The Enhanced Tribological Properties of NiAl Intermetallics: Combined Lubrication of Multilayer Graphene and WS2

In recent years, reducing friction and wear-related adverse impacts on efficiency and durability in moving mechanical systems has gained increased attention. Herein, the search continues for novel materials and lubricants that can potentially reduce friction and wear. As one of the emerging self-lubricating materials, the tribological potential of graphene has been researched deeply. This article was dedicated to explore the combined lubrication of multilayer graphene (MLG) and WS₂. The as-prepared sample of NiAl–1.5 wt% MLG–5 wt% WS₂ (NB) exhibited excellent tribological properties. During the sliding process, a continuous lubricating film was formed to provide the low-strength junctions at the interface, reducing the friction coefficient and wear rate. Moreover, the MLG played the role of reinforcement particles and improved loading carrying ability.     

石墨烯/MoS2复合涂层多环境下的摩擦学性能

以MoS2作为润滑剂,以石墨烯(GE)作为润滑添加剂,采用喷涂法在GCr15钢样片表面制备不同含量的GE/MoS2复合涂层。利用HSR-2M型高速往复式摩擦磨损试验机测试涂层在干摩擦及海水环境中的摩擦磨损性能,并分析了磨痕形貌及磨损机制。结果表明:添加适量石墨烯可明显改善MoS2涂层的摩擦磨损性能,且海水环境中涂层的摩擦因数、磨损率均低于干摩擦;在干摩擦和海水环境下,随着石墨烯含量的增加,GE/MoS2复合涂层的摩擦因数和磨损量均呈现先下降后上升的趋势,当石墨烯质量分数为0.8%时,摩擦磨损性能最优。干摩擦下MoS2涂层的磨损机制为疲劳磨损、黏着磨损和磨粒磨损,GE/MoS2复合涂层主要为磨粒磨损;而在海水环境下几种涂层均仅出现磨粒磨损。     

Tribological Properties of TiAl Matrix Self-Lubricating Composites Containing Multilayer Graphene and Ti3SiC2 at High Temperatures

An investigation is conducted on the unexplored synergistic effects of multilayer graphene (MLG) and Ti₃SiC₂ in self-lubricating composites for use in high-temperature friction and wear applications. The tribological properties of TiAl matrix self-lubricating composites with different solid lubricant additions (Ti₃SiC₂-MLG, MLG) are investigated from room temperature to 800°C using a rotating ball-on-disk configuration. Tribological results suggest the evolution of lubrication properties of MLG and the excellent synergistic lubricating effect of MLG and Ti₃SiC₂ as the testing temperature changes. It can be deduced that MLG has great potential applications as a promising high-temperature solid lubricant within 400°C, and a combination of MLG and Ti₃SiC₂ is an effective way to achieve and maintain desired tribological properties over a wide temperature range.     

Tribological Characterisation of Graphene Oxide as Lubricant Additive on Hypereutectic Al-25Si/Steel Tribopair

The performance of a lubricant greatly depends on the additives it involves. However, recently used additives produce severe pollution when they are burned and exhausted. Therefore, it is necessary to develop a new generation of green additives. Graphene oxide (GO) is considered to be environmentally friendly. The scope of this study is to explore the fundamental tribological behavior of graphene, the first existing 2D material, and evaluate its performance as a lubricant additive. The friction and wear behavior of 0.5 wt% concentrations of GO particles in ethanol and SAE20W50 engine oil on a hypereutectic Al-25Si alloy disc against steel ball was studied at 5 N load. GO as an additive reduced the wear coefficient by 60–80% with 30 Hz frequency for 120 m sliding distance. The minimum value of the coefficient of friction (0.057) was found with SAE20W50 + 0.5 wt% GO. A possible explanation for these results is that the graphene layers act as a 2D nanomaterial and form a conformal protective film on the sliding contact interfaces and easily shear off due to weak Van der Waal's forces and drastically reduce the wear. Scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and Raman spectroscopy were used for characterization of GO and wear scars.     

Tribochemical Transformation of Nano TiO2 to Ilmenite on the Surface of Wearing Steel Parts: Antiwear Action of Nano TiO2 as an Additive in Engine Oil

TiO₂ nanoparticles of average size about 20–30 nm were hydrothermally synthesized from TiCl₄ under mild acidic conditions. The nanoparticles were mixed with dispersant and base oil to give a partially transparent concentrate with 1.5 wt% of Ti content. The concentrate was dispersed in hexane and base oil to characterize, respectively, by transmission electron microscopy (TEM) and dynamic light scattering (DLS). The concentrate was diluted with base oil to a parts per million level of Ti containing dispersion blends that were evaluated for wear and friction control performance. Nano TiO₂ containing fully formulated oil blend showed excellent load-bearing capability in Swingung, Reibung, Verschleiβ (SRV; oscillation, friction, wear) tests. Four-ball test results show that the wear scar diameter was considerably reduced to 0.30 mm for TiO₂-added blend compared to neat base oil (0.60 mm). The performance of TiO₂-added blend was comparable to secondary zinc dialkyl dithiophospate (ZDDP)-added blend under identical condition. Raman spectra of the worn surface on the tested ball revealed the presence of ilmenite (FeTiO₃) and no deposits of pure TiO₂.     

Effect of Temperature on Tribological Properties and Wear Mechanisms of NiAl Matrix Self-Lubricating Composites Containing Graphene Nanoplatelets

Studies have been carried out to explore the friction and wear behaviors of NiAl matrix self-lubricating composites containing graphene nanoplatelets (NG) against an Si₃N₄ ball from 100 to 600°C with a normal load of 10 N and a constant speed of 0.2 m/s. The results show that NG exhibits excellent tribological performance from 100 to 400°C compared to NiAl-based alloys. A possible explanation for this is that graphene nanoplatelets (GNPs) contribute to the formation of a friction layer, which could be beneficial to the low friction coefficient and lower wear rate of NG. As the temperature increases up to 500°C, the beneficial effect of GNPs on the tribological performance of NG becomes invalid due to the oxidation of GNPs, resulting in severe adhesive wear and degradation of the friction layer on the worn surface of NG. GNPs could hold great potential applications as an effective solid lubricant to promote the formation of a friction layer and prevent severe sliding wear below 400°C.     

Tribological Characteristics of Aqueous Graphene Oxide,Graphitic Carbon Nitride,and Their Mixed Suspensions

The tribological performance of graphene oxide (GO), graphitic carbon nitride (g-C₃N₄), and their mixed (g-C₃N₄/GO) aqueous suspensions was investigated. The 0.06 wt% GO, 0.06 wt% g-C₃N₄, and 0.06 wt% 1:1 g-C₃N₄/GO suspensions reduced the coefficient of friction (COF) by 37, 26 and 37% and wear mark radius by 19.1, 16.0 and 19.6%, respectively, in comparison with water. Pure g-C₃N₄ and GO suspensions showed unstable lubrication in the tests with relatively high loads and speeds, while the g-C₃N₄/GO mixed suspension had superior tribological performance in all tested conditions. This is because in the mixed suspension g-C₃N₄ agglomerates became smaller, and GO nanosheets exhibited fewer wrinkles and less stacking, which enabled the formation of a layer of tribo-composite film. As a result, the friction, wear and tribo-corrosion were reduced during sliding.     

Antiwear and Extreme Pressure Properties of Nanofluids for Industrial Applications

This study investigates the effect of CuO, TiO₂, Al₂O₃, and multiwalled nanotube (MWNT) nanoparticles at various treat rates on the tribological properties, namely, wear, coefficient of friction (COF), and pressure of seizure (p_oz), of metalworking fluids during lubricating processes in diverse industrial applications. Results are reported based on two methods: wear scar diameter (WSD) and COF by ASTM D5183 and p_oz by the Institute for Sustainable Technologies–National Research Institute (ITEePib) Polish method for testing lubricants under scuffing conditions. Results showed significant improvements with small filler concentrations of nanoparticles. CuO nanofluids showed a diminishment of 86% for WSD at 0.01 wt%, whereas TiO₂ resulted in an increase in p_oz of up to ～250% at 0.05 wt% compared to pure conventional fluid.     

Preliminary Study of Nano- and Microscale TiO2 Additives on Tribological Behavior of Chemically Modified Rapeseed Oil

This study compared the tribological evaluation of chemically modified rapeseed oil as a potential biodegradable automotive lubricant with and without nano- and microscale titanium dioxide (TiO₂) particles, focusing on the influence of TiO₂ particles to improve the friction reduction and antiwear characteristics of chemically modified rapeseed oil. TiO₂ nano- and microscale particles of anatase phase and rutile phase were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Further, the analysis of chemically modified rapeseed oil with and without TiO₂ additives was carried out to determine its tribological behavior using a pin-on-disc tribometer. The experimental results showed that the addition of TiO₂ nanoparticles exhibited good friction reduction and antiwear properties compared with the addition of microscale TiO₂ and without TiO₂ additives to chemically modified rapeseed oil. Nanoscale TiO₂ is suitable as an antiwear additive in chemically modified rapeseed oil.     

Tribological Behavior of Deagglomerated Active Inorganic Nanoparticles for Advanced Lubrication

The tribological behavior of novel, deagglomerated, and active molybdenum disulfide (MoS₂) nanoparticles as additives in paraffin oil is presented. In a novel approach, the MoS₂ nanoparticles were activated by their intercalation with organic molecules, particularly triglycerides (canola oil) and lecithin (source of phosphorus). A four-ball tribological test setup was used to measure the wear scar diameter, the coefficient of friction, and the extreme pressure properties of such formulated paraffin oils. The results showed significant influence of this uniquely designed MoS₂ nanostructured additive on the coefficient of friction (0.07), the wear scar diameter, and the extreme pressure (315 kg) properties of the paraffin oil. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive x-ray spectroscopy (EDS) were also used for investigating size, the surface morphology, and the elemental composition of the nanoengineered lubricant. The characterization revealed a particle size less than 100 nm and the elemental composition analysis of the wear track showed the presence of Mo, S, and P in the tribofilm, explaining the observed improvements in the tribological properties.     

Tribological Behaviour of Nanostructured Al2O3-3 wt% TiO2 Coating Against Steel in Dry Sliding

Nanostructured and conventional Al₂O₃-3 wt% TiO₂ coatings were deposited by atmospheric plasma spraying. The wear and friction properties of both coatings against a steel ball under dry friction conditions were examined. It was found that the wear resistance of the nanostructured Al₂O₃-3 wt% TiO₂ coating was superior to that of the corresponding conventional counterpart. The improvement in wear resistance of the nanostructured coating was attributed to its higher toughness and cohesion strength between splats. As for the nanostructured coating, the wear mechanism was mainly adhesion with micro-abrasion at low loads (20 N). At high loads (80 N), the wear of the nanostructured coating was controlled by plastic deformation and associated delamination along the splat boundaries, which was similar to that of the conventional coating at low loads. However, the failure of the conventional coating was predominantly brittle fracture within the splats and delamination between splats at high loads.     

Microstructural Characterization of Wear Particles Formed During Tribological Stressing of TiC and Ti(C,N) Coatings

An attempt was undertaken to obtain a better understanding of the tribological properties of two wear-resistant coatings on tool steel by structural and microchemical analysis of wear particles using a transmission electron microscope. Coatings were deposited by physical vapor deposition and plasma-assisted chemical vapor deposition techniques and tribological properties were derived from reciprocating sliding tests of the coatings against alumina balls. Three types of wear particles were identified by electron diffraction and energy dispersive X-ray spectroscopy: nanocrystalline rutile (TiO₂), nanocrystalline graphite and microcrystalline graphite. Low coefficients of friction, of the order of 0.2, were attributed to the formation of solid lubricant films of sub-stoichiometric TiO_2-x Magnéli phases and/or graphite.     

Modification of Graphene Platelets and their Tribological Properties as a Lubricant Additive

Graphene platelets were chemically modified in a reflux reaction with stearic and oleic acids. Examination of the surface features of the graphene platelets before and after modification by infrared spectroscopy and ultraviolet–visible spectrophotometer revealed that the modification led to an improvement in the dispersion of graphene platelets in base oil. The tribological behavior of the lubricating oil containing modified graphene platelets (MGP) was further investigated using a four-ball machine. The results indicated that the oil containing only 0.075 wt% of MGP clearly improved the wear resistance and load-carrying capacity of the machine. Scanning electron microscopy and energy dispersive spectrometer performed to analyze the wear scar surfaces after friction confirmed that the outstanding lubrication performance of MGP could be attributed to their small size and extremely thin laminated structure, which allow the MGP to easily enter the contact area, thereby preventing the rough surfaces from coming into direct contact.     

Tribological behaviour of plasma sprayed Al2O3 and TiO2 ceramic hard coatings under dry contact

Plasma sprayed ceramic coatings are used in a number of industries in which surface modification of components to compare tribological properties is important: so hence, are evaluations of their tribological properties. This paper presents a study on the wear behaviour of three ceramic coatings — Al₂O₃, TiO₂ and Al₂O₃-TiO₂combination — in the load and speed ranges of 5 to 50 N, and 0.3 to 10 m/s, respectively, on which few data are available in the literature. The tests were carried out using a standard dry sand rubber wheel abrasion test and a pin-on-disc machine under dry sliding conditions. It was found that a stick-slip effect seems to occur at low sliding speeds, and transition takes place at a sliding speed of around 4 m/s. Of the three ceramic coatings, TiO₂ was found to be the most wear resistant, with the least friction coefficient, although it is less hard than the Al₂O₃ coatings. Scanning electron microscopy of the surface shows evidence of wear mechanisms such as plastic deformation, transfer-film formation, micro cracks, and grain pull-out in the coatings.     

Tribological properties of 2 novel Mo/B–based lubricant additives in polyalphaolefin

Two kinds of Mo/B oleic diethanolamide derivatives (coded as YXM and YXB) were synthesised, and their tribological properties were evaluated using a 4‐ball machine. Results indicate that the 2 novel additives show excellent antiwear and extreme pressure properties. When 2.5 wt% YXM was added into the base oil, the wear scar diameter was reduced by 42.2%, and the P _B value was increased by 170.4%; when 2.5 wt% YXB was added into the base oil, the wear scar diameter was reduced by 23.1%, and the P _B value was increased by 167.1%. The worn surfaces of the lubricated GCr15 steel were analysed by using scanning electron microscopy and X‐ray photoelectron spectroscopy. It is indicated that the variation of tribofilm species produced by a chemical reaction between the additives and the steel surface plays an important role in inhibiting wear and friction. A model was used to analyse the action mechanism. According to the analysis, the tribofilm is composed of an adsorption layer and a reaction layer, and it could effectively protect the steel surfaces from direct contact.     

Study on Tribological Performance of NiAl Matrix Self-Lubricating Composites Containing Graphene at Different Loads

This study aimed to explore the possibility of improving the tribological performance of NiAl matrix composites by graphene addition. Friction and wear experiments of as-prepared specimens were conducted under different conditions using a pin-on-disk wear testing machine. NiAl matrix composites containing graphene showed satisfactory performance in friction coefficient and wear resistance compared to NiAl matrix composites without graphene. For the active effect of graphene, the friction coefficient and wear rate of NiAl matrix composites were maintained at relatively lower values. The beneficial antifriction and antiwear effects of graphene gradually failed when the applied load was above 8 N. Graphene in NiAl matrix composites played an active role in the formation of a friction layer, which was beneficial to the lower friction coefficient and wear rate. In light of this research, graphene plays an active role in reducing the friction coefficient and wear rate. Hence, graphene has great potential in applications as an effective solid lubricant to promote tribological behavior.     

Various MoS2-, WS2- and C-Based Micro- and Nanoparticles in Boundary Lubrication

Various solid lubricant particles have been experimentally evaluated as possible additives to oils. However, information in terms of a direct comparison of their tribological properties is still missing. In this study, we have compared the tribological properties of seven different solid lubricant micro- and nanoparticles as additives in polyalphaolefin (PAO) oil: MoS₂ nanotubes, MoS₂ platelets (2 and 10 μm), WS₂ nanotubes, WS₂ fullerene-like nanoparticles, graphite platelets (20 μm) and multi-walled carbon nanotubes. The experiments were performed in the boundary lubrication regime under a contact pressure of 1 GPa (Hertz, max) using a ball-on-disc tribotester. In general, the particles significantly decreased the friction and wear compared to the base PAO oil. We found that it was the material of the particles that largely determined their tribological performance. The effect of the size of the particles was much less important, and the morphology (shape) of the particles had little or no influence. We have also investigated the effect of ultrasonication during suspension preparation on particle damage and found that the solid lubricant particles were not notably affected, except the MoS₂ and WS₂ nanotubes, which became somewhat shorter.     

Tribological Properties of Adaptive Ni-Based Composites with Addition of Lubricious Ag2MoO4 at Elevated Temperatures

The Ni-based self-lubricating composites with addition of 10 and 20?wt% Ag₂MoO₄ were fabricated by powder metallurgy technique, and the effect of Ag₂MoO₄ on tribological properties was investigated from room temperature to 700?°C. The tribo-chemical reaction films formed on rubbing surface and their effects on the tribological properties of composites at different temperatures were addressed according to the surface characterization by SEM and Micro-Raman. The results show that the Ag₂MoO₄ decomposed into Ag and Mo during the high-temperature fabrication process. The friction coefficient and wear rate of the composites decrease with the increasing of temperature and Ag₂MoO₄ contents and the composites with addition of 20?wt% Ag₂MoO₄ exhibits the lowest friction coefficient (0.26) and wear rate (1.02?×?10^?5?mm³?N^?1?m^?1) at 700?°C. The composition of the tribo-layers on the worn surfaces of the composites is varied at different temperatures. It is proposed that the improving of tribological properties of the composites at high temperatures are attributed to the synergistic lubricating effect of silver molybdate (reproduced in the rubbing process at high temperatures) and Fe oxide (transfer from disk material to the pin) formed on the worn surface.     

Wear and Friction of TiAl Matrix Self-Lubricating Composites against Si3N4 in Air at Room and Elevated Temperatures

More durable, low-friction bearing materials over a wide temperature range are needed for turbine components and other high-temperature bearing applications. The current study reported the tribological properties of TiAl matrix self-lubricating composites (TMC) containing MoS₂ (a low-temperature lubricant, below 500°C), hBN (a medium-temperature lubricant, below 600°C), and Ti₃SiC₂ (a high-temperature lubricant, above 600°C) designated as MhT against an Si₃N₄ counterface at temperatures ranging from 25 to 800°C in air. The load was 10 N and the sliding speed was 0.2 m/s for all tests. Tribological studies indicated that TMC containing MhT showed a lower friction coefficient and wear rate in comparison to TiAl-based alloy at all test temperatures, which was attributed to the excellent synergetic lubricating effect of MoS₂, hBN, and Ti₃SiC₂. TMC containing 5 wt% MhT exhibited the best tribological properties over a wide temperature range.     

Tribological Analysis of a Hydrodynamic Journal Bearing under the Influence of Synthetic and Biolubricants

This study investigated the tribological characteristics of journal bearings exclusively for automotive applications under the influence of a synthetic lubricant (SAE20W40) and chemically modified rapeseed oil (CMRO) as a biolubricant, dispersed with TiO₂, WS₂, and CuO nanoparticles used as antiwear additive. The effects of synthetic and nanobased biolubricants on the tribological behavior of the hydrodynamic journal bearing were examined using a journal bearing test rig by measuring the coefficient of friction, oil film thickness, and wear under a load of 10 kN and a speed of 3,000 rpm. The test results show that CuO nanoadditives that are added to the biolubricant exhibit outstanding wear and friction reduction behavior, better than that with synthetic lubricants as well as other nanobased biolubricants. The inclusion of CuO nanoparticles in the biolubricant decreased the coefficient of friction by 27% and wear by about 47% compared to a synthetic lubricant. Additionally, investigations were performed using atomic force microscopy (AFM) and scanning electron microscopy (SEM) to study the surface morphology and surface roughness behavior of the tested bearing surfaces.