High-temperature Lubricants Research Articles

Ultralow friction polymer composites containing highly dispersed and thermally robust microcapsules

The heat-resisting property of microcapsules as additives directly determine the selection of matrix materials and the molding process of composite materials, which greatly affect the comprehensive properties of materials. In this research, thermally robust polyimide (PI) was used as shell material to synthesize microcapsules by solvent evaporation method, and the synthesized microcapsules were treated by soaking them in dopamine hydrochloride solution for improving their dispersion property in the matrix. The SEM and infrared spectra results showed that the PAO (Poly alpha olefins)@PI microcapsules with the dimeter of ~ 20 µm and the oil content of 60 wt% were successfully coated with polydopamine (PDA) shells. It was demonstrated that the strong electrostatic repulsion of PDA structure made the microcapsules better dispersed in the epoxy resin, so as to play a better role in lubrication, thus resulting in a COF (Coefficient of friction) decrease of composite from 0.108 to 0.038. The high temperature lubrication performance of composites was also investigated and the experimental results shown that the PAO@PI/PDA microcapsules could provide high lubrication performance with a low COF(0.074) at 190 ℃.

Properties of high-density silica fume-based gel and its potential use in high-temperature lubricants and geopolymer binders

Properties of high-density silica fume-based gel and its potential use in high-temperature lubricants and geopolymer binders

Impressive high-temperature lubrication of carbon/epoxy composites endowed by the microscopic dimensionality of carbon fillers

Epoxy resin (EP) as a friction material suffers from serious friction and wear in high temperatures. Adding various carbon fillers into EP to form carbon/EP composites is one of the solutions to this concern. However, the correlation between the filler's dimensionality and their friction properties under high temperature conditions is missing. Herein we construct a comparable dimensional model system of carbon fillers (i.e., one- to three-dimensional carbon nanocage assemblies) to reveal the dimensional effect in high temperature lubrication. Compared with EP, a merely 0.10 wt% of one-dimensional filler can reduce the composite's friction coefficient and wear rate by 36% and 95% at 30 °C, respectively; while for those filled with other dimensionalities, the corresponding decreases are less than 24% and 60%. Even at very close to EP's glass transition temperature of 150 °C, it still maintains a low friction coefficient only with a slight increase in wear. The enhanced high temperature lubrication performance is first attributed to the advantage of one-dimensional fillers to suppress the EP matrix's creep and then easily sliding in the softened transfer film. This study provides a new view for the design of carbon fillers used in EP-based high temperature lubrication composites.

Influence of alkaline species on the high temperature lubrication of molten carbonate

Ionic liquid with the melting points lower than 100 °C is a promising lubricant used ranging from automotive industry to aerospace application, to reduce the friction consumed energy loss and wear caused failure. This work investigated the high temperature lubrication effect of three different molten alkaline carbonate (high-temperature ionic liquid). The results suggest that the lubrication properties of the alkaline carbonate is alkaline species dependent, the carbonate of potassium shows a better lubrication than sodium and lithium carbonate from 730 to 825 °C. At 920 °C, the alkaline carbonate decomposes and reacts with iron oxide to form an alkali ferrite, the tribo-layer of the reactant shows promising anti-wear, and the Li2Fe3O4 has a better lubricity than NaFeO2 and KFeO2. This study reports the concept of high-temperature ionic liquid lubricant, particularly on the roles of alkaline species. The high-temperature ionic liquid lubricant concept can potentially open up a new direction for the design and application of novel high temperature lubricants.

High-temperature tribological properties of diamond-like carbon films: A review

Abstract The rapid development of aerospace industry has made more and more machinery parts of equipment working at high temperature. Due to the lubrication failure of lubricating oil and grease at high temperature, solid lubricant coatings are almost the only effective method to achieve super low friction at high temperature. In recent years, the tribological properties of diamond-like carbon (DLC) films have been extensively studied at high temperature. The present study reviews the microstructure of DLC films and the influence of doping different elements on the structure of DLC films. Second, the mechanical properties and thermal stability of pure DLC films and DLC doped with different elements are also described. DLC films have different microstructures and tribological properties by different preparation methods. Finally, the high-temperature lubrication failure mechanism of DLC films and the tribological properties of DLC films when doped with different elements are discussed from the macro and micro perspectives.

Research on the Effect of Temperature on Tribological Properties of PTFE Composites under Oil Lubrication Conditions

PTFE and its composites are widely used in various reciprocating sealing materials due to their extremely low friction coefficient. As pure PTFE has poor wear resistance at high temperature, it is necessary to study the tribological properties of PTFE with different fillers under the condition of high temperature and oil lubrication. The friction and wear properties of PTFE and PTFE composite material filled with bronze powder, carbon powder, carbon fiber, glass fiber and MoS2 powder were studied by standard friction and wear test using SRV-4 tribotester. Results showed that the wear resistance was all improved indicating that the fillers increased the wear resistance of PTFE, PTFE composite filled with MoS2 has the lowest coefficient at ambient temperature and the highest at high temperature, PTFE composites filled with carbon fiber have the lowest wear rate at all temperatures.

A study of alkali polyphosphate/borate/carbonate for high temperature lubrication of silicon steel using ball-on-disc tests

For hot metal forming at high temperatures, lubricant is required to reduce friction and wear, as well as improve the product surface quality. Inorganic compound has been regarded as a candidate to replace the traditional oil/water lubricant for the forming process. Friction and wear behaviour of three inorganic compounds, including sodium polyphosphate, sodium carbonate, sodium borate were evaluated under ball-on-disc tests at high temperature for high speed steel/silicon steel counterparts to simulate the hot rolling process. The results show that all the three compounds can reduce the friction and wear. Sodium polyphosphate is more corrosive with the oxide scale than others, which is believed to contribute to the descaling of red scale of silicon (Si) steel. Mechanisms by which the inorganic compounds improve the tribological behaviours were discussed here. Simulation results indicate that the molecules of sodium polyphosphate and sodium borate show a much higher binding energy on the iron oxide surface than that of sodium carbonate. The binding energy is mainly contributed from the ionic and the covalent interactions. The ionic part comes from the interaction between the Na+ cations and the oxide surface, while the covalent part comes from the chemical bonds between Fe and oxygen of the lubricants. Both of them contribute to the adhesion of the lubricants on the steel surface and are vital to the friction and wear performance of the lubricants.

Self-lubricating behavior of Fe22Co26Cr20Ni22Ta10 high-entropy alloy matrix composites

Eutectic high entropy alloys (EHEAs) have high temperature stability, good mechanical properties, and are promising for tribological applications at high temperatures. To study the high temperature lubrication behavior, Fe 22 Co 26 Cr 20 Ni 22 Ta 10 −(BaF 2 /CaF 2 ) x ( x =3−20, wt.%) composites were prepared by spark plasma sintering (SPS), with BaF 2 /CaF 2 eutectic powder used as solid lubricant. The lubrication behavior and mechanical properties were studied at both room and high temperatures. With the increase of the content of BaF 2 /CaF 2 eutectic powder, the friction coefficients and the wear rates of the composites at 600 and 800 °C decrease significantly. The composites with eutectic powder content of 15 and 20 wt.% have the best lubricating performance at 600 °C, with low friction coefficient and wear rates, mainly due to the good mechanical properties of EHEA matrix, the lubrication effect of BaF 2 /CaF 2 phase and the oxides formed on the worn surface.

High temperature negative wear behaviour of VN/Ag composites induced by expansive oxidation reaction

Ultra-low wear or non-wear of moving parts is highly desirable because wear limits the service life and reliability of components, particularly under high temperatures. In this study, VN/Ag composites were prepared using vacuum hot-pressing sintering, and their microstructure and high-temperature tribological behaviour were studied. The results demonstrated that the tribological properties of VN ceramics remarkably improved because of metallic Ag. In particular, negative wear was detected in the VN/Ag composites at 700 °C. During the high-temperature tribology process, the evolution of Ag, V2O5, Ag3VO4, and AgVO3 caused by Ag and VN on the worn surface played a significant role in lubrication. In addition, the cell volumes of AgVO3 and Ag3VO4, which were produced via the expansive tribochemical reaction, were 75% and 103% larger than the sum of the cell volumes of VN and Ag. The cell volume expansion compensated for the mechanical damage caused by the wear, possessed an excellent role in wear reduction, and thus contributed to the improvement of high-temperature lubricating materials with high reliability and long service lives.

Research on Real Surface Stability of Cone Bit Sliding Bearing Under Repeated Contact Condition

The cone bit is the most principal rock breaking tool in drilling engineering. The statistical analysis of field data shows that the early damage and failure of sliding bearing is one of the main reasons that affect the service life and performance of the cone bit in the real drilling process. Aiming at the complex working environment of cone bit sliding bearing with heavy load, high temperature and mixed lubrication, the paper establishes a multilevel line contact model of rough surface and carries out the finite element modeling and analysis from the perspective of contact mechanics. Then the Von Mises stress, Residual normal deformation and Inelastic dissipated energy are obtained under the different cycles of loading-unloading. The results show that with the increase of cycles of loading-unloading, the part of edge area of the line contact enters into elastic shakedown and the asperities in the central area occur irreversible plastic deformation, which has a significant influence on the stability of the sliding bearing of the cone bit.

Совместимость высокотемпературных смазок

The state and prospects of research in the field of compatibility of viscous lubricants are analyzed. A new stand for mixing lubricants was presented, simulating the operation of a roller bearing in a wide temperature range. A method has been developed for testing the compatibility of high-temperature lubricants in terms of thermomechanical and thermo-oxidative stability. The results of a study of the compatibility of complex lithium, super-alkaline complex sulfonate and ureate lubricants are presented.

Long-Term Lubrication at 500 °C Using Continuously Replenishable Solid Lubricating Film Polymerized In Situ by Gasified Monomers PA and PPD

Through the introduction of gas-phase monomers phthalic anhydride (PA) and p-phenylenediamine (PPD), replenishment of lubricants during high-temperature friction processes could be realized. According to Fourier transform infrared spectroscopy (FTIR) and gas chromatography–mass spectrometry (GC-MS) analyses, in a 10-min ball–disc friction test at 500 °C, the introduced monomers contacted and polymerized in the gas phase to form solid products with the structure of imides or long carbon chains, which provided superior thermal stability. Solid lubricating films were generated on the disc surface by the physical deposition of these polymerized products and then fall off and attach to the contact position of the ball to form a transfer film. Compared to nonlubricated friction, the coefficient of friction (COF) was reduced from 0.54 to 0.24, and the wear rates of the balls and disc were reduced from 8.32 × 10−6 to 0.65 × 10−6 mm3·N−1·m−1 and from 2.62 × 10−4 to 7.48 × 10−6 mm3·N−1·m−1, respectively. With continued friction but no further introduction of monomers, the solid lubricating film generated in the initial 10 min could provide even more remarkable lubrication for at least the next 15 min, with a minimum COF of 0.01. This could be related to the reinforcing and synergistic lubricating effect of carbonized product powders that gradually formed a continuous phase on the polymerized products’ matrix. After the COF increased, low friction could be re-attained by reintroduction monomers, but lubrication would be limited by the previous wear. This novel lubricating film shows potential in high-temperature lubrication, because it has both the effectiveness and stability of solid lubrication and the replenishability of gas lubrication.

Graphite-based solid lubricant for high-temperature lubrication

High-temperature solid lubricants play a significant role in the hot metal forming process. However, preparing high-temperature solid lubricant is formidably challenging due to the stern working conditions. Here we successfully develop a new type of eco-friendly high-temperature graphite-based solid lubricant by using amorphous silica dioxide, aluminum dihydrogen phosphate, and solid lubricant graphite. The solid lubricating coating exhibits excellent tribological properties with a very low friction coefficient and good wear protection for workpiece at high temperature under the air atmosphere. An array of analytical techniques reveals the existence of solid lubricant graphite in the lubricating coating after the high-temperature friction test. A synergistic effect between the protective surface film and the solid lubricant graphite is proposed to account for such superior lubricating performance. This work highlights the synergistic effect between the protection layer and the lubricant graphite and further provides the insight in designing the high-temperature solid lubricant.

Cold Spraying: A New Alternative Preparation Method for Nickel-Based High-Temperature Solid-Lubrication Coating

Cold spraying was first used for the purpose of preparing nickel-based high-temperature lubrication coatings. High-quality In625-Cr2O3-Ag composite coatings were deposited by a high-pressure cold-spray system, and their tribological properties were evaluated at 20 and 1000 °C by a high-temperature tribometer. The microstructure, composition, and wear mechanisms of the coatings were analyzed by x-ray diffraction, scanning electron microscopy, and Raman spectroscopy. The measurements showed that the cold-sprayed In625-Cr2O3-Ag composite coatings have a very dense structure, good bonding strength to substrate, low friction coefficient, and excellent wear resistance. The friction coefficients of the In625-Cr2O3-Ag coatings were around 0.3 and the wear rates of the coating were maintained at about 10−5 mm3/N m at 20 and 1000 °C. The experimental observation of the wear tracks revealed that the silver provided lubrication at 20 °C. As the temperature increased up to 1000 °C, a lubrication layer with low shear strength made up of Ag2MoO4 and Cr2O3 was formed on the wear track.

Synergistic lubrication of Ag and Ag2MoO4 nanoparticles anchored in plasma-sprayed YSZ coatings: Remarkably-durable lubricating performance at 800 °C

The high-temperature tribological properties of plasma-sprayed YSZ coatings are enormously weakened by intrinsic cracks and pores, brittleness and lubrication deficiency. Therefore, we are attempting to employ Ag and Ag2MoO4 nanoparticles together, as high-temperature lubricant additives, to chemically modify YSZ coatings. With aid of vacuum impregnation and hydrothermal reaction, Ag and Ag2MoO4 nanoparticles were first anchored in the defects of YSZ coatings. The two nanoparticles dramatically reduced the coefficients of friction and wear rates of YSZ coatings under ultrahigh peak Hertzian contact stress at 800 °C, endowing YSZ coatings with an extremely long lifetime and bringing negligible wear damage to the friction pair. It is liquid lubrication and the formation of stable tribofilm that jointly contribute to the remarkably-durable lubricating performance.

Microstructure of HVOF-sprayed Ag–BaF2⋅CaF2–Cr3C2–NiCr coating and its tribological behavior in a wide temperature range (25 °C to 800 °C)

Ag–BaF2⋅CaF2–Cr3C2–NiCr composite powders were prepared by physically blending commercial BaF2⋅CaF2–Cr3C2–NiCr and Ag powders. Ag–BaF2⋅CaF2–Cr3C2–NiCr composite coatings were deposited on Inconel 718 alloy substrate by high velocity oxy-fuel (HVOF) spraying. The friction and wear behavior of the coatings under dry sliding against Si3N4 balls from 25 °C to 800 °C was evaluated with a ball-on-disk high temperature tribometer. The microstructure and composition of the samples were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectrometer. Results showed that the composite coatings were mainly composed of hard phase of Cr3C2, binder phase of NiCr, high-temperature lubrication phase of fluorides and low-temperature lubrication phase of Ag. The fluorides existed in the forms of both crystal particles and amorphous state, while the silver featured as typical thermally sprayed splats. Due to the high flame temperature, some fluorides have been oxidized to chromates and around 30 wt% of Ag was lost during spraying. In addition, it was found that Ag content had an important influence on the composite coating, and an appropriate dosage of metallic silver could effectively improve the tribological performance of the coating. The generation of AgCrO2 at moderate (500 °C and 650 °C) temperature and BaCrO4 at high temperature (800 °C) could contribute to the decline in friction coefficients and wear rates of Ag–BaF2⋅CaF2–Cr3C2–NiCr coatings.

Tribological performance of environmental friendly ionic liquids for high-temperature applications

High-temperature liquid lubricants are often composed of petroleum-based oils. Recently, the lubrication industry has begun to shift towards environmentally benign lubricants to reduce the use of toxic petroleum-based oils. As a result, there has been a resurgence in the use of bio-based lubricants. These “biolubricants” consist of vegetable oils, synthetic ethers, and polyalkyleneglycols (PAGs) for use as high-temperature lubricants. The largest drawbacks to biolubricants are neither their toxicity nor their lubricity, but rather their thermal instability. Room-temperature ionic liquids (RTIL) are emerging biolubricants that has the potential to replace conventional lubricants at high temperatures. In this investigation 1,3-diakylimidazolium and trihexyl(tetradecyl)phosphonium cations are combined with carboxylate anions to create eco-friendly lubricants for high-temperature applications. Here, these RTILs are compared with bio-based and petroleum-based oils to evaluate their tribological properties through pin-on-disk testing and thermal stability via thermogravimetric analysis (TGA). Additionally, the influence of differing alkyl chain imidazolium cations of the 1-decyl through 1-allyl equivalents and various shape and sized anions are studied. Results indicate that the eco-friendly RTILs exhibit the lowest friction and wear properties as well as superior thermal stability because of their lamellar-like liquid crystal structure, electrostatic potential dipolar, and molecular adsorption layer.

High temperature lubrication and mechanism of sodium carbonate by interface tailoring

This paper reports the potential application of sodium carbonate as an environmentally friendly and inexpensive high-temperature lubricant for hot rolling of steel. This process has been simulated by ball-on-disc sliding tests at temperatures of 645 to 920 °C. Compared with unlubricated conditions, reductions in friction and wear of 68% and 98% respectively were achieved during sliding at 730 °C with a contact pressure of 0.84 GPa. The significant improvement of the tribological properties was attributed to the tribo-induced melting of sodium carbonate at the sliding interface, which acted as a liquid lubrication layer and formed a shear-induced nano-gradient tribofilm structure. The sodium carbonate melt was readily sheared and produced low friction and negligible wear. The nano-gradient tribofilm structure which formed under sliding inhibits cracking and spalling, resulted in a low wear due to strain delocalization. These findings highlight the potential application of a low cost, low hazard sodium carbonate as a high temperature lubricant for hot metal forming. It also provides insights into the tribological mechanisms of high temperature lubrication.

Intrinsic Effect of Alkali Concentration on Oxidation Reactivity and High-Temperature Lubricity of Silicate Melts between Rubbed Steel/Steel Contacts.

The present study investigated oxidation reactivity and hot lubricity of a sodium silicate melt at different Na2O/SiO2 ratios under elevated temperature stimulation. Static oxidation prevention was achieved at 920 °C when the Na2O/SiO2 ratio reached 1:3 (trisilicate) and 1:2 (disilicate), but it started to deteriorate in the case of 1:1 (metasilicate). At a high concentration of sodium (metasilicate), a severe corrosion reaction between the melt and oxide took place that resulted in a composite coating on the steel substrate. This high-temperature reaction accelerated the formation of ionic charges from the steel base and promoted oxidation. However, friction and wear reduction is proportional to an increase in the sodium oxide fraction. Metasilicate (1:1) exhibited excellent lubricity under the hot frictional test at 920 °C compared to other lubricants. It was due to the formation of the sodium-saturated surfaces and an amorphous silica layer, which was associated with the high-temperature reactivity of sodium toward the oxide surface. In addition, the NaFeO2-Fe2O3 composite film, as the reaction product of individual sodium charge and oxide, plays a significant role in maintaining the tribofilm stability for metasilicate, which was not present for disilicate. This study advances the understanding of how sodium-containing compounds perform oxidation prevention and generate lubricity at hot rubbed surfaces.

High temperature tribological behaviors and wear mechanisms of NiAl-MoO3/CuO composite coatings

The MoO3/CuO binary oxides were selected as the potential high temperature lubricants in this work based on the ionic potential and cation polarizability approach correlated to the lubricity of solid oxides. The NiAl composite coatings with addition of 10, 30, and 50 wt% of MoO3/CuO (1:1) were fabricated via atmospheric plasma spraying (APS) technology. The tribological properties of these NiAl-MoO3/CuO composite coatings were evaluated from room temperature to 800 °C, and the basic wear mechanisms were investigated as well. The results show that, at 800 °C, the composite coating with 30 wt% of MoO3/CuO led to the lowest friction coefficient (approximately 0.16) and wear rate (3.7 × 10−5 mm3 N−1 m−1). These superior tribological outcomes were attributed to the synergistic lubricating effect of MoO3, CuO, NiO and NiMoO4 which formed on the worn surfaces via tribo-chemical reactions. Meanwhile, the decomposition of CuMoO4 formed by tribo-chemical reaction and worked synergistically to reduce the friction coefficient and wear rate at high temperatures. Meanwhile, the decomposition of CuMoO4 formed via tribo-chemical reaction of MoO3 and CuO at high temperature was observed at 800 °C sliding.