Extreme Pressure Lubrication Research Articles

Synthesis and Performance Evaluation of High-Temperature-Resistant Extreme-Pressure Lubricants for a Water-Based Drilling Fluid Gel System.

Addressing the high friction and torque challenges encountered in drilling processes for high-displacement wells, horizontal wells, and directional wells, we successfully synthesized OAG, a high-temperature and high-salinity drilling fluid lubricant, using materials such as oleic acid and glycerol. OAG was characterized through Fourier-transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). The research findings demonstrate the excellent lubricating performance of OAG under high-temperature and high-salinity conditions. After adding 1.0% OAG to a 4% freshwater-based slurry, the adhesion coefficient of the mud cake decreased to 0.0437, and at a dosage of 1.5%, the lubrication coefficient was 0.032, resulting in a reduction rate of 94.1% in the lubrication coefficient. After heating at 200 °C for 16 h, the reduction rate of the lubrication coefficient reached 93.6%. Even under 35% NaCl conditions, the reduction rate of the lubrication coefficient remained at 80.3%, indicating excellent lubrication retention performance. The lubricant OAG exhibits good compatibility with high-density drilling fluid gel systems, maintaining their rheological properties after heating at 200 °C and reducing filtration loss. The lubrication mechanism analysis indicates that OAG can effectively adsorb onto the surface of N80 steel sheets. The contact angle of the steel sheets increased from 41.9° to 83.3° before and after hot rolling, indicating a significant enhancement in hydrophobicity. This enhancement is primarily attributed to the formation of an extreme-pressure lubricating film through chemical reactions of OAG on the metal surface. Consequently, this film markedly reduces the friction between the drilling tools and the wellbore rocks, thereby enhancing lubrication performance and providing valuable guidance for constructing high-density water-based drilling fluid gel systems.

Performance of Austenitic High-Nitrogen Steels under Gross Slip Fretting Corrosion in Bovine Serum.

Modular artificial hip joints are a clinical standard today. However, the release of wear products from the head-taper interface, which includes wear particles in the nm size range, as well as metal ions, have raised concerns. Depending on the loading of such taper joints, a wide variety of different mechanisms have been found by retrieval analyses. From these, this paper concentrates on analyzing the contribution of gross slip fretting corrosion at ultra-mild wear rates using a bovine calf serum solution (BCS) as the lubricant. The parameters were chosen based on biomechanical considerations, producing wear rates of some ng/m wear path. In parallel, the evolution of tribomaterial (third bodies) was analyzed as to its constituents and generation rates. It has already been shown earlier that, by an advantageous combination of wear mechanisms and submechanisms, certain constituents of the tribomaterial remain inside the contact area and act like extreme-pressure lubricant additives. For the known wear and corrosion resistance of austenitic high-nitrogen steels (AHNSs), which outperform CoCrMo alloys even under inflammatory conditions, we hypothesized that such steels will generate ultra-mild wear rates under gross slip fretting. While testing AHNSs against commercially available biomedical-grade materials of CoCrMo and TiAlV alloys, as well as zirconia-toughened alumina (ZTA) and against itself, it was found that AHNSs in combination with a Ti6Al4V alloy generated the smallest wear rate under gross slip fretting corrosion. This paper then discusses the wear behavior on the basis of ex situ analyses of the worn surfaces as to the acting wear mechanisms and submechanisms, as well as to the tribological reaction products.

Study on Plugging Microfracture by Using High-Temperature Emulsified Bitumen

A new kind of modified emulsified bitumen used to plug a microcrack was studied. The sizes of high-temperature emulsified bitumen were fit for the sizes of the microcrack, which were approved by the scanning electron microscope and laser particle size analyzer. Some tests have been designed to demonstrate that the polymer could be used to promote the softening point of modified asphalt, and the high-temperature emulsified bitumen has also shown an excellent performance in terms of static filtration, the viscous coefficient, and extreme pressure lubrication, as well as to inhibit ting shale expansion. The permeability recovery could reach 88.26%, which meets the specification requirements. The mud cake, which was formed by high-temperature emulsified bitumen as an additive, was thin, tough, and dense, which was proved by the scanning electron microscope. The process used to obtain this additive was simple, and the performance of the plugging microfracture was excellent, so this kind of plugging agent could have a better application future.

МОДЕРНИЗИРОВАННАЯ МАШИНА ТРЕНИЯ

The study objective is to increase the information value, accuracy and reliability of the experimental assessment results of extreme pressure and antifriction properties of the tested materials. A brief analysis of the work on the creation of test tribo-technical equipment is given. The difference between the designs of friction machines for testing using Reichert and Timken tests is shown. The design of an upgraded friction machine for determining extreme pressure, antifriction and anti-wear properties of lubricants is presented. In the proposed installation, the radial force on the friction unit ("roller - ring" or "bar – ring") is generated by a mechanism of even loading, and the assessment of extreme pressure lubricants is determined at the moment of gripping the rubbing samples, at which the motor shaft stops. As a result of upgrading the machine, it became possible to measure the friction force, the normal load and to read the friction factor, both for the lubricants under study and for friction pairs consisting of structural and instrumental materials. The results of comparative tests on the upgraded friction machine for lubricating and cooling liquids with different contents of extreme pressure, antifriction and anti-wear additives are presented. 
 A new friction machine design based on Reichert machine is developed, which allows testing structural and lubricating materials for friction and wear using both Reichert and Timken tests. At the same time, the accuracy of determining tribo-engineering characteristics of the tested materials is increased. It is found that as a result of equipping the friction machine with an even loading system and force measuring sensors, it becomes possible to determine extreme pressure and anti-friction properties of lubricants and structural materials, as well as to estimate the value of the friction factor.

Lubricity and mechanism of catechol-based biomimetic lubricant in water-based drilling fluid

In this study, the lubrication performance and underlying mechanism of catechol-based biomimetic lubricants in water-based drilling fluids were investigated. A catechol-based biomimetic lubricant, L3,4, was synthesized by acid and oleyl alcohol utilizing the strong underwater adhesion of DOPA. Besides, the significant influence of phenolic hydroxyl group positioning on the adhesion performance, and consequently, the lubrication and wear resistance properties of the lubricants were revealed. Lubrication performance and wear resistance were evaluated through extreme pressure lubrication testers, four-ball friction machines, and scanning electron microscopy. In bentonite, L3,4 exhibited the best lubrication performance, with a low coefficient of friction (COF) of 0.06 at a 1% addition, a wear scar diameter of 0.365 mm, and a temperature resistance of 210 ℃. In contrast, L3,5 showed moderate lubricity with a COF of 0.16, while L2,5 showed no lubrication capabilities. X-ray photoelectron spectroscopy was used to analyze the composition and thickness of the surface lubrication film, revealing that the phenolic hydroxyl structure enhances the adhesion ability of lubricants on metal surfaces. L3,4, containing a catechol structure, formed a dense organic film of thickness exceeding 100 nm on the metal surface through bidentate metal-ligand bonds; L3,5, with a meta-hydroxy structure, formed a lubrication film of thickness lower than 80 nm through hydrogen bond adsorption; and L2,5, with a para-hydroxy structure, formed a lubrication film of thickness lower than 20 nm. L3,4 addressed the inadequate lubrication exhibited by ester-based lubricants in water, attributed to their insufficient adhesion, which prevented the formation of an effective lubrication film on the surface of drilling pipe.

The mechanisms of inhibition and lubrication of clean fracturing flowback fluids in water-based drilling fluids

Abstract This study presents a novel approach for the reuse of uncontaminated fracturing flowback fluids to improve the inhibitory and lubricating properties of water-based drilling fluids (WBFs), curb environmental pollution arising from flowback fluids, and substantially mitigate the expenses associated with WBFs. The experimental design was optimized using orthogonal experiments and range analyses, whereby the modified rubber powder was set at 2.0%, xanthan gum at 0.15%, and a plant phenol to modified complexing agent ratio of 1:0.01. The assessment of the performance evaluation tests indicated that the use of uncontaminated fracturing flowback fluids as the base water can remarkably enhance the inhibitory and lubricating properties of WBFs. Precisely, this approach reduces the linear expansion rate from 62.31% to 21.25%, the reduction rate of extreme pressure lubrication coefficient by 87.98%, and the reduction rate of mud cake sticking factor by 59.86%. This investigation has established the potential environmental and economic benefits of reusing clean fracturing flowback fluids in WBFs.

Tuning the interfacial behavior of extreme pressure lubrication by stearic acid-modified TiO2 nanoparticles

The development of high-performance lubricants under extreme pressure (EP) is of great significance for reducing energy waste and protecting ecology in heavy industries such as aerospace, large machinery, and so on. Sulfurized isobutylene (SIB) has been explored as one of the most effective EP additives for oil-based lubricants and delivered promising friction-reducing performance. However, the excessive corrosion caused by SIB on the metal surface seriously reduces the instrument’s lifetime and hinders its extensive practical application. Herein, we develop stearic acid-modified TiO2 nanoparticles (SA-TiO2) as a lubricant additive to improve the EP lubrication performance of obtained composite lubricant (CL). During EP friction, the SA-TiO2 can tune the interfacial structure of tribopair and form a high-strength nano-ceramic film to improve tribological performance. Meanwhile, the SA-TiO2 can also compensate for the high wear caused by SIB, thus significantly enhancing the antiwear, friction reduction, and EP properties by 27%, 20%, and 25%, respectively, when compared with the traditional lubricant (TL) obtained by only SIB. Benefiting from the above synergistic effects, the CL can significantly lower the SIB contents while maintaining high EP performance (4900 N weld load). These findings demonstrate a promising eco-friendly lubricant and provide new insights into the mechanism study for EP lubrication.

Enhanced extreme pressure lubrication performance and load carrying capability of gallium-based liquid metal reinforced with MoSe2 and WSe2 nanoparticles

Ga-In-Sn liquid metal containing MoSe2 and WSe2 nanoparticles was prepared via the mechanical blending technology, and their extreme pressure lubricating behaviors were studied on a high-frequency linear-oscillation tribometer. The blending of nanoparticles and Ga-In-Sn is reversible, and the viscosity of liquid metal is increased with the content of nanoparticles. The introduction of MoSe2 and WSe2 nanoparticles makes the load-bearing capacity of liquid metal increase (exceeding 2000 N) as compared with that of Ga-In-Sn (1600 N). Among these liquid metal lubricants, the 3.0 wt% WSe2/Ga-In-Sn exhibits the best lubricating ability (0.112) and anti-wear property (4.17 ×10−8 mm3/Nm). The improvement of extreme pressure lubrication performance of liquid metal benefits from tribo-films with various nanocrystals, which avoids the adhesive wear and seizure failure of tribo-pairs.

Robust superhydrophobic TiO2@carbon nanotubes inhibitor with bombax structure for strengthening wellbore in water-based drilling fluid

Shale gas has become one of the most promising energies to cope with the ever-increasing energy demand, while wellbore instability incidents frequently occur due to the hydration and subsequent swelling of shale during the long horizontal drilling process. In this paper, a novel superhydrophobic carbon nanotube composite for high-efficiency water-based drilling fluid was prepared by the combination of the chemical vapor deposition method and the in-situ precipitation method. The prepared composite can form a superhydrophobic adsorption layer with high roughness and low surface free energy on the rock surface, achieving hydration inhibition by wettability alteration. The functional groups, surface morphology, electrical properties, and element valence of the synthesized composite were characterized by FTIR, SEM, zeta potentiometer, and XPS technique, result evidenced that the product was prepared as expected design. The effect of superhydrophobic carbon nanotube composites on the rheology and filtration properties of drilling fluid was studied, the drilling fluid can maintain favorable viscosity and shear force after adding the composite; the linear expansion rate test, the contact angle measurement, and lubrication experiments were performed to evaluate the inhibition and lubrication performance, the linear expansion rate of core decreased from 59.1 % to 21.9 % after treated with 1 % composite solution for 16 h, the wettability of rock surface can be altered from liquid-wetting to strong hydrophobicity, the reduction rate of extreme pressure lubrication coefficient was 46.9 %, and the zeta potential of shale decreased with the increasing concentration of composite. The possible explanation for its excellent performance could be that the superhydrophobic carbon nanotube composite can form a dense hydrophobic adsorption layer on the shale surface through electrostatic attraction, and an anchoring structure between the neighboring crystal lattices can be preferentially formed by the amino groups in the non-polar end of the molecule, which can alleviate the intrusion of drilling fluid, achieving the inhibition of the hydration and expansion of shale.

One-Step Process of Mixed Oleic Acid Esters and Its High Temperature Lubrication Properties in Bentonite Gelling Suspension.

In recent years, with the increase in requirements for horizontal wells, ultra-high depth wells, small wells and branching wells, it has become increasingly important to deal with the conflict between drilling safety and bottomhole friction. In order to meet the requirements of complex boreholes and deepwater drilling processes, it is crucial to improve the performance of ester-based lubricants. Oleic acid esters are relatively stable and have high lubricity at low temperature, however, these can be hydrolyzed at high temperature. However, the structure of carboxylic acids and alcohols can significantly affect the performance of synthetic esters. In order to solve the problem of balancing the high-temperature performance and low temperature performance of oleic acid esters with different structures, we propose a new oleic acid esterification process. After mixing methanol and ethylene glycol, it is reacted with oleic acid, and the mixed oleate prepared is named MEO-21, and the optimal esterification conditions are obtained as follows: the reaction time is 3 h, the reaction temperature is 150 °C, and concentrated sulfuric acid is the catalyst. MEO-21 not only achieves an extreme pressure lubrication coefficient reduction rate (Δf) of 86.57% at room temperature, but maintains a stable performance after hot rolling at high temperatures. Hot rolling at 150 °C for 16 h, Δf was 85.25%, hot rolling at 180 °C for 16 h, Δf was 89.56%. MEO-21 was used as a base oil with other industrial by-product oils to compound and produce a high-temperature-resistant lubricant that was named L-541, L-541′s Δf was 90.39% at room temperature. L-541 was hot-rolling at 120 °C, 150 °C and 180 °C for 16 h, the Δf was stabled at 89%.

Applying ionic liquids as oil additives for gearboxes: Going beyond the state of the art by bridging the nano-scale and component level

Ionic liquids (ILs) have been used effectively in many applications for reducing problems related to friction and wear. In this work, the potential of ILs as an anti-wear and extreme pressure lubricant additive for high load-carrying gearbox applications such as helicopter transmissions has been studied. Two halide-free ILs: {{rm{P}}_{8881}}{left({{rm{BuO}}} right)_2}{rm{PO}}_2^ - (1) and {{rm{P}}_{8881}}{left({{rm{MeO}}} right)_2}{rm{PO}}_2^ - (2), which are blended at 5 wt% each into a standard non-additivated FVA2 base oil (BO) are examined. Their solid—liquid interface, friction and load-carrying capacity, and wear (scuffing) behavior are studied on the nano-, lab-, and component-scale, respectively, at a different range of temperature and loading conditions by using the atomic force microscopy (AFM), Schwing—Reib—Verschleiß (SRV) friction tests, and Brugger tests, as well as forschungsstelle für zahnräder und getriebebau (FZG) back-to-back gear test rig. The AFM analysis shows nearly no change of adhesion over the full range of studied temperature for the IL blends compared to the BO. Similarly, IL blends demonstrate a very stable coefficient of friction (COF) of around 0.16, which even decreases with increasing test temperatures ranging from 40 to 120 °C. A clear reduction in COF up to 25% is achieved by adding only 5 wt% of the investigated ILs in the BO, and the Brugger tests also show a pronounced enhancement of load-carrying capacity. Finally, on the component-scale, a significant improvement in gear scuffing performance has been observed for both used IL blends. A detailed characterization of the wear tracks from the SRV friction tests via the transmission electron microscopy (TEM) revealed the formation of a phosphate (P—O)-based amorphous tribo-chemical layer of about 20 nm thickness. Therefore, this work may present an approach for ILs to be used as an additive in conventional lubricants due to their ability to enhance the lubrication properties, making them an alternative lubricant solution for high load-carrying gearbox applications.

Extreme pressure lubrication between ceramic and bearing steel with liquid metal

The behaviors of extreme pressure (EP) lubrication for tribo-pairs between silicon nitride (Si3N4) and bearing steel (GCr15) with the lubricants of gallium-based liquid metal (GBLM) and Gear Oil (GO) have been studied on the four-ball test (FBT) machine. The experimental results demonstrated that temperature with GBLM directly measured at the bottom of FBT liquid pool was linearly proportional to the applied load and rotating speed, which was consistent with the variation trend of interfacial temperature simulated by COMSOL. These experimental and simulated results have identified that GBLM lubricant could significantly reduce interfacial temperature and was more suitable for EP lubrication due to its high thermal conductivity than that of GO. Moreover, some experimental results showed that the wear scar diameter with GBLM was smaller than that with GO under the same EP working condition. It has been proved that different materials in Si3N4-GCr15 tribo-pairs did not weld together even in a hard EP working condition. This work also indicated that the new ideas for synthesizing materials were urgent as the tribo-pairs and EP lubricants with high thermal conductivity, which could improve the reliability and feasibility of the EP working condition in the industrial field.

Water-based drilling fluid for ultra-long horizontal intervals in Changqing oil and gas field

In the past two years, several horizontal wells with ultra-long horizontal intervals were completed in Changqing oil and gas field. The longest horizon interval reached 4466 m, which set a record of the longest onshore horizontal well in Asia. There were a lot of difficulties such as high friction, mudstone collapse, and sand carrying that puzzled the drilling of wells with ultra-long horizontal intervals. To solve these problems, some key treatment agents were screened to form a novel water-based drilling fluid system (CQSP-RH). The yield point and extreme pressure lubrication coefficient of the novel system were 18 Pa and 0.058, respectively. The filtrate volume of the novel system was only 1.9 mL at room temperature and was 12 mL at 120 °C. When the cuttings were rolled for 16 h at 120 °C, the primary recovery of them could reach 98.64%. Subsequently, the novel system was applied to wells with ultra-long horizontal intervals. The friction resistance between drilling tools and sidewall was controlled within 500 KN; the solid contents of drilling fluid was controlled within 10%. The results proved that the novel system have superb properties and tremendous potential to drill deeper horizontal wells.

Ga-based liquid metal as an extreme pressure lubricant for steel-ceramic pairs

Ga-based liquid metal as an extreme pressure lubricant for steel-ceramic pairs

Preparation and application of an environmentally friendly compound lubricant based biological oil for drilling fluids

As the basic raw material of bio-oil based eco-friendly lubricant, a special selected by-product vegetable acidified oil (AO) was modified by vulcanization, esterification, or vulcanization followed by esterification. The optimized vulcanization process conditions are 1% sulfur powder catalyzed, temperature 130 ℃, reaction time 2 h, while the optimized esterification process requires 20% glycerol and 1% H2SO4 catalysis, reaction temperature 220 ℃, reaction time 3 h. We compounded modified AO, diluent, pour point depressant and emulsifier into an advanced drilling lubricant F-1. F-1 has excellent performances in bentonite drilling fluids, the extreme pressure lubrication coefficient reduction rate (Δf) in fresh water mud is 86.84%, and 85.76% in 4% NaCl salt water mud. After aging at 150 ℃ for 16 h, its Δf is improved compared with room temperature. Adding F-1 to the basic bentonite mud system, the filtration loss of drilling fluids decreased from 10 mL to 6.5 mL, the apparent viscosity and plastic viscosity experienced little change before and after aging. The new bio-oil compound lubricant has an excellent temperature resistance, a high salt contamination resistance and cost-effective. Vulcanization and esterification processes help to improve the lubricity and reduce foaming rates.

Investigation of interaction of extreme pressure additive, load and sliding speed parameters with silver nano-particles in wear environment

This study aims to minimize the wear of brass-based sliding bearing materials by using extreme-pressure and nano-silver added lubricants. The nano-fluids used in the experiments were characterized by the Zeta test, size measurement, absorbance graphs, wettability analyses and TEM imaging. The effect of extreme-pressure (5%, 10% and 15%) and nano-silver (1%, 5% and 9%) concentration ratios and the interaction of lubricants with load and speed parameters were analyzed with ball-on-plate wear experiments. The results were analyzed by evaluating the friction coefficient and wear volume values, as well as SEM and 3D topography images. It has been found that 5% extreme pressure lubricant reduces friction coefficient by 32.82% and volume loss by 89.51% compared to base lubricant. According to the results, the lowest friction coefficient (0.0276), volume loss (0.042 mm3) values and the best surface images were obtained at 1% concentration. Furthermore, the tribological performance decreased as the concentration of extreme-pressure and nano-silver increased, and optimum extreme-pressure and nano-silver concentrations were obtained as 5% and 1%, respectively. Using additives, different load (10N, 20N and 30N) and speed (10 rpm, 25 rpm, 40 rpm) parameters, Taguchi’s L9 fractional factorial experimental design was created for interaction analyses. With the Taguchi analysis of the design, 5% extreme pressure added lubricant, 10N load and 40 rpm speed parameter combination was determined as the optimum test condition and base lubricant, 30N load and 25 rpm speed parameters were determined as the worst test condition. According to the variance analyses results, it was determined that the lubricant condition was the most effective parameter on the coefficient of friction (67.79%), volume loss (51.07%) and surface roughness (45.43%).

Determination of Lubricant Layer Thickness with an Allowance for Oil Absorption Capacity of Contacting Surfaces

The paper describes an analytical model for calculating an extreme pressure lubricant layer thickness with an allowance for oil absorption capacity of contacting surfaces. The model is practically assessed in laboratory conditions. The experimenting work shows that the speed of the relative displacement of contacting surfaces and the oil absorption capacity of their rough layers contributes to the thickening of the lubricant. The analysis of the results shows that it is the oil absorption capacity of rough layers that has the strongest influence on the change in the thickness of the extreme pressure lubricant layer.

Synthesis and tribological investigation of 4-vinyl guaiacol–based thioether derivatives as multifunctional additives and their interactions with the tribo surface using quantum chemical calculations

Novel 4-vinyl guaiacol based thioether derivatives were synthesized in a three-step reaction procedure by thiol-ene coupling as the key step. The synthesized compounds were characterised by spectroscopic techniques and evaluated for their tribological and antioxidant properties in two different base oils namely epoxy2-ethylhexyl esters of karanja fatty acids (EKE) and dioctyl sebacate (DOS). It was found that the synthesized products were exhibited superior antioxidant performance compared to butylated hydroxytoluene (BHT). All the three synthesized additives were improved the tribological properties of the base oil EKE and DOS. Dithio derivative at 0.75 wt% reduced the wear scar diameter by 36% and at 1 wt% improved the weld point by 33% of base oil EKE. Surface and elemental analysis result suggests that in the tribochemical process the synthesized thioether derivatives decompose and form an effective tribofilms on interacting surfaces. X-ray Photoelectron Spectroscopy (XPS) of the surface lubricated with base oil containing DMFD was evidence for the formation of tribofilm with FeS, FeSO4 and Fe2O3. The antiwear behaviour of the additives was well correlated with quantum chemical calculations. Overall the dithio derivative is more effective as antiwear, extreme pressure and antioxidant bio lubricant additive than other thioether derivatives.

Insights into the tribological behavior of IF-WS2 nanoparticle reinforced mild extreme pressure lubrication for coated chromium/bulk grey cast iron interface

This study reports a novel synergetic approach combining nano-lubrication and conventional extreme pressure additivation, to explore the tribological performance of piston ring/cylinder liner conformal contact. Three typical lubricating formulations, viz, (i) PAO (poly-alpha-olefin) base oil (ii) base oil with mild extreme pressure (MEP) additive, and (iii) base oil with composite blend of mild extreme pressure (MEP) additive and WS2 nano-particles, were investigated using an ASTM G-99 Standard customized universal tribometer for evaluating friction and wear behavior of coated chromium/bulk grey cast iron (CI) tribopair. The lubricant formulations were tested at engine working temperature of 200 °C, reciprocated under a normal load of 30 N, stroke length of 10 mm and a constant sliding velocity of 0.2 ms−1. Wear attributes were evaluated by employing non-contact based 3 D optical profilometry. For assessment of tribo-surface morphology and associated surface characterization, Elemental Dispersion Spectral (EDS) incorporated Scanning Electron Microscope (SEM) was utilised. Green Laser Raman spectroscopy investigated tribo-chemistry, synergetic interactions and tribo-film formations. A state approaching super-lubricity and ultralow friction was achieved by sliding grey CI (Plateau Honed) cylinder liner against electroplated chrome stainless steel top compression ring with PAO10 base oil ultrasonically dispersed with 1 vol% of Isopropyl phenyl Phosphate (IPP), a mild extreme pressure (MEP) triaryl phosphate additive & 1 wt.% of WS2. Results obtained therein demonstrated four dominating forms of wear on the cast iron surface, i.e. plowing wear, abrasive wear, adhesive wear and oxidative wear. Counterpart chromium surface exhibited plowing and abrasive wear only. This substantial friction and wear reduction are attributed to the coalesced intrinsic characteristics of MEP and IF-WS2 additives, thus improving the overall lubrication characteristics of base oil.

High load capability, sticking scale inhabitation and promising lubrication of sodium carbonate coating for steel/steel contact at high temperature

Adequate lubrication for the sliding contacts is responsible for the energy saving and long service life. In this work, load-dependence of tribological behaviours of sodium carbonate coating on the stainless steel was evaluated by ball-on-disc friction test at high temperatures. The results suggested that this sodium carbonate coating showed promising lubrication even under high applied load of 1800 N (Hertz pressure is 6.14 GPa). Apart from the improvement of lubricity, it can also inhibit adhesive wear that transfer oxide scale from the disc to the ball under dry sliding condition. The desirable lubrication and load-carrying capability were attributed to the frictional heat induced in-situ formed sodium carbonate melt that produced an easily sheared tribo-interface, as well as the reconstruction of the oxide scale. The sodium carbonate coating with a superior load capability at high temperature is initially reported here. This finding is believed to bring new perspective of high-temperature, extreme-pressure lubrication design with the easily accessible carbonate salt.