Self-lubricating Materials Research Articles

Mechanical and tribological properties of FeS/Cu–Bi self-lubricating materials reinforced with copper-plated steel fibers

PurposeThis study aims to investigate the effect of steel fibers on the mechanical and tribological properties of FeS/Cu–Bi self-lubricating materials.Design/methodology/approachThe microstructure of the material was characterized by scanning electron microscopy. Tests on the crushing strength, impact toughness and tribological properties of materials were conducted using a universal electronic testing machine, a 300 J pendulum impact testing machine and an M200 ring-block sliding tribometer, respectively.FindingsThe mechanical properties of the material initially increased and then stabilized with increased copper-plated steel-fiber length. When the length of the copper-plated steel fiber was 7 mm, the mechanical properties of the material reached stability. Compared with the material without a copper-plated steel fiber, its crushing strength and impact toughness increased by 32.6% and 53%, respectively. A copper-plated steel fiber with a length of 7 mm lay flat in a copper matrix can strengthen the friction interface and enrich the lubricant. Accordingly, the antifriction and wear resistance of the materials increased by 17.6% and 55%, respectively.Originality/valueThe effects of copper-plated steel fibers on the properties of FeS/Cu–Bi self-lubricating materials were clarified. This work can serve as a reference for improving material performance and its engineering applications.

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.

Oil-Loaded Mesoporous Silica to Enhance the Lubrication of Polypropylene Resin Composite Materials

Polymer self-lubricating materials have advantages such as low friction coefficient, good wear resistance, and high work efficiency, giving them wide application potential in friction and wear. This work fabricated polymer-based self-lubricating materials by incorporating oil-loaded mesoporous silica nanoparticles (MSNs + YR1800) in the polypropylene resin (PP). The effects of different content of MSNs + YR1800 on the tribological and mechanical properties of the obtained self-lubricating composite materials were studied. The results indicate that the content of MSNs + YR1800 in composite materials significantly impacts their tribological properties. When the content of MSNs + YR1800 was 10 wt%, the coefficient of friction reduced to 0.09,which was 84.5% lower than for PP and 78.6% lower than for composite materials containing 5 wt% mesoporous silica nanoparticle (MSNs). Compared with pure PP, the wear rate decreases from 4.93 × 10−11 m3∙Nm−1 to 4.43 × 10−13 m3∙Nm−1, which is reduced by two orders of magnitude. The excellent tribological properties of composite materials are attributed to the high specific surface area, large pore volume, strong adsorption capacity, and high oil loading capacity of mesoporous silica nanoparticle as nanofillers. The MSNs + YR1800 release lubricants to form a lubricating oil film during the friction process under load conditions, preventing direct contact between the friction pair and the surface of the composite material. Compared with polymer-silica hybrid oil-loaded microcapsules, MSNs + YR1800 can effectively reduce lubricant leakage, prolong operation life, improve lubrication efficiency, and ensure the continuous and stable existence of lubricating oil films.

Tribological Properties of PEEK and Its Composite Material under Oil Lubrication

PEEK (Poly Ether Ether Ketone) is a high-performance thermoplastic polymer with excellent mechanical, thermal and chemical stability. PEEK has good performance, and is widely used in hydraulic motors. However, there are few studies on the friction and wear properties of materials under the condition of oil lubrication with wide application. The modification of PEEK and the expansion of its application have become a hot research topic in the industry. This study focuses on the modification of the design of PEEK and explores the friction and wear characteristics of self-lubricating materials under different modification schemes. Friction and wear samples were prepared using PEEK-modification pelletizing and injection-molding processes, followed by fixed-condition friction and wear tests. The tribological mechanisms and wear properties of the materials under different modification schemes were analyzed, leading to the identification of several sets of improved reinforced materials. Experimental results demonstrate that modified materials can enhance surface tribological performance, with the best modification effect observed at an SCF filling rate of 15%. The modified PEEK material can better meet the requirements of specific applications, such as high-temperature environments, chemically aggressive environments, or applications requiring high strength and wear resistance.

Two-step printing bionic self-lubricating composite surface fabricated by selective laser melting ink-printed metal nanoparticles

The combination of self-lubricating materials and surface texture was a promising strategy to improve tribology performance. The designed parameters and manufacturing methods of the textured composite surface were pivotal in fully harnessing this synergistic effect. Inspired by natural structures such as the scapharca subcrenata shell, trimeresurus stejnegeri snakeskin, crocodile, and tree frog toe pad surface, bionic self-lubricating composite surfaces (BSCSs) with different textures were prepared on AISI 4140 steel substrate to enhance tribological properties. These BSCSs combined self-lubricating composite material (SLCM) with copper (Cu) material in bionic patterns using the selective laser melting ink-printing metal nanoparticles manufacturing method. Tribological properties and worn surfaces of the BSCSs with various design parameters were analyzed under dry sliding conditions. Results indicated that the synergy effects of printed Cu and SLCM texture effectively reduced friction coefficient and improved wear resistance of the BSCSs. The SLCM texture density and the size of array element in the BSCSs were found to influence the types of lubricating film formed during the sliding process, thereby affecting the tribological performance. This investigation provided a potential surface design strategy and a more flexible manufacturing method for surface engineering.

Fabrication and Tribological Performance of Self-Lubricating Porous Materials and Composites: A Review.

Porous materials have recently attracted significant attention in the aerospace and biomedical fields for addressing issues related to friction and wear. Porous materials are beneficial in applications where continuous lubrication is not feasible or for components that operate under extreme conditions, such as high speeds, elevated temperatures, and heavy loads. The pores can serve as reservoirs for liquid lubricants, which are gradually released during the operation of the components. The tribological properties of these materials depend on their porosity, the lubricants used, and any additional additives incorporated into the porous materials. This review article provides insight into common fabrication techniques for porous materials and examines their tribological performance for all three classes of materials-polymers, metals, and ceramics. Additionally, it discusses design criteria for porous self-lubricating materials by highlighting the critical properties of both the substrate and lubricants.

Tribological behaviours of Si3N4-hBN composites /2507 stainless steel sliding pair in electroplating wastewater

In the wastewater treatment device, the core moving parts (such as the check valve in the pump body) are prone to failure due to wear and corrosion. There is an urgent need to develop high-performance self-lubricating materials suitable for moving components in electroplating wastewater. Therein, the tribological properties of Si3N4 (silicon nitride) based composites with the addition of hBN (hexagonal boron nitride) against 2507 duplex stainless steel in electroplating wastewater were investigated using a Pin-On-Disc (POD) tribometer. The results show that the addition of hBN to the ceramic matrix could effectively improve the tribological properties of Si3N4 materials. The friction coefficient and wear rate of Si3N4 are lowered to 0.14 when the hBN content reaches 30 wt%, which is attributed to the formation of a lubricating films (containing hBN, Si(OH)4 and Cu and its oxides) on the worn surfaces. A segmental test results indicate that the lubricating film undergoes processes such as formation, spalling, and regeneration during the friction process. Meanwhile, hBN and Si(OH)4, due to their inherent structural characteristics, can lubricate and protect the worn surfaces. The molecular dynamics simulation results indicate that Cu and its oxides are prone to slip under normal and transverse forces, and have a positive effect on reducing friction.

ANALYTICAL STUDY OF DURABILITY AND CONTACT CHARACTERISTICS OF METAL-POLYMER COMPOSITE SLIDING BEARINGS FOR MEANS OF TRANSPORT

The field of application of metal-polymer bearings is vast: transport of various types, processing industry equipment, medical equipment, various types of maintenance equipment, etc. With the use of the developed generalized author's analytical method of metal-polymer plain bearings on the basis of which it is laid the author's research methodology of materials wear kinetics at sliding friction (dry, lubricated), calculation of their durability is carried out. Contact parameters are also determined. Metal-polymer bearings with a bushing made of PA6, PA66 polyamide and PA6 based composites filled with glass (PA6 + 30GF) and carbon (PA6 + 30CF) dispersed fibres, molybdenum disulphide (PA6 + MoS2) and oil filled cast polyamide (PA6 + oil) are considered. These polyamides (unfilled and filled), as self-lubricating materials, are widely used in this type of dry friction sliding bearings. The predictive estimation of durability of investigated bearings depending on loading, polymer materials Young's modulus, their wear resistance and sliding friction coefficient is executed. Regularities of change from the specified factors of bearing's durability and the maximum contact pressures are established. Experimental indicators, diagrams, and wear resistance characteristics of the specified polymeric materials are presented. The results of researches of sliding friction coefficient and modulus of elasticity for carbon steel (0.45%C) – polyamides tribocouples are presented.

Study on the tribological performance of self-lubricating thrust ball bearings with different embedded features

PurposeThe purpose of this paper is to develop a new type of embedded solid self-lubricating thrust ball bearing for conditions where grease lubrication cannot be used and to analyze its tribological performance under different lubrication characteristics (lubrication position, width and filling amount).Design/methodology/approachLubrication parameters such as position (a), width (W) and filling amount (Q) were considered. Grooves were made on the raceway with a fiber laser and solid self-lubricating materials were applied through scraping. The frictional behavior of the new bearing was analyzed using a vertical test rig and the bearing’s surface topography was examined with a noncontact profilometer to study wear mechanisms.FindingsThe new inlay thrust ball bearings exhibited excellent lubrication effects and effectively controlled the temperature rise of the bearings. When a is 0 degrees, W is 0.5 mm and Q is 16 mg, the bearing experiences the least wear, and the friction coefficient and temperature are the lowest, measuring 0.001 and 41.52 degrees, respectively. Under the same experimental conditions, compared to smooth bearings without solid lubrication, the friction coefficient decreased by 96.88% and the temperature decreased by 59.74%.Originality/valueThis study presents a self-lubricating thrust ball bearing designed for conditions where grease lubrication is not feasible. A comprehensive investigation was conducted on its surface morphology, wear mechanisms and tribological performance. This work provides valuable insights into the research of self-lubricating thrust ball bearings.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-03-2024-0073/

Tribological Properties of Composites Based on Single-Component Powdered Epoxy Matrix Filled with Graphite.

Composites based on powdered single-component epoxy matrix are an alternative technological solution for composites produced using liquid epoxy resins. This article describes in detail the process of producing graphite-reinforced composites for tribological applications. The advantages and disadvantages of technological processes where the matrix is a single-component epoxy powder were demonstrated, and the properties of the obtained materials were examined. A series of composite materials with the graphite filler with sizes below 10 μm and below 45 μm and weight additions of 5, 10, 20, 30% were produced. Mechanical tests and tribological tests conducted with the pin-on-block method were performed, and the mechanism of tribological wear was described. The conducted research allowed us to conclude that the incorporation of graphite, regardless of particle size, above 10% by weight results in a significant reduction in the friction coefficient (approximately 40-50% lower than in unfilled epoxy resin), which is beneficial in the production of cheap self-lubricating materials.

Friction and corrosion behaviors of the copper reinforced with MoS2 nano-layers coated with silver

The effect of 10 wt% alumina, 20 wt% (10Al2O3-10MoS2), and 30 wt% (10Al2O3-10MoS2-10Ag) reinforcements on the tribological and corrosion properties of copper was investigated. The nanocomposites were prepared by the ball milling coating method and then fabricated by the cold and hot compaction technique. The copper's hardness increased gradually from 96 HV to 227 HV for the 30 wt% (Al2O3-MoS2-Ag) representing an increase of 136.48 %. Adding 30 wt% (Al2O3-MoS2-Ag) to the copper reduced the wear rate from 22 mg/min to 0.3 mg/min under 50 N applied load, owing to the presence of two types of self-lubricating materials, MoS2 and Ag. This nanocomposite recorded the lowest mean coefficient of friction of 0.166 compared with 0.23 for copper. Adding the alumina increased the copper corrosion rate to 3.83 mm/year due to increased oxidation ratio that facilitates the penetration of the electrolyte. However, the Cu/(Al2O3-MoS2-Ag) sample recorded corrosion rates of 0.467 mm/year compared with 0.446 mm/year for copper.

Preparation and properties of FeS/iron-based self-lubricating materials by chemical nickel plating-mechanical alloying

PurposeThis paper aims to investigate the effect of chemical nickel plating and mechanical alloying on the mechanical and tribological properties of FeS/iron-based self-lubricating materials as well as the wear mechanism of the materials.Design/methodology/approachSurface modification of FeS powder was carried out by chemical nickel plating method and mechanical alloying of mixed powder by ball milling. The mechanical properties of the material were tested by tribological testing by M-200 ring block type friction and wear tester. Optical microscope was used to observe the surface morphology of the material and the transfer film on the surface of the mate parts, and scanning electron microscope and EDS were used to characterize the wear surface.FindingsMechanical alloying ball milling was carried out so that the lubricating particles in the matrix are uniformly dispersed; nickel-plated layer enhances the interfacial bonding of FeS and the matrix, and the combination of the two improves the mechanical properties of the material, and at the same time the friction side of the surface of the lubrication of FeS lubricant transfer film formed is denser and more intact, and the friction coefficient of friction side and the wear rate of the material have been greatly reduced.Originality/valueThis work aims to improve the mechanical and tribological properties of FeS/iron-based self-lubricating materials and to provide a reference for the preparation of materials with excellent overall properties.

Tribological Performance and Enhancing Mechanism of 3D Printed PEEK Coated with In Situ ZIF-8 Nanomaterial.

Polyether ether ketone (PEEK) is esteemed as a high-performance engineering polymer renowned for its exceptional mechanical properties and thermal stability. Nonetheless, the majority of polymer-based lubricating materials fail to meet the contemporary industrial demands for motion components regarding high speed, heavy loading, temperature resistance, and precise control. Utilizing 3D printing technology to design and fabricate intricately structured components, developing high-performance polymer self-lubricating materials becomes imperative to fulfill the stringent operational requirements of motion mechanisms. This study introduces a novel approach employing 3D printing technology to produce PEEK with varying filling densities and conducting in situ synthesis of zeolitic imidazolate framework (ZIF-8) nanomaterials on its surface to enhance PEEK's frictional performance. The research discusses the synthetic methodology, characterization techniques, and tribological performance evaluation of in situ synthesized ZIF-8 nanomaterials on PEEK surfaces. The findings demonstrate a significant enhancement in frictional performance of the composite material under low-load conditions, achieving a minimum wear rate of 4.68 × 10-6 mm3/N·m compared to the non-grafted PEEK material's wear rate of 1.091 × 10-5 mm3/N·m, an approximately 1.3 times improvement. Detailed characterization and analysis of the worn surface of the steel ring unveil the lubrication mechanism of the ZIF-8 nanoparticles, thereby presenting new prospects for the diversified applications of PEEK.

Friction and wear performance of aluminum-based self-lubricating materials derived from the 3D printed graphite skeletons with different morphologies and orientations

Using selective laser sintering 3D printing, this study shapes graphite in sphere, flake, and fiber morphologies into skeletons with various orientations. These skeletons are then used to create graphite/aluminum alloy composite self-lubricating materials. The results show that graphite morphology and orientation greatly affect the friction and wear properties of these composites. Graphite fiber exhibits the worst friction and wear performance. Perpendicular flake graphite forms a uniform, continuous lubricating film with high thermal conductivity for heat dissipation, preventing severe wear. Spherical graphite modifies the friction surface, achieving the lowest friction coefficient (0.2 ± 0.02) and wear rate (6.64 ×10−4 mm3/Nm) due to protective film, filling, and ball bearing effects.

Ultralow friction and low wear behavior of in-situ formed NiTiO3 from 60NiTi alloy at 350 °C

Self-lubricating materials of NiO–TiO2 binary system have been rarely studied. In this paper, the friction experiments between 60NiTi discs and Si3N4 balls under dry friction conditions were carried out in ambient air from room temperature (RT) to 400 °C. The mechanical properties of each phase of 60NiTi after the friction experiments at different temperatures are measured by nanoindentation tests. The results show that the mechanical properties of the NiTi2 phase are best, and overall mechanical properties of 60NiTi get worse at 400 °C. The coefficient of friction (CoF) and wear rate basically drop from RT to 350 °C and rise at 400 °C. The behavior of ultralow friction and low wear is achieved at 350 °C with a CoF of 0.069 and a wear rate of 0.990 (mm3/mN) × 10−5. As temperature rises, the in-situ formed NiTiO3 ceramic plays a key role in improving tribological properties. The friction mechanisms at different temperatures are discussed systematically.

The Influence of Graphite Filler on the Self-Lubricating Properties of Epoxy Composites.

In this work, epoxy composites filled with flake graphite of various size (less than 10 μm and less than 45 μm) were produced. The aim of the research was to develop a self-lubricating material with favorable tribological properties, i.e., reduced friction coefficient compared to unfilled epoxy resin and limited abrasive wear. The research material was produced using technical epoxy resins based on bisphenol A. The detailed process of composite production was described, and typical technological problems were considered. The addition of graphite led to an increase in dynamic viscosity, which positively limits the phenomenon of sedimentation, but an increase in the filler content also led to an increase in the porosity of the material. A series of tests have shown that the addition of graphite above 5% by weight allows for a reduction in the friction coefficient from 0.6 to 0.4 and significantly reduces the material's tendency to abrasive wear.

Effect of self-lubricating carbon materials on the tribological performance of ultra-high molecular weight polyethylene

For over five decades, ultra-high molecular weight polyethylene (UHMWPE) has been the standard material for total knee replacements (TKR). Zero wear of the UHMWPE would be ideal; however, due to the natural knee movements, wear damage to the UHMWPE articulating surface is inevitable. The generated wear debris results in joint mechanical instability, reduced joint mobility, increased pain, and implant loosening. Because of these issues, the research on the materials in TKRs has increased their survival rate for up to 20 years; however, in younger patients, the durability of the UHMWPE component decreases due to increased physical activity. Hence there is a constant need for highly wear-resistant tribological pairs for TKRs. Carbon-based materials have an excellent balance between lubricating and mechanical properties and have shown great promise in tribological applications. This study used self-lubricating cubic titanium carbide (c-TiC) and multiwalled carbon nanotubes (MWCNTs) to improve the UHMWPE wear resistance further. The combination of carbon-based materials decreased the material loss by about 41.7 % compared to the UHMWPE vs. bare steel ball tribological pair. The improvement, attributed to the c-TiC self-lubricating coating surface, is close to 5 %. Cold flow and burnishing were the predominant wear mechanisms observed in all the systems; more subtle wear processes were detected for the sliding couple with c-TiC self-lubricating coating. Meanwhile, polymer delamination and micrometer-sized debris formation were the main wear mechanisms in the UHMWPE-MWCNT vs. bare steel ball system. The adhesion work obtained from the electronic structure calculations shows a more significant interfacial interaction of the CNTs on the c-TiC surface. This interaction can be associated with the layer formation that protects the surface from wear and friction.

Research on maintenance-free design and low friction characteristics of industrial robot sliding components

With the continuous progress of industrial automation, the application of industrial robots in various fields has become increasingly common, and ensuring their efficient and stable operation and reducing maintenance costs is crucial. This study used powder metallurgy technology, combined with multiple sintering-rolling processes and oil-immersed vacuum assistance, to successfully prepare Fe-Cu-Ni-Sn-graphite oil-immersed self-lubricating composite materials to meet this demand. In-depth microstructure and wear surface studies revealed that this porous oil-immersed self-lubricating composite material exhibits long-term low friction and high wear resistance and reduces the friction coefficient by 40% compared to untreated samples after a specific composite process. In addition, the material exhibits excellent friction performance in the high-temperature pin-on-disc friction and wear test machine. Even after continuous sliding for 24 hours, its friction coefficient remains low and stable. The study also found that its lubrication mechanism may be attributed to solid-liquid synergistic lubrication, thanks to the appearance of oil-graphite mixtures around the wear track. This design ensures high rigidity and reduced frictional loss, providing a strong reference for the design and optimization of sliding components of industrial robots, and is highly suitable for the widespread application of industrial robots.

Friction Evolution of Graphite Bearing Impregnated with Polymer Subjected to Vibration Fretting at High Temperature

To address friction and wear challenges in dry contacts, manufacturers often employ self-lubricating materials. Graphite and its derivatives stand out as particularly suitable due to their exceptional tribological properties. However, under intense friction conditions, graphite can experience a decline in lubricating efficiency due to severe abrasive wear. This abrasive damage results in elevated activated carbon surfaces with increased surface energy, fostering greater adhesion between sliding surfaces. The low friction coefficient of graphite is not an inherent property but rather a consequence of water vapor adsorption by the material. Beyond 150 °C, desorption of the vapor occurs, leading to a transition in the friction coefficient from µ = 0.1 to µ = 0.6. To address this issue, impregnation solutions for self-lubricating materials have been developed, with various compositions tailored to specific objectives. Common types include molybdenum disulfide, soft metals and polymers. In this predominantly experimental study, the impact of polymer impregnation on the evolution of friction force and wear rate in graphite material bearings subjected to a dry fretting contact under severe thermal stresses at 270 °C was investigated. Additionally, the mechanical stresses in the bearings throughout different phases of our tests were analyzed using a numerical model.

Effect of ball–material ratio on Cu-Bi mixed powder and self-lubricating material properties

Purpose This study aims to investigate the effects of ball–material ratio on the properties of mixed powders and Cu-Bi self-lubricating alloy materials. Design/methodology/approach Cu-Bi mixed powder was ball milled at different ball–material ratios, and the preparation of Cu-Bi alloy materials was achieved through powder metallurgy technology. Scanning electron microscopy, X-ray diffraction and Raman spectroscopy were conducted to study the microstructure and phase composition of the mixed powder. The apparent density and flow characteristics of mixed powders were investigated using a Hall flowmeter. Tests on the crushing strength, impact toughness and tribological properties of self-lubricating alloy materials were conducted using a universal electronic testing machine, 300 J pendulum impact testing machine and M200 ring-block tribometer, respectively. Findings With the increase in ball–material ratio, the spherical copper matrix particles in the mixed powder became lamellar, the mechanical properties of the material gradually reduced, the friction coefficient of the material first decreased and then stabilized and the wear rate decreased initially and then increased. The increase in the ball–material ratio resulted in the fine network distribution of the Bi phase in the copper alloy matrix, which benefitted its enrichment on the worn surface for the formation a lubricating film and improvement of the material’s tribological performance. However, a large ball–material ratio can excessively weaken the mechanical properties of the material and reduce its wear resistance. Originality/value The effects of ball–material ratio on Cu-Bi mixed powder and material properties were clarified. This work provides a reference for the mechanical alloying process and its engineering applications.