Reduction In Friction Coefficient Research Articles

Rapid In Situ Preparation of Conductive Graphite-like Films on Polymer Surfaces via Hydrogen Plasma Technology.

Many special polymer materials with high strength, low density, and high processability have been developed for the substitution of metal products in recent years; however, their electrical insulation properties sometimes limit their application in medicine, electronics, and aerospace fields. Constructing a conductive layer on polymers may be a promising strategy for conquering these problems, but simply obtaining a high-quality conductive layer remains a challenge. Here, we develop a universal strategy to in situ fabricate a conductive graphite-like film on various polymer surfaces based on a simple one-step gas plasma ion implantation method. Theoretical and experimental results confirm that the reducibility of free radicals and the electrophilicity of cations in plasma are critical for the formation of graphite-like films on polymer surfaces. Compared with argon and oxygen plasma, hydrogen plasma with strong reducing hydrogen radicals and weak electrophilic hydrogen cations can produce the highest degree of graphitization of graphite-like films. The as-prepared polymers treated by hydrogen plasma ion implantation presented good surface conductivity and reduced friction coefficient, which has great potential for application in medicine, electronics, and aerospace fields.

Enhanced tribological performance of PLA/CNC composites: A comparison with phenolic resin and nylon

PLA has been developed to replace plastic because it is degradable. For more advanced applications, more research is needed on PLA. This study investigates the tribological properties of phenolic resin, nylon, and PLA/CNC composites under varying sliding distances and loads. Both phenolic resin and nylon demonstrate exceptional wear resistance and stable friction coefficients. PLA/CNC composites exhibit improved wear resistance, showing a 17% reduction in friction coefficient at a 3 wt.% CNC content. While the wear volume of PLA/CNC composites increases with sliding distance, the addition of CNC enhances PLA’s self-lubricating properties and overall wear resistance. The correlation between dissipated energy and wear volume confirms that higher CNC content significantly improves the durability of PLA. These findings suggest that CNC has considerable potential as an additive to enhance the tribological performance of PLA composites, making it a valuable material for various applications requiring superior wear resistance.

Enhanced creaminess of plant-based milk via enrichment of papain hydrolyzed oleosomes

There is an increased consumer demand for plant-based milk in substituting dairy milk due to the ethical, health concerns and environmentally-friendly choice. However, perceived creaminess as dominant attributes present a big challenge in consumer acceptance for those milk alternatives. In this study, we developed a novel and easily scalable strategy to enhance the creaminess of soy milk via enrichment of oleosomes. The soybean oleosome creams were extracted and hydrolyzed with papain, resulting in formation of oil droplets with more phospholipid and less protein at the surface, which significantly reduce friction coefficient in the presence of saliva (from 0.15 to 0.03 at a speed around 50 mm/s). Moreover, blending papain-hydrolyzed oleosome creams with raw soy milk enables the creation of a plant-based milk that matches the nutritional profile, lubrication properties, and creaminess of full-fat dairy milk. QCM-D and passive microrheology were employed to characterize hydration of oleosomes into the mucin layer and relevant viscosity change, suggesting that papain hydrolyzed oleosome might decrease friction coefficient via hydration lubrication mechanism. This approach could be applied to enhance the creaminess mouthfeel and nutritional profile of plant-based milk.

Achieving precise graphenization of diamond coatings below the interfacial thermal stress threshold

Abstract Diamond coatings possess numerous excellent properties, making them desirable materials for high-performance surface applications. However, without a revolutionary surface modification method, the surface roughness and friction behavior of diamond coatings can impede their ability to meet the demanding requirements of advanced engineering surfaces. This study proposed the thermal stress control at coating interfaces and demonstrated a novel process of precise graphenization on conventional diamond coatings surface through laser induction and mechanical cleavage, without causing damage to the metal substrate. Through experiments and simulations, the influence mechanism of surface graphitization and interfacial thermal stress was elucidated, ultimately enabling rapid conversion of the diamond coating surface to graphene while controlling the coating's thickness and roughness. Compared to the original diamond coatings, the obtained surfaces exhibited a 63–72% reduction in friction coefficients, all of which were below 0.1, with a minimum of 0.06, and a 59–67% decrease in specific wear rates. Moreover, adhesive wear in the friction counterpart was significantly inhibited, resulting in a reduction in wear by 49–83%. This demonstrated a significant improvement in lubrication and inhibition of mechanochemical wear properties. This study provides an effective and cost-efficient avenue to overcome the application bottleneck of engineered diamond surfaces, with the potential to significantly enhance the performance and expand the application range of diamond-coated components.

Tribological and mechanical endowments of polyoxymethylene by liquid‐phase exfoliated graphene nanofiller

AbstractIn this study, a viable route to the development of a high‐performance polyoxymethylene (POM)‐based nanocomposite is proposed to overcome tribomechanical‐related issues in high‐precision sliding parts. Prior to melt‐blending, graphene nanoplatelet (GNP) filler was processed via a series of liquid‐phase exfoliation and surface modification with 3‐aminopropyltriethoxysilane. Results indicate that GNP is successfully exfoliated with minimum defect ratio and improves interfacial bonding within the matrix. Uniform dispersion and stable load‐transfer capability of POM/GNP with 0.5 wt% loading significantly enhanced flexural, tensile and impact strength by overall 26.4%, in contrast to unfilled POM. Dry friction tests against a steel ball also showed the lowest reduction in friction coefficient and wear rate by 22% and 40.6%, respectively, at the same amount of GNP loading due to the large specific surface coverage and lubricious transfer film chelation onto the steel counterface. Furthermore, dissipated energy accumulation by friction work was calculated in the sliding interfaces based on friction force–displacement hysteresis loop where the POM/GNP 0.5 wt% wear surface consumed ca 21.7% less energy in a dry frictional shearing process compared to neat POM. However, lack or excess loading of processed GNP exhibited insufficient or poor matrix–filler adhesion and led to deterioration of the composite properties due to particle agglomeration which can cause stress concentration and serve as a failure site. The adoption of the proposed methodology would demonstrate excellent material characteristics in thin‐walled precision parts where both mechanical and tribological performances are the primary concern. © 2024 Society of Chemical Industry.

Fabrication of Vanadium Oxide-encapsulated Hybrid Carbon Nanospheres for Enhanced Tribological Performance.

A new sulfur-containing carbon nanospheres encapsulated with vanadium oxide (V@SCN) is synthesized through a one-pot oxidation polymerization and then carbonization method. The prepared V@SCNs exhibit good dispersibility as a lubricant additive, which is owing to the inherited lipophilic organic functional groups in the sulfur-containing carbon shell derived from the carbonization of polythiophene. The agglomeration and precipitation of metals in the base oil are also avoided through the encapsulation of lipophilic carbon shells. The stress and thermal simulation results show that the vanadium oxide core bestows upon the carbon nanospheres enhanced load resistance and superior thermal conductivity, which contributes to their excellent tribological properties. Introducing 0.04M-V@SCN to the base oil leads to favorable tribological characteristics, such as a fourfold rise in extreme pressure capacity from 250 to 1050N, a reduction in friction coefficient from 0.2 to ≈0.1, and a substantial decrease in wear by 90.2%. The lubrication mechanism of V@SCNs as lubricant additive involves the formation of a robust protective film on the friction pair, which is formed via complex physical and chemical reactions with the friction pair during friction.

Advancing self‐lubricating technology: Selective laser sintering molding assisted development of copper‐based polytetrafluoroethylene /graphite composites

AbstractThis study introduces an innovative technique for the fabrication of copper‐based polytetrafluoroethylene (PTFE)/graphite self‐lubricating composites. By harnessing the exceptional capabilities of selective laser sintering (SLS), we efficiently create three‐dimensional, continuous, and porous graphite preforms. Following this, the composite is formed through a combination of electroplating and vacuum extrusion methods. Subsequently, PTFE was vacuum impregnated into the microporous structure of the graphite preforms, and the composites were obtained through freeze‐drying, plasticizing, and machining processes. The resulting copper‐based PTFE/graphite self‐lubricating composites exhibit an exceptional blend of properties. Notably, there is a significant reduction in the average coefficient of friction, dropping from 0.14 to 0.02, and a marked decrease in the wear rate, from 1.358 × 10−5 to 1.109 × 10−5 mm3/N·m, as compared to graphite as a standalone lubricant. This represents a substantial improvement in performance, underscoring the effectiveness of the proposed fabrication method.Highlights The porous graphite with controllable shape distribution was prepared. Surface copper plating improves surface bonding. Controllable copper matrix composites with double lubricant were prepared. The average friction coefficient is as low as 0.02.

Tribological characteristics of graphene nanoplatelets-filled PTFE under dry sliding and sea water environmental conditions

This study focuses on enhancing the tribological performance of polytetrafluoroethylene (PTFE) composites by incorporating graphene nanoplatelets (GNPs) through compression moulding technique. The main aim of the research was to investigate how varying weight percentages of GNP (1 wt %, 3 wt % and 5 wt %) influence the friction and wear properties of PTFE composites under both dry sliding and saline water environment. A significant reduction in the coefficient of friction (COF) and wear rate was observed with the addition of GNP, particularly in seawater. Specifically, the reduction of COF in sea water reached up to 58.765% with 3% of GNP compared to dry sliding. For wear reduction, a reduction of up to 90.247% was observed with 5% GNP in sea water condition. These findings reveal the potential of GNP-filled PTFE composites in applications requiring enhanced tribological properties in both dry and aqueous environments. The originality of this work lies in the comprehensive analysis of the environmental influence on GNP-filled PTFE composites, providing understandings of their applicability in marine environments.

Study on the sliding tribological behavior of ZIF-8 under lubricating grease conditions

ZIF-8 is widely applied in lubrication, adsorption, and catalysis owing to its unique physicochemical properties. Previous experimental studies have demonstrated its feasibility as a lubricant additive. In the present work, the lubricating performance of ZIF-8 as an additive to lithium-based grease is quantitatively and dynamically analyzed at the atomic scale using molecular dynamics simulations. Friction wear experiments are also conducted to elucidate the lubrication mechanism of ZIF-8. The simulation and experimental results indicate that the incorporation of ZIF-8 effectively enhances the antifriction and antiwear characteristics of lithium grease. The most significant improvement in the lubrication performance of the grease is obtained at a mass fraction of 2.0 wt. % ZIF-8, which reduces the friction factor μ of the grease by about 17.0% and the wear by ∼40.0%. Furthermore, the molecular dynamics simulations reveal that ZIF-8 primarily functions as a ball bearing under low-load conditions. However, under high-load conditions, ZIF-8 undergoes significant deformation and primarily acts as a filler. This explains the experimentally observed significant reduction in friction coefficient after the addition of ZIF-8. The results of this study provide a theoretical foundation for the development of new environmentally friendly grease additives.

CHARACTERIZATION OF ALUMINIUM METAL MATRIX COMPOSITES REINFORCED WITH SILICON CARBIDE AND NICKEL PARTICULATES

This research article presents the procedure for the fabrication of Aluminium alloy (LM25) based metal matrix composites containing particulates of silicon carbide (10 wt. %) and nickel (0, 5 and 10 wt. %). Using the vortex casting technique, three composites were formulated and characterized as per ASTM standards. Microstructure analysis using "scanning electron microscopy" reveals the uniform distribution of reinforcing particulates within the base matrix without clustering. "Energy dispersive spectroscopy" illustrates the presence of ingredients within the composites. "X-ray diffraction" patterns indicate the formation of mesoporous NiSiAl compound within the composite resulting from internal reactions. The "optical microscopy" reveals the refinement of grain structure with the inclusion of nickel particulates within the composites. The influence of the composition of reinforcing particulates that is, silicon carbide and nickel on the properties of the base matrix was explored. An enhancement in the microhardness, tensile strength, wear resistance and traction force and a reduction in friction coefficient was observed together with a marginal reduction in elongation and the porosity level is also under the controlled limits (<5%).

Influences of friction stir processing on the microstructure and properties of TC4 titanium alloy by laser metal deposition

To enhance the properties of TC4 titanium alloy samples prepared by Laser Metal Deposition (LMD), while minimizing metallurgical defects and increasing relative density of the samples, the advanced Friction Stir Processing (FSP) technology was employed to conduct a refined secondary modification on the LMD-deposited TC4 titanium alloy samples. The comprehensive influences of FSP on the microstructure and properties of the as-deposited TC4 titanium alloy were emphatically investigated. The results reveal that the as-deposited TC4 titanium alloy exhibits a microstructure characterized primarily by columnar grains interspersed with a minor amount of equiaxed grains in the vertical section. After FSP treatment, the microstructure transforms into a new morphology where more refined equiaxed grains coexist with bimodal structures. Meanwhile, on the horizontal plane, the existing equiaxed grains are further refined, and the microstructure gradually transitions from the original Widmanstätten and basketweave structures to a more uniform laminar structure. Accordingly, the transformation of the microstructure leads to enhanced mechanical properties of the TC4 titanium alloy. Compared to the untreated as-deposited titanium alloy, the hardness of the FSP-processed samples significantly increases by 46.9 HV1 on the horizontal plane and 33.8 HV1 on the vertical plane. Additionally, the reduction in friction coefficient (from 0.47 to 0.41), a substantial decrease in wear mass (3.7 mg), and a slight improvement in the corrosion resistance of the titanium alloy collectively demonstrate the effectiveness of the FSP process in enhancing the performance of as-deposited TC4 titanium alloy.

Development of polyols analogous to neopentyl glycol and trimethylolpropane for the production of oleic acid-based biolubricants

Vegetable oils and animal fats have been known and used as lubricants and fuels since ancient times. However, the chain structure of the triacylglycerols (TAGs) generate limitations that discourage the use of these raw materials as lubricants. As an alternative to improve the physicochemical and thermo-oxidative characteristics of natural oils, the use of polyols without the β-hydrogens in the triacylglycerols structure is an efficient solution for the production of biolubricants. In this context, a series of polyols, analogous to trimethylolpropane (TMP) and neopentyl glycol (NPG) was synthesised and applied in the synthesis of polyol esters based on oleic acid. These esters were prepared by homogeneous catalysis using p-toluenesulfonic acid (p-TSA) and are intended for use as biolubricants. The synthesised polyols were characterized by one and two-dimensional NMR. The derived polyol esters were purified and had their structure confirmed by 1H and 13C NMR, infrared spectroscopy, and mass spectrometry. The polyol esters showed high viscosity index (189 – 222), thermo-oxidative stability (Tonset between 258 and 285 °C), and low melting points (between –19.4 and –47.6 °C). Furthermore, polyol esters showed reduced friction coefficients (0.021 – 0.041) and scar wear diameter on the metallic surface (0.274 – 0.448 mm). In addition to the satisfactory results of thermal stability and lubricity, which suggest the potential of these molecules as lubricants, all molecules were considered environmentally safe when evaluated through the Zebrafish toxicity model.

Role of different density negative micro-pillars textured H13 surfaces on enhanced wettability and tribological performance

The present study investigates how varying negative micro-pillar densities on H13 alloy, used in hot-forming dies, affect wettability with different fluids and tribological performance, alongside detailed morphological analysis. Recast materials, pockmarks, micro-voids, micro-cracks, and globules of debris are observed on EDM textured surfaces, and challenges are form accuracy and debris entrapment with higher textured density. The functional stressed surfaces, evident from XRD analysis, display hydrophobic properties with water and hydrophilic characteristics with mineral-oil-based emulsion. Increased texture density enhances these properties. Wettability properties transition of fabricated functional surfaces occurs within fluid surface energies of 48 to 72.8 mN/m. The coefficient of friction (COF) of the lower-density patterned surface is 20.42 % lower than the untextured surface, and the higher-density pattern shows a 13.48 % COF reduction compared to the lower-density surface. Key wear mechanisms include abrasion, adhesion, sharp edges and adhered debris deformation, and localized plastic deformation for untextured and textured surfaces.

Tribological properties of the P and S-free protic ionic liquids as water-based lubricants

Three kinds of P and S-free 1,8-Diazabicyclo[5.4.0] undec-7-ene water-soluble protic ionic liquids (PILs) were successfully synthesized and applied as additives in water-1,2-Propylene glycol (PG). The physicochemical properties of PILs and the anti-friction, anti-wear and anti-corrosion properties were investigated. Research results demonstrated that the addition PILs lubricant additive could greatly improve the tribological properties of water-1,2-PG. The addition of 5 wt% PILs with long alkyl chain will result in the reduction of friction coefficient and wear volume by about 45 % and 95 %, respectively. Meanwhile, the PILs with long-chain show more effect lubrication behavior than the short one. In addition, the obtained PILs also possess excellent anti-corrosion properties as water-based lubrication additives. The elemental analysis of the contact area showed that the PILs would generate a chemical reaction film during the friction process, and the carboxylate anion could form a chemical and physical adsorption film on the surface of contact area, which would provide better anti-friction and anti-wear properties.

Investigation of tribology and life prediction of polymer coatings on 7N21 aluminum alloy under dry sliding wear

To improve the tribological properties of the 7N21 aluminum alloy under dry sliding wear conditions, three E44-PI-PAI composite coatings filled with varying contents of MoS2, h-BN and VN were designed. The mechanical and tribological performances of these coatings were evaluated using scratch experiments, nanoindentation, and sliding wear experiments. After identifying the optimal coating, the engineering constants of the coating were determined using tensile experiments. Finally, a simulation analysis of the reciprocating wear life was performed using ABAQUS and a custom-developed UMESHMOTION subroutine. The results indicate that the optimal ratio of MoS2, h-BN and VN in the designed polymer coating is 4:3:4. The coefficient of friction (CoF) and wear rate of the optimal coating are 0.189 and 0.444×10−14 m3/Nm, representing a 67 % reduction in CoF compared to the 7N21 aluminum alloy. The L2 coating demonstrates excellent compatibility, featuring a surface roughness (Ra) of 0.630 μm, a uniform thickness of 10±2 μm, an optimal bonding strength at level 0, and a nanohardness of 0.391 GPa, meeting the requirements for engine bearings. The maximum deviation between the simulated wear life prediction and experimental results is only 8.11 %.

Friction Coefficient Evolution of Si3N4 Binary Coating with a Stoichiometric Ratio of 57/43

Friction coefficient depends on various factors or surface characteristics during tribological testing, and this friction coefficient can be modified by altering the properties of one of the two contacting surfaces. It is crucial to monitor the friction coefficient continuously, not only at the conclusion of the test. This research examined the evolution of friction coefficient of silicon nitride (Si3N4) coating and H13 steel over different sliding distances (250, 500, 750, 1000 m). The study assessed surface wear and oxidation through three-dimensional profilometry and SEM/EDX. The findings indicated a reduction in friction coefficient by 22%, a decrease in wear rate by 88%, and a reduction in wear volume by 87% when comparing the silicon nitride coated steel to the uncoated steel. Furthermore, the changes in friction coefficient provided insights into the timing of the complete fracture of the hard coating.Graphical abstract

Characterization of Nano-kaolin and its enhancement of the mechanical and corrosion resistance of epoxy coatings

This study compares the effects of varying concentrations of nano-kaolin and titanium dioxide on the mechanical and corrosion resistance of epoxy coatings. Characterization techniques such as TEM, XRD, Raman, FTIR, XPS, and AFM revealed surface features of nano-kaolin: the particle size reached the nanoscale, the XRD diffraction peak at 2θ = 25.3° disappeared, Raman peaks broadened with decreased intensity, and a blue shift occurred in the FTIR spectra for various functional groups. Compared to pure epoxy coatings, the composite epoxy coating with 10 wt% nano-kaolin showed an 83.87 % increase in adhesion, an 81.82 % improvement in impact resistance, and a 61.42 % reduction in friction coefficient; while a 20 wt% titanium dioxide composite coating showed a 74.19 % increase in adhesion, a 75.76 % improvement in impact resistance, and a 46.9 % reduction in friction coefficient. Electrochemical tests indicated that a composite coating with 10 wt% nano-kaolin, after soaking in 3.5 wt% NaCl solution for 960 hours, achieved a corrosion efficiency of 98.87 % and an impedance modulus of 108.8Ω.cm2, which was three orders of magnitude higher than that of pure epoxy resin, increasing corrosion resistance by 57.14 %; whereas a 20 wt% titanium dioxide composite coating reached a corrosion efficiency of 89.29 % and an impedance modulus of 106.6Ω.cm2 after the same conditions, increasing corrosion resistance by 17.86 % compared to the pure epoxy resin. The composite coating with 10 wt% nano-kaolin exhibited superior mechanical and corrosion resistance, outperforming the 20 wt% titanium dioxide coating. Mechanical and corrosion mechanisms suggest that the uniformly dispersed nano-kaolin inhibits interactions between epoxy resin molecules and carries the external load, thereby enhancing intermolecular cohesion. Improved adhesion and impact resistance indirectly extend the coating's lifespan by prolonging the path of corrosion media through the coating to the substrate. The novel coating modification method proposed in this study effectively replaces titanium dioxide and enhances the coating's mechanical and corrosion resistance, offering a new solution for corrosion prevention in metal materials.

Investigation of effects of environmental conditions on wear behaviors of glass fiber reinforced polyester composite materials

AbstractGlass fiber reinforced polymer (GFRP) composites can be subjected to different environmental conditions such as temperature, humidity, ultraviolet radiation, hydrothermal cycle, acidic and alkaline solution in environments where they operate. These environmental conditions cause different damage mechanisms in composites such as pore formation, micro‐cracks, delamination, fiber breakage, fiber/matrix interface separation, plasticization, swelling and surface color change. In this study, wear properties of hybrid glass fiber reinforced polymer composites exposed to various environmental conditions for constant load (60 N), speed (500 rpm) and 2 h were examined comprehensively, depending on material content and environmental conditions. In this experimental study, the service conditions in glass fiber reinforced composites were simulated using different artificial aging environments such as acidic environment, hydrothermal cycle and UV radiation. In addition to the material content, it appears that the environmental conditions to which composites are exposed has a significant effect on friction coefficient. Considering environmental conditions, it is seen that the acid environment and hydrothermal cycle have reduced wear resistance of GFRP composites, while UV radiation improved wear resistance of the composites. In C2 sample, the wear rates under different conditions are 1.87 × 10−14 m3/Nm in non‐treated sample, 6.05 × 10−14 m3/Nm in acid environment, 4.79 × 10−14 m3/Nm in hydrothermal cycle and 0.59 × 10−14 m3/Nm in UV radiation.Highlights Friction coefficient of glass fiber reinforced polyester (GFRP) is higher under aged condition compared to non‐treated. Glass fibers used in correct proportions can reduce friction coefficient in GFRP. GFRP exposed to environmental conditions has an important effect on wear. Acid environment and hydrothermal cycle has reduced wear resistance of GFRP. UV radiation improved wear resistance of GFRP composite.

WSCF coatings tested under various environmental conditions: A multivariate tribological analysis

This study examines the influence of carbon (C) and fluorine (F) on the tribological and mechanical properties of WSCF coatings. WSCF-coated substrates were prepared with varying levels of C (10.4 to 18.7 at%) and F (5.3 to 9.3 at%) using DC reactive magnetron sputtering. Tribological performance was evaluated at 25 °C and 200 °C in dry and lubricated conditions. Alloying led to thicker, more amorphous, denser, and smoother coatings. An exceptional coefficient of friction (COF) as low as 0.008 was observed for WSCF2 (15.4 at% C and 9.3 at% F). Principal component analysis (PCA) revealed high F-doped coating in WSCF2 demonstrated improved tribological performance, resulting in a 38 % reduction in COF at 25 °C and dry conditions.

Microstructure, hardness, and tribological properties of Ni-Co/ SiO2 nanocomposite coating produced through pulsed current electrodeposition

This study investigates the development of Ni-Co/SiO2 nanocomposite coatings on mild steel surface using pulsed-current electrodeposition method. The effects of incorporating SiO2 nanoparticle and varying its concentration on the coatings' microstructure, microhardness, wear resistance, and frictional properties were assessed using field-emission electron microscopy, X-ray diffraction, Vickers microhardness testing, and dry sliding wear tests. The results indicated that the coatings exhibited two-phases of Ni-Co solid solution (α) with a face-centered cubic (FCC) crystal structure and hexagonal Co, a refined crystallite size of approximately 31 nm for Ni-Co and about 25 nm for Ni-Co/SiO2, along with a colony-like morphology that did not show any preferred growth direction. The amount of Ni-Co solid solution increased with the addition of SiO2 nanoparticles. The composite coatings demonstrated enhanced microhardness of 581 HV, which is 52 % greater than that of the Ni-Co coating, as well as improved wear resistance and a reduced friction coefficient compared to the unreinforced alloy coating. However, higher SiO2 content adversely impacted the tribological properties due to nanoparticle agglomeration. Analysis of the worn surfaces revealed a transition from abrasive wear to oxidative wear with increasing applied force for the coatings.