Worn Steel Surfaces Research Articles

Imidazolium Ionic Liquids As Antiwear and Antioxidant Additive in Poly(ethylene glycol) for Steel/Steel Contacts

Three imidazolium-based ionic liquids containing sterically hindered phenol groups were synthesized. The cation was 1-(3,5-ditert-butyl-4-hydroxybenzyl)-3-methyl-imidazolium, and the anions were tetrafluoroborates, hexafluorophosphates, and bis(trifluoromethylsulfonyl)imide. The physical properties of the synthetic products and of poly(ethylene glycol) (PEG) with the additive were evaluated. The oxidative stability of 0.5 wt % 1-(3,5-di-tert-butyl-4-hydroxybenzyl)-3-methyl-imidazolium hexafluorophosphates in PEG were assessed via rotating bomb oxidation test (RBOT), thermal analysis, and copper strip test. The tribological behaviors of the additives for PEG application in steel/steel contacts were evaluated on an Optimol SRV-IV oscillating reciprocating friction and wear tester as well as on MRS-1J four-ball testers. The worn steel surface was analyzed by a JSM-5600LV scanning electron microscope and a PHI-5702 multifunctional X-ray photoelectron spectrometer. RBOT test, thermal analysis, and copper strip test results revealed that synthesized ionic liquids possessed excellent antioxidant properties. Tribological application results revealed that these could effectively reduce friction and wear of sliding pairs compared with the PEG films used without the additives. Specifically, (BHT-1)MIMPF(6) exhibited better antiwear properties at an optimum concentration of 1 wt %. At this level, its antiwear property significantly improved by 100 times with respect to using just the PEG base oil. Boundary lubrication films composed of metal fluorides, organic fluorines, organic phosphines, and nitride compounds were formed on the worn surface, which resulted in excellent friction reduction and antiwear performance.

Synthesis, Physicochemical, and Tribological Characterization of S-Di-n-octoxyboron-O,O′-di-n-octyldithiophosphate

Dialkyldithiophosphates (DTPs) of zinc(II), copper(II), and other metals have been extensively used as multifunctional additives in lubricants to control friction and reduce wear in mechanical systems. Among these DTP compounds, zinc dialkyldithiophosphates (ZnDTPs) are the most common additives extensively used for more than 60 years. These additives form a protective film on steel surfaces and, thus, control friction and reduce wear. However, ZnDTPs contain zinc and large amounts of phosphorus and sulfur, which impair the environment, both directly and indirectly, by adversely affecting the performance of catalytic converters of various automobiles. For this reason, environmental legislation imposes limitations on concentrations of phosphorus, sulfur, and zinc in the lubricants. In this work, we report on zinc-free S-di-n-octoxyboron-O,O'-di-n-octyldithiophosphate (DOB-DTP) lubricant additive with amount of phosphorus and sulfur reduced by half in a molecule as compared with ZnDTPs. DOB-DTP was synthesized by a reaction in two steps under inert nitrogen atmosphere. The final product, a viscous liquid, was characterized by the elemental analysis, FT-IR, multinuclear (1)H, (13)C, (31)P, and (11)B NMR spectroscopy and thermal analyses. Tribological performance of a mineral oil with this new additive was evaluated in comparison with O,O'-di-n-butyl-dithiophosphato-zinc(II) (ZnDTP) using a four-ball tribometer. The surface morphology and the elemental composition of the tribofilms were characterized using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS). The results show that DOB-DTP has a considerably better antiwear performance and higher stability of the coefficient of friction with time as compared with ZnDTP. Both phosphorus and sulfur were detected by the EDS on the worn steel surfaces at all concentrations of additives in the base oil.

Performance and anti‐wear mechanism of Cu nanoparticles as lubricating oil additives

PurposeThe purpose of this paper is to study the tribological performance and anti‐wear mechanism of Cu nanoparticles as lubricating oil additives.Design/methodology/approachAn end‐face wear testing apparatus is used to measure the tribological properties of Cu nanoparticles as lubricating oil additives and using a commercial SJ 15W/40 gasoline engine oil for comparison. Electrical contact resistance (ECR) is measured on a universal nano and micro tester‐2 tribometer to detect the formation of tribo‐film generated by Cu nanoparticulate additive. The worn steel surfaces are investigated by scanning electron microscope (SEM), energy dispersive spectra (EDS) and X‐ray photoelectron spectroscopy (XPS).FindingsThe results show that Cu nanoparticles used as an oil additive can improve the anti‐wear and friction‐reduction performance of SJ 15W/40 gasoline engine oil remarkably. The results of SEM, EDS and XPS show that a deposit film containing metallic copper can form on the worn surface, which has a film thickness of about 120 nm.Originality/valueThis investigation establishes a baseline of Cu nanoparticles used as lubricating oil additives under face‐to‐face contact work conditions. Thus, the results are reliable and can be very useful for further applications of Cu nanoparticle additives in industry.

Characterization and nano-mechanical properties of tribofilms using Cu nanoparticles as additives

Cu nanoparticles were dispersed into SN 650 oil to improve the lubricating properties of the oil and in-situ generate a thin copper film on the rough steel surface in the process of sliding friction. SEM, XPS and nano-indentation tester were utilized to investigate the morphology, chemical state and nano-mechanical properties of the film, respectively. Results show that the friction-reducing and anti-wear properties of SN 650 oil have been improved by adding Cu nanoparticles. A metallic copper film, with a low hardness and a thickness of approximately 5 μm, has been formed on the worn steel surface under the lubrication of SN 650 oil containing 1 wt.% Cu nanoparticles. The film, which bonds well with the substrate steel by a metallurgical bonding, separates the two contact surfaces and provides a fast relaxation of the contact stress. An ideal tribological structure with a soft surface film and a hard sub-surface has been formed on the worn surface, which was considered as the main reason why Cu nanoparticles possessed the excellent tribological properties.

Acoustic Emission Signals and Wear Phenomena on Severe-Mild Wear Transition

The relationship between acoustic emission (AE) signals and wear phenomena in severe-mild wear transition is discussed on the basis of the results of observations of wear particles and worn surfaces of steel. Each wear mode, severe wear or mild wear, is reproduced for a different sliding velocity. The influence of relative humidity on mild wear is examined. We found a reduction in the true area of contact and the size of wear particles decreases the AE signal level in severe-mild wear transition. In the mild wear mode, an increase in the number of transfer particles lying between the sliding surfaces decreases the AE signal level. Further, a linear relationship is observed between the AE mean value and the specific wear rate, regardless of the wear mode. This is because the AE signals generated by the formation and removal of transfer particles mainly originate under conditions of repeated dry rubbing.

Tribological investigation of CaF 2 nanocrystals as grease additives

Calcium fluoride (CaF 2) nanocrystals with average grain size of 60 nm were synthesized via a precipitation method. The morphology and structure of nanocrystals were characterized by means of transmission electron microscopy (TEM) and X-ray powder diffraction (XRD). TEM and XRD showed that CaF 2 nanocrystals are cubic particles in submicron scale. The tribological properties of the prepared CaF 2 nanocrystals as an additive in lithium grease were evaluated with a four-ball tester. The results indicated that these nanocrystals exhibit excellent antiwear, friction reduction and extreme pressure (EP) properties. It was also found that the EP and antiwear capabilities of the grease are not proportional to the content of CaF 2 nanocrystals but there existed a certain value. The rubbed surface after friction test was investigated with X-ray photoelectron spectroscopy and scanning electron microscopy to understand the action mechanism. The results show that a boundary film mainly composed of CaF 2, CaO, iron oxide and some organic compounds was formed on the rubbed surface after friction test and the thickness of boundary film was about 12 nm. The disproportion of stoichiometric ratio of Ca and F in boundary lubrication film indicates that tribochemical reaction of CaF 2 nanocrystals occurred on the worn steel surface at severe tribological conditions.

High temperature tribological behaviors of nano-diamond as oil additive

The tribological behaviors of the nano-diamond particles including the nano-diamond and the nano-diamond modified were studied at high temperature using SRV multifunctional test system. The worn steel surfaces were analyzed by means of X-ray photoelectron spectroscopy (XPS). The results show that nano-diamond particles can obviously improve the antiwear and friction reducing properties of the base oil at high temperature and the high load. The friction coefficient of the nano-diamond is very low at 200 °C when the test load is not more than 20 N. This tribological behaviors should attributed to the similarly to “ball bearing” lubrication action of the nano-diamond particles, so the movement between tribological pairs become sliding/rolling. The nano-diamond modified by dimer ester possesses excellent antiwear and friction reducing performance at 500 °C and load 500 N. The tribochemical reaction film between the nano-diamond particles and the renascent wear surface plays dominating lubrication role and the presence of the dimer ester on the rubbing surface can be propitious to form lubrication film containing nano-diamond on the worn surface at high temperature and high load.

Friction-reducing and antiwear behavior of metal halide-stabilized linear phosphazene derivatives as lubricants for a steel-on-steel contact

A series of novel metal halide-stabilized linear phosphazene derivatives were synthesized. The friction-reducing and antiwear abilities of the resulting products as the lubricants for a steel-on-steel contact were comparatively investigated on an Optimol SRV oscillating friction and wear tester. The morphology of the worn steel surface was observed on a scanning electron microscope, while the chemical states of some typical elements on the worn steel surface were examined by means of X-ray photoelectron spectroscopy. It was found that both the side branch structures and central metals influenced the friction-reducing and antiwear behaviors of the synthetic derivatives as the lubricants, which was related to the different adsorption activities of the organic compounds composed of different organic ingredients and metallic ions on a nascent metal surface. All the synthetic lubricants except for the iron (III) derivative showed increased antiwear abilities with increasing metallic ionic radius. A protective layer originated from the tribochemical reaction together with the adsorbed boundary lubricating layer containing organic fluorine compounds, nitrogen oxide, and Fe3(PO4)2 plays an important role in improving the friction and wear behavior of the steel-on-steel system.

Effect of polyethylene-graft-maleic anhydride as a compatibilizer on the mechanical and tribological behaviors of ultrahigh-molecular-weight polyethylene/copper composites

Ultrahigh-molecular-weight polyethylene/copper (UHMWPE/Cu) composites compatibilized with polyethylene-graft-maleic anhydride (PE-g-MAH) were prepared by compression molding. The effects of the compatibilizer on the mechanical, thermal, and tribological properties of the UHMWPE/Cu composites were investigated. These properties of the composites were evaluated at various compositions, and worn steel surfaces and composite surfaces were examined with scanning electron microscopy and X-ray photoelectron spectroscopy. The incorporation of PE-g-MAH reduced the melting points of the composites and increased their crystallinity to some extent. Moreover, the inclusion of the PE-g-MAH compatibilizer greatly increased the tensile rupture strength and tensile modulus of the composites, and this improved the wear resistance of the composites. These improvements in the mechanical and tribological behavior of the ultrahigh-molecular-weight-polyethylene-matrix composites with the PE-g-MAH compatibilizer could be closely related to the enhanced crosslinking function of the composites in the presence of the compatibilizer. Moreover, the compatibilizer had an effect on the transfer and oxidation behavior of the filler Cu particulates, which could be critical to the application of metallic-particulate-filled polymer composites in engineering. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 948–955, 2004

The tribological behavior of thiophosphates as additives in rapeseed oil

Two kinds of thiophosphate, tri- n-octyl thiophosphate and tri- n-octyl tetrathiophosphate, were synthesized. The tribological behavior of the synthetic compounds and tricresyl phosphate as additives in rapeseed oil for steel-steel frictional pair was investigated with a four-ball machine. The relationship between the additive structure and tribological properties was explored, while the lubrication mechanisms of the additives were investigated as well. Thus the worn surfaces of the steel ball lubricated with the additive-containing rapeseed oil were analyzed by means of X-ray photoelectron spectrometry and scanning electron microscopy, and the elemental compositions and distributions in the worn steel surfaces were observed and determined with an EPMA-810Q electron probe micro-analyzer. It has been found that the synthetic thiophosphates as additives in rapeseed oil at proper concentrations show better tribological properties than tricresyl phosphate. Tribochemical reactions were involved for steel–steel frictional pair lubricated with the rapeseed oil containing thiophosphates, with the formation of a boundary lubricating and protecting film composed of glyceride of rapeseed oil and tribochemical reaction products of the lubricants. This contributes to improve the tribological properties of the rapeseed oil base stock.

The tribological behaviour and mechanism of action of sulphur‐containing borate esters in rape seed oil

AbstractThree sulphur‐containing borate esters and one borate ester based on boric acid and n‐octanol were synthesised. The antiwear and friction‐reducing properties of these synthetic compounds as additives in rape seed oil were examined using a four‐ball machine. The relationship between the additive structure and tribological properties was explored, and the lubrication mechanisms of the additives investigated. The worn surfaces of a steel ball lubricated with the additive‐containing rape seed oil were analysed using X‐ray photoelectron spectroscopy and scanning electron microscopy. The elemental compositions of, and distributions in, the worn steel surfaces were determined with an electron probe micro‐analyser. It was found that sulphur‐containing borate esters as additives in rape seed oil at appropriate concentrations can be effective in improving antiwear and friction‐reducing behaviour. The rape seed oil base stock experiences competitive adsorption and tribochemical reactions with additives on the rubbing steel surface. The introduction of the active element sulphur into the borate ester additives functions to improve the tribological behaviour of the base stock by increasing the rate of formation of a protective layer on the rubbing steel surface. However, the tribological behaviour of the additives is not dependent on the number of sulphur atoms in the additive molecules, and further work is needed to investigate the possible dependence of this behaviour on the ratio of boron to sulphur in the additive molecules.

The tribological behaviors of succinimide-modified lanthanum hydroxide nanoparticles blended with zinc dialkyldithiophosphate as additives in liquid paraffin

Lanthanum hydroxide nanoparticles modified with succinimide (coded as Succ-nano La) were prepared in laboratory. The tribological behavior of the synthesized nanoparticles blended with zinc dialkyldithiophosphate (ZDDP) as additives in liquid paraffin (LP) to a total concentration of 5 wt.% was investigated on a four-ball machine. The surface morphologies and elemental distributions of the worn steel ball surfaces were examined with scanning electron microscopy (SEM) and electron probe microanalysis (EPMA), respectively. The chemical states of some typical elements on the worn steel surfaces were analyzed with X-ray photoelectron spectroscopy (XPS). As a result, the best extreme pressure behavior was obtained at a weight fraction of 1:4 for Succ-nano La/ZDDP. The best antiwear ability was obtained at a weight fraction of 2:3 or 3:2 for Succ-nano La/ZDDP, which was accompanied by a parallel improvement in friction-reduction. Surface films consisting of La 2O 3, ZnO 2, sulfides, N-containing organic compounds and P-containing compounds were detected. The improvement in the friction-reduction and antiwear properties was attributed to these tribochemical products.

Influence of Surface Roughness and Oil Ageing on Various Ceramic-Steel Contacts under Boundary Lubrication

The friction and wear behaviour of four structural ceramics (two aluminium oxides of different purity, a silicon nitride and a tetragonal zirconia polycrystal) have been investigated under boundary lubrication against a 100C6 hard steel (52100 steel). The effect of three initial surface roughnesses of the ceramics is studied. Lubrication is by a commercial oil used ‘as received’ (new oil) and ‘aged’ (used oil). Tests are performed on an alternating ‘pin-on-plate’ tribometer. The friction and wear responses are analysed in terms of three main parameters depending on the mechanical preparation mode of the ceramics surface: the roughness magnitude, the morphology of the asperities (sharps or blunts) and the mechanical strength of the asperities. The evolution of these parameters during sliding leads to significant changes of tribological behaviour and contact pressure. The friction and wear transitions result from changes of the lubrication mode where roughness and oil have a competitive action. The wear processes of the ceramic surfaces include fracture mechanisms of the asperities and/or polishing by the mechanochemical action of the lubricant and submicronic ceramic wear debris. The worn surfaces of steel exhibit either abrasion grooves or a continuous metallic layer covering the steel. A running-in effect is observed on both silicon nitride and zirconia but does not occur on aluminas. The stronger running-in effect is observed with used oil. The used oil can lead to a very smooth sliding surface on the ceramic and allows particularly low friction coefficients and steel wear, but only after a more severe initial degradation process ESCA analyses on steel reveal the occurrence of a reaction film generated through chemical reactions with the oil.

Changements de régime de lubrification dans les contacts rugueux acier-céramiques

The friction and wear behaviour offour structural ceramics (two aluminium oxides of different purity, a silicon nitride and a tetragonal zirconia polycrystal) has been investigated under boundary lubrication against a 100C6 hard steel (52100 steel). The effect of three initial surface roughnesses of the ceramics is studied. Lubrication is by a commercial oil used as received(new oil) and aged (used oil). Tests are performed on an alternating pin-on-platetribometer. The friction and wear responses are analysed in terms of three main parameters depending on the mechanical preparation mode of the ceramics surface : the roughness magnitude, the morphology of the asperities (sharp or blunt) and the mechanical strength of the asperities. The evolution of these parameters during sliding leads to significant changes of tribological behaviour and contact pressure. The friction and wear transitions result from changes of lubrication mode where roughness and oil have a competitive action. The wear processes of the ceramic surfaces include fracture mechanisms of the asperities and/or polishing by the mechano-chemical action of the lubricant and submicronic ceramic wear debris. The worn surfaces of steel exhibit either abrasion grooves or a continuous metallic layer covering the steel. A running in effect is observed on both silicon nitride and zirconia but does not occur on aluminas. The stronger running-in effect is observed with used oil. The used oil can lead to a very smooth sliding surface on the ceramic and allows particularly low friction coefficients and steel wear, but only after a more severe initial degradation process. ESCA analyses on steel reveal the occurrence of reaction film generated through chemical reactions with the oil.

The abrasive wear of steel during rolling-sliding contact with rock counterfaces

In many mining operations ( e.g. excavation, drilling, tunnelling, rock crushing), metallic components are forced against abrasive rocks in a complex motion. This study examines the relative importance of combined rolling and sliding motion in the two-body abrasive wear of a low carbon tempered martensitic steel against rock counterfaces. A novel wear test rig has been used to vary the amount of rolling and sliding motion between a rotating steel cylinder and a counter-rotating sandstone (highly abrasive) or limestone (much less abrasive) disc. Weight loss measurements reveal that the wear rate of the steel increases as the amount of motion against the rock counterface is reduced from pure sliding to about 50% sliding (and about 50% rolling). With further reductions in the amount of sliding motion, the wear rate of the steel is reduced because of the formation of corrugations on the sandstone and limestone rock surfaces. Scanning electron microscopy shows that when the amount of motion is reduced from pure sliding to about 50% sliding, the topographical and subsurface physical properties of the worn steel and rock surfaces are modified. Following large amounts of sliding motion (70–80% sliding), the worn steel surface is heavily deformed by shearing in the sliding direction and many of the minerals in the worn rock counterface are crushed and compacted. Reducing the motion to 50% sliding leads to a reduction in the depth of the plastically sheared layer in the worn steel, and the rock surface shows a considerable reduction in the amount of mineral crushing and compaction, with many of the abrasive grains maintaining some angularity. It is concluded, therefore, that the increasing wear rate of the steel with the amount of rolling motion, until the onset of rock surface corrugations, probably results from the rock counterface retaining a higher proportion of angular abrasive minerals.

Grinding and Abrasive Wear

To explore the relationship between grinding and abrasive wear, a range of differing experiments has been performed. These include simple wear tests, dynamometer measurements of grinding forces, simple scratch tests with both idealized indentors and abrasive grits, and the microscopic examination of abrasive wheels and worn surfaces of steel. It is suggested that grinding and abrasive wear should be regarded as essentially similar mechanisms. The anomalies which occur with heat-treated steels, of a range of hardness, in both grinding and abrasive wear may be attributable to the influence of ploughing which affects the efficiency of the action of individual grits.