Effect of Ag nanoparticles additive on the tribological behavior of multialkylated cyclopentanes (MACs)

Monodisperse Ag nanoparticles with a particle size of about 6–7 nm and low volatile multialkylated cyclopentanes (MACs) lubricant were prepared. The effect of Ag nanoparticles as additive in MACs base oil on the friction and wear behavior of MACs was investigated. The friction and wear test of a steel disc sliding against the same steel counterpart ball was carried out on an Optimal SRV oscillating friction and wear tester. The morphology and elemental distribution of the worn surface of both the steel ball and steel disc and the chemical feature of typical element thereof were examined using a JEM-1200EX scanning electron microscope (SEM) equipped with a Kevex energy dispersive X-ray analyzer attachment (EDS) and X-ray photoelectron spectroscope (XPS), respectively. Friction and wear test indicates that the wear resistance and load-carrying capacity of MACs base oil were markedly raised and its friction coefficient changed little when 2% Ag nanoparticles were added in it. Results of SEM/EDS and XPS show that Ag nanoparticles were deposited on the friction pair surfaces to form low shearing stress metal Ag protective film in rubbing process.     

Sliding friction and wear performance of Ti6Al4V in the presence of surface-capped copper nanoclusters lubricant

The friction and wear properties of Ti₆Al₄V sliding against AISI52100 steel ball under different lubricative media of surface-capped copper nanoclusters lubricant—Cu nanoparticles capped with O,O′-di-n-octyldithiophosphate (Cu-DTP), rapeseed oil and rapeseed oil containing 1 wt% Cu-DTP was evaluated using an Optimol SRV oscillating friction and wear tester. The wear mechanism was examined using scanning electron microscopy (SEM) and X-ray photoelectron spectrosmeter (XPS). Results indicate that Cu-DTP can act as the best lubricant for Ti₆Al₄V as compared with rapeseed oil and rapeseed oil containing 1 wt% Cu-DTP. The applied load and sliding frequency obviously affected the friction and wear behavior of Ti₆Al₄V under Cu-DTP lubricating. The frictional experiment of the Ti₆Al₄V sliding against AISI52100 cannot continue under the lubricating condition of rapeseed oil or rapeseed oil containing 1 wt% Cu-DTP when the applied load are over 100 N. Surprisingly, the frictional experiment of Ti₆Al₄V sliding against AISI52100 steel can continue at the applied load of 450 N under Cu-DTP lubricating. The tribochemical reaction film containing S and P is responsible for the good wear resistance and friction reduction of Ti₆Al₄V under Cu-DTP at the low applied load. However, a conjunct effect of Cu nanoparticle deposited film and tribochemical reaction film containing S and P contributes to the good tribological properties of Ti₆Al₄V under Cu-DTP at the high-applied load.     

Tribological properties of 2 novel Mo/B–based lubricant additives in polyalphaolefin

Two kinds of Mo/B oleic diethanolamide derivatives (coded as YXM and YXB) were synthesised, and their tribological properties were evaluated using a 4‐ball machine. Results indicate that the 2 novel additives show excellent antiwear and extreme pressure properties. When 2.5 wt% YXM was added into the base oil, the wear scar diameter was reduced by 42.2%, and the P _B value was increased by 170.4%; when 2.5 wt% YXB was added into the base oil, the wear scar diameter was reduced by 23.1%, and the P _B value was increased by 167.1%. The worn surfaces of the lubricated GCr15 steel were analysed by using scanning electron microscopy and X‐ray photoelectron spectroscopy. It is indicated that the variation of tribofilm species produced by a chemical reaction between the additives and the steel surface plays an important role in inhibiting wear and friction. A model was used to analyse the action mechanism. According to the analysis, the tribofilm is composed of an adsorption layer and a reaction layer, and it could effectively protect the steel surfaces from direct contact.     

Tribological Effects of BN and MoS2 Nanoparticles Added to Polyalphaolefin Oil in Piston Skirt/Cylinder Liner Tests

We report in this article the friction and wear results of polyalphaolefin (PAO 10) base oil with the addition of 3 wt% boron nitride (BN) and molybdenum disulfide (MoS₂) nanoparticles with nominal size of 70 and 50?nm, respectively. The formulations were tested using cast iron cylinder liner segments reciprocating against aluminum alloy piston skirt segments at 20, 40, and 100?°C. The results showed that, at a load of 250?N and a reciprocating frequency of 2?Hz, BN did not lower friction whereas MoS₂ nanoparticles were very effective at reducing both friction and wear, compared with the base oil. The viscosities of both formulations were similar to the base oil, which allowed for a direct comparison between them. Raman spectroscopy showed the formation of an aligned MoS₂ layer on the cast iron liner surface, which most likely functions as a tribofilm. In the case of the cast iron liner tested with BN nanolubricant, no traces of BN were found. The effect of surfactants was also studied, and it was found that some surfactants were not only beneficial in dispersing the nanoparticles in oil, but also in producing some reduction in friction and wear, even when used as stand-alone additives in PAO 10.     

Antiwear,Antifriction, and Extreme Pressure Properties of Motor Bike Engine Oil Dispersed with Molybdenum Disulfide Nanoparticles

This work presents studies on the antiwear, antifriction, and extreme pressure properties of motor oil dispersed with MoS₂ nanoparticles. Commercial oil (SAE 20W-40 grade) is dispersed with stabilized MoS₂ nanoparticles in 0.25, 0.5, 0.75, and 1 wt%. The test oils are tested for antiwear, antifriction, and extreme pressure properties on a four-ball wear tester. The wear and friction offered by nanolubricants has decreased remarkably compared to the commercial base oil. The weld load and load wear index of oils dispersed with nanoparticles were improved substantially compared to the commercial base oil. Metallographic studies conducted on the wear balls from the extreme pressure test show that nanoparticles are deposited on the worn area along with additives in the oil, thereby preventing welding of the surfaces. An optimum weight fraction is arrived at for best performance. A synergy between the additives in the oil and dispersed nanoparticles has been observed, resulting in less dispersion for best results. It is found that beyond an optimum weight percentage of nanoparticles, the trends tend to reverse, resulting in greater wear and friction.     

Tribochemical Transformation of Nano TiO2 to Ilmenite on the Surface of Wearing Steel Parts: Antiwear Action of Nano TiO2 as an Additive in Engine Oil

TiO₂ nanoparticles of average size about 20–30 nm were hydrothermally synthesized from TiCl₄ under mild acidic conditions. The nanoparticles were mixed with dispersant and base oil to give a partially transparent concentrate with 1.5 wt% of Ti content. The concentrate was dispersed in hexane and base oil to characterize, respectively, by transmission electron microscopy (TEM) and dynamic light scattering (DLS). The concentrate was diluted with base oil to a parts per million level of Ti containing dispersion blends that were evaluated for wear and friction control performance. Nano TiO₂ containing fully formulated oil blend showed excellent load-bearing capability in Swingung, Reibung, Verschleiβ (SRV; oscillation, friction, wear) tests. Four-ball test results show that the wear scar diameter was considerably reduced to 0.30 mm for TiO₂-added blend compared to neat base oil (0.60 mm). The performance of TiO₂-added blend was comparable to secondary zinc dialkyl dithiophospate (ZDDP)-added blend under identical condition. Raman spectra of the worn surface on the tested ball revealed the presence of ilmenite (FeTiO₃) and no deposits of pure TiO₂.     

Synergistic effect of diisopropyl phosphite and over‐based calcium sulphonate additives on tribological properties of AISI 52100 steel/Al2O3 ceramics

The friction‐reducing and anti‐wear effect of the 500SN base oil containing diisopropyl phosphite (T451) and over‐based calcium sulphonate (KT5447) on AISI 52100 steel/Al₂O₃ ceramic were investigated with a ball‐on‐disc tribometer at a light load of 200 N and a high load of 400 N. The results indicate that the 500SN base oil containing T451 and KT5447 appears to have a synergistic effect on the pair. For the light load of 200 N, the effective composition is 3 wt% T451 + 2–3 wt% KT5447. For the high load of 400 N, the combination of T451 and KT5447 appears to have a synergistic friction‐reducing and anti‐wear effect. The scanning electron microscope images show that ploughed grooves, pitting, spalling and corrosion are the dominant wear modes for both 200 and 400 N. However, no evidence for the formation of the expected sulphur‐containing or phosphorus‐containing chemical compound is found according to X‐ray photoelectron spectroscopy analysis of the worn steel ball surface at both loads. Copyright © 2011 John Wiley & Sons, Ltd.     

Improving the AW/EP ability of chemically modified palm oil by adding CuO and MoS2 nanoparticles

Improvement in the anti-wear (AW) and extreme pressure (EP) ability of chemically modified palm oil (CMPO) by adding nanoparticles was experimentally evaluated. Nanolubricants were synthesized by adding 1 wt% copper(II) oxide (CuO) and 1 wt% molybdenum disulfide (MoS₂) nanoparticles to CMPO. The AW/EP properties of the formulations were evaluated by four-ball and sliding wear tests. Wear surfaces were analyzed by scanning electron microscopy, along with energy-dispersive X-ray and micro-Raman scattering spectroscopy. The MoS₂ nanoparticles exhibited better AW/EP properties than did the CuO nanoparticles. The addition of 1 wt% oleic acid as a surfactant facilitated the reduction of agglomerates.     

Antifriction and Antiwear Properties of an Ionic Liquid with Fluorine-Containing Anion Used as Lubricant Additive

Tribological behavior of trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl) imide [P₆₆₆₁₄][NTf₂] ionic liquid (IL) used as additive in a diester oil at concentrations of 0.25, 0.5 and 1 wt% was studied in this research. The IL solubility in the base oil was measured using the inductively coupled plasma mass spectrometry (ICP-MS) technique, and corrosion analysis was done at room temperature at relative humidity of 49–77%. Tribological tests were conducted for 30 min at room temperature, 15 Hz frequency, 4 mm of stroke length, a load of 80 N (corresponding to 2 GPa of maximum contact pressure) and relative humidity of 35–53%. Friction coefficient was recorded during tests, and the wear scar was measured by confocal microscopy. Worn surface was also analyzed by SEM, EDS and XPS. Results showed that a saturated solution of [P₆₆₆₁₄][NTf₂] in the base oil contains about 30 wt% of IL and corrosion activity for the highest concentration of IL (1 wt%) was not found after a 20-day test. Although the base oil and the mixtures had similar friction behavior, only the 1 wt% sample exhibited slightly lower wear volume than the base oil. SEM images exhibited similar wear track width (707–796 µm) and wear mechanism (adhesive) for all samples tested. In addition, the EDS spectra only showed the elements present in the steel. Finally, the XPS measurements could not detect differences regarding iron chemical state among the samples, which is consistent with the tribological behavior obtained.     

Tribological behaviour of two imidazolium ionic liquids as lubricant additives for steel/steel contacts

In this paper two room-temperature ionic liquids (ILs), 1-hexyl-3-methylimidazolium tetrafluroborate [HMIM][BF₄] and 1-hexyl-3-methylimidazolium hexafluorophosphate [HMIM][PF₆], have been studied as 1%wt. additives of a mineral hydrocracking oil for steel–steel contacts. Rheological properties of the mixtures and base oil were determined over shear rates and temperatures ranging 1–1000 s^?1 and 40–100 °C, respectively. Friction and wear testing was made using a block-on-ring tribometer set for pure sliding contact and XPS was used to analyze wear surfaces. [HMIM][PF₆] and [HMIM][BF₄] increased the viscosity of the base oil and decreased friction and wear. Friction and wear reduction are related to reactivity of the anion of the ionic liquids with surfaces forming FeF₃, B₂O₃, and species such as P₂O₅ or PO₄^3?.     

WC–ZrO2 composites: processing and unlubricated tribological properties

In the present work, we report the processing and properties of WC–6 wt.% ZrO₂ composites, densified using the pressureless sintering route. The densification of the WC–ZrO₂ composites was carried out in the temperature range of 1500–1700 °C with varying time (1–3 h) in vacuum. The experimental results indicate that significantly high hardness of 22–23 GPa and moderate fracture toughness of ∼5 MPa m^1/2 can be obtained with 2 mol% Y-stabilized ZrO₂ sinter-additive, sintered at 1600 °C for 3 h. Furthermore, the friction and wear behavior of optimized WC–ZrO₂ composite is investigated on a fretting mode I wear tester. The tribological results reveal that a moderate coefficient of friction in the range from 0.15 to 0.5 can be achieved with the optimised composite. An important observation is that a transition in friction and wear with load is noted. The dominant mechanisms of material removal appear to be tribochemical wear and spalling of tribolayer.     

Sliding Wear of Electrically Conductive ZrO<Subscript>2</Subscript>−WC Composites Against WC–Co Cemented Carbide

ZrO₂-based composites with WC addition can be successfully machined by electrical discharge machining (EDM) in demineralised water. ZrO₂ composites with 40 vol.% WC were produced from nanocrystalline and micrometre sized WC starting powders in order to compare their tribological behaviour. Friction and wear data are obtained on wire-EDM’ed ZrO₂–WC composite flats sliding against a WC–Co cemented carbide pin using a small-scale pin-on-plate testing rig. Correlations between wear volume, wear rate and friction coefficient on the one hand and material properties and test conditions on the other hand were elucidated. The experimental results revealed that the grain size of the electro-conductive WC-phase exhibits a strong influence on the friction and wear behaviour of the ZrO₂-based composite.     

Alkyl Imidazolium Ionic Liquids as Friction Reduction and Anti-Wear Additive in Polyurea Grease for Steel/Steel Contacts

Five room temperature ionic liquids (ILs), 1-butyl-3-methylimidazolium hexafluorophosphate (L-P104), 1-hexyl-3-methylimidazolium hexafluorophosphate (L-P106), 1-octyl-3-methylimidazolium hexafluorophosphate (L-P108), 1-decyl-3-methylimidazolium hexafluorophosphate (L-P110), and 1-hexyl-3-methylimidazolium tetrafluoroborate (LB106) were studied as 1 wt% additives of polyurea grease for steel/steel contacts. Their tribological behaviors as additives of polyurea grease for steel/steel contacts were evaluated on an Optimol SRV-IV oscillating reciprocating friction and wear tester and an MRS-1J (G) four-ball tester at room and high temperatures. The friction test results showed that the ILs, as 1 wt% additives in polyurea grease for steel/steel contacts, had better friction reduction and anti-wear properties at high temperature than at room temperature, and ILs can significantly improve the friction reduction and anti-wear properties of polyurea grease compared with base grease containing 1 wt% of zinc dialkyldithiophosphate (T204). The excellent tribological properties are attributed to the formation of a surface protective film composed of FeF₂, nitrides, and compound containing the P–O bonding on the lubricated metal surface by a tribochemical reaction. The ordered adsorbed films and good miscibility of ILs with the base grease also contributed to the excellent tribological properties. Wear mechanisms and worn steel surfaces were studied by a PHI-5702 multifunctional X-ray photoelectron spectrometer and a JSM-5600LV scanning electron microscope.     

Effects of Glass-to-Rubber Transition on the Friction Properties of ZrO2 Reinforced Polybenzoxazine Nanocomposites

The present work is a generic study to examine the effects of the glass-to-rubber transition of resin matrix on the friction and wear characteristics of zirconium oxide (ZrO₂) reinforced polybenzoxazine nanocomposites, in relation to the content of ZrO₂. The thermal and tribological properties of the nanocomposites were measured by dynamic mechanical thermal analysis (DMA) and friction test, respectively. DMA results revealed that the storage modulus and T _g values of the nanocomposites increased with increasing ZrO₂ content to 4 wt%, due to the exceptional mechanical strength of ZrO₂ particles and the interfacial adhesion between ZrO₂ and matrix to restrict the segmental motion of polymer. The friction coefficient (COF) values as a function of applied load (50?C750?N) for the nanocomposites under testing temperatures (50, 100, 200, 250, and 300?°C) were measured. Comparable to the pure resin, the nanocomposites possessed relatively higher COF values with the increase of applied pressure under varying temperatures, which resulted from the reinforcement of ZrO₂. It is noted that the nanocomposites containing 4 wt% ZrO₂ occupied relatively higher modulus and glass transition temperature, resulting in better capability to stabilize the friction coefficient and wear rate under the applied conditions. In addition, the friction mechanism of the nanocomposites were proposed based on the experimental and reference results.     

Wear properties of two-phase Al2O3/ZrO2 (Y2O3) ceramics at temperatures from 296 to 1073 K

Reciprocating sliding friction experiments were conducted with various two-phase, directionally solidified Al₂O₃/ZrO₂ (Y₂O₃) pins sliding on B₄C flats in air at temperatures of 296, 873, and 1073 K under dry sliding conditions. Results indicate that all the Al₂O₃/ZrO₂ (Y₂O₃) ceramics, from highly Al₂O₃-rich to ZrO₂-rich, exceed the main wear criterion requirement of 10⁻⁶ mm³ N⁻¹ m⁻¹ or lower for effective wear-resistant applications. Particularly, the eutectics and Al₂O₃-rich ceramics showed superior wear properties. The composition and microstructure of Al₂O₃/ZrO₂ (Y₂O₃) ceramics played a dominant role in controlling the wear and friction properties. The controlling mechanism of the ceramic wear, friction, and hardness was an intrinsic effect involving the resistance to shear fracture of heterophase bonding and cohesive bonding and the interlocking microstructures at different scales in the ceramics.     

Microstructure and tribological characteristics of ZrO2–Y2O3 ceramic coatings deposited by laser-assisted plasma hybrid spraying

ZrO₂–Y₂O₃ ceramic coatings were deposited on AISI 304 stainless steel by both a low-pressure plasma spraying (LPPS) and a laser-assisted plasma hybrid spraying (LPHS). Microstructure and tribological characteristics of ZrO₂–Y₂O₃ coatings were studied using an optical microscope, a scanning electron microscope, and an SRV high-temperature friction and wear tester. The LPHS coatings exhibit distinctly reduced porosity, uniform microstructure, high hardness and highly adhesive bonding, although more microcracks and even vertical macrocracks seem to be caused in the LPHS coatings. The ZrO₂ lamellae in the LPHS coatings before and after 800°C wear test consist mainly of the metastable tetragonal (t′) phase of ZrO₂ together with small amount of c phase. The t′ phase is very stable when it is exposed to the wear test at elevated temperatures up to 800°C for 1 h. The friction and wear of the LPHS coatings shows a strong dependence on temperature, changing from a low to a high wear regime with the increase of temperature. At low temperatures, friction and wear of the LPHS coatings is improved by laser irradiation because of the reduced connected pores and high hardness in contrary to the LPPS coating. However, at elevated temperatures, the friction and wear of the LPHS coatings is not reduced by laser irradiation. At room temperature, mild scratching and plastic deformation of the LPHS coatings are the main failure mechanism. However, surface fatigue, microcrack propagation, and localized spallation featured by intersplat fracture, crumbling and pulling-out of ZrO₂ splats become more dominated at elevated temperatures.     

Effect of Particle Concentration on Tribological Properties of ZnO Nanofluids

In this research, oleic acid surface-modified ZnO nanoparticles were successfully dispersed into 60SN base oil. The distribution of ZnO nanoparticles in the lubricant was tested by transmission electron microscopy. The friction and wear properties of nanofluids were evaluated with a four-ball tester, and the morphologies of wear scars were measured by a scanning electron microscope (SEM) and a surface profiler. Results show that oleic acid can improve the stability of ZnO nanoparticles in the lubricant; oil-based nanofluids with ZnO nanoparticles could remarkably reduce friction and wear. When the amount of oleic acid added was 8 wt% and ZnO nanoparticles was 0.5 wt%, the coefficient of friction and average diameter of the wear scars were minimum and the fluid exhibited better friction-reducing and antiwear properties.     

Lubrication effectiveness investigation on the friendly capped MoS2 nanoparticles

The compatibility and effectiveness of nanoparticles with the existing additives in formulated oil are still unclear. In the present study, some lubricant additives were selected to modify nanoparticles to obtain friendly capped nano‐MoS₂. Various polyisobutyleneamine succinimide (PIBS) concentrations were applied to investigate the lubrication effectiveness of capped nano‐MoS₂. The results showed that the reduction in COF and wear volume of friendly capped nanoparticles without PIBS reached about 35% and 75% in comparison with those of the base oil respectively. However, the average coefficient of friction and wear volume loss of nano oil increased with PIBS concentration in the range of 0.05%–1%. By scanning electron microscope, energy‐dispersive X‐ray spectroscopy and X‐ray photoelectron spectroscopy analysis, it is identified that (i) MoS₂ tribofilm was formed on the wear track for the oil with nano‐MoS₂ and (ii) wear scar was smooth for nano‐MoS₂ with low PIBS concentration and without PIBS, while it showed plowing wear when containing high PIBS concentration. Copyright © 2016 John Wiley & Sons, Ltd.     

Mechanical properties and tribological behavior of ZrO<Subscript>2</Subscript> thin films deposited on sulfonated self-assembled monolayer of 3-mercaptopropyl trimethoxysilane

A silane coupling reagent (3-mercaptopropyl)trimethoxysilane (abridged as MPTS) was self-assembled on a single-crystal Si substrate to form a two-dimensional organic monolayer (MPTS-SAM). The terminal –SH group in the MPTS-SAM film was in-situ oxidized to –SO₃H group to endow the film with good chemisorption ability. Then ZrO₂ thin films were deposited on the oxidized MPTS-SAM by way of the enhanced hydrolysis of aqueous zirconium sulfate (Zr(SO₄)₂·4H₂O) in the presence of aqueous HCl at 50 °C, making use of the chemisorption ability of the –SO₃H group. The thickness of the ZrO₂ films was determined with an ellipsometer, while their morphologies and corresponding friction forces were analyzed by means of atomic force microscopy. The hardness and elastic modulus of the ZrO₂ thin films were determined on a Nanoindentation II (MET) instrument. The macro-friction and wear behaviors of the ZrO₂ films sliding against an AISI-52100 steel ball were examined on a unidirectional friction and wear tester and the worn surface morphologies observed on a scanning electron microscope (SEM). As the results, the as-deposited ZrO₂ thin film at a deposition duration of 100 h is about 100 nm thick, it decreases to 48 nm after annealing at 500 °C and further decreases to 45 nm after heating at 800 °C. The as-deposited ZrO₂ film is relatively rougher, with the rms to be about 1.0 nm, while the ZrO₂ thin films heated at 500 and 800 °C have surface roughness rms of 0.76 nm and 0.68 nm, respectively. The ZrO₂ film annealed at 800 °C has a high hardness to elastic modulus (H/E) ratio (0.062) as compared to the as-deposited ZrO₂ film and the film annealed at 500 °C. Both the two annealed ZrO₂ films show excellent wear-resistance as they slide against AISI-52100 steel at a normal load below 2.0 N, while the one annealed at 800 °C has better wear-resistance. The differences in the friction and wear behaviors of the as-deposited ZrO₂ film, the ZrO₂ film annealed at 500 °C and that annealed at 800 °C are attributed to their different micro structures and compositions. Since the ZrO₂ films was well adhered to the underlying MPTS-SAM, it might find promising application in the surface-protection of single crystal Si and SiC subject to sliding at small normal load in microelectromechanical systems (MEMS).     

Characterisation of ZrO2 layers deposited on Al2O3 coating

The paper describes a method of coating combining two different layer types. The first layer is Al₂O₃ produced by plasma spraying with a thickness of around 200 μm which was deposited on a stainless steel substrate. Subsequently, ZrO₂ layers were deposited on to the Al₂O₃ coating by a sol–gel process using a dip coating technique. The dip coating process was repeated in order to see the influence of the number of ZrO₂ layers. Moreover, the effect of annealing temperature was investigated. In order to study their tribological behaviour, the coatings were subjected to micro-scale abrasion, scratch testing and ball-on-disc tests. The result shows that sol–gel ZrO₂ top layers reduce friction and enhance the wear resistance of the coating system.