Tribochemical Reaction Film Research Articles

Effect of Nitrogen Atoms Number and Spatial Location on Tribological Properties of Nucleobase Derivatives

Four kinds of ashless, non-phosphorus and non-sulfur oil-soluble compounds of nucleobase derivatives were evaluated as lubricant additives in poly(ethylene glycol) (PEG) for steel–steel contact under room temperature, and their electrochemical corrosion behaviors were measured by Tafel polarization. The morphologies and chemical features of the worn surfaces were investigated by scanning electron microscope and X-ray photoelectron spectroscopy (XPS). The results showed that the nucleobase derivatives as 2 wt% additive show excellent load-carrying capacity, friction-reducing and anti-wear performance. It is also found that the tribological performance of the two purine derivatives is better than that of the two pyridine derivatives. The corrosion behaviors of four PEGs with 2 wt% different nucleobase derivative additives on pure coppers exhibit much better than those of pure PEG. The XPS results indicated the excellent tribological properties are attributed to the formation of tribochemical adsorption and chemical reaction films on the worn surfaces, which may prevent the sliding surfaces from straight asperity contact and markedly improve friction-reducing and anti-wear behaviors.

Tribological Properties of Oleylamine-Modified Ultrathin WS2 Nanosheets as the Additive in Polyalpha Olefin Over a Wide Temperature Range

Ultrathin WS2 nanosheets modified by oleylamine (OM) were prepared via a solution-phase method at a relatively high temperature of 300 °C. The thermal stability of the as-prepared WS2 nanosheets was evaluated by thermogravimetric analysis. The tribological properties of as-synthesized WS2 nanosheets as the additive in polyalpha olefin (PAO6) were evaluated with a four-ball machine and a reciprocating tribometer over a wide temperature range from room temperature to 200 °C. The morphology and elemental composition of worn steel surfaces were analyzed with a scanning electron microscope, a three-dimensional optical profiler, an energy dispersive spectrometer and an X-ray photoelectron spectroscope. Results show that OM as the modifier is able to improve the dispersibility of WS2 nanosheets in PAO6 base oil. At a mass fraction of 2.0 % in PAO6 base oil, as-synthesized WS2 nanosheets exhibit excellent antiwear and friction-reducing performance over the selected temperature range. This is because as-synthesized WS2 nanosheets as the additive in PAO6 are able to form adsorbed film with a low shear force and tribochemical reaction film composed of W, Fe and O elements on the worn steel surface.

Friction and Wear Characteristics of Hot-Pressed NiCr–Mo/MoO3/Ag Self-Lubrication Composites at Elevated Temperatures up to 900 °C

NiCr-based high-temperature self-lubricating composites with Ag/Mo/Ag–MoO3/Ag–Mo were prepared by the powder metallurgy method, respectively. The mechanical and tribological properties of the composites rubbing against alumina balls were investigated from room temperature to 900 °C. The tribo-chemical reaction films formed on the sliding surface and their effects on the tribological properties of composites at different temperatures were analyzed by SEM and Micro-Raman. The results showed that the triboloical properties of NiCr-based composites were improved by adding alloying elements or a solid lubricating phase; meanwhile, the composites containing Ag–MoO3 or Ag–Mo exhibited even better triboloical properties than those with Mo or Ag at high temperatures. The lowest friction coefficient of the NCr–MoO3–Ag composite is around 0.19 and that of the NiCr–Mo–Ag composite is around 0.20; both composites exhibited an optimal wear rate in the order of magnitude of 10−6 mm3 N−1 m−1 at high temperatures. XRD and Micro-Raman results indicated that the composition of the tribo-layers formed on the worn surface of the composites varies with different testing temperatures. Compounds such as Ag2MoO4, NiCr2O4 and NiO, which formed on the rubbing surface at high temperature, worked synergistically to improve the tribological properties of the NiCr-based composite at high temperatures.

Improving Tribological Properties of Multialkylated Cyclopentanes under Simulated Space Environment: Two Feasible Approaches.

Space mechanisms require multialkylated cyclopentanes (MACs) more lubricious, more reliable, more durable, and better adaptive to harsh space environments. In this study, two kinds of additives were added into MACs for improving the tribological properties under simulated space environments: (a) solid nanoparticles (tungsten disulfide (WS2), tungsten trioxide (WO3), lanthanum oxide (La2O3), and lanthanum trifluoride (LaF3)) for steel/steel contacts; (b) liquid additives like zinc dialkyldithiophosphate (ZDDP) and molybdenum dialkyldithiocarbamate (MoDTC) for steel/steel and steel/diamond-like carbon (DLC) contacts. The results show that, under harsh simulated space environments, addition of the solid nanoparticles into MACs allows the wear to be reduced by up to one order magnitude, while liquid additives simultaneously reduce friction and wear by 80% and 93%, respectively. Friction mechanisms were proposed according to surface/interface analysis techniques, such as X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (TOF-SIMS). The role of solid nanoparticles in reducing friction and wear mainly depends on their surface enhancement effect, and the liquid additives are attributed to the formation of tribochemical reaction film derived from ZDDP and MoDTC on the sliding surfaces.

In Situ Fabrication of Low-Friction Sandwich Sheets Through Functionalized Graphene Crosslinked by Ionic Liquids

Graphene is considered a wonder material for fundamental research and industrial application, whereas its poor dispersibility and incompatibility in lubricants have impeded the application for solving lubrication problems. Here, in situ fabrication of effectively functionalized graphene sheets was developed through a moderate electrochemical method for exfoliating graphite into graphene sheets in ionic liquids solution. The as-fabricated graphene sheets with the charged groups of ionic liquids (ILs) could be self-assembled together to form the multilayer sandwich structure through the electrostatic interaction. Self-assembly multilayer graphene (MLG) exhibits so high-density coverage of functional groups that some amorphous regions are formed on the graphene basal plane, which significantly improves its dispersibility and stability in ILs lubricant. Moreover, the functionalized MLG as a novel lubricant additive greatly enhances the friction-reducing and antiwear abilities for the contact of steel/steel (friction coefficient and wear volume lubricated by ILs with MLG at applied load of 200 N and 150 °C were reduced by up to 55.9 and 84.2 %, and under high vacuum were reduced by up to 36 and 94.3 % with pure ILs as a comparison, respectively), which is attributed to the synergies of ILs and MLG because ILs with functionalized MLG can form the physical adsorptive film and tribo-chemical reaction film on the rubbing surface during friction process.

Preparation and characterization of CrAlN/TiAlSiN nano-multilayers by cathodic vacuum arc

Superhard CrAlN/TiAlSiN nano-multilayers deposited at various substrate bias voltages were produced on the surface of Si (100) wafers and high-speed steels by cathodic vacuum arc. The microstructures of these coatings were investigated systematically by X-ray diffraction (XRD), X-ray photoelectron spectroscope (XPS), scanning electron microscope (SEM) and high-resolution transmission electron microscope (HRTEM), in association with mechanical property characterization. The HRTEM observation shows that these coatings have a nano-multilayer structure containing alternatively fcc-(Cr,Al)N sublayer and amorphous sublayer with some nanocrystalline fcc-(Ti,Al)N phases embedded in this amorphous matrix. The coherent epitaxial growth structure is observed along the {100} crystal plane of the fcc-(Cr,Al)N phase and the {100} crystal plane of the fcc-(Ti,Al)N phase. The orientation relationship between them is as follows: {100}(Cr,Al)N//{100}(Ti,Al)N and [001](Cr,Al)N//[001](Ti,Al)N. Mechanical property characterization shows that the coating hardness is dependent on the substrate bias voltages, and the friction coefficients of these coatings with a higher substrate bias voltage are found to be much lower than those of the coatings deposited at a lower substrate bias voltage. The improvement of the friction coefficient is attributed mainly to the formation of tribochemical reaction films. In addition, the much lower friction coefficient can also be related to the higher hardness and fracture toughness.

Preparation of lanthanum trifluoride nanoparticles surface-capped by tributyl phosphate and evaluation of their tribological properties as lubricant additive in liquid paraffin

LaF3 nanoparticles surface-capped by tributyl phosphate (denoted as TBP–LaF3) were prepared by in situ surface modification route. The size, morphology and phase structure of as-prepared TBP–LaF3 nanoparticles were analyzed by means of X-ray diffraction and transmission electron microscopy. The thermal stability of as-synthesized TBP–LaF3 nanoparticles was evaluated based on thermogravimetric analysis, and their tribological properties as additive in liquid paraffin were evaluated with a four-ball friction and wear tester. Moreover, the morphology of worn steel surfaces was analyzed with a scanning electron microscope, and the composition and chemical state of typical elements on worn steel surfaces were examined with an X-ray photoelectron spectroscope. Results show that as-synthesized TBP–LaF3 nanoparticles possess good thermal stability and excellent anti-wear and load-carrying capacities as well as good friction-reducing ability. This is because, on the one hand, TBP as the surface-modifier is able to improve the dispersibility of LaF3 nanoparticles in liquid paraffin and allows good adsorption of LaF3 nanoparticles on sliding steel surfaces. On the other hand, active P element of TBP can form tribochemical reaction film on sliding steel surfaces. As a result, the boundary lubricating film consisting of adsorbed LaF3 nanoparticles and tribochemical reaction film results in greatly improved friction-reducing and anti-wear abilities as well as load-carrying capacity of the lubricant base stock and gives rise to significantly reduced friction and wear of the steel–steel sliding pair.

Study of the Conductivity and Tribological Performance of Ionic Liquid and Lithium Greases

Ionic liquid (IL) lubricating greases were prepared using 1-hexyl-3-methylimidazolium tetrafluoroborate and 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl) amide as base oil and polytetrafluoroethylene (PTFE) as thickener, respectively. Three kinds of lithium greases were also prepared using lithium ILs ([Li(PAG)]X) as base oil and PTFE as thickener. 1-Ethyl-3-methyl imidazolium hexafluorophosphate as an additive was added to the PAG grease, which was prepared using polyalkylene glycol monobutyl ether (PAG) as base oil and PTFE as thickener. The conductivities and tribological properties of the prepared lubricating greases were investigated in detail. Scanning electron microscopy and X-ray photoelectron spectroscopy were employed to explore the friction and wear mechanism. The results showed that the IL and lithium lubricating greases have conductivities and excellent tribological properties. Especially, IL greases have the highest conductivity. The excellent tribological properties are attributed to the formation of boundary films consisting of both tribo-chemical reaction films and physical absorption films, while high conductivities are attributed to the intrinsic electric fields of the ILs.

Tribological Properties and Wear Mechanisms of NiCr–Al2O3–SrSO4–Ag Self-Lubricating Composites at Elevated Temperatures

NiCr–Al2O3–SrSO4–Ag self-lubricating composites were prepared by powder metallurgy method and the tribological properties of composites were evaluated by a ball-on-disk tribometer against alumina ball at wide temperature range from the room temperature to 1,000 °C in air. The linear coefficient of thermal expansion was evaluated for investigation of thermal stability of composites. The tribo-chemical reaction films formed on the rubbing surfaces and their effects on the tribological properties of composites at different temperatures were addressed according to the surface characterization by SEM, XRD, and XPS. The results show that the NiCr–Al2O3 composite with addition of 10 wt% SrSO4 and 10 wt% Ag exhibits satisfying friction and wear properties over the entire temperature range from room temperature to 1,000 °C. The composition of the tribo-layers on the worn surfaces of the composites is varied at different temperatures. The synergistic lubricating effect of SrAl4O7, Ag, and NiCr2O4 lubricating films formed on worn surfaces were identified to reduce the friction coefficient and wear rate from room temperature to 800 °C. Meanwhile, at 1,000 °C, the SrCrO4 and NiAl2O4 was formed on the worn surfaces during sliding process, combining with the NiCr2O4, Al2O3, Cr2O3, Ag, and Ag2O, which play an important role in the formation of a continuous lubricating film on the sliding surface.

Tribological Properties of Adaptive Ni-Based Composites with Addition of Lubricious Ag2MoO4 at Elevated Temperatures

The Ni-based self-lubricating composites with addition of 10 and 20 wt% Ag2MoO4 were fabricated by powder metallurgy technique, and the effect of Ag2MoO4 on tribological properties was investigated from room temperature to 700 °C. The tribo-chemical reaction films formed on rubbing surface and their effects on the tribological properties of composites at different temperatures were addressed according to the surface characterization by SEM and Micro-Raman. The results show that the Ag2MoO4 decomposed into Ag and Mo during the high-temperature fabrication process. The friction coefficient and wear rate of the composites decrease with the increasing of temperature and Ag2MoO4 contents and the composites with addition of 20 wt% Ag2MoO4 exhibits the lowest friction coefficient (0.26) and wear rate (1.02 × 10−5 mm3 N−1 m−1) at 700 °C. The composition of the tribo-layers on the worn surfaces of the composites is varied at different temperatures. It is proposed that the improving of tribological properties of the composites at high temperatures are attributed to the synergistic lubricating effect of silver molybdate (reproduced in the rubbing process at high temperatures) and Fe oxide (transfer from disk material to the pin) formed on the worn surface.

Tribological Behaviors of Nanocrystalline Nickel Coatings under Lubricated Conditions

In this paper, nickel coatings (on phosphor bronze substrates) were prepared using pulse electrodeposition method. The friction and wear behaviors of nanocrystalline nickel coating compared with coarse-grained nickel coating against AISI 52100 steel were investigated using l-butyl-3-octylimidazolium tetrafluoroborate ionic liquid and perfluoropolyether as a reference lubricant on reciprocating ball-on-flat UMT-2MT 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. The results indicated that NC nickel coatings have better tribological properties than that of coarse-grained nickel coatings under lubricated conditions. This was partly attributed to the high hardness of the NC nickel coating and L-B408 ionic liquid formed tribochemical reaction films under NC nickel coatings.

Base medium effect on the tribological behavior of oil‐water double soluble bismuth dithiophosphate

Purpose – The purpose of this paper is to understand the effect of base media on the tribological performance and tribochemistry of bismuth thiophosphate additive.Design/methodology/approach – The oil‐water double soluble additive bismuth dithiophosphate was prepared and identified. The contributions of the two base media on the additive tribological behavior and the tribofilm components were comparatively studied.Findings – The extreme pressure (EP) and friction‐reducing properties are remarkably improved with water substituted for paraffin as the base medium. The EP performance of the lubricating media containing this additive mainly results from the tribochemical reaction film on the rubbing surface, not from the viscosity of the base media. In water or paraffin medium, the adsorption process of this additive from the lubricant bulk onto the rubbing surface and the components and the properties of the tribochemical reaction films formed are different, which have important effect on the tribological per...

The study on lubrication action with water vapor as coolant and lubricant in cutting ANSI 304 stainless steel

Water vapor is a new type of environmental friendly coolant and lubricant. In this study, the friction test was carried out by using the water vapor as lubricant, and the friction pair was made of cement carbide K20 and ANSI 304 stainless steel. In order to study the lubricating action of water vapor as coolant and lubricant in cutting ANSI 304 stainless steel, experiments were carried out with K20 cutter. Through chemical state analyses of elements on tool–chip interface by means of XPS and Gibbs free energy calculation, the chemical reaction process was discussed between water molecule, oxygen atom and fresh tool–chip interface. Experimental results showed that an adsorption film and a tribo-chemical reaction film are formed on the tool–chip surfaces due to its excellent penetration performance and ability to form boundary lubrication layer. The multi-dimensional metal-oxide formed during the reaction weaken the mutual action between tool bulk material and chip. The cutting force and tool flank wear are reduced rapidly, and hence the tool wear is reduced about 50–75% compared with dry machining.

Imidazolium hexafluorophosphate ionic liquids as high temperature lubricants for steel–steel contacts

A series of long-chain 1,3-dialkyl imidazolium ionic liquids (ILs) were synthesized and evaluated as lubricants for steel–steel contacts both at room temperature and 150 °C. Relationship between the alkyl chain length and the tribological properties of the ILs was investigated in detail. The results indicated that the ILs bearing long alkyl side chains have excellent friction-reducing and anti-wear properties, especially at high temperatures and high loads. The worn surfaces of steel discs were observed and analyzed by scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). The friction reduction and load carrying capacity were supposed to be due to the formation of high quality boundary films consisting of both tribochemical reaction film and the ordered absorption film.

Superlow friction behavior of Si-doped hydrogenated amorphous carbon film in water environment

Si-doped hydrogenated amorphous carbon (a-C:H:Si) film was prepared using hybrid radio frequency plasma-enhanced chemical vapor deposition (R.F. PECVD) and non-balanced magnetron sputtering deposition technique. The microstructure of the film was characterized by means of Raman spectrometry, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD), while its friction behavior in water environment was investigated using a ball-on-disc tribometer. Results show that the a-C:H:Si film has typical diamond-like characteristics, and Si doped with a relative atomic concentration of about 3.9% in the film mainly exists in the form of Si, SiC, and SiO 2, while it shows a superlow friction coefficient of about 0.005 in water environment when sliding against Si 3N 4 ball. The superlow friction behavior of the hybrid diamond-like-carbon (DLC) film could be attributed to the formation of a tribochemical reaction film and boundary lubrication layer mainly consisting of colloidal silica generated from tribochemical reactions between silicides and water molecules.

Friction and Wear Properties of Cyanex 302-Modified MoS2 Micro-Sized Spheres as Additive in Liquid Paraffin

The friction and wear properties of MoS 2 micro-sized spheres (MS-MoS2) modified by Cyanex 302 (bis(2,4,4-trimethylpentyl) monothiophosphinic acid) as additive in liquid paraffin (LP) were studied and compared with those of commercial colloidal MoS 2 (CC-MoS 2 ) on a four-ball tester and an Optimol SRV oscillating friction and wear tester in a ball-on-disc contact configuration. The worn surfaces were examined with SEM and XPS, respectively. The results showed that the Cyanex 302-modified MS-MoS 2 was a better extreme-pressure and antiwear and friction-reducing additive in LP than CC-MoS 2 . The boundary lubrication mechanism could be deduced as the effective chemical adsorption film formed by the alkyl and active elements (S, O, and P) in Cyanex 302 and tribochemical reaction and deposition film containing MoS 2 , Fe 2 O 3 , and FePO 4 . Moreover, the coexistence of sliding and rolling frictions in the lubricant of MS-MoS 2 /LP also contributed to the enhanced tribological properties.

Tribological properties of Cyanex 301‐modified MoS2 nano‐sized hollow spheres in liquid paraffin

PurposeThe purpose of this paper is to investigate the tribological properties of MoS2 nano‐sized hollow spheres in liquid paraffin (LP) and the corresponding action mechanism. Morever, its feasibity of industrial application as an oil additive in the industrial lubrication field is also explored.Design/methodology/approachThe tribological properties of MoS2 nano‐sized hollow spheres (NH‐MoS2) modified by Cyanex 301(di‐(2,4,4‐trimethylpentyl) dithiophosphinic acid) with size of 200 ∼ 300 nm in LP are studied and compared with those of the commercial colloidal MoS2 (CC‐MoS2) on a four‐ball tester and an Optimol SRV Oscillating friction and wear tester in a ball‐on disk configuration. The worn surfaces of the lower flat disc are examined with a scanning electron microscopy and an X‐ray photoelectron spectroscopy, respectively.FindingsResults show that NH‐MoS2 is a better extreme‐pressure additive and anti‐wear (AW) and friction‐reducing additive in LP than CC‐MoS2. Under the optimum concentration of 0.5 per cent for both NH‐MoS2 and CC‐MoS2 and the load of 400 N, the friction coefficient of NH‐MoS2 + LP and CC‐MoS2 + LP decreases about 43.8 and 6.3 per cent, and the wear volume loss decreases about 60.3 and 12.0 per cent compared with the pure LP. The boundary lubrication mechanism for NH‐MoS2 + LP can be deduced as the effective chemical adsorption protective film formed by the long chain alkyls R and active elements (S and P) in the modification layer and tribochemical reaction film containing the tribochemical products of the additive. Moreover, sliding and rolling frictions co‐exist in NH‐MoS2 + LP, doing contributions to the good tribological properties as well.Originality/valueIn this paper, the Cyanex 301‐modified MoS2 nano‐sized hollow spheres with diameter of 200 ∼ 300 nm are firstly added into LP to investigate its tribological properties. The excellent AW and friction‐reducing properties indicate that this MoS2 hollow spheres product is a good oil additive, and the fundamental data presented here will be useful for its further industrial application in the future.

Sliding friction and wear performance of Ti 6Al 4V in the presence of surface-capped copper nanoclusters lubricant

The friction and wear properties of Ti 6Al 4V 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 Ti 6Al 4V 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 Ti 6Al 4V under Cu-DTP lubricating. The frictional experiment of the Ti 6Al 4V 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 Ti 6Al 4V 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 Ti 6Al 4V 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 Ti 6Al 4V under Cu-DTP at the high-applied load.

Investigation of the Tribological Properties of Surfactant-Modified MoS2 Microsized Spheres in Base Oil 500 SN

The tribological properties of MoS2 microsized spheres (MS-MoS2) with diameter of 0.5–3μm modified by self-prepared surfactant quaternary ammonium salt of 2-undecyl-1-dithioureido-ethyl-imidazoline (SUDEI) as an additive in base oil 500 SN were investigated and compared with those of commercial colloidal MoS2(CC-MoS2) on a four-ball tester and an Optimol SRV oscillating friction and wear tester in a ball-on-disk contact configuration. The worn surfaces of the bottom flat disk were examined with scanning electron microscopy and X-ray photoelectron spectroscopy. It was found that the MoS2 microsized spheres product was a much better extreme-pressure additive and antiwear and friction-reduction additive in 500 SN than commercial colloidal MoS2(CC-MoS2). Under the appropriate concentration of 0.1% and 0.25% for MS-MoS2 and CC-MoS2 and the load of 400N, the friction coefficient of MS-MoS2/oil and CC-MoS2/oil decreased about 25.0% and 12.5% and the wear volume loss decreased about 50.4% and 12.9% compared with the pure base stock. The boundary lubrication mechanism could be deduced as the effective chemical adsorption film formed by the long chain alkyl (C11H23) and active elements (S and N) in the surfactant SUDEI and tribochemical reaction film composed of the tribochemical reaction products.

Study on the tribological properties of surfactant-modified MoS 2 micrometer spheres as an additive in liquid paraffin

Tribological properties of MoS 2 micrometer spheres modified by self-prepared surfactant as an additive in liquid paraffin (LP) are studied and compared with those of the commercial colloidal MoS 2 on a four-ball tester and an Optimol SRV oscillating friction and wear tester. The worn surfaces are examined with SEM and XPS, respectively. Results show that MoS 2 micrometer sphere is a much better extreme-pressure additive and anti-wear and friction-reducing additive in LP than the commercial colloidal MoS 2. The boundary lubrication mechanism can be deduced as an effective chemical adsorption protective film formed by the long chain alkyl and active elements (S and N) in the prepared surfactant and tribochemical reaction film composed of the tribochemical reaction products of the additive. Moreover, sliding and rolling frictions exist simultaneously in the MoS 2 micrometer spheres /LP lubricating system, which also do more contributions to the good tribological properties.