with long-term stability in tribological tests. This work provides a novel strategy for constructing coatings with remarkable tribological performances and promotes the application of CeO2@MoS2 nanohybrid as an additive to improve material properties.

Investigation on mechanical and tribological properties of PTFE nanocomposites reinforced by surface-modified graphene using molecular dynamics simulations

Surface-modified nanoparticles are commonly used to improve the mechanical properties and wear resistance of polytetrafluoroethylene (PTFE). However, fewer studies have been devoted to quantitatively revealing the action mechanism of graphene (Gr) modified with different functional groups on the mechanical and tribological properties of PTFE. Herein, the effects of four functional groups (−OH, −NH2, −COOH, and −COOCH3 functional groups) on the surface of Gr nanosheets on the mechanical and tribological properties of PTFE nanocomposites are studied using molecular dynamics simulations. The results indicate that the incorporation of functional groups to the Gr surface is able to significantly improve the mechanical properties and wear resistance of the nanocomposites, and the COOH-functionalized Gr nanosheet shows the best reinforcing effect due to the synergistic effect of its own high surface roughness and strong interfacial interaction between itself and the matrix. It is also found that the friction coefficient of the nanocomposites is obviously increased by the inclusion of functionalized Gr nanosheets, and the greater the surface roughness of the functionalized Gr nanosheet, the more significant the growth of the friction coefficient of the nanocomposites. The pull-out test and confined shear simulation reveal that due to the increased interfacial shear strength and the isolation of functional groups, an inhomogeneous transfer film is formed at the friction interface, leading to a decreased anti-friction property. This study provides some guidance for the future design and development of polymer nanocomposites with excellent mechanical and tribological performance for use in extreme service conditions.

Study on ultra-low friction performance of PTFE film combined with water-based ionic liquid lubrication at electrical contact interfaces

By polytetrafluoroethylene (PTFE) films on the surface of steel disc and using water-based ionic liquids as lubricants, the solid-liquid synergistic effect of PTFE films and water-based ionic liquids was systematically investigated. The results showed that PTFE films exhibited excellent tribological performance and maintained good insulation capabilities under electrical conditions in the sliding electrical contact interface. When using water-based lactate Ionic liquids as lubricants, the PTFE film achieved a COF of less than 0.01 under a load of 2 N, realizing ultra-low friction. The analysis of the lubrication mechanism revealed that two types of protective films were formed on the PTFE film and steel friction pair surfaces. These protective films effectively prevented direct contact between the friction pairs, significantly enhancing tribological performance.

Wear-resistant phenolic composites reinforced with attapulgite and short carbon fibers for applications subjected to both dry and oil-lubricated sliding

Attapulgite (AT) nanofibers were integrated into phenol-formaldehyde resin (PF) and PF composites reinforced with short carbon fibers (CF). Inclusion of AT significantly enhances the wear resistance of PF under both dry and oil-lubrication conditions. The hybrid nanocomposites, reinforced with both AT and CF, exhibit a high mechanical strength. Interestingly, AT and CF lower synergistically the friction coefficient of PF subjected to harsh dry sliding conditions. The hybrid nanocomposites exhibit excellent tribological performance under both dry and oil-lubrication conditions. Tribofilms’ nanostructures were comprehensively analyzed for disclosing dominant tribological mechanisms. Outcome of this work provides new ideas for developing tribo-materials of a high adaptability to various dry/oil-lubrication conditions.

Alleviating internal stress in diamond-like carbon films for enhanced tribological performance under high contact pressure via interface texturing

Diamond-like carbon (DLC) films have found widespread applications across numerous fields due to their exceptional properties. Nevertheless, their significant internal stress has restricted their further utility, particularly in scenarios involving high-contact pressure conditions. In response to this challenge, we fabricated diamond-like carbon films with nano-depth interface texture. This nano-depth interface texturing technique helps alleviate the internal stress within the carbon film, thereby enhancing the tribological performance of diamond-like carbon films with textured interfaces, especially under high contact pressure. We successfully fabricated textured carbon films with a thickness of 1 μm, which exhibited excellent tribological performance even under pressures exceeding 1 GPa. Through atomistic molecular dynamics simulations, internal stress testing, and cross-sectional transmission electron microscopy imaging, we observed that the incorporation of nano-depth interface texturing resulted in an approximate 47.62 % increase in the thickness of the transition layer between the silicon substrate and the carbon film. Furthermore, there was a notable reduction of about 30 % in the internal stress exhibited by the carbon films. These findings are expected to expand the application of carbon films under higher contact pressure and facilitate the production of thicker films.

Tribological properties of oil-impregnated porous PTFE composites using CA as a novel pore-forming agent

PurposeThis paper aims to prepare an oil-impregnated porous polytetrafluoroethylene (PTFE) composite with advanced tribological properties using citric acid as a novel pore-forming agent.Design/methodology/approachCitric acid (CA) was used to form pores in PTFE, and then oil-impregnated PTFE composites were prepared. The pore-forming efficiency of CA was evaluated. The possible mechanism of lubrication was proposed according to the tribological properties.FindingsThe results show CA is an efficient pore-forming agent and completely removed, and the porosity of the PTFE increases with the increase of the CA content. The oil-impregnated porous PTFE exhibits an excellent tribological performance, an increased wear resistance of 77.29% was realized in comparison with neat PTFE.Originality/valueThis study enhances understanding of the lubrication mechanism of oil-impregnated porous polymers and guides for their tribological applications.

A dual-phase Fe-Co-Ni-Cr-Mn high entropy alloy thin film with superior strength and corrosion-resistance

Improving the mechanical properties of high-entropy alloys (HEAs) with a face-centered cubic (fcc) structure is critical for their potential applications. In this work, a Fe-Co-Ni-Cr-Mn thin film was prepared and deposited with a power of 360 W. This alloy thin film exhibits a dual-phase microstructure consisting of a fcc matrix and sigma phase (σ phase) precipitates. The 360 W-film shows ultra-high strength-ductility synergy, with a hardness of 10.4 GPa, yield strength of 6.2 GPa, and a fracture strain of ∼25 % (micro-pillar compression tests). The excellent mechanical properties can be mainly attributed to the grain size effect, the hardening effect of the σ precipitates, and deformation twinning. Moreover, this alloy thin film exhibits excellent tribological performances and corrosion resistance. Our results demonstrate high potential of the dual-phase HEA thin film for industrial applications as high-performance protective coating materials.

The synthesis and tribological behaviour of a phosphorus-free triazine organic molybdenum as friction modifier

A phosphorus-free triazine-based organic molybdenum compound (DCDM) was designed and synthesized by using the click chemistry approach, and its friction-reducing and anti-wear properties were evaluated in PAO10 base oil. The results indicated that DCDM exhibited excellent tribological performance, with a reduction of approximately 35% in friction coefficient and about 46% in wear scar diameter, due to the synergy effect between Mo and S. Surface analysis by EDS and XPS revealed the formation of MoO3, Fe2(SO4)3, FeS, and MoS2 in the friction film. And it was furhter confirmed that the presence of MoS2 in the friction film contributed most significantly to the enhancement of the friction-reducing and anti-wear properties of the developed triazine-based organic molybdenum compound in PAO10 base oil.

Extremely enhanced friction and wear performance of hydrogen-free DLC film at elevated temperatures via Si doping

Hydrogen-free diamond-like carbon (DLC) films have garnered significant attention as a highly efficient solid lubrication material, but poor high-temperature lubrication and wear resistance limit their further application. Here, silicon-doped DLC (Si-DLC) films with different Si contents were deposited using a superimposed HiPIMS-DCMS deposition system to improve their high-temperature lubrication and wear resistance performance. The influence of Si content on the microstructure, mechanical and high-temperature friction and wear behavior of Si-DLC films was investigated. The results showed that Si-DLC films had a dense structure and nanoscale smooth surface. The Si doping enhanced the adhesion strength and relieved the residual stress of Si-DLC films, but decreased the hardness and Young's modulus. Meanwhile, Raman and XPS spectroscopy revealed significant local structural changes in Si-doped DLC films. Furthermore, the results showed that DLC films doped with low Si content displayed excellent tribological performance at elevated temperatures due to the graphite lubricating layer on the surface of wear marks. Specifically, Si-DLC film with 3.31 at% Si had an ultra-low average friction coefficient of 0.04 at 450 °C and still provided effective lubrication at temperatures up to 500 °C. In contrast, pure DLC film failed to lubricate at 450 °C due to the severe graphitization transition and Si-DLC film with 17.47 at% Si quickly failed to lubricate at 200 °C due to the SiC and SiO2. This work sheds light for the high-temperature application of DLC films doped with low Si content by superimposed HiPIMS-DCMS deposition system.

Synergistic effect of NiCr-Cr3C2 + Y2O3 to enhanced performance of Ti-based composite fabricated by laser cladding

The surface modification technology, which is of great significance in aerospace, energy, and other fields, is based on reinforcement. In this study, a titanium-based composite material system, formed using laser cladding and based on NiCr-Cr3C2 + Y2O3 dual additives, was investigated. TiC reinforcement particles were generated in situ through the reaction between NiCr-Cr3C2 and Ti6Al4V during the cladding process. Additionally, Ni and Cr elements provided solid solution-strengthening effects to the matrix. Meanwhile, Y2O3 particles were introduced ex-situ, effectively eliminating defects in the coating and inhibiting the dendritic growth of TiC particles. This process enhanced the dispersion-strengthening effect of TiC. The titanium-based composite material, incorporating NiCr-Cr3C2 + Y2O3, exhibited excellent tribological performance, displaying a wear rate of approximately 4.22 × 10−4 mm3·N−1·m−1.

A robust method for assessing the macroscale tribological behaviour of solid lubricant nanoparticles

Reducing friction and wear is crucial for efficiency and longevity in tribological systems. Solid lubricant nanoparticles show great potential in this context but lack deposition control methods and tribological performance investigations under conditions closer to real systems. The present study used drop-casting to deposit multi-layer graphene (MLG) and carbide-derived carbon (CDC) nanoparticles on AISI1020 steel substrates. Tribological performance was evaluated using a ball on flat tests with an incremental load increase in a reciprocating motion. Results indicate a minimum coverage threshold for effective lubrication and highlight substrate topography's critical role. This research enhances understanding of nanoparticle deposition process optimization and control, showing an excellent tribological performance of MLG and CDC nanoparticles in solid lubricated systems.

Hierarchical design of microcapsules-based epoxy resin coating enhanced with Ti3C2Tx for improving thermal, tribological, anti-corrosive performance

Self-lubricating coating has sparked significant research interest due to its remarkable tribology performance. However, traditional microcapsules-based self-lubricating coating still faces challenges in long-term serviceability and poor anti-corrosion performance. In this paper, a novel self-lubricating epoxy resin coating was proposed based on hierarchical design and energy wear theory. Microcapsules (MC) containing Polyalphaolefin (PAO40) were prepared via the solvent evaporation approach. Ti3C2Tx MXene (T) with high thermal conductivity was then incorporated into the MC-enhanced epoxy resin coating (EP) to construct the novel self-lubricating EP coating (T-MC-EP). Compared to the EP coating, the thermal conductivity of the T-MC-EP coating increased by 79.4%. Finite element analysis indicated that T constructed thermally conductive network in the coating, serving as the main heat carrier. Furthermore, the wear rate decreased by 91.2%, primarily attributed to the formation of lubricating oil film during friction and the reduction of epoxy resin molecular oxidation fracture caused by friction heat. After 31 days of salt spray testing, the T-MC-EP coating also exhibited superior anti-corrosion performance. This work provides an innovative insight into designing multifunctional coating, including excellent mechanical, thermal, tribological, and anti-corrosive performance.

Temperature-induced wear micro-mechanism transition in additively deposited nickel alloys with different solid lubricants

Additive manufacturing of self-lubricating alloys plays a crucial role in the production of complex wear-resistant components and in expanding repair capabilities, especially for intricate wear parts with low tolerances (e.g. with cooling channels). Herein, we report a novel approach providing nickel-based alloy with an excellent tribological performance in dry sliding contacts. Laser-deposited self-lubricating nickel alloys, infused with anti-wear additives of molybdenum disulfide, nickel sulfide, copper sulfide, or bismuth sulfide, were subjected to dry sliding wear tests against an alumina ball counterbody at a temperature range of up to 800 °C. The self-lubricating alloys exhibited a significant decline in friction (43 %) and wear (45 %) at room temperature, 400 °C (friction 40 %, wear rate 55 %), and 600 °C (MoS2-based, friction 58 %, wear rate 75 %). The MoS2-based alloy coating demonstrated excellent performance characteristics up to 800 °C (friction coefficient ⁓0.25, wear rate 11 × 10−6 mm3 N−1 m−1) due to the formation of a ‘glazed’ tribolayer. Wear mapping allowed to identification of a critical condition for self-lubricating alloys where positive transitions in wear mechanisms led to a synergistic lubrication mode involving the formation of tribologically induced new lubricious phases such as silver molybdate or nickel-bismuth intermetallic. This work provides a comparative evaluation of the micromechanisms, surface transitions, and tribochemistry of solid lubricants at a wide temperature range and a variety of applications.

Study on the tribological properties and corrosion resistance of the modified NiZnAl-LDH coating on anodic aluminum surface

The porous structure of anodized aluminum creates an opportunity for corrosive media to contact the aluminum substrate, resulting in diminished corrosion resistance and wear performance under adverse conditions. In this study, ternary hydrotalcite containing Ni, Zn, and Al elements, named NiZnAl-LDH, was synthesized on anodized aluminum surfaces using an in-situ growth method. The corrosion and wear resistance of the aluminum substrate were further enhanced by intercalation modification with sodium molybdate. The impact of synthesis parameters, including pH, reaction temperature, and reaction time, on the corrosion and wear resistance of the coating was investigated. Morphology, structure, and properties of the coating were analyzed. The results confirm the synthesis of NiZnAl-LDH modified with sodium molybdate intercalation. Electrochemical tests revealed that immersing NiZnAl-LDH in a sodium molybdate solution with a pH of 9.5 for 2.5 h at 35 °C resulted in a minimum self-corrosion current density of 4.131 × 10−8 A cm−2, significantly enhancing the corrosion resistance of the coating. Friction tests demonstrated a coating friction coefficient of 0.28, indicating excellent tribological performance. The discussed process parameters in this study provide valuable insights for the synthesis and application of LDH, expanding the application of aluminum alloys in the field of corrosion resistance and wear resistance.

Fabrication of a novel hydrophobic zinc borate/polydopamine/talc nanocomposite with sandwich-like structure for enhanced tribological properties

Two-dimensional layered materials (2DLMs) as lubricant additives have received increasing attention due to their low interlaminar shear stress, outstanding chemical stability and lubrication effects, but the extreme pressure properties, dispersion and dispersion stability in base oils are poor. Herein, a hydrophobic zinc borate/polydopamine/talc (OA-ZB/PDA/TA) nanocomposite with sandwich-like structure is prepared by hydrothermal-assisted intercalation combined with mechanical activation process using natural talc 2DLMs as substrate and oleic acid (OA) as a surface hydrophobic modifier and peeling aid. No obvious sedimentation of OA-ZB/PDA/TA occurs in the rapeseed oil after 15 d, while pure TA is significantly deposited after 12 h, showing superior dispersion and dispersion stability. The OA-ZB/PDA/TA used as a lubricant additive in rapeseed oil exhibits excellent tribological performances under the loads from 147 to 784 N, particularly, wear scar diameter and coefficient of friction reduce by 51.4 and 33.7 % under 392 N, respectively, and the maximum nonseizure load (PB) increases by 27.0 % relative to pure TA. The TA-ZB-TA "sandwich-like" structure gives full play to the synergistic lubrication between ZB NPs and TA, resulting in the sliding and rolling effects under low load, friction film and rolling effect under medium load, and friction film under high load. Our work provides a new avenue for the enhanced extreme pressure properties and dispersion stability of 2DLMs in base oil.

Design of herringbone grooved thrust bearing for locomotive turbocharger rotor

The herringbone texture exhibited excellent tribological performance to minimize friction and wear. However, the application of this texture in the development of grooved thrust bearings is limited. Therefore, in this study, an attempt was made to design an oil-lubricated herringbone grooved thrust bearing for high-speed locomotive turbochargers. The designed bearing accommodates the axial load generated due to the pressure difference between the turbine and compressor wheel. The bearing design starts with applying Newton’s second law to predict the thrust load acting on the locomotive turbocharger rotor. The thrust load is calculated analytically and is found to be 4.54 kN for a design rotor speed of 1,00,000 rpm. Further, the herringbone grooved thrust bearing has been modeled numerically using non-linear Reynolds equation. The modified Reynolds equation is discretized using the finite volume method (FVM) and solved by successive over-relaxation (SOR) methodology to determine the static characteristics over the bearing surface. The developed HGTB is found to have a suitable load-carrying capacity of 4.6 kN, frictional torque of 0.25 N.m, and power loss of 2.98 kW. Further, a parametric analysis has been carried out to study the influence of design parameters such as the number of grooves, helix angle, angular groove width, groove depth, and speed on load-carrying capacity, frictional torque, and power loss.

Heterostructured three-dimension MXene/short carbon fiber to enhance thermal, mechanical and tribological properties of epoxy composites

Polymer composites play an essential role in the field of friction materials. However, severe environment is still big challenges for their application. Three-dimension MXene/short carbon fiber (SCF) was prepared to improve the thermal, mechanical, and tribological performance of epoxy resin. When the mass ratio of MXene to SCF is 1:150, the MXenes are uniformly anchored on the surface of SCF under the strong hydrogen bonding interaction, leading to stable heterostructure and abundant surface functional groups. Owing to the excellent synergy between the MXene and SCF, the modified epoxy composite exhibits superior mechanical and thermal properties, as well as high thermal conductivity. Moreover, it has excellent tribological performance with an average friction coefficient of 0.44 and a specific wear rate of 3.0 × 10-6 mm3·N-1 ⋅m-1 in 2 hours, which reduced by 35.3% and 97.1% than those of epoxy resin, respectively.