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This present review article discusses about the effect of solid lubricant additive in surface composite coating deposited by laser cladding and alloying process. Wear and friction is challenging problem in moving machinery parts subjected to rubbing action or sliding motion. Therefore to reduce the wear and friction of sliding machinery parts, coated layer is deposited on the surface of machine component to prevent from surface damage due to wear. Laser cladding and alloying is advanced manufacturing technology by which hard and wear resistant coating material is deposited on the surface of soft conventional materials by use of high power laser energy as heat source to provide good metallurgical adherence between coating and substrate materials. The coating materials generally used for enhancing the friction and wear resistance properties of conventional materials are advanced ceramics, advanced composites, nanomaterials and advanced alloys like high entropy alloys. When solid lubricants are added to these coating materials in limited amount then the friction and wear properties of developed surface improves. The solid lubricant additive in coating materials can reduce the friction coefficient and wear rate of materials. The solid lubricant materials acts as anti-friction and anti-wear agent in the coating materials. The most commonly used solid lubricants are h-BN, CaF2, MoS2, WS2, BaF2 and graphite. In this article the effect of these solid lubricant material on wear resistance and friction coefficient of coated surfaces produced by laser alloying and cladding techniques are described. The various engineering materials used for manufacturing of moving or sliding parts are ferrous materials, titanium alloys, aluminium alloys, magnesium alloys and copper alloys. In this article the coating deposited on these materials with solid lubricant additives by laser cladding and alloying process are reviewed. The problem arises during developing solid lubricant additive coating and its remedies are described.

Aluminum Metal Matrix Composites (MMCs) are preferred over other traditional materials in aerospace, automotive, and marine applications due to their superior enhanced properties. A significant literature has been studied in this regard, and it has been found that processing conditions can be tuned to achieve homogeneous Al-composites structure. The incorporation of ceramic particles has been revealed to be necessary for these composites to achieve the required strength and hardness. Additionally, using agro/industrial waste materials as additional reinforcement, such as fly ash, red mud, and rice husk ash, reduces the density of composites without compromising mechanical and wear characteristics. The addition of soft reinforcements to hard reinforcements reduces the brittleness of composites, according to the literature review. It has been found that incorporating solid lubricants into these composites aids in the development of a protective tribolayer at the interface, minimising wear and plastic deformation. Overall, the study indicates that Al-based hybrid composites offer a lot of potential as a replacement for ceramic reinforced composites and unreinforced Al-alloys in a variety of automotive applications that need low cost, high strength-to-weight ratio, and improved wear resistance. In this study, an attempt is made to combine various aspects of the mechanical and wear behaviour of Al-MMCs, as well as the prediction of the Mechanical and Tribological properties of Aluminum MMCs.

In this research, the effect of fine-grained microstructure on the friction coefficient compared to the coarse-grained one in the ring-compression test of copper samples is investigated. The equal channel angular pressing process was performed on annealed copper at room temperature and in the Bc route in three consecutive passes. Then, the ring-compression test was carried out on the ring-shaped samples at room temperature and in three conditions: dry, with Molybdenum disulfide, and graphite lubricants with deformation rates of 12.5, 25, 37.5, 50, and 62.5%. The calibration curves were provided using the finite element method and analysis of variance was employed to investigate the effect of parameters on friction coefficients. The results showed that the friction coefficients in ECAPed copper in the first and second passes while using graphite and Molybdenum disulfide lubricants are similar. ECAPed copper in the third pass and annealed copper, respectively have lower friction coefficients when being lubricated with graphite and Molybdenum disulfide lubricants compared to other copper samples. Additionally, in all copper samples, except for ECAPed copper in the third pass, the Molybdenum disulfide lubricant decreased the friction coefficient more compared to graphite lubricant.

As a type of thermal structure ceramic, vanadium nitride (VN) ceramics are widely used in harsh conditions, such as high temperatures, variable temperatures, or oxidizing atmospheres. However, high...

This paper reports on a study of the high-temperature tribological performance of self-lubricating nickel-based composite clad. A porous and crack free clad containing matrix, reinforcement, and lubricant phase is developed on titanium 31 alloy using microwave irradiation. The microstructure of both NiCrSiB/WC and NiCrSiB/WC/Ag/BaF2 clad revealed very good metallurgical bonding with the substrate. The average microhardness of NiCrSiB/WC and NiCrSiB/WC/Ag/BaF2 clad is 710.58 HV and 650.25 HV respectively, is comparatively higher than the titanium 31 substrate (320 HV). The addition of Ag and BaF2 solid lubricants in the clad endowing clad to operate at a broad temperature range. Compared with the NiCrSiB/WC clad, solid lubricant encapsulate clad has shown very low friction coefficient and wear rates. The sliding wear characteristics of the clad were investigated by varying load and temperatures. The results revealed that oxide phases (NiO and Cr3O) and lubricant phases (Ag and BaWO4) formed at low and high temperatures are adequate to reduce delamination and material loss.

Poly-tetrafluoroethylene (PTFE) is a well-known solid lubricant, but its poor wear resistance limits its tribological applications. Certain carbonaceous fillers reduce PTFE wear rate by up to 4000-fold with no sacrifice of the friction coefficient; whereas the responsible mechanisms remain unclear. We systematically studied the effects of three graphene fillers with different aggregate strengths (graphene nanoplates, few-layer graphene and single-layer graphene) on the wear resistance of graphene-PTFE composites. The results found (1) graphene of weak aggregate strength outperform that of strong aggregate strength by 100 times in wear reduction, (2) strong correlations between wear rate, tribofilm carboxylate signal intensity and filler-matrix area per unit composite mass. The carboxylate signals likely correspond to chemical bonding between mechanochemically degraded PTFE, graphene and the steel counterface within highly crosslinked and adherent transfer films and worn polymer surfaces. Results in this study support two independent (primary versus secondary) wear reduction hypotheses in literature which were further backed by DFT simulations of filler-matrix interactions, TEM/EDS analysis of wear debris, SEM/EDS images of the polymer surfaces, and environmental test results in a dry argon (Ar) atmosphere. The results of this paper are also of instructive value for the development of solid lubricants with highly controllable wear characteristics.

Nanoparticles (NPs) of solid lubricants (SLs) as solo particles have proved to be excellent anti-wear additives (AWAs), anti-friction additives (AFAs), and extreme-pressure additives (EPAs) for greases. However, hardly any efforts are made to investigate possible synergism/antagonism in the functioning of NPs when added in combination. Graphite is well known as very efficient AWA and AFA but less effective as EPA, whereas PTFE is more known as very efficient EPA and less efficient as AWA and AFA for greases. Hence, it was thought worthwhile to explore the potential of these two particles together as EPA, AWA, and AFA for possible synergism, using multiple combinations of NPs of PTFE (P) and graphite (G) in various amounts (0, 1, 2, 3, and 4 wt. %) keeping the total amount fixed at 4%. It was observed that combo-particles in typical amounts proved to show synergistic action as EPA and AWA. However, as AFA, they showed antagonistic behaviour. In the case of EP, the highest gain (100%) was recorded for combo-grease (1% G and 3% P). In the case of AW performance, all combo-greases showed synergism and showed almost similar benefits (52–62%, depending on the load). However, a clear antagonism was observed in AF performance, barring one combination (1% G and 3% P). The wear mechanism was discussed using various analytical techniques such as scanning electron microscopy (SEM), Raman spectroscopy, and X-ray photo-electron spectroscopy (XPS).

Purpose This study aims to compare the influence of different solid lubricants on the friction stability of a non-asbestos disc brake pad. Design/methodology/approach Three brake pads were developed using three lubricants, namely, non-asbestos brake pad with sulfide mix (NASM), non-asbestos brake pad with bismuth sulfide (NABS) and non-asbestos brake pad with molybdenum disulfide (NAMO). Sulfide mix was indigenously developed by physically mixing friction modifiers, alkaline earth chemicals and various metallic sulfides homogeneously dispersed in graphite medium. The physical, chemical, mechanical and thermal properties of brake pads were characterized as per industrial standards. The tribological performances were studied using the Chase testing machine as SAE-J661-2012. The worn surface of the pads was studied using scanning electron microscope to analyze the dominating wear mechanism. Findings NASM was excellent in fade as well as wear resistance. NABS was better from a wear point of view, but fade resistance was moderate despite its higher cost. NAMO fared average in fade and wear despite its excellent dry lubricating properties. NASM was excellent in terms of fade as well as wear resistance. Originality/value Among the selected metal sulfides, the indigenously developed sulfide mix was better than the other two sulfides, which indicates that the synergetic effect of metal sulfides was always preferable to the individual sulfides.

Funding Information: We are grateful to B. J. Irving for carefully reading the manuscript. G.Z. thanks the National Science Foundation of China (NSFC, grant nos 11834017 and 61888102) and the Strategic Priority Research Program of CAS (grant no. XDB30000000) for their support. M.L. thanks the ESI Fund and the OPR DE International Mobility of Researchers MSCA-IF III at CTU in Prague (no. CZ.02.2.69/0.0/0.0/20_079/0017983) for their support. L.D. gratefully acknowledges the financial support from the Academy of Finland (grant no. 3333099). D.S. thanks the support from NSFC (grant no. 61734001). K.W. and T.T. acknowledge support from the Elemental Strategy Initiative conducted by the MEXT, Japan, A3 Foresight by JSPS and the CREST (JPMJCR15F3), JST. M.L., P.N. and T.P. acknowledge support from the project Novel Nanostructures for Engineering Applications CZ.02.1.01/0.0/0.0/16_026/0008396. This work was supported by the Ministry of Education, Youth and Sports of the Czech Republic through the e-INFRA CZ (ID:90140). T.P., V.E.P.C. and A.S. acknowledge support from the European Union’s Horizon 2020 research and innovation program under grant agreement no. 721642: SOLUTION. The data and materials are available from the corresponding authors upon request. The authors acknowledge the use of the IRIDIS High Performance Computing Facility, and associated support services at the University of Southampton, in the completion of this work. Publisher Copyright: © 2021, The Author(s), under exclusive licence to Springer Nature Limited. MoS2/graphite and MoS2/h-BN interfaces are shown to have ultra-low friction coefficients, whereas edges and interface steps mainly contribute to the friction force. Two-dimensional heterostructures are excellent platforms to realize twist-angle-independent ultra-low friction due to their weak interlayer van der Waals interactions and natural lattice mismatch. However, for finite-size interfaces, the effect of domain edges on the friction process remains unclear. Here we report the superlubricity phenomenon and the edge-pinning effect at MoS2/graphite and MoS2/hexagonal boron nitride van der Waals heterostructure interfaces. We found that the friction coefficients of these heterostructures are below 10(-6). Molecular dynamics simulations corroborate the experiments, which highlights the contribution of edges and interface steps to friction forces. Our experiments and simulations provide more information on the sliding mechanism of finite low-dimensional structures, which is vital to understand the friction process of laminar solid lubricants.

The present study aims to assess the effect of Ag/BaF2 solid lubricant encapsulation in the nickel-based composite coatings for high-temperature tribological applications. The composite coatings (NiCrSiB/WC and NiCrSiB/WC/Ag/BaF2) have successfully been fabricated on the titanium 31 substrate by tungsten inert gas (TIG) cladding technique. The influence of the TIG processing current on the microstructure, microhardness, and fracture toughness was investigated. Mechanical characteristics of the coatings were further correlated with the microstructural morphologies. The coating fabricated at 70 A exhibited significantly higher hardness than other coatings. The tribological performances of the NiCrSiB/WC/Ag/BaF2 composite coatings were superior to those of the NiCrSiB/WC coatings at both low (200 °C) and high (600 °C) temperatures. The synergistic lubrication effect of the Ag/BaF2 solid lubricant combination provided lubrication at a wide range of temperatures. The addition of these solid lubricants in the nickel-based coating helped achieve the low coefficient of friction of 0.2 and lower wear rates. Particularly, oxide phases (such as NiO, TiO, Ni3Ti3O, and W3O) formed on the worn surface at 600 °C, and the lubricant phases (Ag, Ag2F, and Ba (TiO3)) provided excellent resistance to wear.

Textured cutting insert filled with solid lubricants is one of the best alternative cooling methods in metal cutting industries. The problem associated with textured insert is the supply of solid l...

Polytetrafluoroethylene (PTFE) is characterized by outstanding non-stick properties and very low friction coefficients under tribological load. However, PTFE is incompatible with almost all other polymers exhibits cold flow and a low wear resistivity. However, PTFE can be modified e.g. in the presence of air by using high-energy radiation to achieve carboxylic acid fluorid- (-COF), carboxyl- (-COOH) functional groups and persistent perfluoroalkyl (peroxy) radicals. The hydrophilic functional groups of radiation-modified PTFE can be used to generate a chemically covalent coupling with other monomers/polymers (e.g. polyamides) via addition reactions. Another approach to get a chemical bonding of modified PTFE is the use of radicals for the covalent attachment of olefinic groups (e.g. in oils) through radical reactions. It is already known that the dispersion of modified PTFE in synthetic oils at elevated temperatures results in very stable PTFE-oil dispersions, which have improved tribological properties and are compatible with metals.The aim of this study is the development of novel tribologically effective materials based on radiation-modified PTFE, oil and polyamide 66 (PA66). In the first synthesis step, a chemical coupling between selected oils and various types of PTFE was performed. The bonding was proved by fourier-transform infrared spectroscopy (FTIR) after removing oil excess and further extraction of insoluble residue. Additional electron spin resonance measurements (ESR) showed that the linkages mainly resulted from radical reactions. The second processing step was the chemical coupling of PA66 and oil-modified PTFE by reactive extrusion. In order to get an idea about the influence of the chemical bonding of both lubricants with the polymer matrix on the mechanical material properties compared to origin PA66, multipurpose test specimens according to ISO 3167 were prepared by injection molding. It was found, that even bigger amounts of bonded lubricants did not deteriorate the mechanical characteristics in a significant manner. Finally, initial tribological testing of the novel materials was carried out by using a block on ring tribometer test set up. The antifriction and wear behaviour, as well as the transfer film thickness, were analyzed subsequently.

The present research work investigates the effect of solid lubricants tin and graphite independently or combines on the wear behavior of sillimanite-reinforced aluminum matrix composites. Composites containing 10 wt.% sillimanite mineral were fabricated using the stir casting route. Further, 1 wt.% of graphite and also tin and also both added to form the new composites. Optical microscopy revealed a homogeneous distribution of tin, graphite and sillimanite mineral throughout the prepared materials. The addition of sillimanite particles to the base alloy refined the silicon morphology. Microhardness of the composites revealed a good interfacial bonding of sillimanite particles with the base alloy. Further, the addition of sillimanite particles and lubricating agents decreased the wear rate and coefficient of friction of the composites. Maximum reduction in wear rate and coefficient of friction was observed for sillimanite-reinforced composites with both tin and graphite as lubrication agents. For industrial sustainability, the wear property of prepared composite was also compared with the traditional brake drum material, i.e., cast iron. The wear rate of the sillimanite-reinforced composites with both tin and graphite as lubrication agents was in tune with the cast iron brake drum, which is used in the automobile industries. SEM analysis revealed that at low loads, abrasive wear was dominant, whereas, at higher loads, adhesive wear was dominant for material removal.

The Al2O3-MoS2 ceramic-based lubricating coating was prepared via introducing MoS2 dry film lubricant into the micro-defects of thermally sprayed Al2O3 coating by paint spraying method. The microstructure, mechanical properties and tribological behaviors of the as-received Al2O3-MoS2 coating are thoroughly evaluated. The results illustrated that MoS2 was mainly concentrated on the shallow surface of the Al2O3 coating, and thus more compact and smoother Al2O3-MoS2 coating was obtained. Meanwhile, the mechanical properties of the Al2O3 coating did not change significantly after the introduction of MoS2. The tribological experiments illustrated that compared with the Al2O3 coating, the friction coefficient and specific wear rate of the Al2O3-MoS2 coating under different loads were greatly reduced due to the generation of the lubricating layer. Especially under the load of 5 N, the friction coefficient was as low as 0.36, and the wear rate (1.49 × 10−5 mm3 (N m)−1) was about one order of magnitude lower than that of Al2O3 coating (2.53 × 10−4 mm3 (N m)−1). This research established a new and simple way to prepare ceramic-based self-lubricating coatings by using temperature-sensitive solid lubricants.

Due to increased awareness of ecological and health related problems, the researchers are actively searching for renewable and biodegradable cutting lubricants. Vegetable oils with solid lubricants are being explored as a potential source of environmentally helpful lubricants due to good combination of biodegradability, renewability and fabulous lubrication performance. Although sunflower oil poses good cooling capability, yet its application has not been explored extensively in drilling. Therefore, in this research work minimum quantity lubrication (MQL) technique with Al2O3-mixed vegetable-oil-based cutting fluid was implemented. The main objective of this experiment is to analyze the performance of various coolant-lubricant environments (dry, flood, pure MQL and nanofluid MQL) with regard to drilling forces, surface roughness, drill tip temperature and tool wear mechanism in the drilling of AISI 321 stainless steel by using HSS drill tools. In the MQL conditions, coolant supply rate and air pressure are fixed at 120 mL/hr and 6 bar respectively. In addition to explore the cooling capabilities of sunflower oil, nano-Al2O3 were added to the sunflower oil to prepare different concentration (0.5 wt.%, 1.0 wt.% and 1.5 wt.%) nanofluids. Results indicated that MQL drilling with Al2O3-mixed vegetable-oil-based cutting fluid achieved much better performance as compared to the dry, wet and pure MQL drilling. Thrust force, torque, surface roughness and drill tip temperature approximately reduced 44 %, 67 %, 56 % and 26 % respectively at the 30th hole under nanofluid MQL drilling (with 1.5 wt.% of aluminium oxide nanoparticles) as compared to flood conditions. Moreover, tool wear rate reduced significantly while machining under NFMQL conditions. Better results of nanofluid MQL drilling may be attributed to the fact that NFMQL is capable for producing higher cooling effect due to the lubrication characteristics of nanoparticles.

Ceramics are widely used in machining of high temperature alloys i.e., Co-based Haynes 25 alloy due to its superior characteristics. The present paper is focused on the performance of whisker-reinforced ceramic cutting tool (WRCCT) under nano-sized solid lubricants dispersed in MQL (nanofluid-MQL) during turning of Co-based Haynes 25 alloy. The turning experiments were performed under several cutting environments (dry, base fluid MQL (BF-MQL), hBN based nanofluid MQL (hBN-NMQL), MoS2 based nanofluid MQL (MoS2-NMQL), graphite based nanofluid MQL Gr-NMQL) by varying cutting speed (200 and 300 m/min) and feed rate (0.1 and 0.15 mm/ rev) values. Initially, the viscosity and thermal conductivity of nanofluids were evaluated and then the prepared nanofluids were used for machining experiments. The results reveal that the rate of increase in thermal conductivity coefficient relative to base cutting fluid was 11.90% in hBN-nanofluid, 16.29% in MoS2-nanofluid and 14.12% in Gr-nanofluid. In terms of machining performance, on the one hand, the minimum surface roughness was obtained from Gr-NMQL assisted machining, on the other hand, the hBN-NMQL has been successful in limiting of notch wear and nose wear values. Compared to dry turning, the temperature was reduced up to 27.18% with hBN doped nanofluids, while it was 34.95% with MoS2 doped nanofluids and 29.32% with graphene doped nanofluids. WOS:000640976400001 2-s2.0-85101375298

Ceramic powders such as yttrium oxide and aluminum oxide have been extensively used to coat the inner walls and components of chambers used in semiconductor fabrication processes. Fine powders are used to form a dense coating layer by techniques such as thermal spray coating. However, fine powders exhibit strong cohesive forces due to surface roughness and interparticle van der Waals forces. This results in low flowability, a nonuniform powder feed, and nonuniform coatings. Microwave O2 plasma is proposed to improve the flowability of fine Y2O3 powder for a uniform powder supply in the spray coating process. Microwave O2 plasma flames produce a high temperature with active oxygen species at atmospheric pressure. The active oxygen species of plasma are incorporated into the lattice of powder particles, electrically stabilizing the powder, decreasing the static electricity, and reducing interparticle van der Waals forces. In addition, the surface of the fine powder is melted and smoothed by the high temperature of the microwave plasma, so that the powder acts as a dry lubricant. The processed powder was employed to coat a surface using atmospheric thermal spray coating, and the coating was characterized in comparison to a coating produced using commercial powder. The plasma-treated powder produced a coating with higher density and strength and lower porosity and surface roughness. The plasma-treated powder has a high flowability of 2.38 g s−1 and an apparent density of 2.07 g cm−1. Accordingly, the coating layer has a higher adhesion strength of 8.75 MPa and hardness of 651 HV0.3. In addition, its surface roughness of 0.9 μm and porosity of 0.2% are lower than those of a commercial sample.

A method is proposed for increasing the wear resistance of friction pairs by placing solid lubricants within the macro-relief prepared by deformational cutting. Austenitic steel 12Kh18N10T specimens are studied after deformational cutting: metallographic studies of the structure, hardness measurement, investigation of chemical composition through the volume of an edge by mapping energy­dispersive spectra. Tribological tests are conducted for specimens with introduction of macro-relief obtained by deformational cutting, fluoroplastic, and thermally expanded graphite. Results demonstrate the efficiency of using deformational cutting when creating friction pairs, both in terms of increased austenitic steel wear resistance due to the TRIP effect, and use of the macro-relief in terms of placing solid lubricant within a friction surface structure.

To enhance the friction and wear resistance of GCr15/PTFE sliding contact surfaces, the synergistic lubrication effect of micro-textures and solid lubricants were studied in this paper. Micro-textures were processed on GCr15 samples by Nd:YAG laser, which were filled with MoS2. Tribological performance tests were carried out on a Rtec-MFT 5000 tester. Tribological properties were optimal with the textures density of 20% and depth of 9 µm. A continuous composite solid lubricating film was formed by PTFE and MoS2. As load increases, friction coefficient of the sample shows a rapid decline and then stabilizes. With the increase of reciprocating frequency, friction curve of the sample shows a trend of slight fluctuation. When frequency is 2.7 Hz, friction coefficient is the lowest. Tribological properties of PTFE/GCr15 contact surfaces could be significantly optimized by micro-textures and MoS2, which performs favorable prospect of engineering application such as guide rails, bearings, machinery seal, etc.

The intense heat generation during machining is critical to the workpiece quality. Coolant and lubrication therefore play decisive roles in machining. The conventional cutting fluids employed in machining have certain limitations with regards to their use for ecological and economic reasons. However the need for sustainable manufacturing and better surface quality urged to explore the merits of the lubricants that are eco-friendly such as solid lubricants that are proved to be a feasible alternative to the conventional cutting fluids. Solid lubricants, if employed properly, could control the machining zone temperature effectively by intensive removal of heat from the machining zone. If friction at the tool and workpiece interaction can be minimized by providing the effective lubrication, the heat generated can be reduced to some extent. It will also help reduce wear, thus improving the tool life and the surface finish. These are also used to reduce the force and the energy consumption. So the performance of the solid lubricant needs to be evaluated from tribological point of view. For this, an open tribometer has been envisaged to get the friction coefficient between the coated carbide tool and the austenitic stainless steel AISI 304 workpiece at machining - type situations. Hence this study investigate the effects of the machining parameters and the different machining environments on the machinablity aspects namely surface roughness, tool wear, tool - chip contact length, net cutting specific energy, chip morphology and the chip thickness ratio while machining austenitic stainless steel AISI 304 by TiAlN coated tungsten carbide inserts of the different tool geometry. To show the effectiveness of the solid lubricant, a comparative performance analysis, under the different environments was conducted. Results indicate that there is considerable reduction in the average flank wear (35%–60%), net cutting specific energy (40%–49%); tool-chip contact length (40%–60 %), chip thickness ratio (32%–65%) and the surface roughness (10%–39%) with the solid lubricant assisted machining compared to that of wet and dry machining. This study established that the solid lubricant assisted machining is an eco-friendly sustainable manufacturing process for the industry.

This work investigates the coefficient of friction (COF) at room temperature between tool steel 1.2343 and aluminum alloys EN AW-5182, EN AW-6016 as-delivered (T4) and EN AW-6016 naturally aged (T4*) using a strip drawing tribometer. In order to simulate the contact conditions of industrial sheet metal forming processes, the surfaces of the steel pins and of the aluminum strips were maintained as-delivered, i.e., the pins were wire-cut from a hardened and ground plate and the strips were cut from electrical discharge textured (EDT) and dry-lubricated sheets. Two sliding velocities, 50 mm/s and 250 mm/s, and two nominal contact pressures, 10 N/mm2 and 20 N/mm2, were considered. The sliding distance on each strip was 0.5 m. Each pair of pins was utilized for testing 10 or 20 strips to study the influence of increasing the sliding distance on the COF. Before and after the tribological experiments, surface topographies of selected pins and strips were analyzed using 3D optical surface profilometry, optical microscopy and scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDS). Strain hardening due to plastic surface deformation of the strips was investigated using an automated hardness tester. In general, an increasing trend of the COF was observed with increasing sliding distance. The mean COF obtained for each of the tests was in the range of 0.09−0.17; however, it was considerably higher if aluminum was transferred from the strip to the pins. Moreover, moist pin surfaces were identified to increase the COF, as the originally dry lubricant became pasty and sticky which promoted entrapment of abraded aluminum particles. Slightly higher strain hardening of alloy EN AW-5182 compared to alloy EN AW-6016 caused less flattening of the strip asperities and more severe wear of the pin surface.

The current study is carried out to understand the various wear mechanisms of the friction materials and improve their wear and frictional properties. The investigation has been conducted on three types of brake pads; a real automotive pad and two other composite formulations. One of the formulated composites comprises graphite lubricant. The Pads are subjected to; surface analysis using EDXS, SEM, and mapping investigations before and after the wear test, to evaluate the surface properties. The results demonstrate better wear and friction properties for the formulated material comprising the lubricant. The surface investigations exhibit abraded phases from the real pad after service. The wear modes in the real pad are; physical and chemical reactions in the form of corrosive layers and metallic oxides, deep cracked surface due to the thermal fatigue, abrasive wear, and glazed surface. On the other hand, the abrasive and fragmental wear, and fatigue cracks are the wear modes in the graphite-free formulated sample, while a glazed surface is the dominant wear mode in the material containing graphite. A high diffusion of the graphite lubricant on the pad surface after friction actions has been proved. As a result, a protective film formed on the surface, leading to reduce the aggressive friction between the mating surfaces and enhances the adhesion forces between the hard particle and the composite mixture, keeping them embedded inside.

Graphene is well-known as one of the best solid lubricants for its superlubricity and high mechanical strength. Weak adhesion leading to low interfacial compatibility is a significant challenge of ...

Simple n-alcohols, such as 1-dodecanol, show anomalous film-forming and friction behaviour under elastohydrodynamic lubrication (EHL) conditions, as found inside bearings and gears. Using tribometer, diamond anvil cell (DAC), and differential scanning calorimetry (DSC) experiments, we show that liquid 1-dodecanol undergoes pressure-induced solidification when entrained into EHL contacts. Different solid polymorphs are formed inside the contact depending on the temperature and pressure conditions. Surprisingly, at moderate temperature and pressure, 1-dodecanol forms a polymorph that exhibits robust macroscale superlubricity. The DAC and DSC experiments show that superlubricity is facilitated by the formation of lamellar, hydrogen-bonded structures of hexagonally close-packed molecules, which promote interlayer sliding. This novel superlubricity mechanism is similar to that proposed for the two-dimensional materials commonly employed as solid lubricants, but it also enables the practical advantages of liquid lubricants to be maintained. When the pressure is increased, 1-dodecanol undergoes a polymorphic transformation into a phase that gives higher friction. The DAC and DSC experiments indicate that the high-friction polymorph is an orthorhombic crystal. The polymorphic transformation pressure coincides with the onset of dimple formation in the EHL films, revealing that the anomalous film shapes are caused by the formation of rigid orthorhombic crystals inside the contact. This is the first demonstration of macroscale superlubricity in an EHL contact lubricated by a non-aqueous liquid that arises from bulk effects rather than tribochemical transformations at the surfaces. Since the superlubricity observed here results from phase transformations, it is continuously self-replenishing and is insensitive to surface chemistry and topology. This discovery creates the possibility of implementing superlubricity in a wide range of machine components, which would result in enormous improvements in efficiency and durability.

Epoxy resin is one of the most widely used thermoset polymers in high-performance composite materials for lightweight applications. However, epoxy has a high coefficient of friction, which limits its tribological applications. In this study, the effect was investigated of different weight fractions of solid lubricant graphene nanoplatelets (GNPs), ranging from 0 to 4.5 wt%, on mechanical and adhesive wear performance of epoxy. Adhesive wear tests covered mild and severe wear regimes. The correlation of tribological and mechanical properties was studied as well. Scanning electron microscopy (SEM) was used to observe the failure mechanisms for both tribological and mechanical samples after each test. The results revealed that the addition of GNPs to the epoxy improved its stiffness and hardness but reduced its fracture strength and toughness. Adhesive wear performance exhibited high efficiency with GNP additions and showed reductions in the specific wear rate, the coefficient of friction, and the induced interface temperature by 76%, 37%, and 22%, respectively. A fatigue wear mechanism was predominant as the applied load increased. Most importantly, severe wear signs occurred when the interface temperature reached the heat distortion temperature of the epoxy. The tribological, and mechanical properties showed only a weak correlation to each other. The addition of GNPs to epoxy by less than 4.5 wt% was highly efficient to improve the wear performance while maintaining the fracture strength and toughness. Fourier transform infrared spectroscopy (FTIR) analysis shows no chemical interaction between the epoxy matrix with GNPs, which implies its physical interaction.

High temperature applications of self-lubricated sliding surfaces have gained industrial importance during the recent years. One popular system is based on sintered Ni-Cr composites with addition of solid lubricants. In the present work these composites were prepared under controlled sintering conditions with different combinations of solid lubricants (MoS2, Ag and CaF2) at 1200 °C under flowing argon. The physical properties such as sintered density, relative density and porosity were studied. The microstructures and phase studies of the Ni-Cr based composites were conducted using SEM analysis while the hardness of the composites was measured by Vickers Micro Hardness Tester. The friction tests were conducted with ball on disc configuration following ASTM G-99-95a standard. The MoS2 solid lubricant provides best lubrication at room temperature which is demonstrated by a low friction coefficient compared to pure Ni-Cr composites. The SEM pictures of worn out tracks show solid debris distribution, and filling of pores with solid lubricant phases. The time taken for stabilization of friction coefficient also varies with the type of solid lubricant. Dual and multiple additions of solid lubricants are also able to reduce the friction of coefficient compared to pure Ni-Cr composite.

The study focuses on fabricating the Composites where Al 7075 as matrix material, Fly Ash and Graphite as reinforcement material by using Stir Casting arrangement with proper distribution of ash particles all over the specimen. Fly-ash can be used for preparing MMC’s which can turn industrial waste into industrial wealth. This can also solve the problem of storage and disposal of fly ash. The composition of the casted specimen is 90 wt% Al7075 alloy which has to be kept as constant, and varying the type of the solid lubricants: graphite, and Fly ash. The samples of Al7075 were fabricated with different weight percentages of (0, 3, 6, and 9 wt%). Al7075 composites are successfully fabricated through the stir casting process. The casted specimens are machined for the necessary testing as per the ASTM standards. The mechanical properties like tensile strength, compression strength, and hardness of the fabricated composites are evaluated by conducting experimental tests while the wear properties were evaluated via the pin-on-disc method.

Aluminium alloys are known for their high strength, wear and outstanding corrosion resistance. These alloys have proved their worth in various sectors such as automotive, aerospace, marine, defense and numerous other industrial applications. Owing to the incorporation of different reinforcement in aluminum alloys, it is relatively easier to develop novel composites with desirable properties. The selection of reinforcement is based upon the desired properties and wettability of the base matrix. Various aluminum alloy series have been evolved in the recent past and are still being explored. Researchers have extended the properties of different series of aluminium alloys by reinforcing them with other materials, it be ceramics, metals and solid lubricants, etc. The identification of the particular series at a time becomes an issue for scientists and researchers, and many authors have reviewed the work performed on various aluminum alloys. This paper attempts to bring forth the wear and frictional behavior of two aluminum alloys, AA 6061 and AA 6082. The work performed on these alloys in the previous years has been thoroughly reviewed with respect to their tribological performance and discussed here. This paper will enlighten researchers about the existing wear and frictional behavior of various materials based on the said series, and it will be a great concern for the researchers.

This research deals with development of hybrid aluminium composite through traditional stir casting route. Varying weight percentage of alumina (8% & 12%) and constant weight of graphite (5%) are choosen to improve the basic and friction behaviour of aluminum .Pin on disc tribometer was utlized to under the wear behvaiour of developed composite at constant wear parameter viz constant load, velocity, and slding distance. The output showed that addition of reinforcement increase the hardness of fabricated composite. Likewise incremental percentage of alumina improvise the wear resistance of composite, this might be owing the addition of solid lubricants that forms tribo layer between the pin and contour disc parts.

Metalworking fluids are widely used to increase productivity and quality of metal cutting. However, these metalworking fluids possesses the problems in terms of the effect on environment and health of the worker. Hence, various approaches to provide cooling and lubrication are explored such as mist cooling, high-pressure cooling, minimum quantity lubrication (MQL), nano fluids, solid lubricants, etc. In this regards, the present work exhibits the performance evaluation of vegetable-based minimum quantity lubrication (MQL) in drilling of aluminium alloy. This drilling tests have been performed in different cutting environments such as Dry, flood cooling, MQL with castor oil, MQL with sunflower oil with uncoated HSS twist drill. The effect of various drilling parameters have been analysed by measuring surface roughness, axial thrust, and torque produced. The comparison of results indicates effectiveness of the vegetable-based MQL in terms improved surface finish and reduction in axial thrust and torque during drilling.

In order to enhance the turning efficiency various types of cutting fluids have been used in machining processes. The synthetic nature of these fluids restricts its uses in turning. These are dangerous to the worker’s health as well as to the environment because of disposal issues. Therefore, the focus on cutting oils has switched from synthetic/semi-synthetic lubricants to biodegradable and nano solid lubricants. Recently, to enhance the cutting performance solid lubricants (MoS2, Caf2, HBN, WS2) blended in vegetable oils have been used in turning. In this study the critical review of different vegetable oils, bio-oils, solid-lubricants and carbon based nano-solid lubricants while turning of hard-to-cut materials has been conducted.

Fast development in nanotechnology as of present days enable the development of advance metal matrix nano composites (MMNCs) for different requesting fields of building and medications like aviation, protection, automobiles, hardware, materials, science, vitality, condition, data and correspondence, purchaser products biotechnology and so forth. Carbonous material like graphite, carbon nanotubes (CNTs), carbon foams, carbon nano fibers (CNFs) and graphene are attractive reinforcement materials for self-lubricating MMNCs due to excellent electrical, mechanical and thermal properties along with lubricious nature. These materials act as solid lubricants in aluminum, titanium and magnesium MMCs for lightweight submission wherever fluid lubrication is difficult or ineffective. Besides, fluid lubricants are not ecological gracious, let go some quantities of impurity to environment. The growth of self- grease MMNCs is a significant for green or environmental gracious tribology. However, there is still some challenging problems that need to be resolved such as agglomeration of nano- size particle, low wet ability and a poor interface between particles and matrix. The results reveal that reinforcing self-lubricating carbon us materials to metal matrix decrease both coefficient of roughness and dress in rate.

The nanofriction properties of hexagonal boron nitride (h-BN) are vital for its application as a substrate for graphene devices and solid lubricants in micro- and nano-electromechanical devices. In this work, the nanofriction characteristics of h-BN on Si/SiO2 substrates with a bias voltage are explored using a conductive atomic force microscopy (AFM) tip sliding on the h-BN surface under different substrate bias voltages. The results show that the nanofriction on h-BN increases with an increase in the applied bias difference (Vt−s) between the conductive tip and the substrate. The nanofriction under negative Vt−s is larger than that under positive Vt−s. The variation in nanofriction is relevant to the electrostatic interaction caused by the charging effect. The electrostatic force between opposite charges localized on the conductive tip and at the SiO2/Si interface increases with an increase in Vt−s. Owing to the characteristics of p-type silicon, a positive Vt−s will first cause depletion of majority carriers, which results in a difference of nanofriction under positive and negative Vt−s. Our findings provide an approach for manipulating the nanofriction of 2D insulating material surfaces through an applied electric field, and are helpful for designing a substrate for graphene devices.

The application of fluoride-based solid lubricants in wear resistant materials is increasing rapidly, especially in advanced materials that need to operate at elevated temperatures. However, a concise and consistent discussion on this important class of fluoride lubricants and their tribological characteristics in advanced materials is not available. This review aims to provide a comprehensive discussion on various fluoride solid lubricants used as additive in a composite material or as coatings at a wide range of operating conditions. A brittle-ductile transformation above ∼400 °C allows their lubricating nature. Furthermore, fluorides provide a synergistic effect if they react with other metallic or non-metallic compounds at high temperature. Finally, this article highlights the industrial applications of fluoride solid lubricants in wear resistant components.

A device design is proposed that makes it possible to obtain composite castings of sliding bearings based on babbitt by mixing alloying additives from antifriction powders of solid lubricants (graphite, molybdenum disulfide, etc.) into the melt, having a density significantly lower than the density of babbitt itself. The principle of mixing is based on the use of numerous turbulent flows resulting from the rotation of a gating rod with a wire pile in the melt material, the packing density coefficient of which is not less than 0.1. Due to the suction effect of these flows, non-metallic particles of solid lubricant powder do not float to the surface of the melt and, after crystallization, remain in the body of the casting. The supply of alloying powder of solid lubricant is carried out simultaneously with the supply of the babbitt melt through the central and distribution gating channels made in a rotating rod. Under the action of centrifugal forces, powder particles and melt material flow through distribution channels to the walls of the mold (mold), passing through the rotation zone of the metal pile. In this case, intensive mixing of the powder particles with the melt material occurs due to the suction effect of turbulent flows arising behind the moving pile. In addition, as a result of the rotation of the wire pile, dendritic constituents are crushed in babbitt castings. Metallographic studies of the castings obtained on the developed device have shown that the structure of the casting obtained by traditional technology contains large quantities of solid crystals of intermetallic compounds SnSb and Cu3Sn, while in the structure of the casting obtained using the proposed device, along with the aforementioned intermetallic compounds, particles of solid lubricant C + MoS2powder embedded in the crystallized melt are observed.

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

Disorder in the contact between an amorphous slider and a crystalline substrate leads to a cancellation of lateral forces. Atomically flat, rigid surfaces exhibit structural superlubricity, with the frictional stress in circular contacts of radius a vanishing as 1/a. The inclusion of elasticity allows relative motion of domains on the surface in response to the random interfacial forces. The competition between disorder and elastic deformation is predicted to limit structural superlubricity and produce a constant frictional stress for a larger than a characteristic domain size λ that depends on the ratio of the shear modulus G to the magnitude of interfacial shear stresses τ0. Extensive simulations of a flat, amorphous punch sliding on a crystalline substrate with different system sizes and G/τ0 are used to test scaling predictions and determine unknown prefactors that are needed for quantitative analysis. For bulk systems, we find an exponential decrease of the large a frictional stress and 1/λ with increasing G/τ0. For thin free-standing films, the stress and 1/λ are inversely proportional to G/τ0. These results may help explain the size-dependent friction of nanoparticles and plate-like materials used as solid lubricants.

Purpose The purpose of this study is the influence of various combinations of metal sulfides on the tribological performance of brake pads. Design/methodology/approach Three brake pads were prepared using the possible combination of any two of the solid lubricants from Bismuth trisulfide (Bi2S3); Tin disulfide (SnS2) and Antimony trisulfide (Sb2S3) are chosen and blended with molybdenum disulfide and graphite. The tribological performance was compared with the brake pad containing aftermarket sulfide mixture. The tribological performance parameters such as performance coefficient of friction, fade percent, recovery percent, wear thickness loss, time is taken to reach the maximum temperature and fluctuation of friction were investigated using Chase tribometer adopting IS 2742 Part-4 (1994) test procedure. Findings The friction stability of the brake pad with 4Wt% of MoS2, Bi2S3 and SnS2 was observed to be better, but it showed poor wear performance and aggressive towards the rotor, whereas the brake pad contained 4Wt% of MoS2, Bi2S3 and Sb2S3 exhibited improved wear performance. Originality/value This paper explains the influence of the combination of multiple metal sulfide in the tribological performance of the copper-free brake friction composite. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-07-2020-0249/

Two-dimensional (2D) materials, including graphene-family materials and molybdenum disulfide (MoS2), have been used as solid lubricants because of their low interlayer shear strength. In this study, a fluorinated graphene (FG)–MoS2 nanocomposite coating was deposited on a stainless-steel substrate with a laser surface textured dimple array. The FG–MoS2 nanocomposite coating deposited on a textured surface led to the reduction in the coefficient of friction to 0.036, and it significantly reduced wear and extended the lifetime compared with those obtained using the MoS2 coating. The excellent tribological performance is attributed to the synergetic effect between FG and MoS2 nanoflakes and the function of texture, where the MoS2 nanoflakes dominate the lubrication performance because of interlayer shearing, and the FG nanoflakes suppress the influence of external humidity on MoS2 nanoflakes because of their hydrophobic nature. Meanwhile, the textured surface can promote the formation of a tribofilm through changing the stress distribution at the sliding interface and act as a reservoir for nanoflakes, leading to a much lower friction and longer lifetime. This has implications for the development of functional surfaces with excellent lubrication and wear-resistance performances with 2D materials.

Cold extrusion is an established technology for the production of dimensionally accurate components in large series. Due to the high material and energy efficiency, a resource-saving manufacturing of high-performance parts is possible. Forming at room temperature leads to an advantageous grain structure and work hardening of the material, resulting in components with favorable operating characteristics. Nevertheless, a challenge is the generation of residual stresses during forming, which are influencing the fatigue behavior. The modification of the tribological conditions is one method for influencing the parts’ residual stress state. However, the high strength and work hardening of the materials formed at room temperature leads to high tribological loads between billet and die. These challenges are intensified by the increasing use of stainless steels due to growing demands for corrosion resistant components. The aim followed within this paper is therefore to investigate the applicability of typical lubricant coatings in the forward rod extrusion of stainless steels. For this purpose, the ferritic stainless steel X6Cr17 (DIN 1.4016) and the ferritic-austenitic stainless steel X2CrNiMoN22-5-3 (DIN 1.4462) are extruded with an equivalent plastic strain of ε̅ ≈ 1. The research is performed with a molybdenum disulfide (MoS2), a soap and a polymer-based lubricant coating. For reproducing different contact conditions, the die geometry is varied with die opening angles of 60°, 90° and 120°. The suitability of the lubricants is evaluated using the integrity of the lubricant coating after forming. From the correlations between process forces, temperatures and surface integrity, recommendations for the application of the researched lubricants are derived.

The aim of this work was to achieve improved dispersibility of hydrophobic dry lubricants in aqueous media through plasma activation. As a result, the use of wet-chemical environmentally questionable substances – for example, certain surfactants – to ensure the dispersibility of such particles can be avoided. These plasma-activated particles can be further embedded in electroless nickel (Ni) coatings to improve wear behaviour. Thus, the hydrophobic polymeric powders polyimide and polyetheretherketone and the ceramic powder hexagonal boron nitride (BN) were activated with atmospheric pressure plasma using a diffuse coplanar dielectric barrier discharge system. The generation of polar chemical bonds on the powder surface resulted in an improved dispersibility of the powders in aqueous media. This led to a higher deposit volume of the particles in electroless nickel dispersion coatings. The modified bonding conditions at the powder surfaces were analysed with infrared and X-ray photoelectron spectroscopy. Optical microscopy and scanning electron microscopy investigations showed the deposit of the activated dispersed phase in the coatings. Furthermore, the wear behaviour of the coating was tested by using the Taber abraser test. The plasma activation led to surface modifications – namely, linkage of polar groups at the powder surfaces – and therefore to improved dispersibility. The deposition of the particles in the electroless nickel coatings was possible with all three materials, and the wear resistance of the coatings was improved.

The influence of modifying additions on the strength and tribological properties of titanium nitride composites has been examined. The lowest contact angle (25–30°) is shown by the PG12N-01 alloy, containing chromium, boron, silicon, and carbon. Relatively porousless structures can be produced in the TiN–PG12N-01 system when chromium carbide and carbon are introduced into the composite as graphite, contributing to the formation of TiCN to improve wetting and adhesion. Graphite introduced additionally as an impurity remains after sintering as an individual uniformly distributed phase integrated into the overall composite structure. This graphite can successfully act as a dry lubricant, improving the service characteristics. In addition, it activates sintering of the composite allowing it to become almost porousless. The optimum sintering temperature falls in the range 1450–1500°C depending on carbon and metal matrix contents. The resultant composites have 300–500 MPa strength and 16.1 GPa hardness. The highest strength can be reached through an optimum combination of graphite and PG12N-01 matrix. The mechanical characteristics deteriorate when the amount of these components is higher or inadequate. The antifriction characteristics of the materials have been tested by dry end friction (at a speed of 8 m/sec, 50 MPa pressure in the contact area, and 10 km sliding path) against a 65G steel counterface with 60 HRC hardness: friction coefficient has been found to be 0.27–0.3 and wear resistance 0.2 ± 0.02 μm/km. The developed ceramic materials thus have high strength and antifriction characteristics and can be used in dry friction conditions at high speeds and loads.