High-temperature Lubricants Research Articles

A new wear-resistant component system of copper-based composite materials: Modified sepiolite-complex ceramic powder

To balance mechanical strength, friction stability, and low wear, a novel wear-resistant component system: modified sepiolite-complex ceramic powder, was employed in copper-based composite materials, leading to the successful preparation of samples with outstanding mechanical and frictional performance. The material exhibits high friction stability, low wear, and the simultaneous occurrence of a high friction coefficient, which may be caused by uniquely composed dual friction film. The external layer of the friction film consists of Cu2O, Fe2O3, and CaO metal-films, while the internal layer consists of B2O3 film, graphite, and sepiolite. Additionally, modified sepiolite (composed of sepiolite, CaCO3 and enstatite) plays a dual role in wear resistance and high-temperature lubrication. Furthermore, the Gradient Boosting Decision Tree (Gbdt) model was found to provide more meaningful guidance for predicting friction coefficients.

Enhancing mechanical performance and high-temperature lubrication enabled by MoS2/WB2 nanolayered films

Molybdenum disulfide (MoS2) films are widespread application in aerospace, nuclear, mechanical, and electronic fields owing to their unique structural characteristics and inherent interlayer slip. However, their utility is hindered by environmental susceptibility, particularly oxidation at elevated temperatures and in humid environments, limiting their effectiveness. Herein, we report a nanocomposite integrating MoS2 with WB2 by periodic alternating arrangement, synthesized using magnetron sputtering technology. This nanolayered architecture effectively harnesses the synergistic properties of both materials, imparting exceptional mechanical properties, superior environmental adaptability and efficient high-temperature lubrication. Methodical experiments and atomistic simulations reveal the incorporation of WB2 promotes preferential growth of MoS2 along the (002) plane, yielding an impressive hardness-to-elastic modulus ratio of approximately 0.1. The resultant film demonstrates notable achievements: a minimal friction coefficient of 0.056 and a specific wear rate of 1.88 × 10−7 mm3 N−1 m−1 in humid air. These findings are primarily stem from the interaction between MoS2 nanosheets and metal-oxide nanoparticles at the sliding interface. Remarkably, even at 400 °C, the engineered MoS2/WB2 nanocomposite achieves low friction and wear under high contact stress, outperforming conventional MoS2-based materials. This innovative design, complemented by insights into the high-temperature friction mechanism, holds promise for advancing the development of robust and high-temperature-resistant lubricants.

The influence of polydiethylsiloxane (PDES) concentration on the tribolfilm of chlorophenyl silicone oil (CPSO) under high-temperature lubrication

As pivotal structural component, steels operating at high temperatures play a vital role in promoting the development of advanced equipment technology. Enduring and efficient lubricants are critical bottleneck for the construction of high-temperature frictional subsystems. Polydiethylsiloxane oil (PDES) significantly reduces the coefficient of friction (COF) (9.80–16.74 %) and wear rate (28.95–54.59 %) in the Si3N4–8Cr4Mo4V system without sulfur and phosphorus anti-wear additives at 250 °C. With only 1 wt% PDES, there is a remarkable 28.95 % wear rate reduction in the Si3N4–8Cr4Mo4V frictional system. The enhanced lubrication performance come from the Si–O tribofilm at lower PDES concentrations (1–15 wt%). Once exceeding a PDES concentration of 30 wt%, the as-formed Si–O tribofilm transitions to a Fe–Mo compound film, exhibiting superior friction reduction and wear resistance properties.

Elevated temperature tribological assessment of Ni-based cermet self-lubricating coatings deposited by cold spray

Solid lubricant coatings provide reduced friction and wear resistance and hence finding widespread application in harsh environmental conditions, such as gas turbine, aircraft, and internal combustion engines. It is apparent that single lubricant fails to offer effective lubrication over wide temperature range. Hence, two or more solid lubricants are mutually incorporated to achieve the appropriate lubrication by their synergy under harsh service conditions. The current investigation is being carried out to evaluate the synergistic impact of different solid lubricants viz. silver (Ag), molybdenum disulfide (MoS2), hexagonal boron nitride (h-BN) and chromium oxide (Cr2O3) on the frictional properties of coatings from room temperature (RT) to 800 °C. Cold spraying process has gathered extensive acceptance for the development of metallic and metallic-ceramic coatings. The current study elucidated the tribological characteristics of cold sprayed nickel-based high temperature lubrication coatings, namely, Ni-Al-MoS2-Ag (NB0), Ni-Al-MoS2-Ag-5 wt% h-BN (NB5), Ni-Al-MoS2-Ag-7.5 wt% h-BN (NB7.5), Ni-Al-MoS2-Ag-10 wt% h-BN (NB10) and Ni-Al-MoS2-Ag-Cr2O3–7.5 wt% h-BN (NB7.5 + 7 wt% Cr2O3) against Al2O3 ball in an operative testing regime from (RT-800 °C) using ball-on-disc tribometer. Results indicated that NB7.5+ 7 wt% Cr2O3 coating exhibited remarkable self-lubricating and wear resistance properties as compared to other coatings. However, NB7.5+ 7 wt% Cr2O3 revealed slightly higher coefficient of friction (COF) in compare to NB7.5 coating till 400 °C, and beyond that it showed a decreasing trend and lesser COF in compare to other coatings. The observed wear mechanisms at different temperatures were discussed in detail after analyzing the morphologies of worn surface. The pivotal role played by the participating solid lubricants were also discussed in detail which help in to provide the continuous compacted layers at the worn surfaces at elevated temperature.

Control of the tribological temperature dependence of hydrogenated amorphous carbon films by doping with W

While numerous strategies have been developed to enhance the high-temperature performance of amorphous carbon films, challenges persist regarding high coefficients of friction and wear rates within the mid-temperature range (200–300 °C). In this study, we developed a series of a-C:H(W) films with varying tungsten concentrations and systematically investigated their wear and friction characteristics using Al2O3 ceramic balls at different temperatures. The results reveal that the a-C:H(W) film (W3) with a WC target current of 0.3 A exhibits friction coefficients of 0.10 and 0.06 at 300 °C and 500 °C, respectively. The addition of hydrogen to the film enables stable lubrication in the intermediate temperature range. The presence of carbide facilitates the formation of a continuous protective layer during friction at 500 °C. Additionally, the inclusion of tungsten trioxide effectively reduces friction during high-temperature lubrication. Overall, this a-C:H(W) film shows promise in addressing the challenges of high-temperature wear in mechanical engineering applications under harsh operating conditions.

The significance of low and high temperature solid lubricants for brake friction applications and their tribological investigation

Solid lubricants like metal sulfides and fluorides are important ingredients in stabilizing the friction in brake pads. It is essential to consider the oxidation temperature and the compatibility of the metal sulfides. This study emphasises the importance of incorporating a variety of solid lubricants based on oxidation temperature regimes. Low-temperature solid lubricants such as molybdenum disulfide, iron sulfide, and bismuth sulfide, as well as high-temperature solid lubricants such as tin(II)sulfide, tin(IV)sulfide, and calcium fluoride were used in the preparation of brake pads. The combination of low and high-temperature solid lubricant mix was tested for tribological performance in brake pads. The results show the necessity of using both low and high-temperature solid lubricants to enhance the tribological performance of brake pads.

A critical review on functionally graded ceramic materials for cutting tools: Current trends and future prospects

Abstract This review is an attempt to explore the challenges that need to be addressed to fully utilize the potential of ceramic-based functionally graded cutting tools (FGCTs). The various aspects covered in the review include the most recent experimental and numerical work related to FGCTs, the current research trends and the need for these tools, the identification of potential material combinations, synthesis techniques and their limitations, and finally a presentation of the most recent work. To find general tribological performance, various wear mechanisms involved in the cutting process are explored. Some recent experimental and numerical works related to the self-lubricating phase in functionally graded structure and the need for self-lubricating ceramic tools, identifying potential high-temperature solid lubricants, and their limitations are also discussed. More recent and dominating fabrication methods are also discussed in detail along with a brief review of some promising methods. The implementation of numerical modeling and computational frameworks validated through experiments is found to lead to the design and development of cost-effective and efficient FGCTs. Finally, some research gaps are identified and future directions for innovative FGCT materials are proposed.

Ultralow friction polymer composites enabled by the solid–liquid core microcapsules at high temperatures

The application of oil-containing microcapsules for lubrication at high temperatures has been a great challenge due to the volatilization and viscosity reduction of the oil. In this study, thermostable SiO2 was selected as the shell and WS2 silicone oil dispersion as core to prepare heat-resisting solid–liquid compound microcapsules. The tribological properties of the composites at high temperatures were evaluated, and the lubrication mechanism of the solid–liquid coupled microcapsules was investigated. The results showed that the microcapsule composites were able to maintain low friction coefficient (COF) and wear rates at high temperatures (COF of 0.098, 73 % lower than pure epoxy, and wear rate of 4.87 × 10-6 mm3/N·m, two order of magnitude lower than pure epoxy, at 300 ℃), and in addition, the compressive strength of the composites was improved due to the excellent mechanical properties of SiO2. The strategy proposed in this study is expected to be a general solution and can be extended to other polymer composites with excellent high-temperature lubrication properties by incorporating microcapsules with different solid–liquid core in the matrix.

Influence of Concentration of Sodium Metasilicate and Descaling on the High Temperature Lubricating Effects Evaluated by Hot Rolling Mill

Lubricant is vital to improve energy efficiency and workpiece durability for the moving counterpart. High-temperature lubricants are important for the hot rolling process to reduce the rolling force and protect the roller and the strips. The current paper concerns eco-friendly sodium metasilicate as a high-temperature lubricant. A hot rolling mill is employed to evaluate the lubrication effect of sodium metasilicate. The influence of crucial factors of concentration of lubricant and descaling is discussed; the rolled surface was analyzed by scanning electron microscopy, energy dispersive spectroscopy, and 3D profilometer. The results depict that the sodium metasilicate can reduce the rolling force by about 7.8% when the concentration of sodium metasilicate is 18% and above, and descaling of the hot stripe makes the lubrication effect more effective, which can reach a 12.7% reduction in the rolling force. This lubrication is attributed to the formed melts of the sodium silicate layer that offers an easy shearing interface. For the un-descaled samples, the lubricant will be compacted and mixed with the oxide scale, and weakens the lubrication effect. This work suggests that sodium metasilicate can be a high-temperature lubricant for hot rolling; descaling is vital, not only for the quality of the product but also for the efficiency of the lubricant. This work will also be useful for the concentration selection of glass lubricant.

Robust design of durable PTFE/graphene hollow fiber composite membrane for high-temperature lubricant recycling

Nowadays, the lubricant recycling becomes difficult due to its complex composition and high viscosity. Reinforced hollow fiber membranes (HFM) have been widely used in various separation fields due to their controllable separation accuracy, large specific area, backwashability, as well as low operation and maintenance requirements. Herein, a durable polytetrafluoroethylene (PTFE)/graphene (GE) hollow fiber composite membrane (HFCM) with high temperature resistance was designed through the laminated-sintering process to solve the lubricant issue. The membrane featured a solid three-layer reinforced structure and compared with the pure GE membrane, the adverse effects from GE brittleness are efficiently avoided, which ultimately improved the membrane flexibility and morphological stability. Moreover, this PTFE/GE HFCMs showed superior high-temperature resistance and lipophilicity with an oil contact angle of 0°. With a reasonable regulation of lubricant temperature and GE content, the membrane flux exceeded 917 L·m−2·h−1·bar−1 and stabilized at 458 L·m−2·h−1·bar−1 after 12 h of membrane operation at 150 °C. The membrane flux remained at a relatively high level of 103 L·m−2·h−1·bar−1 after four cycles, with a flux recovery over 83 %. In addition, the membrane separation-efficiency up to 99.02 % for activated carbon in lubricants. Overall, the PTFE/GE HFCMs presented great potential for recycling lubricants or other heavy crude oils at high temperatures.

Tribological performance for an Mg alloy subjected to sliding at elevated temperatures: A comparison between Al2O3 and MoS2 nano additives in silicone oil-based lubricant

Magnesium (Mg) and its alloys are crucial for energy-efficient vehicles due to their strong and lightweight properties, necessitating high-temperature fabrication and lubrication to reduce oxidation, friction, and wear. This paper investigated the tribological performance of lubricating oil using different particles to a Mg alloy subjected to contact sliding in an open system at high temperatures up to 250 °C. The overall experimental results showed improved tribological performances by using the two types of nanoparticles / nanoparticle-clusters (concentration ≥ 0.5 wt%) compared with the base silicone oil. The mechanisms by which the two types of nano lubricants improved the tribological performance are different. Al2O3 particles provided a more stable Al-rich anti-wear surface at higher temperatures in the range of 200–250 °C, while a tribo-chemical reaction film was formed with MoS2 additives, generating MoO3 and MgSO4. It is generally concluded that Al2O3 has more positive effect in terms of reduced coefficient of friction and wear rate as comparison to MoS2.

The Synergistic Lubrication Effects of h-BN and g-C3N4 Nanoparticles as Oil-Based Additives for Steel/Steel Contact.

The synergistic effect of different types of solid particles in liquid lubricants is of great interest. In this work, g-C3N4 nanosheets were initially prepared using a calcination method and then as-prepared, and h-BN were used as lubricating additives to the white oil. A comparison between the mixed additives and the single g-C3N4 or h-BN additives revealed that the base oil with the addition of g-C3N4 and h-BN showed the best lubricating properties. The results show a 12.3% reduction in friction coefficient, resulting in a 68.6% reduction in wear rate compared to the white oil when filled with 0.5 wt% g-C3N4 and h-BN (1:1 by weight). Moreover, the addition of g-C3N4 and h-BN improves the high-temperature lubrication properties of the white oil. However, the friction coefficient and wear rate increase with increasing oil temperature. The large contact area between g-C3N4 and its sliding counterpart and the strong adhesive force between h-BN and its sliding counterpart improve the film formation efficiency, leading to enhanced tribological properties under oil lubrication conditions.

Synthesis and mechanism of environmentally friendly high temperature and high salt resistant lubricants

With the exploration and development of deep and ultra-deep oil and gas, high torque and high friction during the drilling of deep and ultra-deep wells become one of the key issues affecting drilling safety and drilling speed. Meanwhile, the high temperature and high salt problem in deep formations is prominent, which poses a major challenge to the lubricity of drilling fluids under high temperature and high salt. This paper reports an organic borate ester SOP as an environmentally friendly drilling fluid lubricant. The performance evaluation results show that when 1% lubricant SOP is added to the fresh water-based mud, the lubrication coefficient decreases from 0.631 to 0.046, and the reduction rate of lubrication coefficient is 92.7%. Under the conditions of 210 °C and 30% NaCl, the reduction rate of lubricating coefficient of the base slurry with 1% SOP was still remain 81.5%. After adding 1% SOP, the wear volume decreased by 94.11% compared with the base slurry. The contact resistance experiment during the friction process shows that SOP can form a thick adsorption film on the friction surface under high temperature and high salt conditions, thus effectively reducing the friction resistance. Molecular dynamics simulation shows that lubricant SOP can be physically adsorbed on the surface of drilling tool and borehole wall through hydrogen bond and van der Waals force. XPS analysis further shows that SOP adsorbs on the friction surface and reacts with metal atoms on the friction surface to form a chemically reactive film. Therefore, under high temperature and high salt conditions, the synergistic effect of physical adsorption film and chemical reaction film effectively reduces the frictional resistance and wear of the friction surface. In addition, SOP is non-toxic and easy to degrade. Therefore, SOP is a highly effective and environmentally friendly lubricant in high temperature and high salt drilling fluid.

Effect of Cr3C2 content on microstructure, mechanical and tribological properties of Ni3Al-based coatings

To broaden the applicability of Cr3C2 -reinforced Ni3Al-based coatings, which possess exceptional high-temperature strength and anti-friction properties for high-temperature solid lubrication, this study examined the influence of varying Cr3C2 concentrations (0 wt%, 10 wt%, 15 wt%, and 20 wt%) on the phase composition, microstructure, mechanical performance, and friction and wear behaviors of Ni3Al-based coatings from 25 °C to 800 °C. The findings indicated that decarburization of Cr3C2 took place during HVOF spraying, forming Cr7C3. The remarkable high-temperature lubricity of all coatings can be attributed to the synergistic lubrication effect resulting from the precipitation of soft metal Ag, the brittle-plastic transformation of MoO3, and high-temperature solid lubricants such as NiCr2O4 and Ag2MoO4, which are induced by high-temperature friction. The second phase strengthening of Cr3C2 and the solute effect in the Ni3Al matrix phase significantly improved the hardness and toughness of the coatings, thereby enhancing their wear resistance. Notably, the coating containing 15 wt% Cr3C2 exhibited the lowest coefficients of friction (COFs) and wear rates (WRs) (10−5 mm3·(N·m)−1), ranging from 0.60 to 0.26 and 14.48 to 2.01 at 25 °C to 800 °C, which can be ascribed to the coordination between lubricity and mechanical strength.

Thermal stability and flammability of several quaternary ammonium ionic liquids

With the development of potential large-scale industrial application of quaternary ammonium ionic liquids in the fields of gas separation, high-temperature lubricants and even rocket propellants, deep investigations are required to reveal the possible hazards of thermal decomposition, the flammability and the hazardous gaseous products. In this study, the thermal stability of five typical quaternary ammonium ionic liquids, [N2222][NTF2], [N2222][PF6], [N2222]Br, [N4444]Br and [N4444][PF6], were studied using thermogravimetric analyser (TGA). The results show that the thermal stability of ionic liquids follows an order of [N2222][NTF2] > [N2222][PF6] > [N4444][PF6] > [N2222]Br > [N4444]Br, indicating that the thermal stability is obviously affected by the anion, with an order of [NTF2]− > [PF6]− > Br−. Besides, increasing the alkyl chain length in the cation will reduce the thermal stability. In addition, Fire Testing Technology (FTT) cone calorimeter was used to investigate the flammability and found that the longer alkyl chains of quaternary ammonium ionic liquids make great contribution on larger the total heat release, the peak value of heat releasing rate and shorter ignition time. Moreover, with the same cation, [N2222]Br and [N4444]Br were shortened the ignition time and produced larger amount of heat than [N2222][PF6] and [N4444][PF6], respectively. It clearly shows that the risk of fire is also affected by the anion, with an order of Br− > [PF6]− > [NTF2]−. Finally, the decomposition products were measured by thermogravimetry coupled with Fourier-transform infrared spectroscopy (TG-FTIR), and it is deduced that the nucleophilic Br− from [Nmmmm]Br (m = 2,4) and F− from the [NTF2]− and [PF6]− during decomposition will attack the alkyl chain of the cation, which generated gaseous products such as fluoroalkanes, bromoalkanes, olefins, etc.

Tribological behavior of Cu-modified polymer-derived SiBCN ceramics at elevated temperature

SiBCN ceramics were prepared and modified with copper (10, 20 and 30 wt%) by polymer-derived ceramics route. The polymer-to-ceramic transformation of the precursor was investigated and the tribological behavior of the SiBCN and Cu-SiBCN ceramics at 800 °C was studied in terms of composition, microstructure, high-temperature friction properties and wear mechanism. It turned out that copper incorporation enhanced the tribological performances of the ceramics both at ambient and elevated temperatures. The average friction coefficient of SiBCN was 0.23 at 800 °C, while it decreased to 0.18 with the wear rate reduced by one magnitude order after introducing 30 wt% Cu. The generated lubricious CuO-SiO2 tribo-film originating from the tribo-chemical reaction was the major high-temperature lubrication mechanism for the Cu-SiBCN composites.

Mechanism of thermoviscoelasticity driven solid-liquid interface reducing friction for polymer alloy coating

High-temperature ablation is a common failure phenomenon that limits the service life of the transmission parts on heavy-duty machines used in heavy load, high temperature, high shock conditions due to in-sufficient supply of lubricating oil and grease. Traditional self-lubricating coatings prepared by inorganic, organic or organic-inorganic hybrid methods are prone to be oxidated at high temperatures to lose their friction reducing function, so that it is difficult to meet the engineering requirements of high-temperature lubrication. We design viscoelastic polymer coatings by a high-temperature self-lubricating and wear-resistant strategy. Polytetrafluoroethylene (PTFE, Tm = 329 °C) and polyphenylene sulfide (PPS, Tg = 84 °C, Tm = 283 °C) are used to prepare a PTFE/PPS polymer alloy coating. As the temperature increases from 25 to 300 °C, the PTFE/PPS coating softens from glass state to viscoelastic state and viscous flow state, which is owing to the thermodynamic transformation characteristic of the PPS component. Additionally the friction coefficient (µ) decreased from 0.096 to 0.042 with the increasing of temperature from 25 to 300 °C. The mechanism of mechanical deformation and surface morphology evolution for the PTFE/PPS coating under the multi-field coupling action of temperature (T), temperature-centrifugal force (T-Fω), temperature-centrifugal force-shearing force (T-Fω-Fτ) were investigated. The physical model of “thermoviscoelasticity driven solid-liquid interface reducing friction” is proposed to clarify the self-lubricating mechanism determined by the high-temperature viscoelastic properties of polymers. The high-temperature adjusts the viscosity (η) of the coating, increases interface slipping and intensifies shear deformation (τ), reducing the friction coefficient. The result is expected to provide a new idea for designing anti-ablation coatings served in high temperature friction and wear conditions.

Tribo-induced catalytically active oxide surfaces enabling the formation of the durable and high-performance carbon-based tribofilms

Carbon-containing tribofilms have attracted significant interest in the lubrication research despite a scarcity of information on their high-temperature performance under severe boundary conditions. In this study, high-temperature lubrication of the carbon tribofilm produced from cyclopropane carboxylic acid (CPCa) and NiAl-layered double hydroxide (LDH) nanoparticles was evaluated. NiAl-LDH nanoparticles significantly enhanced the friction stability and antiwear performance of CPCa by over 90% at 50°C and 100°C, comparable to the benchmark zinc dialkyldithiophosphates (ZDDPs). The highly graphitic amorphous carbon tribofilms and the fine-grain intermediate tribolayer constructed by the thermal decomposition products of NiAl-LDH contributed to such excellent lubrication performance. This study paves a pathway in developing functional anti-wear additives for the durable and high-performance carbon-containing tribofilms at high temperatures.

Lubrication mechanisms of Nb-contained oxides characterizing tribochemistry of NiAl/Nb/Ag composites coatings revealed by the density functional theory (DFT) computation

In this work, the lubrication mechanisms of Nb-contained oxides were revealed by using the density functional theory (DFT) computation. Concretely, a series of Nb-contained oxides, e.g. Nb2O5, AgNbO3 and NiNb2O6 were generated through tribochemistry during the friction process of the fabricated NiAl/Nb/Ag coatings as the temperature was increased, and the friction coefficients decreased from 0.51 to 0.54 at low temperatures to 0.24 – 0.27 at elevated temperature. Computational results showed that the binding energy of the Nb – O bond (−15.3 eV) in Nb2O5 was much higher than those of the Ag – O (−0.59 eV) and Ni – O (−0.90 eV) bonds in AgNbO3 and NiNb2O6, indicating that the latter Ag – O and Ni – O bonds were much easier to be fractured or broken under the friction force. AgNbO3 and NiNb2O6 registered better lubrication performances than Nb2O5, which could account for the excellent tribological performance of the coatings at elevated temperatures. This investigation contributes to revealing the high-temperature lubrication mechanisms of Nb-contained oxides.

Promoted high-temperature lubrication and surface activity of polyolester lubricant with added phosphonium ionic liquid

The effect of two types of additives, trihexyltetradecylphosphonium bis(2-ethylhexyl)phosphate and tricresyl phosphate on the tribological behavior of the polyolester based lubricant (POE) has been studied. Experiments revealed the lubricant equipped with both additives had friction reduction (up to 4 times) and a smaller wear rate (by almost 2 orders) of sliding steel surfaces in a wide range of temperature conditions in comparison to original POE and POE with each additive separately. Characterization revealed the formation of the phosphorous-rich film on the wear track that was responsible for observed friction and wear reduction. The rate of the film formation evaluated using Quartz Crystal Microbalance was found to increase with temperatures thus suggesting better efficiency of the steel surface protection during sliding.