Influence of Steel Type on the Propensity for Tribochemical Wear in Boundary Lubrication with a Wind Turbine Gear Oil

Tribochemical wear may occur at the interface between a surface and a lubricant as a result of chemical and mechanical interactions in a tribological contact. Understanding the onset of tribochemical wear damage on component surfaces requires the use of high resolution techniques such as transmission electron microscopy (TEM). In this study, two steel types, case carburized AISI 3310 and through-hardened AISI 52100, were wear tested using a ball-on-disk rolling/sliding contact tribometer in fully formulated commercial wind turbine gearbox oil under boundary lubrication conditions with 10% slip. With the exception of steel type, all other test conditions were held constant. Conventional tribofilm analysis in the wear tracks was performed using X-ray photoelectron spectroscopy, and no significant composition differences were detected in the tribofilms for the different steel disk types. However, TEM analysis revealed significant tribochemical wear differences between the two steel types at multiple length scales, from the near-surface material microstructure (depth < 500 nm) to the tribofilm nanostructure. Nanometer-scale interfacial cracking and surface particle detachment was observed for the AISI 52100 case, whereas the tribofilm/substrate interface was abrupt and undamaged for the AISI 3310 case. Differences in tribofilm structure, including the location and orientation of MoS₂ single sheet inclusions, were observed as a function of steel type as well. It is suggested that the tribochemical wear modes observed in these experiments may be origins of macroscopic surface-initiated damage such as micropitting in bearings and gears.     

Tribochemical Processes and Wear Resistance of Polymeric Materials

Tribochemical transformations of polyphenylquinoxaline (PPQ) and a composite material on its basis containing graphite are investigated. A mass-spectrometric analysis shows that in the polymer surface layers the destructive-structurizing processes occur on friction that changes the structure and properties of the surface layer. It is shown that, in the presence of a graphite filler, the tribochemical transformation character also changes. Based on the investigation data, a general scheme of tribochemical changes of PPQ is proposed and their relation to wear is suggested.     

Tribochemical behaviour of the selected mesogenic additive in n-hexadecane

Summary Tribochemical behaviour of the selected mesogenic compound (4-butylcyclohexanoic acid p-hexaoxyphenyl ester) was investigated by means of ball-on-disk machine at ambient and elevated temperatures. To selection of the thermal conditions of tribological tests DSC technique was used and to analyse tribochemical products layered on the wear tracks—SEM/EDS, FTIRM and XPS ones. Obtained results show that the mesogen dissolved in n-hexadecane is an effective antiwear additive which decreases temperature of the lubricant. This is favoured mainly by tribochemical processes.     

Tribochemical Wear of Rail Steels Lubricated with Synthetic Ester-Based Model Lubricants

Headchecks are a common type of damage in heavily loaded curved freight tracks. This paper deals with synthetic ester formulations' ability to prevent damage caused by headchecks through mild tribochemical wear. An experimental study pertaining to wear and friction of two rail steels lubricated by two synthetic ester base fluids, TMP-oleate and TMP-C₈-C₁₀, has been carried out. Six different free fatty acids were used in this study to act as performance additives. Three of the fatty acids were mono-acids with different, straight, carbon chain lengths (stearic acid C₁₈, decanoic acid C₁₀ and octanoic acid C₈), one was a mono-unsaturated straight-chain fatty acid (oleic acid C_18:1) while two were dibasic acids with intermediate carbon chain length (C₉ and C₁₀). Each fatty acid was blended with either ester, one at a time. The tests were carried out by using a high frequency reciprocating friction and wear test machine. In these tests, the gage face/wheel flange contact was simulated, and all tests were conducted in the boundary lubrication regime. An initial contact pressure of 316 MPa and a maximum sliding speed of 0.11 m/s were employed during the tests. The tests showed a wide range of wear rates, as well as different surface features depending on the interactions between synthetic esters, fatty acids and steel. The use of stearic and azaleic acid in lubricating rail steels results in very smooth surfaces with significant differences in their wear rates.     

Tribochemical effects on the friction and wear behaviors of diamond-like carbon film under high relative humidity condition

Friction and wear behaviors of diamond-like carbon (DLC) film in humid N₂ (RH-100%) sliding against different counterpart ball (Si₃N₄ ball, Al₂O₃ ball and steel ball) were investigated. It was found that the friction and wear behaviors of DLC film were dependent on the friction-induced tribochemical interactions in the presence of the DLC film, water molecules and counterpart balls. When sliding against Si₃N₄ ball, a tribochemical film that mainly consisted of silica gel was formed on the worn surface due to the oxidation and hydrolysis of the Si₃N₄ ball, and resulted in the lowest friction coefficient and wear rate of the DLC film. The degradation of the DLC film catalyzed by Al₂O₃ ball caused the highest wear rate of DLC film when sliding against Al₂O₃ ball, while the tribochemical reactions between DLC film and steel ball led to the highest friction coefficient when sliding against steel ball.     

Tribological Characteristics and Tribochemical Reactions of Various Ceramics Lubricated with HFC-134a Gas

The role of tribochemical products in the friction and wear reduction of ceramics with different fractional ionic character in CF₃CH₂F (HFC-134a) gas was investigated using a ball-on-disk type tribometer. Without exposure to air, the wear tracks on the disks were characterized with the aid of a micro-spot X-ray Photoelectron Spectroscope (XPS) whose analytical chamber was connected to the friction chamber of the tribometer. Further, the adsorption and desorption behaviors of HFC-134a molecules on the nascent surfaces of the ceramics were studied using an adsorption test apparatus in high vacuum. It was found that the lubricating effect of HFC-134a gas was closely related to the fractional ionic or covalent characters of the ceramics. HFC-134a gas was more effective in lubricating ionic ceramics than the covalent ceramics. XPS analysis revealed that metal fluorides were mainly formed on the frictional surfaces of the ionic ceramics, whereas the composition of the tribochemical products on the frictional surfaces of the other ceramics was complicated. The adsorption tests proved that HFC-134a was decomposed to an olefin CF₂=CHF on the nascent surfaces of the ionic ceramic Al₂O₃ and the covalent ceramics. However, the formation of organic fluorine-containing compounds was not detected on the frictional surfaces of the ionic ceramics by XPS. This result implies that the mechanism of tribochemical reactions is strongly dependent on the bond type of ceramics. It is concluded that the low friction and wear of the ionic ceramics in HFC-134a gas result from the metal fluorides formed with high surface concentration on the sliding surfaces.     

Tribochemical behavior of Ni ion implanted pure iron lubricated with ZDDP as an additive

An investigation of the tribochemical behavior of Ni ion implanted pure ionwas performed. Ni ion implantation increases the wear resistance of pure iron by 30–120% when liquid paraffin is used as lubricant. The wear resistance of ion implanted pure iron increases with increase in surface residual compressive stress, and decreases with increase in microhardness. When liquid paraffin containing zinc dialkyldithiophosphates (ZDDP) is used as lubricant, the wear resistance of a Ni ion implanted specimen is lower than that of an unimplanted one. This is because the wear of the specimen is controlled by the properties and amount of the antiwear reaction film, and the mechanical strengthening induced by Ni ion implantation plays a less important role in affecting the wear rate than the tribochemical effects. The existence of Ni element in the implanted pure iron retards the reactions of iron with active elements S and Zn from the additive, reduces the amount of surface antiwear film formed during the wear process, and changes the compositions of the films.     

摩擦化学反应对发动机油润滑耐久性能的影响

利用SRV高温摩擦磨损试验机比较了两种分别属于GF-2和GF-3等级，含有MoDTC摩擦改进剂的发动机油的耐久性。结果表明，由于GF-3等级发动机油能使活塞环和缸套试样表面更加平整光滑，且由于Ca清静剂与MoDTC／ZDTP的协同作用，通过摩擦化学反应，在摩擦表面形成良好的摩擦反应膜，从而使它拥有更好的润滑耐久性能。     

Tribochemical Effects on Tribological Properties of Self-Mated Zirconia Ceramic in HFC-134a Gas

Tribochemical effects on the tribological properties of self-mated zirconia ceramic in CF₃CH₂F (HFC-134a) were investigated using a ball-on-disk type environmental tribometer. The friction chamber of the tribometer was attached to a micro-spot X-ray Photoelectron Spectrometer (XPS) for ensuring that surface analysis be conducted without exposuring the frictional surfaces to air. It was found that HFC-134a gas was an effective lubricant for zirconia ceramic, especially at a pressure higher than 10³ Pa. The products of tribochemical reactions between zirconia and HFC-134a molecules were detected. The amount and chemical state of the tribochemical products seemed to control the tribological behaviors. Thus, the role of tribochemical products on the tribological properties of zirconia in HFC-134a gas at 10⁴ Pa was studied in detail under applied loads of 0.6–5.0 N and sliding speed of 0.04–0.35 m/s. It was found that severe tribochemical reactions occurred at low speeds and high loads. The formation of ZrF₄ accelerated the chemical wear of zirconia, and raised the friction. Zirconia ceramic is suitable for use at moderate load and sliding speed under a reactive environment.     

Experimental Simulation of Tribochemical Reactions Between Borates Esters and Steel Surface

In this study, tribochemical reactions of borate ester additives on steel surfaces were simulated experimentally by gas phase lubrication. Trimethylborate (TMB) was employed as a model molecule of the borate chemical function. TMB was introduced under gas phase up to 5 hPa in a new tribometer dedicated to gas phase lubrication. Friction tests were conducted at room temperature. In order to identify the nature of the generated tribofilm, X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) analyses were carried out inside and outside the track of the tested samples. The results showed a reduction of the friction coefficient down to 0.2 by increasing the TMB gas pressure. This reduction in friction was induced by the formation of a tribofilm of iron oxide partially digested by a borate glass network. The reduction in friction was attributed to the formation of the borate glass. The digestion of abrasive iron oxides by the borate glass was purported to be responsible for the reduction in the wear. The tribochemical reaction of TMB on steel surfaces is discussed in relation to the hard and soft acid base (HSAB) principle.     

Tribochemical interactions of Si-doped DLC film against steel in sliding contact

This study concerns the effects of tribochemical interactions at the interface of Si-DLC (silicon-doped diamond-like carbon) film and steel ball in sliding contact on tribological properties of the film. The Si-DLC film was over-coated on pure DLC coating by radio frequency plasma-assisted chemical vapor deposition (r.f. PACVD) with different Si concentration. Friction tests against steel ball using a reciprocating type tribotester were performed in ambient environment. X-Ray photoelectron spectroscopy (XPS) and auger electron spectroscopy (AES) were used to study the chemical characteristics and elemental composition of the films and mating balls after tests. Results showed a darkgray film consisting of carbon, oxygen and silicon on the worn steel ball surface with different thickness. On the contrary, such film was not observed on the surface of the ball slid against pure DLC coating. The oxidation of Si-DLC surface and steel ball was also found at particular regions of contact area. This demonstrates that tribochemical interactions occurred at the contact area of Si-DLC and steel ball during sliding to form a tribofilm (so called transfer film) on the ball specimen. While the pure DLC coating exhibited high coefficient of friction (∼0.06), the Si-DLC film showed a significant lower coefficient of friction (∼0.022) with the presence of tribofilm on mating ball surface. However, the Si-DLC film possesses a very high wear rate in comparison with the pure DLC. It was found that the tribochemical interactions strongly affected tribological properties of the Si-DLC film in sliding against steel.     

Tribochemical and Thermochemical Reactions of Stearic Acid on Copper Surfaces Studied by Infrared Microspectroscopy

The tribochemistry of copper with stearic acid was studied using a pin-on-disc wear tester under boundary lubrication conditions. Wear, as measured by surface profilometry, indicated that stearic acid was able to reduce the wear fourfold. Surface analysis by Fourier Transform Infrared (FTIR) microspectroscopy revealed that cupric stearate was formed during the rubbing process by tribochemical reactions. The reaction product was confirmed by model compounds and was also found to be comparable with those from the static thermal experiments of stearic acid on copper surface at 140°C-160°C. The affinity between the chemisorbed stearic acid and bidentate copper stearate complex is believed to be responsible for the formation of a protective film on the copper surfaces to reduce the wear from further propagation.     

Tribochemical Reactions and Lubricating Effects of Fluorinated Methanes for Al2O3 Ceramic

It has been found that CF₃CH₂F (HFC-134a) gas is an effective lubricant for several ceramics because of the formation of fluorine-containing tribochemical products. To understand the influence of the molecular structure of fluorine-containing gases on the lubricating characteristics, the lubricating effects and tribochemical reactions of some fluorinated methanes for Al₂O₃ ceramic were studied. X-ray Photoelectron Spectroscopy (XPS) and Time-of-Flight Secondary Ion Mass Spectroscopy (TOF-SIMS) were used to identify the chemical structure of tribochemical products. It was found that the friction and wear of Al₂O₃ ceramic were dependent on the molecular structure of the reacting fluorocarbon gases. The lowest friction was obtained in CH₂F₂. CHF₃ showed the best anti-wear effect. The results of surface analyses indicate that greater amounts of tribochemical products are produced when Al₂O₃ rubs in CH₂F₂ than in CF₄ and CHF₃ gases. C–C/C–H/carbon and AlF₃, which are mainly formed on the sliding surface in CH₂F₂, are responsible for the low friction. The mechanism of tribochemical reactions of the different environmental molecules on the nascent surface of Al₂O₃ was also discussed.     

Tribochemical interactions between Zndtp,Modtc and calcium borate

Tribochemical interactions between antiwear zinc dithiophosphate (Zndtp), friction modifier molybdenum dithiocarbamate (Modtc) and overbased detergent calcium borate (OCB) lubricant additives have been investigated. Friction tests were performed in mild wear conditions under boundary lubrication, in order to enhance tribochemical surface effects. The nature of tribofilms formed was studied by coupling high‐resolution TEM on wear fragments and inside‐wear‐scar, micro‐spot XPS in the same location of the wear track (so‐called dual analysis). The performance of the Modtc/Zndtp mixture is mainly due to the generation of MoS₂ single sheets and the digestion of MoO₃ in the zinc polyphosphate glass formed. The final result of the tribochemical reaction is a two‐phase tribofilm composed of (i) non‐oriented MoS₂ sheets (friction modifier) embedded in a carbon‐rich phase and (ii) a mixed Zn/Mo polyphosphate glass (antiwear). The Modtc/OCB mixture has a similar antiwear mechanism except that the oxide is not completely eliminated, due to the softer action of borate anion compared with phosphate one. Compared to the data obtained with binary combinations (Modtc/Zndtp, Modtc/OCB and Zndtp/OCB), we show here that the ternary system Modtc/Zndtp/OCB provides both a low wear rate and an ultralow friction value, while adding detergent and anti‐corrosive properties to the formulation. Our analytical data indicate that the synergistic effect can be attributed to an outstanding nanostructure of the tribofilm formed. It is composed of a single‐phase material containing perfectly oriented MoS₂ single sheets embedded in a calcium and zinc borophosphate glass. The ternary system produces a smart material in the interface, because both functions (antiwear and friction reduction) are correlated. Compared to phosphate alone, the mechanism by which MoS₂ sheets have been oriented in the borophosphate could be related to aligned molecules of the glassy polymer in the direction of sliding. This revised version was published online in July 2006 with corrections to the Cover Date.     

Tribochemical Reactions of Cutting-Edge Material During Secondary Wood-Product Cutting

In this paper, evidence of tribochemical reactions of a cutting-edge material during cutting of secondary wood products (SWP) is reported. The heat of frictional contact of the cutting edge with material of the SWP is a source of rapidly increasing temperature in the cutting zone. Once the cutting edge reaches a certain level of wear, the temperatures generated are high enough to initiate thermal decomposition of the basic components of the material being cut. Applying Quantum Chemical (QC) methods, with semiempirical results verified using Density Functional Theory (DFT), it was determined that some products of thermal degradation of the principal components of SWP stabilize cobalt, from the cobalt binder in cemented carbide tool material, in an oxidized state via octahedral hydroxy organometallic complexes.     

Tribochemical effects on the friction and wear behaviors of a-C:H and a-C films in different environment

Friction and wear behaviors of hydrogenated amorphous carbon (a-C:H) and hydrogen-free amorphous carbon (a-C) films sliding against Si₃N₄ balls were investigated in different testing environments. The result showed that two films with extreme chemical disparity (one hydrogenated, and the other hydrogen free) showed distinct different friction and wear behaviors, and the friction and wear behaviors of the both films were strongly dependent on the environment. For a-C:H films, much low friction coefficient and wear rate were obtain in dry N₂. In the water and/or oxygen containing environments, the friction coefficient and wear rate of a-C:H films were obviously increased. On the contrary, a-C films only provided low friction coefficient and wear rate in the presence of water and/or oxygen in the test chamber. In dry N₂, the highest friction coefficient and wear rate were observed for a-C films. By investigating the worn surfaces of the films using XPS, it was proposed that the environment dependence of the friction and wear behaviors of the films was closely related with the friction-induced chemical interactions between the films and water and/or oxygen molecules. The specific roles of hydrogen, water and oxygen molecules and their tribochemical effects on the friction and wear mechanism of the films are discussed.     

Tribochemical synthesis of zinc ferrite

A comparative tribochemical study of zinc ferrite synthesis from -FeOOH + 2ZnCO₃·3Zn(OH)₂ and -FeOOH + 2ZnCO₃·3Zn(OH)₂ was carried out. It was found that the end product of tribochemical activation is thermally unstable, partially inverse, zinc ferrite, (Zn_0.74Fe_0.26)_tetra[Fe_1.74Zn_0.26]_octaO₄. The synthesis kinetics is rate-limited by the tribochemical dehydration of the two polymorphous forms of Fe(III) oxyhydroxides and is considerably higher for the -FeOOH + 2ZnCU₃ · 3Zn(OH)₂ system.     

Pressure Dependence of ZnDTP Tribochemical Film Formation: A Combinatorial Approach

Combinatorial testing has been performed on zinc dialkyldithiophosphate (ZnDTP)-containing lubricants, to investigate the effects of contact pressure on the formation of tribochemical films. Contact pressures ranging from 25 to 500 MPa were applied in ball-on-disc tribotests with oscillating load. Both the ball and the disc were investigated by means of small-area and imaging X-ray photoelectron spectroscopy (XPS). The thickness and the composition of the reaction layer were estimated from the XPS data. The thickness of the reaction layer in the tribologically stressed areas of the ball and of the disc increased with both temperature and contact pressure. The reaction layer mainly consisted of short-chain poly(thio)phosphates, shorter chains being observed at higher contact pressures. At high pressures, the presence of a thick, high-toughness short-chain poly(thio)phosphate layer can explain the lower friction and dimensional wear coefficients observed. On the ball, similar anti-wear film formation mechanisms were observed as on the disc, zinc sulphide being deposited in the post-contact region.     

Tribochemical machining of polycrystalline diamond using ferrous tool materials

Abstract

This article studies the tribochemical machining of polycrystalline diamond (PCD) by utilizing ferrous tool material as the cutter. The influence of cutting parameters and different ferrous materials on the material removal rate of the PCD workpiece has been investigated. The material removal rate increases with the increase of the rpm of ferrous “cutter”, AISI 1020 steel is unable realize the tribochemical machining, and the material removal rate of using AISI 1045 steel was higher than that of using W2-21/2 steel, e.g. when rpm was 3000, the material removal rate of using AISI 1045 was 0.059?mm/min, and using W2-21/2 it was 0.020?mm/min. The surface roughness of the machined PCD workpiece using W2-21/2 (0.40?μm) was slightly improved in comparison to that produced using AISI 1045 (0.47?μm). The influence of hydrogen catalysis on tribochemical machining of PCD has been investigated. Compared with no use of steam, if a large amount of steam is continuously injected the material removal rate will significantly increase, e.g. when the rpm was 3000 (using AISI 1045) the material removal rate of no steam was 0.059?mm/min, while with steam it was 0.082?mm/min.     

Tribochemical Reactions of Ionic Liquids Under Vacuum Conditions

Ionic liquids are expected to function as novel lubricants owing to their attractive characteristics such as high thermal stability and low vapor pressure. In order for ionic liquids to be used as lubricants, knowledge of their corrosion and lubricating properties must be obtained. However, the reaction mechanism and decomposition of ionic liquids have not yet been sufficiently clarified. In this study, we elucidate the tribological properties and tribochemical reaction mechanism by analyzing outgassing generated by the decomposition or reaction of ionic liquids [EMIM][DCN], [EMIM][TCB], and [BMPL][TCB] on a sliding surface. From our results, [BMPL][TCB] showed the lowest friction coefficient and [EMIM][DCN] had a lower friction coefficient than [EMIM][TCB]. In all cases, outgassing from the ionic liquid was confirmed, and main outgassing products were derived from the cation. [BMPL][TCB] had the largest amount of outgassing. Time-of-flight secondary ion mass spectroscopy analysis showed that tribochemical reactions involving the anion occurred. From sliding tests and experimental analyses, it is revealed that the [DCN] anion showed superior lubricating properties to the [TCB] anion.