Tribological Properties Of MoS2 Research Articles

Tribological properties of trimethylolpropane oleate synthesized through esterification reaction with nano-MoS2 catalysts of different shapes

PurposeThis study aims to investigate the catalytic performance and tribological properties of MoS2 powder.Design/methodology/approachIn this work, the authors attempted to use MoS2 nanoparticles (nano-MoS2) as a catalyst to synthesize trimethylolpropane oleate (TMPTO) by esterification of trimethylolpropane and oleic acid. The small amount of highly dispersed nano-MoS2 catalyst remaining in TMPTO needed not to be separated and could be used as a lubricant modifier directly to achieve the purpose of improving the lubricity performance of TMPTO.FindingsThe results demonstrated that nano-MoS2 had good catalytic esterification ability and achieved in situ dispersion of about 0.191% nano-MoS2 in TMPTO while catalyzing the synthesis of base oil. After high-speed centrifugal sedimentation treatment, the product TMPTO still retained about 0.008% of nano-MoS2. The above-synthesized TMPTO has significantly better lubricity performance than commercially available TMPTO, in which the friction coefficient and wear rate could be reduced by 75%.Originality/valueThe results of this study provide an idea for the design of catalysts for ester oil synthesis.

A review on tailoring the corrosion and oxidation properties of MoS2-based coatings

This review discusses the corrosion and oxidation properties of MoS2 and MoS2 based coatings, their effect on the tribological properties of MoS2, and the recent progress in tailoring the corrosion resistance properties of MoS2 based coatings.

Tribological properties of MoS2 and CaF2 particles as grease additives on the performance of block-on-ring surface contact

Recently, the performance effects of lubricant additives on greases have been actively investigated. In order to improve their properties of anti-friction, load-carrying capacity, wear resistance, corrosion resistance, and temperature-enhancing, some additives are added to greases. Determining the appropriate additive ratios is one of the most important research topics in tribology. In this study, friction, wear, and contact temperature were analyzed by adding MoS2 and CaF2 additives to the lithium soap grease. The experiments were carried out at different revolutions (200, 500 and 800 rpm), additive ratios (0.25, 0.5, 1, 1.5 and 2 wt%) and contact loads (72, 108 and 144 N) using a block-on ring tester. The structure and morphology of additives analyzed by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The effects of additives on surface morphology and roughness were also characterized with the scanning electron microscopy (SEM) and profilometer. In addition, energy dispersive spectrometry (EDS) was used to detect the elements present on the wear scar surfaces. Results reveal that the MoS2 and CaF2 additives can improve the wear resistance of lithium grease and reduce the friction coefficient. In this experimental study, suitable additive ratios that are anti-wear and friction-reducer were found to be in the range of 1–1.5 wt% for both additives. Besides, both additives continued their friction-reducing characters at over the room temperatures. While the MoS2 additive oil gives the lowest friction and wear values, the same ratio of CaF2 additive oil shows a more stable operation.

Tribological properties of MoS<SUB align="right">2 thin films deposited by RF magnetron sputtering technique

Tribological properties of MoS<SUB align="right">2 thin films deposited by RF magnetron sputtering technique

A molecular dynamics study on the tribological behavior of molybdenum disulfide with grain boundary defects during scratching processes

The effect of grain boundary (GB) defects on the tribological properties of MoS2 has been investigated by molecular dynamics (MD) simulations. The GB defects-containing MoS2 during scratching process shows a lower critical breaking load than that of indentation process, owing to the combined effect of pushing and interlocking actions between the tip and MoS2 atoms. The wear resistance of MoS2 with GB defects is relevant to the misorientation angle due to the accumulation of long Mo-S bonds around the GBs. Weakening the adhesion strength between the MoS2 and substrate is an efficient way to improve the wear resistance of MoS2 with low-angle GBs.

Nanoscale Friction Behavior of Transition-Metal Dichalcogenides: Role of the Chalcogenide

Despite extensive research on the tribological properties of MoS2, the frictional characteristics of other members of the transition-metal dichalcogenide (TMD) family have remained relatively unexplored. To understand the effect of the chalcogen on the tribological behavior of these materials and gain broader general insights into the factors controlling friction at the nanoscale, we compared the friction force behavior for a nanoscale single asperity sliding on MoS2, MoSe2, and MoTe2 in both bulk and monolayer forms through a combination of atomic force microscopy experiments and molecular dynamics simulations. Experiments and simulations showed that, under otherwise identical conditions, MoS2 has the highest friction among these materials and MoTe2 has the lowest. Simulations complemented by theoretical analysis based on the Prandtl-Tomlinson model revealed that the observed friction contrast between the TMDs was attributable to their lattice constants, which differed depending on the chalcogen. While the corrugation amplitudes of the energy landscapes are similar for all three materials, larger lattice constants permit the tip to slide more easily across correspondingly wider saddle points in the potential energy landscape. These results emphasize the critical role of the lattice constant, which can be the determining factor for frictional behavior at the nanoscale.

Effect of applied load on the tribological properties of MoS2–TiL/MoS2–TiH nano-multilayer coating

MoS2–TiL/MoS2–TiH coating (L and H are low and high power of the sputtered Ti target) possesses excellent tribological properties owing to its nano-multilayer structure. In this study, the tribological properties of MoS2–TiL/MoS2–TiH coating were extensively analyzed at different loads. Relative to the MoS2–Ti monolayer coating, the nano-multilayer structure not only improved the wear resistance but also increased the critical load at which the coating began to peel off. The MoS2–Ti coating maintained its lubrication only in the early stage of the test even at a load of 2 N. In contrast, the friction coefficient and wear rate of the multilayer coating were small and stable until the load reached 20 N. The critical load of the optimized MoS2–TiL/MoS2–TiH coating was 10 times that of the MoS2–Ti coating. At excessive loads, the multilayer coating lost its lubrication in the early stage of the test because the coating was completely worn off under such loading.

Influence of the Organic Moiety on the Tribological Properties of MoS2:Glycol Hybrid Nanoparticles-Based Dispersions

MoS2:glycol hybrid nanoparticles were synthetized through a polyol route. Their tribological properties when used as lubricant additives in a PAO 6 base oil were investigated using a pin-on-disk tribometer. An important friction reduction and good anti-wear performances were observed compared to the base oil and to the no modified particles. The MoS2:glycol nanoparticles were characterized by thermogravimetric analysis, transmission electron microscopy, RAMAN spectroscopy, X-ray diffraction, and Fourier transform infrared. Furthermore, the stability of the dispersion was followed by dynamic light scattering. On the other hand, Field Emission Scanning Electron Microscopy, Energy-Dispersive X-ray Spectroscopy, and X-ray Photoelectron Spectrometry analysis showed that the tribofilm formed on the wear surfaces during the friction test is at the origin of the excellent tribological performance of the MoS2 nanoparticles. In particular, it was demonstrated that the interaction of MoS2 with the organic moiety of the nanoparticles plays a key role in the friction reduction and the good anti-wear properties of the dispersions.

Formation and tribological properties of MoS2 self-lubricating porous anodic alumina thin flims

MoS2 self-lubricating films were prepared on long-range ordered porous anodic alumina (PAA) by an electrophoretic deposition (EPD) method. The PAA was prepared by two-step anodization of aluminum plates. Oxalic-acid-based electrolytes were used in the first step and phosphoric-acid-based electrolytes were used in the second step. This process offers a new approach to preparing PAA with wide adjustable boundary distances (43.5–21 nm) by increasing the voltage from 80 V to 100 V. The boundary distances were decreased from 78 nm to 42.2 nm by increasing the solution concentration, which increased the interpore distance. The coefficient of friction and hard-wearing of the MoS2 lubrication film on the PAA were studied by a ball-on-disk friction and wear tester. The results showed that the nanotubes stored MoS2 particles, which provided continuous lubrication.

Structure and tribological properties of MoS2low friction thin films

The main aim of the studies was the deposition of the AlCrN film, covered by molybdenum disulphide (MoS2) – based lubricant, on the austenitic steel substrate. The AlCrN and MoS2 layers were deposited by PVD lateral rotating ARC-cathodes (LARC) and magnetron sputtering technology on the X6CrNiMoTi17-12-2 respectively. Structural characterizations of the MoS2 thin films have been carried out using SEM (scanning electron microscopy) and AFM (atomic force microscopy) to determine the surface topography as well as HRTEM (high-resolution transmission electron microscopy) and Raman spectroscopy for structural investigations. The tribological wear relationships using ball-on-disc test were specified for surface layers, determining the friction co-efficient and mass loss of the investigated surfaces. Tests of the coatings’ adhesion to the substrate material were made using the scratch test. HRTEM investigation shows an amorphous character of the MoS2 layer. In sliding dry friction conditions, the friction co-efficient for the investigated elements is set in the range between 0.4-0.5. The investigated coating reveals high wear resistance. The coating demonstrated a dense cross-sectional morphology as well as good adhesion to the substrate. The good properties of the PVD AlCrN+MoS2 coatings make them suitable in various engineering and industrial applications.

Comparison of Tribological Properties of MoS2 and Graphite-PTFE Coatings and its Impact on Machining of Aluminium by HSS End Mills

In the present paper, a graphite–PTFE composite coating (Gr-x) on an HSS end mill is proposed for machining aluminium. The suitability of this coating was first simulated in a pin-on-disc test and was compared to the performance of MoS2 before evaluation through machining testing. In the tribo-test, both coatings exhibited their extraordinary lubrication properties and could successfully reduce uneven frictional forces as observed with an aluminium pin against uncoated HSS. However, MoS2-coated HSS end mills failed to produce such a favorable impact in machining. SEM images and chip morphology indicate evidence of the adherence of aluminium on the rake surface of a MoS2-coated tool. In contrast, Gr-x coating substantially outperformed MoS2 in the end milling test. Built-up edge (BUE) was completely arrested by Gr-x coating, and a better finish resulted from reduction of cutting force. Under the given machining conditions, the temperature was expectedly below the chemical degradation point of both coating materials and hence environmental humidity seemed to be a critical factor, which weakened the performance of MoS2 but improved that of graphite. Cutting speeds no higher than 60 m/min are recommended for Gr-x coating during end milling of aluminium.

Structural and Tribological Properties of MoS<sub>2</sub>/Polyimide Composites Exposed to Atomic Oxygen Environment

Effects of atomic oxygen (AO) irradiation on the structural and tribological behaviors of MoS2filled polyimide (PI) composites were studied by using ball-on-disc tribometer, infrared spectra, X-ray photoelectron spectroscopy and scanning electron microscopy. It was found that the irradiation of AO induced the destruction of polymer molecular structures and formation of volatile products which induced the change of the structure, morphology and tribological properties of samples. The addition of MoS2filler significantly increased the AO resistance of PI composites due to the formation of MoO3-rich skin layers during AO process. The addition of MoS2improved the tribological properties of PI before and after AO irradiation.

Synergistic lubrication of MoS2 particles with different morphologies in liquid paraffin

PurposeThe purpose of this paper is to explore the synergistic lubrication of MoS2 particles with different morphologies.Design/methodology/approachThe synergistic lubrication of MoS2 particles with different morphologies is evaluated using a four‐fall tribometer in liquid paraffin.FindingsResults show that the morphology of MoS2 has an influence on the tribological properties of MoS2. Both MoS2 nano‐balls and nano‐platelets function as lubrication additives in liquid paraffin better than MoS2 micro‐platelets do. It is also found that there is a synergistic lubrication between two different morphologies of MoS2. The composite MoS2 additives with different morphologies can improve the wear resistance and friction reduction of liquid paraffin more than each of them singly does. The synergistic lubrication between two different MoS2 morphologies results from the cooperation of their different lubrication mechanism.Originality/valueThe paper reveals a synergistic lubrication between two different MoS2 structures. It is very advantageous and practical to partly displace nano‐MoS2 with micro‐MoS2.

Tribological Properties of MoS2 with Different Morphologies in High-Density Polyethylene

The tribological properties of high-density polyethylene (HDPE) modified by MoS2 with different morphologies (nano-spheres, nano-platelets, and micro-platelets) were investigated using an end-face tribometer under dry friction and rapeseed oil lubrication. Under dry friction, MoS2 nano-platelets and nano-spheres exhibited their best properties at 1.0 and 1.5 % (wt%) MoS2 content, respectively. Under oil lubrication, the nano-spheres were better additives in HDPE than the other two. The melting of HDPE was the main wear mechanism under dry friction, whereas abrasive is the main wear mechanism under oil lubrication. The changing wear mechanisms led to anti-wear variations in HDPEs with increasing MoS2 contents. The tribological properties were closely related to the crystallinity and thermo-mechanical properties of MoS2/HDPE. The samples with lower damping factors and better crystallinity showed better tribological properties. The excellent anti-wear properties of nano-spheres can be attributed to the deformation and exfoliation of nano-spheres in the friction process. Nano-platelets and nano-spheres in HDPE are advantageous under dry friction and oil lubrication, respectively. This study better elucidated the relationship between the property and morphology of MoS2 in a polymer.

Study of Tribological Properties of MoS<sub>2</sub>/Cu-Fe Matrix Self-Lubricating Composites Prepared by Induction Sintering at Elevated Temperature

The molybdenum disulfide(MoS2)/copper(Cu)-ferrum(Fe) matrix self-lubricating composites with various amounts of MoS2 additives were prepared by induction heating sintering method combined with the alloying of the Cu-Fe matrix with various metallic elements. As the temperature was increased from room temperature to 800°C, the mechanical and tribological properties of the composites were measured using the universal testing machine and MRH-3 friction-wear tester. The phase compositions and worn surface morphologies of the composites were analyzed by means of X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Meanwhile, wear mechanisms were discussed. It was found that the mechanical and friction/wear properties of MoS2/Cu-Fe matrix self-lubricating composites were related to the induction frequencies and the contents of the MoS2 as the solid lubricant. The increased MoS2 content resulted in increased mechanical and friction/wear properties at first and then decreased subsequently. The composites with proper MoS2 contents and induction frequencies have the lower the friction coefficients and wear rate at room temperature to 800°C. Meanwhile, the self-lubricating films were mainly made up of some compositions, such as pearlite, cementite, sulphide, solid solution alloy of Mo and Fe, molybdenum oxide in elevated temperature; the wear mechanism of composites has been changed from abrasive wear to ploughing wear.

The Effect of Morphology on the Tribological Properties of MoS2 in Liquid Paraffin

The tribological properties of liquid paraffin (LP) containing molybdenum disulfide (MoS2) additives, including nano-balls, nano-slices, and bulk 2H-MoS2, are evaluated using a four-ball tribometer. Results show that all MoS2 additives used can improve the tribological properties of LP, and that nanosized MoS2 particles function as lubrication additives in LP better than micro-MoS2 particles do. The LP with nano-balls presents the best antifriction and antiwear properties at the MoS2 content of 1.5 wt%. This is ascribed to the chemical stability of the layer-closed spherical structure of nano-balls. The Stribeck curves confirm that the rotation speed of 1,450 rpm used is located at the mixed lubrication region under 300 N. MoS2 nano-slices have small sizes and easily enter into the interface of the friction pair with a roughness of 0.032 μm, functioning as a lubricant in LP better than nano-balls do at the MoS2 content of 1.0 wt%. The Stribeck curves also show that the differences between the two nano samples were magnified at high rotation speeds in hydrodynamic lubrication region. The application of nano-slices in high sliding speeds will be more advantageous. This work furthers the understanding of the relationship between the tribological properties and morphology of MoS2.

Preparation and Tribological Properties of MoS2 Nanosheets

AbstractMoS2 nanosheets were successfully synthesized by a micro‐domain reaction method, employing a ball‐milled mixture of MoO3 and S as starting materials. The obtained MoS2 nanosheets are monodisperse, and the length and width are about 100 and 10 nm, respectively. Furthermore, the tribological performances of the as‐obtained MoS2 nanosheets were studied and possible optimized mechanisms were also proposed.

Tribological properties of MoS 2 nano-balls as filler in polyoxymethylene-based composite layer of three-layer self-lubrication bearing materials

POM/MoS 2 nano-balls composite was prepared by adding MoS 2 nano-balls synthesized from Na 2MoO 4 and CH 3CSNH 2 into polyoxymethylene (POM). The comparative POM-based composite blended with micro-MoS 2 particles was also prepared. The obtained POM/MoS 2 composites were used as the polymerical layer in the three-layer self-lubrication materials. The results of tribological tests showed that the POM with MoS 2 nano-balls presented better tribological properties than that with micro-MoS 2. When the content of MoS 2 nano-balls was not more than 1.0 wt%, the POM/MoS 2 nano-balls samples presented lower friction coefficients and smaller wear volumes. However, higher contents of MoS 2 nano-balls than 1.0 wt% were very disadvantageous to the tribological performances. DSC results showed the excessive MoS 2 nano-balls affected the POM crystallinity, and accordingly, the self-lubricating capabilities of these samples were influenced as well. SEM micrographs for wear scars confirmed that the worn manner of the POM sample was changed when the content of MoS 2 nano-balls was increased. XPS analysis showed that MoS 2 nano-balls was transferred to the mated friction surface, on which Mo(IV) was oxidized into Mo(VI) via tribochemical reaction. TEM micrographs of worn debris proposed a wear manner concerning the exfoliation of nano-sheets from MoS 2 nano-balls. The reason for the stable self-lubrication properties of POM/MoS 2 nano-balls composite was ascribed to the forming-destroying of debris clusters in a long-time sliding process.

Tribological properties of MoS2 and carbon fiber reinforced polyimide composites

The tribological properties of carbon fiber reinforced polyimide (PI) composites with different MoS2 containing sliding against GCr15 steel were comparatively evaluated on an M-2000 model ring-on-block test rig. The wear mechanisms were also comparatively discussed, based on scanning electron microscopic examination of the worn surface of the PI composites and the transfer film formed on the counterpart. It was found that small incorporation of MoS2 was harmful to the improvement of friction and wear behaviors of carbon fiber reinforced PI composites. However, it was found that the increasing filler of MoS2 significantly improved the wear resistance and decreased the friction coefficient of carbon fiber reinforced PI composites. It was also found that the tribological properties of MoS2 and short carbon fiber reinforced PI composites were closely related with the sliding condition such as sliding rate and applied load.

Tribological properties of Cyanex 301‐modified MoS2 nano‐sized hollow spheres in liquid paraffin

PurposeThe purpose of this paper is to investigate the tribological properties of MoS2 nano‐sized hollow spheres in liquid paraffin (LP) and the corresponding action mechanism. Morever, its feasibity of industrial application as an oil additive in the industrial lubrication field is also explored.Design/methodology/approachThe tribological properties of MoS2 nano‐sized hollow spheres (NH‐MoS2) modified by Cyanex 301(di‐(2,4,4‐trimethylpentyl) dithiophosphinic acid) with size of 200 ∼ 300 nm in LP are studied and compared with those of the commercial colloidal MoS2 (CC‐MoS2) on a four‐ball tester and an Optimol SRV Oscillating friction and wear tester in a ball‐on disk configuration. The worn surfaces of the lower flat disc are examined with a scanning electron microscopy and an X‐ray photoelectron spectroscopy, respectively.FindingsResults show that NH‐MoS2 is a better extreme‐pressure additive and anti‐wear (AW) and friction‐reducing additive in LP than CC‐MoS2. Under the optimum concentration of 0.5 per cent for both NH‐MoS2 and CC‐MoS2 and the load of 400 N, the friction coefficient of NH‐MoS2 + LP and CC‐MoS2 + LP decreases about 43.8 and 6.3 per cent, and the wear volume loss decreases about 60.3 and 12.0 per cent compared with the pure LP. The boundary lubrication mechanism for NH‐MoS2 + LP can be deduced as the effective chemical adsorption protective film formed by the long chain alkyls R and active elements (S and P) in the modification layer and tribochemical reaction film containing the tribochemical products of the additive. Moreover, sliding and rolling frictions co‐exist in NH‐MoS2 + LP, doing contributions to the good tribological properties as well.Originality/valueIn this paper, the Cyanex 301‐modified MoS2 nano‐sized hollow spheres with diameter of 200 ∼ 300 nm are firstly added into LP to investigate its tribological properties. The excellent AW and friction‐reducing properties indicate that this MoS2 hollow spheres product is a good oil additive, and the fundamental data presented here will be useful for its further industrial application in the future.