To propose an environment benign process; the surface grinding of ‘Ti–6Al–4V-ELI’ was carried out under 20 different grinding-environments viz. dry grinding, conventional flood cooling using ...synthetic fluid and minimum quantity lubrication (MQL) using three types of biodegradable vegetable oils (with and without graphene nanoplatelets). Due to the unique properties of graphene nano-additives viz. exceptionally high thermal-conductivity, superoleophilic nature, adsorption phenomena, large surface area (200 m2/g), interlayer shear-ability and polar bonding of vegetable oils; a synergistic lubrication film was developed that had exhibited excellent grinding performance. The 1.5 wt% graphene in canola oil-based MQL had resulted in 16.9%, 22.1%, 33.83% and 15.1% reduced values of surface roughness (Ra), grinding force (Fn), specific grinding energy and coefficient-of-friction in comparison to conventional flood cooling.
•In-spite of intense R&D on graphene for its myriad applications; its tribological potential is still unexplored.•The experimental study examines graphene nanofluids effectiveness in the surface grinding for green tribology.•The tribological potential of vegetable oils raised by many folds with the aid of graphene nano-additives.•Surface grinding performance is measured in terms of surface roughness, grinding forces, specific grinding energy and COF.•Rheological behavior of nanofluids; SEM, EDX and Raman spectroscopy is also conducted.
Reducing friction is one of the best ways to lower energy consumption and make processes more environmentally friendly. Because of the growing interest in green lubricants, we investigated the ...synergetic effects of graphene quantum dots (GQDs) combined with aqueous glycerol to improve the lubrication performance of self-mated steel contacts in reciprocating sliding motion. As a comparison, the lubrication performance of some other two-dimensional (2D) graphitic materials (graphite, graphene oxide, and graphene nanoplatelets) was also studied. The results demonstrate that the GQDs-based nano-lubricant reduces the running-in period and provides super-low friction at a high contact pressure in the boundary-lubrication regime, with 72% and 53% improvements in anti-friction and anti-wear performance compared with aqueous glycerol. On the other hand, the 2D graphitic materials provide super-low friction in the mixed-lubrication regime due to the dominant polishing effect of the hydroxyl groups. The surface Raman mapping indicates that the 2D graphitic materials were severely damaged by the continuous reciprocating motion owing to their inferior crack resistance. In contrast, the superior deformation resistance of the GQDs helps to develop a tough tribofilm. This lubrication mechanism suggests that internal shearing of graphene layers inside the GQDs significantly reduces the wear and friction during the running-in period, while the in-situ formation of strongly adhered tough tribofilm with more surface coverage contributed to the realization of super-low friction under a high contact pressure. This study demonstrated that GQDs-based green nano-lubricants could provide super-low friction at a high contact pressure in the boundary-lubrication regime, which was so far characteristic mainly for conventional environment-polluting lubricants.
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•Synergism of GQDs and aqeous glycerol is investigated between steel/steel contact.•GQDs provide super-low friction in boundary lubrication regime at a high contact pressure.•GQDs promotes the formations of tough tribofilm with more surface coverage.•2D graphitic materials provide super-low friction in mixed lubrication regime.•Boundary lubrication mechanism of GQDs with aqueous glycerol is proposed.
Achieving macroscale superlubricity on engineering steel by utilizing aqueous green lubricants has gained growing interest, given its substantial potential to reduce energy consumption and carbon ...footprint. However, maintaining superlubricity under diverse sliding conditions over a prolonged duration is a major obstacle for real-scale applications. Herein, we report that a robust and durable tribofilm enabled by a unique lubrication mechanism based on carboxylated graphene quantum dots (CGQDs) in aqueous glycerol triggers macroscale superlubricity in self-mated steel contacts. A dedicated intermittent test was designed to show the superlubricity's robustness and the ability of the tribofilm to adapt to a variety of relevant sliding conditions. Moreover, the boundary film provides an average coefficient of friction of around 0.007 and up to 69 % wear reduction (compared to the base lubricant), resulting in the maintenance of superlubricity at a real final contact pressure of 123 MPa, which increases the upper limit of the contact pressure compared to current aqueous-lubricated steel contacts. The new superlubricity mechanism was enabled by the chemical adsorption of the CGQDs onto the worn metal surface, coupled with the tribo-induced structural degradation and transformation of the CGQDs into layered graphitic structures that generate an adaptable low-shear interface. This work provides new insights into the role of chemical adsorption and structural transformation of CGQDs in achieving superlubricity and is an important step forward for implementing energy-efficient and green lubrication technologies for industrial applications.
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•Graphene quantum dots (GQDs) nano-additives in aqueous glycerol provide super-low friction (µ ≈ 0.012) between self-mated steel contacts.•The super-low friction is observed under a ...contact pressure as high as 316.5 MPa in the boundary lubrication regime (rarely observed for steel/steel contacts).•A 98% improvement in wear performance is observed compared to pure aqueous glycerol without GQDs nano-additives.•A more realistic lubrication mechanism is proposed based on the friction-induced structural degradation of GQDs.
Reducing friction is a promising strategy to decrease material losses and energy consumption in industrial systems. However, in aqueous-lubricated steel contacts, the contact pressure rarely exceeds 50 MPa during super-low friction due to excessive wear. This work demonstrates that even in steel/steel contacts, by combining graphene quantum dots (GQDs) with aqueous glycerol, it is possible to maintain super-low friction (µ ≈ 0.012) under a contact pressure as high as 316.5 MPa. Moreover, the use of GQDs improved the wear performance by 98 % compared to pure aqueous glycerol due to the formation of a tribochemical film, resulting from the electrostatic adsorption of GQDs on the positively charged sites on the worn surface. In particular, the exfoliation of graphene sheets within GQDs, the shearing of graphene layers inside the GQDs, and the OH–OH repulsion between the asperities shortens the running-in period and consequently reduces the friction and wear. At the same time, the formation of a chemically adsorbed tribofilm containing friction-induced structurally degraded GQDs protects the surface from wear and facilitates the maintenance of super-low friction at high contact pressures by improving the load-carrying capacity. This study suggests that green nano-lubricants based on GQDs have immense potential in sustainable engineering.
Green manufacturing has gained extensive attention in the field of manufacturing and processing. Developing biopolymer lubricants, such as hydroxypropyl methylcellulose (HPMC), is an appealing ...research direction. HPMC is an organic polymer with high moisture resistance and formability that is commonly used as an external protective layer on food products and in the pharmaceutical industry. HPMC protective layers demonstrate lubricating and wear-resistance characteristics. However, the practical application of HPMC is limited by its weaknesses such as a short protection life and unstable long-term operation. This deficiency can be ameliorated by adding solid lubricant additives that exhibit high wear resistance. Molybdenum disulfide (MoS2) is a favorable option for green tribological additives. In this study, the effects of MoS2 nanoparticle additive to the tribological properties of a biopolymer coating were investigated. Uniform distributions of MoS2 nanoparticles were observed. X-ray diffraction patterns and Raman spectroscopy analysis revealed excellent structure and crystallinity of MoS2 in the biopolymer coating. The ball-on-disk tribotest results demonstrated that significant improvement can be achieved in the tribological properties of a green composite coating by incorporating MoS2 nanoparticle additives into biopolymer coating. Finally, a MoS2 dominant tribological behavior is discussed.
•The biopolymer HPMC green lubricant has been successfully prepared and its tribology performance has been demonstrated.•The tribological behavior was successfully improved by appropriate amount MoS2 additive.•Crystallizedrystallized MoS2 transfer film plays an important role in reducing friction and providing stable lubrication performance.
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The word “nanotribology” was introduced for the first time in the title of a paper and a book in 1995. This field encompasses fundamental studies of surface characterization, ...adhesion, friction, scratching, wear, and lubrication at the atomic scale. At most solid-solid interfaces of technological relevance, contact occurs at numerous asperities. It is of importance to investigate a single asperity contact in the fundamental tribological studies. A nanoprobe sliding on a surface in probe-based microscopies, including atomic force microscopy (AFM) at ultralow loads, simulates one such contact. AFMs and depth-sensing nanoindentation techniques are also used for nanomechanical characterization. The field is referred to as nanomechanics. AFMs can also be used for nanoelectrical characterization which includes electrical resistance, surface potential, and capacitance mapping.
Research in the field of nanotribology and nanomechanics was initiated by or for the magnetic storage industry in the late 1980s. Later in the mid-1990s, nanotribology and nanomechanics research became important in bio/nanotechnology devices which involve relative motion, as well as ultrathin films. Adhesion, friction and wear issues in bio/nanotechnology devices led to the development of the field of bio/nanotribology. Research in ultrathin films used in the cosmetic industry, including hair, hair conditioner, skin, and skin cream, led to development of the field of nanotribology in cosmetics. Biologically inspired design, adaptation, or derivation from nature, referred to as biomimetics or bioinspiration, can guide us to initiate and produce nanomaterials, nanodevices, and processes in a sustainable and environmentally friendly manner. So called, green nanotribology research is important in this field.
This perspective article presents an overview of fundamental understanding of nanotribology and nanomechanics and their applications in various fields ranging from magnetic storage, bio/nanotechnology, hair and hair conditioner, skin and skin cream, and bioinspiration (green nanotribology).
This paper highlights the future perspectives of sustainable tribology by examining the economic, environmental and social impact of three tribological case studies. One case study examines the ...sustainability and durability of micro-CHP systems looking the tribological phenomena generated within a scroll expander system. The scroll is the main part of a specific micro-CHP system and experiences wear and cavitation damage. The tribological optimization of the scroll expander improves the sustainability of the micro-CHP unit while it has a serious economic and environmental impact to the consumers and to the society in general. Another case study is focused on friction and wear performance of lifeboat launch slipways. The causes of high friction and wear during the RNLI's lifeboat launches along an inclined slipway are investigated with a view to reducing the environmental impact due to slipway panel wear and lubricant release into the marine environment. The project encompasses the sustainable design of slipway panels using design modifications based on tribological investigations to double their lifespan, while environmental and economic impact was significantly reduced by the use of biodegradable greases and water as lubricants. The final case study involves an investigation of recycled plastic materials to replace polyurethane used on skateboard wheels, scooters and similar applications. Polyurethane (PU) is difficult to recycle. With the dwindling resources and environmental problems facing the world today, recycling for both waste reduction and resource preservation has become an increasingly important aspect of sustainability. The tribological results showed that recycled polycarbonate plastic can effectively act as a substitute to polyurethane wheels. Moreover, sustainability considerations showing the environmental benefits of the use of recycled plastics over PU include reducing the CO2 footprint by 50% and the energy consumed by 60%, among other benefits. These case studies emphasise the importance of sustainable tribology in our epoch showing that increased sustainability performance can be achieved through tribology to a significant extent in many cases, providing stability to our world and more viable long term growth to our societies.
The aim of this paper reviews the tribological properties of various polymers and polymer composites to understand its friction and wear behavior. It explores that the role of various lubrication in ...polymer tribology and the importance of green tribology. It deals with the rheological characters of various polymers to describe the flow characters for various manufacturing techniques. It enlightens the importance of using recyclable and biodegradable polymers for environmental safety. It digs out the polymers which are most suitable for fused deposition modeling (FDM) technique. An attempt has been made to encapsulate the fundamental concepts in frictional, wear, flow characteristics and biodegradable nature of various polymers. This article mainly focuses on various behaviors and recent advancement in the area of polymers to a great extent. These aspects contribute to a strong basement for the future developments in the area of polymers and its applications.
In this article, the tribological behavior and energy efficiency of surfaces coated with WC-CoCr/HVOF were evaluated after a laser remelting process, using low and high laser energy densities, ...respectively, 33.3 and 150 J/mm2. The purpose of laser remelting was to adequately modify the microstructure of the coatings and promote better performance during surface sliding. Therefore, the microstructure, phase composition and microhardness of the coatings were investigated, and heat effect on the substrate. During dry and lubricated tribological tests, friction coefficient (COF), wear, and surface roughness also were evaluated. In the dry tests, friction, wear and heat dissipation energies were obtained, which were then correlated with the energy consumed by the tribometer. A HEPR-type biodegradable oil was used in the lubricated tests. The proper formation of W2C and Co3W3C, obtained for the lower energy density, increased the hardness, without weakening the material, while the CrC phase acted as an anti-wear barrier. Whereas for the high energy density, thermal decomposition produced fragile phases, which were easily removed from the matrix during the wear test. The sample tested in as-sprayed condition had a high adhesion and friction compared to the remelted samples. On the remelted surfaces, greater friction stability was obtained. The lower dry friction was not linked to the lower power consumption, a result which was then attributed to the higher heat dissipation from the surface during the tests. Finally, this study proposes a methodology for quantifying the efficiency of sliding surfaces and points to a sustainable solution for tribology.
•An energy-based mathematical model was developed to estimate the sliding efficiency.•A non-linear behavior between laser energy and coating microhardness was obtained.•Laser remelting in the coating lowers COF but not necessarily energy consumption.•The adequate distribution of W2C, Co3W3C and CrC increases the resistance to wear.•The sustainable combination of laser remelting with HEPR oil reduced COF and wear.
Owing to the extreme heat generated during Inconel 718 machining, the application of a minimum quantity lubrication (MQL) strategy is restricted to mild cutting conditions. By incorporating ...vegetable-based cutting oils reinforced by nanoparticles as possible additives, the effectiveness of MQL can be improved in high-speed machining. In this study, hybrid nano-green oils were developed by combining graphene nanoparticles in various volume concentrations with sunflower oil. Subsequently, dispersion stability, thermal conductivity, viscosity, and wetting angle of nano-green oils were measured. An MQL device is used to disperse the smallest amount of nano-green oils throughout the machining area. Later, the experimentally optimized graphene-based green oil is used for milling experiments. Furthermore, hard machining experiments were conducted with cutting speed of 80 m/min, feed rate of 0.2 mm/rev, and depth of cut of 0.5 mm under four different lubricating mediums: dry, flooded, sunflower oil, and 0.7% graphene reinforced sunflower oil. Comparative results show that 0.7% graphene reinforced sunflower oil performs better and reduces surface roughness by 49%, cutting force by 25%, cutting temperature by 31%, and tool wear by 20% as compared to dry machining environment. Finally, elemental analysis of cutting insert reports that adhesion is the major wear mechanism in all mediums.
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