Excellent Tribological Performance Research Articles

Strong, tough and high temperature self-lubricated fibrous monolithic ceramic in Al2O3/Cr2O3 system

A fibrous monolithic ceramic was constructed with Al2O3 fiber cells surrounded by Cr2O3 phase-two kinds of brittle ceramics, to achieve an excellent combination of high strength and toughness, which is usually mutually exclusive in engineering materials. The material was demonstrated to fail in a non-brittle fracture manner and showed a typical rising R-curve behavior with the maximum crack growth toughness of 9.05 MPa m1/2. Meanwhile, the composite ceramic exhibited excellent tribological performance at high temperatures, with the lowest friction coefficient of 0.29 and wear rate of 1.07 × 10−5 mm3/Nm at 600 °C. It was also demonstrated that the thermal stability of Cr2O3 has a great influence on the wear mechanism when the temperature was above 800 °C.

Improving tribological performance of porous oil-impregnated GO/PA6 composites with double lubrication structure

Using carbon nanomaterials to construct self-lubricating polymer materials with porous self-lubricating structures has become an effective way to improve the tribological performance of polymer composites. The synergistic effect between 1.0 wt% graphene oxide (GO) and lubricating oil resulted in excellent tribological properties of polyamide 6 (PA6) composites under different loads and speeds. It indicated that the introduction of GO in porous PA6 matrix (GO/PA6) would provide enhanced tribological performance with the friction coefficient reduction by 23.4% and wear resistance improvement by 36.2%. This was explained by the lubricating oil stored in the pores of PA6 material would be released to the surface of the matrix material under the dual effect of load and temperature during the friction process. The released lubricating oil would formed a solid-liquid double lubrication structure with the well-dispersed GO in the matrix, thus the porous oil-immersed GO/PA6 composite materials demonstrates excellent tribological performance. This work provides a solid-liquid double lubrication strategy for enhancing the tribological properties of self-lubricating polymers, which would promote the self-lubricating polymer composites more widely applied in the field of friction materials.

Functionalized graphene-oxide nanosheets with amino groups facilitate macroscale superlubricity

Graphene-oxide (GO) has been recognized as an excellent lubrication material owing to its two-dimensional structure and weak interlayer interactions. However, the functional groups of GO that can contribute to anti-friction, anti-wear, and superlubricity are yet to be elucidated. Hence, further improvement in GO-family materials in tribology and superlubricity fields is impeded. In this study, macroscale superlubricity with a coefficient of friction of less than 0.01 is achieved by exploiting the high adhesive force between amino groups within aminated GO (GO-NH2) nanosheets and SiO2. It was observed that GO-NH2 nanosheets form a robust adsorption layer on the worn surfaces owing to the high adsorption of amino groups. This robust GO-NH2 adsorption layer not only protects the contact surfaces and contributes to low wear, but also causes the shearing plane to transform constantly from solid asperities (high friction) into GO-NH2 interlayers (weak interlayer interactions), resulting in superlubricity. A SiO2-containing boundary layer formed by tribochemical reactions and a liquid film are conducive to low friction. Such macroscale liquid superlubricity provides further insights into the effect of functional groups within functionalized GO materials and a basis for designing functionalized GO materials with excellent tribological performances.

Preparation and Tribological Properties of Self-Lubricating Epoxy Resins with Oil-Containing Nanocapsules.

The design and development of self-lubricating materials aid in enhancing the tribological performance and prolonging the service life of aero self-lubricating spherical plain bearings. Herein, monodisperse hollow mesoporous carbon nanospheres (HMCNs) with thin shell thickness and uniform particle size were synthesized. Afterward, oil-containing nanocapsules (Oil@HMCNs) were obtained by the impregnation method, which was an innovative approach to prepare nanoscale capsules. The Oil@HMCNs were monodispersed, and the oil content rate could reach 45 wt %. The nanocapsules were applied as additives to achieve the self-lubricating properties of epoxy resin (EP). It was revealed that the coefficient of friction (COF) and the wear rate of EP in dry friction can be decreased from 0.56 to 0.084 and from 50.15 × 10-6 to 0.27 × 10-6 mm3/N/m, respectively. The tribological properties of EP composites in dry friction are better than those of EP with external oil. According to the analysis of friction pairs, the antifriction performance was contributed by the released automatic transmission fluid 6HP (ATF6) from nanocapsules. Meanwhile, the presence of ATF6 effectively could inhibit fatigue wear, and the decrease of compressive strength and surface hardness led to plastic deformation and mechanical polishing. Both resulted in a lower wear rate of EP. In conclusion, this work explored the application possibility of hollow mesoporous materials in lubrication. The prepared EP composites exhibited excellent tribological performances and self-lubricating properties, which were expected to be applied to self-lubricating spherical plain bearings and other mechanical parts.

Exploration and tuning of Al2O3/Mo composite for enhancement of anti-corrosion and tribological characteristics in zinc phosphate conversion coatings

Recently, phosphate conversion coatings have been modified by transition/non-transition metal oxide with distinguished characteristic features such as corrosion resistance, wear resistance, lubrication and adhesion. The present paper explores the development of Al2O3/Mo composite incorporated zinc phosphate coatings on galvanized steel for achieving higher corrosion-resistant characteristics with an added advantage of tribological performance. Incorporation of Mo leads to the phase transformation from γ to α-Al2O3, which ensures the subsequent crystallization of alumina particles by the anisotropic grain growth of Mo content. Particle size, elemental composition and morphology of the Al2O3/Mo composite are tuned for retaining the stable crystalline alpha phase of the composite. The optimum concentration of the tuned content of Al2O3/Mo composite in the phosphating solution can effectively perform as an active nucleating source for the establishment of more compact, homogeneous and dense zinc phosphate crystal growth and coverage in the galvanized steel surface by significantly reducing the activation energy during the phosphating process. The resultant composite phosphate coating ensures the formation of a large quantity of crystalline hopeite rich phase compared to other coatings, which effectively acts as an insulator during the electrochemical reaction by imparting a corrosion-resistant barrier between the substrate and corrosive media. Uniform distribution of composite particles at the grain boundaries and at the bulk grain composition is also achieved. Lower average surface roughness (Sa), root mean square surface roughness (Sq), maximum height (St), surface skewness (Ssk) and higher surface kurtosis (Sku) values are acquired for better anti-corrosion properties with excellent tribological performance. The higher Rp and Rct values with lower Cdl and corrosion rate values of the tuned composition of Al2O3/Mo composite based zinc phosphate coating confirms the better porosity and thereby enhances the corrosion-resistant performance due to the sealing action of the composite.

Novel Nanocomposites Reinforced with Layered Double Hydroxide Platelets: Tribofilm Growth Compensating for Lubrication Insufficiency of Oil Films

Growth of solid tribofilms between moving parts substantially reduces friction and wear, and this is true especially for boundary-lubricated sliding contacts. However, efficacy of the tribofilms relies upon antiwear additives in formulated oil, typically zinc dialkyldithiophosphate, that usually gives rise to adverse environmental impacts. It is desirable to reduce the use of environmentally harmful additives by designing materials of moving parts so that they function properly with base oil lubrication. Herein, CoAl layered double hydroxide (LDH) nanoplatelets were synthesized via a one-step hydrothermal approach. When being lubricated with polyalphaolefin base oil (PAO 4), epoxy nanocomposites reinforced with low-loading LDH exhibit excellent tribological performance. In comparison to neat epoxy, wear of the nanocomposite is reduced by an order of magnitude and friction is decreased by 32%. Our work provides direct evidence that LDH released onto a friction interface facilitates tribofilm growth compensating for lubrication insufficiency of the oil film. This work paves a route for minimizing the dependency on harmful antiwear additives by optimizing tribomaterials.

Heterostructured NiCr matrix composites with high strength and wear resistance

• NiCr-WS 2 composites with nano-Ti addition were prepared by spark plasma sintering. • The in situ reaction between NiCr, WS 2 and Ti leads to the formation of a heterostructure. • The heterostructured composite exhibits balanced mechanical and tribological properties. Self-lubricating composites are required to have excellent tribological performances and good mechanical properties when they are applied as mechanic parts. However, the brittle nature of most lubricants will weaken the mechanical properties of the composites where in order to get the lubricating ability proper amount of lubricants are usually incorporated, bringing challenges for them to get well-balanced mechanical and tribological properties. In this study, NiCr matrix self-lubricating composites with the addition of WS 2 and nano-Ti were prepared via spark plasma sintering. The hard phase of Ni 3 Ti and the lubricant TiS were formed via in-situ reaction at the interface, which surrounded the soft alloy matrix and developed a heterostructure. Compared with the conventional NiCr-WS 2 composite, the heterostructured composite exhibited a high yield strength of 1645 MPa, a low friction coefficient of 0.37 and a wear rate of as low as 2.25 × 10 −5 mm 3 N − 1 m − 1 when sliding. Finite element analysis demonstrated that the heterostructure plays a key role to balance well the mechanical and tribological properties of the NiCr matrix composites.

Friction process analysis of carbon fiber-carbon nanotube multiscale hybrid reinforced epoxy with excellent tribological performance

This study improved the tribological property of epoxy composite by filling carbon fiber-carbon nanotube multiscale hybrid synthesized via the non-corrosive LaCl3 surface treatment method. In the tribological study of composites, the friction process was divided into four stages with the revealing of corresponding mechanisms, and the initial friction process was investigated based on surface analysis results. Notably, the reductions in friction coefficient (81.8%) and wear rate (97.6%) of hybrid reinforced composite distinguish this study from other similar researches, which is due to the lowered surface adhesion and strengthened interfacial property that prevents fiber debonding and avoids three-body abrasive wear. Also, this study analyzed the tribological characteristics of epoxy composite under different reciprocating frequency and load.

Synthesis of novel CuO@Graphene nanocomposites for lubrication application via a convenient and economical method

Graphene-based nano lubricant additives attract more and more attention because of their superior lubricating performance as well as green and ashless properties. Graphene-based nanocomposites exhibit excellent tribological performances due to the synergistic “slide-roll” effect. In this work, we developed a novel nanocomposite constructed by graphene materials (G) and CuO nanoparticles, named CuO@G, which has superior tribological properties to each component (pure CuO or pure graphene materials) and the mixture (Graphene + CuO) under different testing conditions due to the synergistic effect. By adding 0.5 wt% CuO@G to PAO-6 oil, the coefficient of friction (COF) is reduced by more than 50%, and the wear scar almost disappears. The study provides a novel and promising method for the synthesis of graphene-based lubrication nanomaterials, which has high potential for lubrication applications.

Microstructure, mechanical properties and low-temperature tribological behavior of Cr/Cr-W/W-DLC/DLC multilayer coatings on 5A06 Al alloy

In this study, the Cr/Cr-W/W-DLC/DLC multilayer coating was deposited on 5A06 Al alloy using a combination of unbalanced magnetron sputtering system and filter cathode vacuum arc technique. Dry linear reciprocating sliding wear tests were performed to evaluate the tribological properties of the deposited coating at different temperatures from −100 °C to 25 °C. The microstructure, mechanical properties and wear characteristics of the multilayer coating were also characterized by SEM, EDS, nanoindenter and nanoscratch tester, respectively. The results show that, compared with 0 °C and 25 °C, the tribological behavior of the multilayer DLC coating exhibits significant differences at low temperatures. The formation of the transfer layer and the graphitization caused by the flash temperature contribute to explain the excellent tribological performance of the coating at room temperature and 0 °C. The deterioration of the tribological properties of the multilayer coating at subzero temperatures is ascribed to the inhibition of the graphitization process, as well as the oxidation and capillary action of water molecules. Cyclic shear stress and low temperature lead to the formation of microcracks and surface spalling, which also increases the friction coefficient and wear rate of the multilayer DLC coating.

Mass‐produced Cu nanoparticles as lubricant additives for reducing friction and wear

AbstractThis paper reported the tribological behaviours of Cu nanoparticles as lubricant additives. Cu nanoparticles were prepared by an innovative technology called mass‐produced nanoparticles (MPNP). A SRV‐IV friction and wear tester was used to investigate the influence of load on the tribological performance of 0.1 ~ 2 wt% Cu nanoparticles. The results indicated adding 0.1 wt% Cu nanoparticles into PAO6 base oil and 10 W/40 CH‐4 commercial lubricant, reduce the average friction coefficient by 38% and 3%, and decrease the wear rate by 96% and 66% under 300 N, respectively, compared to the lubricants without nanoparticles. The excellent antiwear and antifriction effect could be attributed to the rolling effect caused by the ideal spherical shape and good dispersibility of the prepared Cu nanoparticles and form deposition film on the surface of the friction pair. Therefore, the Cu nanoparticles prepared by MPNP show excellent tribological performance and possess broad prospects in the fields of lubricant additives.

A Review on the Tribological Performances of High‐Entropy Alloys

Wear is an important form of material loss and failure, and it is usually inevitable in almost all mechanical systems with moving parts. The durability and reliability of engineering components are closely related to their wear resistance. Developing advanced materials to alleviate energy and materials losses in moving mechanical systems still remains a great challenge nowadays. The emergence of novel high‐entropy alloys (HEAs) that compose of multiple principal elements holds great promise for the development of materials with extraordinary wear resistance, due to their high hardness, high wear resistance, and excellent corrosion resistance. Herein, the current research progress of the tribology of HEAs under different conditions is reviewed, including high temperature, dry condition, corrosion solution, and oil lubrication. Specifically, the effects of compositions, microstructures, lubricants, and protective oxide layers on the tribological performance of HEAs are summarized. Furthermore, the underlying mechanisms that are responsible for the excellent wear resistance of HEAs under different conditions are discussed. Finally, the current challenges and the future outlooks are emphasized and addressed systematically. In view of the excellent tribological performances and the diversity of compositional design, HEAs have great potential to be applied in a wide range of mechanical systems to minimize wear.

Insight into the Excellent Tribological Performance of Highly Oriented Poly(phenylene sulfide)

Insight into the Excellent Tribological Performance of Highly Oriented Poly(phenylene sulfide)

Thermostability, oxidation, and high-temperature tribological properties of nano-multilayered AlCrSiN/VN coatings

In this study, monolithic AlCrSiN, VN, and nano-multilayered AlCrSiN/VN coatings were deposited using a hybrid deposition system combining arc ion plating and pulsed direct current magnetron sputtering. The microstructure, thermostability, mechanical, oxidation and tribological properties of the coatings were comparably investigated. The multilayered AlCrSiN/VN coating exhibited a face-centered cubic (fcc) structure with (200) preferred orientation and showed the highest hardness (30.7 ± 0.5 GPa) among these three coatings due to the multilayer interface enhancement mechanism and higher compressive stress. The AlCrSiN sublayers effectively prevented the V element from rapid outward diffusion to the surface of AlCrSiN/VN coating at elevated temperatures, which improved the oxidation resistance of the coating. Decomposition of V (Cr)–N bonds occurred at annealing temperatures from 800 °C to 1000 °C and V2N phase appeared at 1100 °C. The AlCrSiN/VN coating showed excellent tribological performance at high temperatures by combining the merits of VN layers for low friction coefficient and AlCrSiN layers for superior oxidation resistance. Compared to VN and AlCrSiN coatings, AlCrSiN/VN coating showed the lowest wear rate of 2.6×10-15 m3/N·m at 600 °C and lowest friction coefficient of 0.26 at 800 °C with a relativity low wear rate of 39.4×10-15 m3/N·m.

Investigations on the effect of silver nanoparticles on performance of coconut oil based cutting fluid in minimal fluid application

In this work, an innovative nanocutting fluid, based on coconut oil was developed by dispersing silver nanoparticles (AgNPs) of size less than 50 nm. The tribological and physical properties of the prepared nanocutting fluid with different volumes of silver nanoparticles were studied. It was found that the addition of 4% by volume of nanoparticles enhanced the properties of the nanocutting fluid compared to the other concentrations studied, thus demonstrating its excellent tribological performance. The effect of the newly developed nanocutting fluid with 4% of silver nanoparticles on cutting performance was also investigated while machining AISI4340 steel with minimal fluid application. Results revealed that the cutting force, cutting temperature, and tool wear are reduced on an average by 22.6%, 12.6%, and 5.3% respectively. It was evident that efficient cooling and lubrication of nanocutting fluid dispersed with silver nanoparticles improved the cutting performance. The outcomes of this work can be considered as a development toward eco-friendly and sustainable machining.

An approach towards energy and material efficient additive manufacturing: Multi-objective optimization of stellite-6 deposition on SS304

Energy and material saving in additive manufacturing (AM) has become the main concern in recent times for sustainable manufacturing. In this study, a 2 kW fiber laser was used in the direct laser metal deposition technique to deposite stellite-6 powder on SS304. Laser power (400–800 W), laser deposition speed (400–800 mm/min) and powder feed rate (10–20 g/min) were considered as input process parameters; whereas laser energy efficiency (LEE), powder deposition efficiency (PDE) and dilution (D) were taken as output responses. An empirical study has been carried out to analyse the combined effect of input process parameters on outputs. Three recently developed multi-objective optimization algorithms were used to maximize LEE and PDE with an optimum dilution, in which Multi-objective bonobo algorithm provided the best Pareto-surface. An improvement of 10% in LEE with maximum PDE was obtained. Microstructure of deposited clad was found to have fine-homogeneous dendrite and inter-dendritic eutectics, which mainly consisted of cobalt phases and carbides. The hardness of the deposited track was found to be three times of that of the substrate, due to the presence of carbides and high cooling rate. The wear rate of the deposited coating was found to be 7.61 × 10–5 mm3/N-m, which was improved 6.6 times to the substrate. A decrease in the pile-up during wear was observed on the deposited surface, which was found to have a correlation with the rheological factor. The ratio of volumetric wear rate to hardness for stellite-6 coating was 1.28 × 10–7 mm3 /N-m/HV (20 times less as substrate), which indicated an excellent tribological performance of the coating. A stable friction-wear time curve was observed for stellite-6 coating and the coefficient of friction was found out to be 0.33.

Wear mechanism of Ag as solid lubricant for wide range temperature application in micro-beam plasma cladded Ni60 coatings

The effect of Ag content on the microstructure, compositions, and wear resistance of micro-beam plasma cladded Ni60 coating was studied. The friction layer formed on the wear surface at different temperatures and its influence on tribological properties were discussed, and wear mechanism of Ag added Ni60 coating were clarified. The results show that adding Ag can effectively improve the wear resistance of cladding layer. The friction coefficient of the cladding layer decreases from 0.40, 0.10 and 0.22–0.20, 0.08 and 0.18 at 25 ℃, 300 ℃ and 600 ℃, respectively. At room temperature, the wear rate of nickel based coating is 14.13 * 10−7 mm/Nm, and reduces to 10.55 * 10−7 mm/Nm with 5%Ag addition. The excellent tribological performance at room temperatures is attributed to the existence of Ag layer formed in cladding process. The addition of silver significantly reduced the degree of abrasive wear. However, at higher temperature of 300 ℃, Ag precipitates from the coating and begins to generate Ag2O oxide, which avoids the direct contact of metal and effectively reduces the friction coefficient. The wear mechanism is oxidation wear and abrasive wear. At 600 ℃, high temperature softening results in obvious adhesive wear of the coating, and Ag particles accumulate on the surface of the cladding layer in the form of "sweating", and results in the formation of self-lubricants with NiO and AgCrO2. Therefore, oxide lubrication layer formation such as Ag2O, NiO and AgCrO2 at high temperatures is benefit for low friction coefficient at elevated temperature.

Tribological Properties of TiO2/BP Nanocomposites as Lubricant Additives for Titanium Alloy Tribopairs

To improve the tribological performance of titanium alloy, the novel nanocomposites titanium dioxide/black phosphorus nanosheets were successfully prepared by a sol-gel method. The effects of the concentration of the black phosphorus nanocomposites, the ratio of TiO2 to black phosphorus, and the load and sliding velocity on the friction and wear of the titanium alloy friction pair under boundary lubrication conditions were investigated using a ball-on-disc tribometer with an orthogonal experimental design. Based on the results of the analysis of variance, the degree of influence of each factor on the friction and wear was obtained. The results show that these factors have different effects on the tribological behavior of Si3N4-Ti6Al4V(TC4) tribopairs. Load has the greatest influence on the friction and wear of the titanium alloy. When the antiwear performance of the upper Si3N4 ball was chosen as the response index, the optimum tribological conditions were obtained: load, 5 N; sliding velocity, 33 mm/s; mass ratio of TiO2 to black phosphorus nanosheets, 2:1; and additive concentration, 0.01%. The excellent tribological performance could be ascribed to the formation of a tribolayer containing nanocomposites, which played the role of buffering and isolating the Si3N4-TC4 tribopairs.

The tribological performance of W-DLC in solid–liquid lubrication system addivated with Cu nanoparticles

Judicious selection of additives having chemical and physical compatibility with the DLC films may help improving the triboligical properties and durability life of DLC-oil composite lubrication systems. In this study, Cu nanoparticles were added to PAO6 base oil to compose a solid-liquid composite lubrication system with W-DLC film. The effects of nanoparticle concentration, test temperature and applied load on tribological performance were systematically studied by a ball-on-disk friction test system. The tribological results illustrated that Cu nanoparticles could lower the coefficient of friction (COF) and dramatically reduce the wear rates of W-DLC films. The optimal tribological behavior was achieved for the 0.1 wt% concentration under 30 °C and the applied load of 100 N. The test temperature and applied load were vital influencing factors of the solid–liquid lubrication system. The bearing effect and soft colloidal abrasive film of spherical Cu nanoparticle contributed to the excellent tribological performance of the composite lubrication system under mild test conditions, meanwhile, the local delamination of W-DLC film and oxidation were the main causes of the friction failure under harsh test conditions. With test temperature and applied loads increase the degree of graphitization of the W-DLC film increased. In conclusion, there are several pivotal factors affecting the tribological performance of solid–liquid lubrication systems, including the number of nanoparticles between rubbing contact area, graphitization of the worn W-DLC films, tribofilms on the worn ball specimens and oxidation formed in friction test, and the dominant factor is determined by the testing condition.

MoS2/CF synergistic reinforcement on tribological properties of NBR/PU/EP interpenetrating polymer networks

NBR based water-lubricated bearings have attracted tremendous attention with the dramatic oil leakage pollution of oil-lubricated bearings even the implementation of environmentally friendly and ecologically sustainable development strategies. In this paper, MoS2 and CF are used to reinforce NBR based IPNs composites. Results reveal that the damping factor of fillers/IPNs composites reaches to 0.75 and their effective damping temperature range accomplishes to 50.3 ℃. The minimum friction coefficient and wear rate are 0.033 and 3.09 × 10−5 mm3/Nm respectively, which is decreased by 51 % and 68 % compared with original IPNs. This indicates that MoS2 and CF have a brilliant synergistic effect on improving damping and tribological properties of IPNs, which is attributed to the prominent dispersion of CF and its synergistic effect with MoS2. The knowledge obtained in this work will be promising for preparing water-lubricated bearings materials with excellent damping and tribological performances.