Tribological performance of an ionic liquid as a lubricant for steel/aluminium contacts

The wear and friction behaviour of an ionic liquid 1‐ethyl‐3‐hexylimidazolium tetrafluoroborate (L206) was investigated as a lubricant for steel/aluminium contacts using an Optimol SRV® oscillating friction and wear tester. The elemental composition and chemical nature of the antiwear films generated on the aluminium surface were analysed using a scanning electron microscope with a Kevex energy dispersive X‐ray analyser attachment (SEM/EDS) and X‐ray photoelectron spectroscopy (XPS). A low friction coefficient (˜0.05) was recorded when lubricating with L206; a small amount of water (5 wt. %) in L206 effectively reduced the wear volume and greatly increased the microhardness of the aluminium alloy, but had little effect on the friction coefficient. The SEM/EDS results showed that severe corrosive wear occurred on the aluminium alloy when lubricating with neat L206, which could be avoided by the addition of water in L206. The XPS results indicated that the species AlF₃, Al₂O₃, AlO(OH), and Al(OH)₃ formed during friction; there was no indication of boron on the worn surfaces.     

Friction and wear behaviour of plasma sprayed WC–12Co coating sliding against Si3N4 under lubrication of ionic liquids

Abstract

The friction and wear behaviour of a WC–12Co coating prepared by plasma spraying sliding against a Si₃N₄ ceramic ball, under the lubrication of liquid paraffin and ionic liquids 1-methyl-3-butylimidazolium hexafluorophosphate and 1-methyl-3-hexylimidazolium hexafluorophosphate at room temperature, was investigated using an SRV tester. The morphology and elemental distribution of the worn coating surfaces were characterised by means of scanning electron microscopy (SEM) equipped with an energy dispersive X-ray analyser (EDXA) attachment, and the chemical state of typical elements in the boundary lubricating film on the worn coating surface was analysed by means of X-ray photoelectron spectroscopy (XPS). The SEM/EDXA analysis shows that phosphorus is uniformly distributed on the worn coating surface lubricated by ionic liquids. The XPS results also indicate that the boundary lubricating film is mainly composed of CoF₂ and PF_x and the tribochemical reaction products contribute to reducing the friction and wear of the plasma sprayed WC–12Co coating.     

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?.     

Tribological Performance of Room-Temperature Ionic Liquids as Lubricant

The tribological performance of room-temperature ionic liquid of alkylimidazolium tetrafluoroborate was evaluated using an Optimol SRV oscillating friction and wear tester in air and a CZM vacuum friction tester in vacuum (1×10^-3 Pa) using a steel/steel (SAE52100) contact. From the results, the ionic liquid exhibits excellent friction-reduction, antiwear proprieties, both in air and vacuum, which are superior to phosphazene (X-1P) and perfluoropolyether (PFPE). During friction, the ionic liquid forms a surface protective film mainly composed of FeF₂ and B₂O₃, which contributes to low friction and wear.     

Effect and mechanism of additives for ionic liquids as new lubricants

Ionic liquids are unique compounds, which exhibit low viscosity, non-flammability, low vapor pressure, and extremely high thermal stability. Therefore, they are expected as candidates for advanced lubricants. Several ionic liquids, derived from cations such as imidazolium, pridinium, ammonium, and anions such as , bis(trifluoromethylsulfonyl)imide (TFSI^-) were examined under boundary conditions. It was found that tribological properties of ionic liquids are better than those of conventional lubricants such as synthetic hydrocarbons, synthetic esters, and fluorinated ethers. Careful analysis of worn surface revealed that tribochemical reactions of ionic liquids take place under these conditions. For example, organic fluoride, iron fluoride, iron sulfate derived from anionic moiety of the ionic liquids were detected by the instrumental surface-analysis with TOF-SIMS and XPS. Tricresylphosphate (TCP) and dibenzyldisulfide (DBDS) were found to improve anti-wear properties of ionic liquids to some extent. Interestingly, both additive-derived compounds and anionic moiety derived ones were detected on the worn surface. Moreover, additive response of ionic liquids was found to be superior to those for conventional lubricants. It was speculated that the unique tribochemical reactions will lead us to design tailor-made lubricants. Lubrication mechanism of ionic liquids is discussed from the viewpoint of tribochemistry.     

Investigation of wear mechanism of SiC particulate-reinforced Al-20Si-3Cu-1Mg aluminium matrix composites under dry sliding and water lubrication

Unreinforced Al-20Si-3Cu-1Mg (ASCM) aluminium alloy and SiC particle reinforced Al-20Si-3Cu-1Mg (ASCM-SiC) aluminium matrix composites were fabricated by powder metallurgy (). The samples were slid against 4Cr13 stainless steel in a reciprocal friction tester under a load of 25 N to 175 N and sliding velocity of 0.3 to 1.2 m s⁻¹ at ambient conditions. The results show that SiC particulate-reinforced aluminium matrix composites possess good wear resistance at dry sliding and less wear resistance under water lubrication. Ploughing wear is the dominant wear mechanism at dry sliding and tribochemical wear is dominant under water lubrication. SEM, AES and XPS were used to examine the wear morphology and surface chemistry.     

Crown-Type Ionic Liquids as Lubricants for Steel-on-Steel System

A series of novel imidazolium-based crown-type phosphate ionic liquid lubricants have been designed and synthesized. Because the anions of ionic liquids are organic phosphate, crown-type ionic liquids would not corrode steel. The crown-type ionic liquids exhibit better tribological properties than conventional lubricants, which were evaluated by a ball-on-flat type Optimol-SRV oscillating friction and wear tester. The chemical compositions of the boundary films generated on the steel worn surfaces were analyzed with the use of a scanning electron microscope and X-ray photoelectron spectrometer. The results indicate that crown-type ionic liquids would generate complex lubricating films, composing organometallic polymer, polyphosphate, FePO₄, Fe₃O₄, etc., lubricated under different loads to exhibit the friction reduction and anti-wear abilities.     

Friction and wear characteristics of lead and its compounds filled polytetrafluoroethylene composites under oil lubricated conditions

The friction and wear properties of Pb, PbO, Pb₃O₄, or PbS filled polytetrafluoroethylene (PTFE) composites sliding against GCr15 bearing steel under both dry and liquid paraffin lubricated conditions were studied by using an MHK-500 ring-block wear tester. The worn surfaces and the transfer films of these PTFE composites formed on the surface of GCr15 bearing steel were then investigated by using a scanning electron microscope (SEM) and an optical microscope, respectively. Experimental results show that filling Pb, PbO, Pb₃O₄ or PbS to PTFE can greatly reduce the wear of the PTFE composites, but the wear reducing action of Pb₃O₄ is the most effective. Meanwhile, PbS increases the friction coefficient of the PTFE composite, but Pb and Pb₃O₄ reduce the friction coefficients of the PTFE composites. However, the friction and wear properties of lead or its compounds filled PTFE composites can be greatly improved by lubrication with liquid paraffin, and the friction coefficients of the PTFE composites can be decreased by one order of magnitude. Optical microscope investigation of transfer films shows that Pb, PbO, Pb₃O₄ and PbS enhance the adhesion of the transfer films to the surface of GCr15 bearing steel, so they greatly reduce the wear of the PTFE composites. However, the transfer of the PTFE composites onto the surface of GCr15 bearing steel can be greatly reduced by lubrication with liquid paraffin, but the transfer still takes place. SEM examination of worn surfaces shows that the interaction between liquid paraffin and the PTFE composites creates some cracks on the worn surfaces of the PTFE composites; the creation and development of the cracks reduces the load-carrying capacity of the PTFE composites, and this leads to deterioration of the friction and wear properties of the PTFE composites filled with lead or its compounds under higher loads in liquid paraffin lubrication.     

Reduction in wear of metakaolinite-based geopolymer composite through filling of PTFE

Metakaolinite-based geopolymer composite containing 5-30% (volume fraction) polytetra-fluoroethylene (PTFE) was synthesized using compound activator composed of aqueous NaOH and sodium silicate at room temperature. Flexural strength, compressive strength and elastic modulus of the composite were measured. Tribological behaviour of the composite sliding against AISI-1045 steel was investigated on an MM-200 friction and wear tester. SEM, EDS and XPS analysis were conducted on worn surfaces and wear debris. The results show that mechanical strength of the composite was lower than corresponding geopolymer while the wear model became mild. The friction process was stable and the wear rate was dramatically reducted by 86-99.4%. The improvement of tribological properties of the composite was attributed to form a brown soft thin layer on the worn surface of the composite containing Fe₂O₃ came from tribochemical reaction. EDS analysis on the worn surfaces indicate the content of Fe increase along with the increase of volume content of PTFE in the composite. Furthermore, the counterpart, the steel ring was also protected from terrible wear as occurred when friction with geopolymer without any filling of solid lubricant. There is a brown thin layer mainly composed of Fe₂O₃ on the steel ring.     

Tribological properties of linear phosphazene oligomers as lubricants

The friction and wear behavior of a steel-on-steel contact lubricated by two novel synthetic linear phosphazene oligomers with different side branches and by perfluoropolyethers (PFPE) was comparatively investigated on an oscillating friction and wear tester. The thermal stability of the lubricants was investigated by means of thermogravimetric analysis. The worn surfaces were analyzed by means of scanning electron microscopy, energy-dispersive spectrometry, and X-ray photoelectron spectroscopy. It was found that the two synthetic linear phosphazene oligomers were more effective than PFPE in increasing the wear-resistance of the steel-on-steel frictional pair. The phosphazene oligomer having aromatic rings had better friction-reducing ability and higher thermal stability, and that having fluoropolyether gave higher load-carrying capacity. Tribochemical reaction was involved in the sliding of steel against steel under the lubrication of the lubricants, with the generation of a protective layer composed of inorganic fluoride FeF₂ and organic compounds consisting of C, F, O, N and P. The protective layer originated from the tribochemical reaction together with the adsorbed boundary lubricating layer containing organic compounds played an important role in improving the friction and wear behavior of the steel-on-steel system.     

Tribological characteristics of silicon nitride at elevated temperatures

A sliding friction-and-wear test for silicon nitride (Si₃N₄) was conducted using a ball-on-disk specimen configuration. The material used in this study was HIPed silicon nitride. The tests were carried out from room temperature to 1000°C using self-mated silicon nitride couples in laboratory air. The worn surfaces were observed by SEM and the debris particles from the worn surfaces were analyzed for oxidation by XPS. The normal load was found to have a more significant influence on the friction coefficient of the silicon nitride than an elevated temperature. The specific wear rate was found to decrease along with the sliding distance. The specific wear rate at 29.4 N and 1000°C was 292 times larger than that at room temperature. The main wear mechanism from room temperature to 750°C was caused by brittle fracture, whereas from 750 to 1000°C the wear mechanism was mainly influenced by the oxidation of silicon nitride due to the increased temperature. The oxidation of silicon nitride at a high temperature was a significant factor in the wear increase.     

Chemical structure of phosphazenes in relation to the tribological properties of a steel‐on‐steel system

The tribological behaviours of a steel‐on‐steel contact lubricated by three different fluids: (i) tetrakis(3‐trifluoromethylphenoxy)‐bis(4‐fluorophenoxy)‐cyclotriphosphazene (X‐1P), (ii) a synthetic bridged cyclotriphosphazene, and (iii) linear phosphazene derivative as base fluids were comparatively investigated on an Optimol SRV oscillating friction and wear tester. The results show that X‐1P records the lowest friction coefficient, and linear phosphazene oligomer gives the lowest wear volume loss of the steel among the investigated lubricants. Moreover, the bridged cyclotriphosphazene shows much better anti‐wear ability than cyclotriphosphazene (X‐1P) at both room and elevated temperatures. The worn surfaces were analysed by means of scanning electron microscopy, energy dispersive spectrometry and X‐ray photoelectron spectroscopy. The results demonstrate that the protective layer originated from the tribochemical reaction together with the adsorbed boundary lubricating layer containing organic F‐containing compounds; nitrogen oxide and FeF₂ played an important role in improving the friction and wear behavior of the steel‐on‐steel system. Copyright © 2009 John Wiley & Sons, Ltd.     

Ionic liquid lubrication of electrodeposited nickel–Si3N4 composite coatings

Nano-Si₃N₄ particles were electrodeposited with nickel on copper substrate from a Ni bath. The friction and wear properties of the Ni/Si₃N₄ composite coating were evaluated while being lubricated with several various oils using a ball-on-disk sliding tester. The morphologies of the worn surfaces were observed using a scanning electron microscope. The chemical states of several typical elements on the worn surfaces were examined by means of X-ray photoelectron spectroscopy (XPS). Results indicated that the electrodeposited Ni/Si₃N₄ composition coating had excellent tribological properties while being lubricated with the ionic liquid. This was partly attributed to the high hardness of the electrodeposited nickel composite coating containing nano-sized Si₃N₄ and the tribochemical reaction between the lubricant and the sliding surface.     

Friction and wear behavior of Ni-P coated Si3N4 reinforced Al6061 composites

Al6061 matrix composite reinforced with nickel coated silicon nitride particles were manufactured by liquid metallurgy route. Microstructure and tribological properties of both matrix alloy and developed composites have been evaluated. Dry sliding friction and wear tests were carried out using pin on disk type machine over a load range of 20-100 N and sliding velocities of range 0.31-1.57 m/s. Results revealed that, nickel coated silicon nitride particles are uniformly distributed through out the matrix alloy. Al6061-Ni-P-Si₃N₄ composite exhibited lower coefficient of friction and wear rate compared to matrix alloy. The coefficient of friction of both matrix alloy and developed composite decreased with increase in load up to 80 N. Beyond this, with further increase in the load, the coefficient of friction increased slightly. However, with increase in sliding velocity coefficient of friction of both matrix alloy and developed composite increases continuously. Wear rates of both matrix alloy and developed composites increased with increase in both load and sliding velocity. Worn surfaces and wear debris was examined using scanning electron microscopy (SEM) for possible wear mechanisms. Energy dispersive spectroscope (EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscope (XPS) techniques were used to identify the oxides formed on the worn surfaces and wear debris.     

The Effect of Hot Extrusion on Mechanical and Tribological Behavior of Ag-Cu/MoS2 Composites

Silver–copper/molybdenum disulfide (Ag-Cu/MoS₂) composites, prepared by powder metallurgy and hot press sintering, were extruded at a temperature of 680°C with extrusion ratios of 10 and 70. Mechanical tests and tribotests were carried on both the hot-pressed and hot-extruded composites. The tribological properties of the composites against a silver coin disc were investigated on a pin-on-disc tester with normal load and sliding speed of 5 N and 0.27 m/s, respectively. The microstructure, wear morphology, and cross section of the worn subsurface were observed by scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) analyses were performed on the worn surfaces of Ag-Cu/MoS₂ composites. The results indicated that the distribution of the MoS₂ particles in the composites was improved and the interfacial strength of Ag/MoS₂ was enhanced during the process of hot extrusion. The hardness, bending strength, and wear resistance of hot-extruded composites increased remarkably due to the presence of the continuous matrix skeleton and the stronger interfacial bonding of Ag/MoS₂. XPS revealed that a chemical reaction had occurred at the worn surface due to the friction heat. Although the dominant wear mechanism was fatigue wear for both the hot-pressed and hot-extruded composites, finer debris and a lower wear rate were observed in hot-extruded composites due to the fact that the nucleation and growth of cracks in the worn subsurface were restrained in the process of tribotest.     

SPN型添加剂对岩石／钢摩擦副摩擦学性能的影响

本文考察了含ＳＰＮ型添加剂的乳化液型水基润滑剂对４５钢－石灰岩摩擦副的摩擦学性能的影响。在销盘实验机进行的摩擦学实验显示这种添加剂有一定的减摩抗磨作用,用扫描电子显微镜（ＳＥＭ）和Ｘ射线光电能谱（ＸＰＳ）对摩擦副进行表面分析表明有硫磷氮等化合物的形成。     

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.     

Tribological Properties of Phosphor Bronze and Nanocrystalline Nickel Coatings Under PAO + MoDTC and Ionic Liquid Lubricated Condition

The friction and wear properties of phosphor bronze and nanocrystalline nickel coatings were evaluated using a reciprocating ball-on-plates UMT-2MT sliding tester lubricated with ionic liquid and poly-alpha-olefin containing molybdenum dialkyl dithiocarbamate, respectively. The morphologies of the worn surfaces for the phosphor bronze and nanocrystalline nickel coatings were observed using a scanning electron microscope. The chemical states of several typical elements on the worn surfaces were examined by means of X-ray photoelectron spectroscopy. Results show that the phosphor bronze and nanocrystalline nickel coatings exhibited quite different tribological behaviors under different lubricants. Phosphor bronze plate shows higher friction coefficient (0.14) and wear rate (3.2 × 10⁻⁵ mm³/Nm) than nanocrystalline nickel coatings (average friction coefficient is 0.097, wear rate is 1.75 × 10⁻⁶ mm³/Nm) under poly-alpha-olefin containing molybdenum dialkyl dithiocarbamate lubricated conditions. The excellent tribological performance of nanocrystalline nickel coatings under above lubricant can be attributed to the formation of MoS₂ and MoO₃ on the sliding surface. a quite a number of C, O and F products on worn surface of phosphor bronze than NC nickel coatings can improve anti-wear properties while using ionic liquid as lubricant.     

Tribological properties of fluorine-containing additives of silicone oil

An oil soluble fluorine-containing octadecylamine salt of decapentylfluorooctanoic acid was synthesized and characterized by Fourier transform infrared spectroscopy (FTIR), ¹H-nuclear magnetic resonance (¹H NMR) and ¹⁹F NMR. The thermal stability of octadecylamine salt of decapentylfluorooctanoic acid was measured by a thermogravimetric (TG) analysis. The anti-wear and friction-reducing properties of the amine salt as a silicone-based lubricating oil additive were evaluated using a four-ball tribotester. The results indicated that both the wear resistance and the load-carrying capacity of a silicone-based lubricating oil 4609 shock absorption liquid were improved and the friction coefficient was decreased by the additive. The wear scar, after being cleaned using an ultrasonic bath in petroleum ether, was characterized with scanning electron microscopy (SEM) and X-ray photoelectron spectrometry (XPS). It was found that the boundary film on the worn surface was composed of fluorine-containing organic film and iron fluoride such as FeF₂, which provided the oil with improved anti-wear and friction-reducing properties.     

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.