Self-lubricating Nanocomposites Research Articles

Self-replenishing lubrication mechanism of nano-silver-reinforced AISI 4140 steel composites under dry sliding for mechanical applications

Wear is one of the most important factors limiting mechanical components' lifespan and durability. In this study, a novel, AISI 4140-Ag steel-based, self-lubricating nanocomposite was manufactured by the spark plasma sintering (SPS) technique. The high-level aim of this investigation is to obtain a deeper understanding of how silver (Ag) at the nanoscale can enhance the self-lubricating layer's replenishment, which aids in maintaining a steady supply of solid lubricant under dry conditions. Tribological experiments were conducted under various loads (30–150 N) at 5 Hz frequency and 300 °C temperature using a Rtec Universal Tribometer (ball-on-disc setup). After that, advanced surface characterization techniques were utilized to illustrate predominant wear modes, lubrication mechanisms, and the chemical identity of the self-lubrication layer. Noticeably, the AISI 4140-Ag nanocomposite reduced the friction coefficient and wear rate by 36.16–51.14 % and 93.40–97.36 %, respectively, compared to the AISI 4140 composite. The excellent self-lubricating performance is mainly attributed to the replenishment of a self-lubricating layer on the substrate material and a transfer layer on the counterbody, composed of AgO and Fe2O3. The results of our study hold considerable promise for the advancement of self-lubricating composites and the enhancement of their durability in mechanical applications.

Investigations on the temperature-dependent tribological behaviour of spark plasma sintered CNT-304 SS self-lubricating nanocomposites

ABSTRACT Herein, we report the tribological behaviour of CNT-304 stainless steel composites at room (28°C) and high temperatures (200°C). Nanocomposites of various CNT concentrations, namely 0.2, 0.5, 1.0, 2.0, 3.0, and 4.0 wt%, were prepared. A significant amount of grain refinement resulted in an increase in CNT loading. A tribological study was carried out at 28°C and 200°C. Wear resistance was found to enhance with an increase in CNT concentration at both temperatures. However, a slightly higher wear rate was observed at 200°C for the samples with CNT content < 3 wt% than their corresponding low-temperature values. About 86%, 91% drop-in wear rate was seen in 2.0 wt% CNT-304 SS, and 4.0 wt% CNT-304SS, respectively, as compared to pure SS at 28°C, which is 54% and 88% decrease at 200°C and is very promising. The decrease in wear volume with CNT content at both temperatures can be ascribed to the self-lubricating and reinforcing nature of CNTs in the metal matrix composites. Severe abrasive wear in the pristine SS samples was slowly changed to mild abrasive and lubricated wear in composites. A systematic study on the tribological behaviour of CNT-SS composites can shed light on the benefits and detriments of using them for various applications. Highlights Incorporation of CNTs into 304 SS matrix caused grain refinement. Wear rate decreased with CNT content and 4.0 wt% CNT-SS showed minimum wear rate while pristine gave the maximum at both 28°C and 200°C. About 86% and 54% decrease in wear rate were observed for 2.0 wt% CNT-304 SS at 28°C and 200°C respectively as compared to the pristine 304 SS sample. Wear rate at 200°C was slightly more than that of room temperature (28°C) for CNT content < 3 wt%. The 3.0 wt% CNT-304 SS and 4.0 wt% CNT-304 SS showed nearly the same wear rate at both ambient and 200°C test.

Numerical simulation of the friction damage mechanism for low wear silver matrix nanocomposite using the discrete element method

• Discrete element simulations vividly show the friction damage mechanism. • Transfer films can effectively inhibit the damage of materials. • Elimination of stress concentration is beneficial to inhibit delamination wear. Silver matrix self-lubricating nanocomposites had broad prospects in many applications owing to the low friction coefficient and high wear resistance. This paper focus on the friction damage mechanism for silver matrix nanocomposite under different dry sliding conditions. According to the DEM (Discrete Element Method) calculations, the stress concentration on the subsurface leads to the initiation and gradual development of cracks during the sliding process. The principal stress and maximum shear stress in the subsurface are the major causes of delamination wear in silver matrix nanocomposite. Solid lubricant in the worn surface shows anti-friction and wear resistance due to its inherent low shear characteristics, resulting in a significant reduction in delamination wear.

Tribological behavior and microstructural evolution of lubricating film of silver matrix self-lubricating nanocomposite

The aim of this study is to fabricate the nanocomposite with low friction and high wear resistance using binary solid lubricant particles. The microstructure and tribological performance of the nanocomposite are evaluated, and the composition and film thickness of the lubricating film are observed and analyzed by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The nanocomposite exhibited improved tribological properties with a friction coefficient as low as 0.12 and a low wear rate of 2.17 × 10−6 mm3/(N·m) in high-purity nitrogen atmosphere. Decreasing sliding speed can increase lubricating film thickness, and the thickest lubricating film is approximately 125 nm. As the film thickness of the lubricating film exceeded 90 nm, the friction coefficient curves became smooth. In compared with WS2, MoS2 can be more effective in forming the transfer layer on the worn surfaces at the initial stage of the tribological process.

Self-lubricating and high wear resistance mechanism of silver matrix self-lubricating nanocomposite in high vacuum

The silver matrix self-lubricating nanocomposite with low friction and high wear resistant was fabricated by nanoscale silver powder, nanoscale tungsten disulfide powder and microscale molybdenum disulfide powder. The friction and wear behaviors were investigated, and the worn surfaces were observed and analyzed by SEM and XPSXPS. The investigations on transfer layer and lubricating film were used to analyze the friction and wear properties of the materials, and self-lubricating and high wear resistance mechanism of the nanocomposite was discussed. Decreasing the velocity could increase the thickness of lubricating film, and the thickest lubricating film (about 117 nm) was achieved at a velocity of 0.1 m/s. It is confirmed that the nanocomposite had a significant improvement in friction and wear properties, the low friction coefficient and high wear resistance in high vacuum were 0.125 and 2.53 × 10−6 mm3/N·m, respectively. The transfer layers and lubricating films containing tungsten disulfide and molybdenum disulfide has better self-lubricating property than the transfer layer containing the single solid lubricant. The synergistic effect of binary solid lubricants was confirmed in Nanocomposite.

Friction and Wear Characterization of Spark Plasma Sintered Hybrid Aluminum Composite Under Different Sliding Conditions

Abstract Friction and wear behaviors of hybrid aluminum matrix self-lubricating nanocomposite, containing varying amount of nano-aluminum oxide (Al2O3) and graphene nanoplatelet (GNP) particles were investigated under dry and boundary lubrication sliding conditions. All the specimens were prepared by ultrasonic probe mixing followed by high-energy mechanical ball milling and spark plasma sintering fabrication route. The objective of this present study is to determine the tribological behavior of GNP as nanoreinforcement under dry and wet lubricating conditions. The wear test was carried out at room temperature on a ball-on-disc reciprocating tribometer with a contact load of 5 N, a frequency of 30 Hz, a stroke of 2 mm, and a sliding distance of 120 m. The chromium-plated chrome steel ball is used as the counter body for tribo-testing. From the results, it has been observed that GNP, as the solid lubricant reinforcement, reduces the friction by 25.33% and 68.14% under dry and wet lubricating conditions, respectively, for the hybrid composite. Reduction in wear volume by 91.15% and 90.50% is observed under dry and wet lubricating conditions, respectively, for the hybrid composite in comparison to the base eutectic Al–Si alloy. The reduction in the coefficient of friction and wear volume for the hybrid composite is attributed to the multilayer two-dimensional GNP nanoparticles that cause easy shearing by forming a conformal protective film layer on the sliding interface. Ultra-mild to severe wear regime was obtained for different composition samples including base composition to hybrid composition.

Enhanced sliding electrical contact properties of silver matrix self-lubricating nanocomposite using molecular level mixing process and spark plasma sintering

The present work aims to synthesize a silver matrix self-lubricating nanocomposite with improved sliding electrical contact properties by using molecular level mixing process and spark plasma sintering. The sliding electrical contact properties of the nanocomposite are fully evaluated, and the microstructural evolution of the lubricating film are analyzed by X-ray photoelectron spectroscopy and scanning electron microscopy. The microstructural evolution of the lubricating film is investigated to determine the influence of sliding speed on the sliding electrical contact properties of the silver matrix self-lubricating nanocomposite, and the self-lubricating mechanism of the silver matrix self-lubricating nanocomposite under vacuum condition is discussed. It is confirmed that Ag-WS2-MoS2 nanocomposite has excellent sliding electrical contact properties under vacuum condition with a high wear-resistance of 1.37 × 10−6 m3/N·m, a low friction coefficient of 0.126, and a contact resistance as low as of 2.16 mΩ. Decreasing the sliding speed increases the lubricating film thickness.

Application of Desirability-Based Multiobjective Optimization Techniques to Study the Wear of Al Self-Lubricating Hybrid Nanocomposites

In this study, novel Al6061–SiC nanocomposites and Al6061–SiC–Gr hybrid nanocomposites were fabricated by ultrasonic cavitation method by adding silicon carbide (SiC) of 0.8 and 1.6% and graphite (Gr) of 0.5 and 1.0% by weight basis for each casting. A Three-level Box–Behnken design of experiment was developed using response surface methodology. Dry sliding wear tests were performed as per the experimental design using a pin-on disc set-up at room temperature. Analysis of variance (ANOVA) was applied to investigate the influence of process parameters viz., load, sliding distance, wt% reinforcement and their interactions on specific wear rate and coefficient of friction. Further, a mathematical model was formulated by applying response surface method in order to estimate the tribology characteristics such as wear and COF of the hybrid nanocomposites. The specific wear rate and coefficient of friction were significantly influenced by % of SiC followed by % of Gr, load and sliding distance. The wear test parameters were optimized for minimizing specific wear rate and COF using desirability function approach. A set of optimum parameter of combination for AMMNC was identified as: SiC 1.36wt%; Gr 0.63 wt%; load 35.65 N and sliding distance 2848 m with specific wear rate of 0.517 g/N-m; coefficient of friction 0.181. The AFM image of Al6061–1.36SiC–0.63Gr hybrid nanocomposite at optimized condition confirmed the improvement in the wear surface smoothness of the hybrid nanocomposite compared to Al6061–SiC nanocomposites.

Synthesis of Ni(Cr)–hBN Nanocomposite by Mechanical Alloying and Its Thermodynamical Evaluation

In the present study, the feasibility of fabricating an Ni(Cr)/hBN self-lubricating nanocomposite by mechanical alloying technique was studied. To achieve this goal, a Ni–20 wt % Cr powders mixture was first milled up to 40 h to produce the nanostructured Ni(Cr) solid solution. hBN particles were subsequently added to Ni(Cr) and further mixed for 3 h. X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM) were performed to study phase transformations and microstructural evolutions during the milling process. The results showed that the dissolution of Cr in Ni started after 5 h and completed after 30 h of mechanical alloying. TEM studies also showed that the 40 h milled Ni(Cr) solid solution had the average grain size of 50 nm. Miedema’s semi-empirical thermodynamic model was used to predict the most stable phases in the Ni–Cr binary system. The results showed that the Gibbs free energy change of solid solution formation (–8.44 kJ/mol) was much lower than that of the amorphous phase (–1.3 kJ/mol) in the chemical composition of Ni–20 wt % Cr, thereby confirming the experimental results. The formation of a fine lamellar structure during the milling process was found to be the main reason for the solid solution formation. The nanostructured Ni(Cr) solid solution showed suitable thermal stability at 800°C. It was also observed that hBN particles were homogenously distributed in the as-fabricated Ni(Cr) after 3 h of mixing. The results of the present study also revealed that the mechanical alloying process could be regarded as a high-potential technique for the fabrication of metal-based self-lubricating composites.

Ultralow Friction Self-Lubricating Nanocomposites with Mesoporous Metal-Organic Frameworks as Smart Nanocontainers for Lubricants.

Smart nanocontainers with stimuli-responsive property can be used to fabricate a new kind of self-lubricating nanocomposite, while the practical potential of the metal-organic frameworks (MOFs) as nanocontainers for lubricants has not been realized. In this work, mesoporous Cu-BTC MOFs storing oleylamine nanocomposites were explored from synthesis and microstructure to self-lubricating characterization. The stress stimuli-responsiveness behavior of the Cu-BTC storing oleylamine (Cu-BTCO) for lubrication has been investigated by subjecting it to macroscopic ball-on-disc friction tests. The steady-state coefficients of friction (COFs) of the Cu-BTC nanocomposites without lubricants were ca. 0.5. In contrast, after oleylamine as the lubricant was incorporated into the Cu-BTC container in the nanocomposite, ultralow friction (COF, ca. 0.03) was achieved. It has been demonstrated that the improved lubricating performance was associated with the lubricating film which was in situ produced by the chemical reaction between the oleylamine released from the nanocontainer and the friction pairs. Therefore, the nanocomposite with smart Cu-BTC container holds the promise of realizing extraordinary self-lubricating properties under stress stimuli.

Effect of In-situ Processing Parameters on the Mechanical and Tribological Properties of Self-Lubricating Hybrid Aluminum Nanocomposites

In the present investigation, aluminum/TiB2/Al2O3 metal matrix composite was fabricated using the liquid metallurgy route. The transmission electron microscopy study was conducted in order to investigate the microstructure of the in-situ processed composites. X-ray diffraction analysis of the composite was performed to investigate the various phases present in the composite. Dry sliding tests were conducted using pin-on-disk tribometer in order to understand the self-lubricating behavior of developed composite. The microstructural characteristics revealed formation of in-situ phases and uniform dispersion of the reinforcement phases throughout the composite. The developed hybrid self-lubricating nanocomposites showed superior mechanical and tribological properties. The superior tribological properties of hybrid composite are attributed to the formation and synergetic effect of TiB2 and Al2O3 particles in the composites. The Al2O3 hard ceramic particles act as the obstacles to the movement of dislocation and thus enhance the mechanical properties. The oxidation of TiB2 on the surface forms H3BO3 and TiO2 tribolayer resulting in superior tribological properties.

Mechanical and tribological properties of self-lubricating metal matrix nanocomposites reinforced by carbon nanotubes (CNTs) and graphene – A review

Rapid innovation in nanotechnology in recent years enabled development of advanced metal matrix nanocomposites for structural engineering and functional devices. Carbonous materials, such as graphite, carbon nanotubes (CNT's), and graphene possess unique electrical, mechanical, and thermal properties. Owe to their lubricious nature, these carbonous materials have attracted researchers to synthesize lightweight self-lubricating metal matrix nanocomposites with superior mechanical and tribological properties for several applications in automotive and aerospace industries. This review focuses on the recent development in mechanical and tribological behavior of self-lubricating metallic nanocomposites reinforced by carbonous nanomaterials such as CNT and graphene. The review includes development of self-lubricating nanocomposites, related issues in their processing, their characterization, and investigation of their tribological behavior. The results reveal that adding CNT and graphene to metals decreases both coefficient of friction and wear rate as well as increases the tensile strength. The mechanisms involved for the improved mechanical and tribological behavior is discussed.

High Temperature Cylinder Sleeve Design Research Self-Lubricating Materials

Cylinder Liner design innovation goal is energy conservation. As the main friction parts engine cylinder liner, reducing friction energy is energy saving basic requirements. Materials research cylinder sleeve is one of the main cylinder liner saving research. Through the piston ring and cylinder liner surface friction dual material hard phase, self-lubricating phase, toughening phase analysis, select compatibility, high strength, heat resistance, good high temperature performance, ease of manufacture, price rational matrix material and an appropriate proportion of nanoscale hard material, self-lubricating materials, ductile materials, using appropriate methods cladding and processing, design developed high-temperature self-lubricating cylinder sets of advanced materials. The latest international high temperature, wear-resistant, self-lubricating materials research: modern nanoα-Al2O3+Ni-base alloy composite materials, Ti2B/Fe metal-ceramic composites, metals and ceramics NiCr-Cr3C2 particles CaF2 self-lubricating composite alloy powder material, NiCr/Cr3C2-WS2 self-lubricating wear-resistant materials were studied and found to TiC, Al2O3 is hard reinforcing phase, CaF self-lubricating phase, NiCr/TiC eutectic toughening phase, high-temperature self-lubricating wear-resistant nanocomposite, and Cr18Ni9 class alloy as base material, by laser cladding method enables conventional cylinder liners manufacturing technological breakthroughs, has practical value.

Tribological performance of hybrid PTFE/serpentine composites reinforced with nanoparticles

The tribological properties tests were conducted on several polytetrafluoroethylene (PTFE)/serpentine solid self-lubricating nanocomposites reinforced with different nanoparticles, such as nano-β-carborundum whisker (β-SiCw), nano-copper and nano-TiO2. The friction coefficient, wear rates, wear surface morphology and transfer film were studied. The experimental results indicated that the nano-fillers remarkably improve the antifriction and wear resistance of these composites. The highest wear resistance was found for composites containing (1) 5% Ser.+5% β-SiCw (modified and treated by titanate coupling agent), (2) 5% Ser.+5% β-SiCw (unmodified with coupling agent) and (3) 5% Ser.+20% nano-Cu. Wear tests and microanalysis showed that the variety of nano-fillers and continuity of transfer film on counterface significantly affected the friction and wear properties of the ternary composites.

Preparation and Properties of Organically Modified Montmorillonite/Nitrile Rubber Nanocomposites

A series of organically modified montmorillonite (OMMT)/nitrile rubber (NBR) nanocomposites were prepared by a simple mechanical-mixing method. The structures of OMMT and the dispersion of OMMT in the rubber matrix were detected by X-ray diffraction (XRD). The mechanical properties of the NBR/OMMT nanocomposites were characterized, and the tribological behaviors of the nanocomposites were evaluated on a ring-block (MRH-3) wear tester. The results showed that the OMMT was homogeneously dispersed in the NBR matrix. The tensile strength of the OMMT/NBR nanocomposites increased with increasing OMMT contents. Both the coefficient of friction (COF) and wear of the nanocomposites decreased remarkably with increasing OMMT content. In addition, the influence of the applied load on the tribological properties of the nanocomposites is discussed. It is expected that the research may be of aid in the rational design and use of solid, self-lubricating nanocomposites under different loading states.

Slow Release of Fullerene-like WS2 Nanoparticles from Fe−Ni Graphite Matrix: A Self-Lubricating Nanocomposite

Densified iron−nickel−graphite blocks were prepared by powder metallurgy processes and subsequently impregnated with a few percent of fullerene-like WS2 nanoparticles (<150 nm), synthesized in a fluidized bed reactor. Using the disc-block setup, the friction coefficient; critical load for seizure, and wear rates were measured. Substantial improvements in all of the tribological parameters were measured with the addition of the fullerene-like nanoparticldes. This behavior is attributed to a slow release of the nanoparticles from the porous matrix onto the block surface and their excellent tribological behavior.