Effect Of Solid Lubricants Research Articles

Structural and sliding wear properties of Ag/Graphene/WC hybrid nanocomposites produced by electroless co-deposition

The main objective of this work has been the deposition of hybrid silver/WC/Graphene nanocomposites and characterization of their tribological behaviors. Graphene as a conductive solid lubricant additive was introduced into Ag matrix from the electrolytes in which submicron WC particles and Graphene nanosheets were suspended. The main purpose for two different reinforcements is to improve both wear and friction properties. The friction and wear behaviors of Ag/WC/Graphene coatings on the metal substrates against M50 steel ball were tested under dry sliding wear conditions. Comprehensive characterizations were performed using Scanning Electron Microscopy, X-Ray Diffraction analysis, Raman spectroscopy and 3D profilometry facilities. Tribological test results have revealed that even small amounts of Graphene addition are able to drastically improve the antifriction and antiwear properties of hybrid nano Ag matrix composites. A possible explanation for these results is that the co-deposition of Graphene not only provides an enhanced effect for nanocomposites to produce better wear resistance, but also forms a local protective layer on the contact surfaces to reduce the friction. The investigation shown that hybrid reinforcements of sub-micron WC and Graphene hold great potential applications as effective load bearing and solid lubrication for Ag matrix composites and possibly for similar alloys.

Co-deposition of Cu/WC/graphene hybrid nanocomposites produced by electrophoretic deposition

Abstract The effects of two different reinforcements of WC and graphene on the structural and tribological properties of copper matrix were investigated. Cu/WC, Cu/graphene and hybrid Cu/WC/graphene nanocomposites were co-deposited by electrophoretic deposition to improve both electrical and tribological behaviors. The friction and wear behaviors of WC and graphene reinforced nanocomposites were investigated against Al2O3 ball under dry sliding wear conditions. Comprehensive characterizations were performed using scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), Raman spectroscopy and 3D profilometry facilities. Tribological test results revealed that small amount of graphene addition was able to drastically improve the antifriction and antiwear properties of hybrid Cu matrix nanocomposites because of its excellent solid lubrication effect. Tribological analysis was shown that hybrid nanocomposite with sub-micrometer WC and graphene reinforcements provided good load-bearing and tribological properties for possible future MEM applications. Wear mechanism investigation has shown that co-deposition of WC and graphene resulted in altering wear mechanisms of the Cu matrix.

Friction and Wear Properties of Different Types of Graphene Nanosheets as Effective Solid Lubricants

Friction and wear properties of graphene nanosheets prepared by different processes as solid lubricant on silicon dioxide have been comparatively studied via calibrated atomic force microscopy. The effects of normal load, humidity, and velocity on the friction were also investigated. All kinds of graphene nanosheets possess friction-reduction properties on the nanoscale. Mechanically exfoliated graphene nanosheets exhibit ultralubrication and zero wear under high pressure due to perfect graphitic structure and a hydrophobic surface. Defects in chemical vapor deposited graphene nanosheets decrease the antiwear and friction-reduction capability. The graphene oxide nanosheets (GOS) show the weakest friction-reduction properties on account of destroyed graphitic structure and a hydrophilic surface. The reduced graphene oxide nanosheets (RGOS) possess better friction reduction than GOS by virtue of hydrophobic surface properties. Both RGOS and GOS have weak antiwear properties due to the destroyed graphitic structure. Antiwear properties are correlated strongly with the structure, and friction depends mainly on the structure and surface properties.

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

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

Mechanical and Tribological Properties of Graphene Modified Epoxy Composites

The effects of graphene content on the mechanical and tribological properties of epoxy composites were systematically investigated. The stiffness, hardness and elastic modulus of the composites increased with increased graphene content due to the higher hardness and elastic modulus of graphene sheets than those of epoxy matrix. The friction and wear of the composites measured using steel ball-on-disc microtribological test decreased with increased graphene content due to the solid lubricating effect of graphene sheets. It could be concluded that the mechanical and tribological properties of the epoxy composites could be significantly influenced by the incorporation of graphene sheets.

Effects of solid lubricants, load, and sliding speed on the tribological behavior of silica reinforced composites using design of experiments

Abstract In the present study, the effects of solid lubricants, braking load and sliding speed on the tribological behavior of Cu/silica composites were investigated using design of experiments and statistical methods. Three types of composites were prepared using different types of solid lubricants (h-BN, graphite, and MoS2) by powder metallurgy. The wear and friction behavior of the composites were evaluated for a range of braking loads (300, 600, and 900 N) and sliding speeds (3, 6, and 9 m/s) in a subscale dynamometer. The composites were characterized for density, hardness, microstructure, wear surface morphology and surface roughness properties. A statistical model was developed to identify the significant factors affecting the wear resistance of the composites. The key findings of our study are: (1) MoS2 reinforced composites possess the highest density, densification, hardness, and lowest surface roughness among the composites, (2) MoS2 is the most effective lubricant in improving the wear resistance of the composites for the selected experimental domain, (3) Amongst the solid lubricant, brake load and sliding speed, the solid lubricant is the most significant factor affecting the wear resistance of the composites, (4) graphite reinforced composites provide higher braking performance at 3 m/s for all loading conditions whereas both h-BN and MoS2 reinforced composites provide better braking performance among composites at higher speed (>3 m/s) and load (>300 N) conditions.

Protective composite coatings obtained by plasma electrolytic oxidation on magnesium alloy MA8

Earlier developed approaches to the formation of composite polymer-containing coatings by plasma electrolytic oxidation (PEO) using various low-molecular fractions of superdispersed polytetrafluoroethylene (SPTFE) have been summarized and a unique method for the formation of composite polymer-containing coatings at the surface of magnesium alloy MA8 has been suggested. The improvement in the corrosion and tribological behavior of the polymer-containing coating can be attributed to the morphology and insulating properties of surface layers and the solid lubrication effect of SPTFE particles. Such multifunctional coatings have high corrosion resistance (Rp = 3.0 × 107 Ω cm2) and low friction coefficient (0.13) under dry wear conditions.The effect of dispersion and ξ-potential of the nanoparticles (ZrO2 and SiO2) used as an electrolyte component for PEO on the composition and properties of the coatings has been investigated. Improvement of the protective properties for coatings with the incorporated nanoparticles has been explained by the greater thickness of the protective layer, relatively low porosity and the presence of narrow non-through pores. The layer with zirconia has an impedance modulus measured at low frequency (|Z|f→0Hz = 1.8 × 106 Ω cm2) more than one order of magnitude higher than the PEO-coating formed in the electrolyte without nanoparticles (|Z|f→0Hz = 5.4 × 104 Ω cm2).

Synergetic Lubricating Effect of WS2 and Ti3SiC2 on Tribological Properties of Ni3Al Matrix Composites at Elevated Temperatures

The tribological behaviors of the Ni3Al-WS2-Ti3SiC2 composites and synergistic effect of composite solid lubricants are investigated from room temperature to 800°C. The results show that the Ni3Al matrix composites (NASC) exhibit excellent tribological properties throughout the test temperatures compared to Ni3Al-based alloy. The excellent tribological properties of NASC are attributed to the synergistic lubricating effect of WS2 and Ti3SiC2. A lubricating film could be formed below 400°C, and an oxidation protection film is formed above 400°C on the worn surface of NASC during the sliding process, leading to low coefficients of friction (0.18–0.39) and wear rates (1.5–3.7 × 10−5 mm3N−1m−1).

Scratch resistance and tribological performance of thermosetting composite powder coatings system: A comparative evaluation

The knowledge of the coating properties in terms of scratch and wear resistance is extremely important to prevent severe damage. This paper focused on the study of a comparative evaluation of the scratch and wear performance of two thermosetting powder coatings filled with different weight fractions of molybdenum disulfide (MoS2) solid lubricant. Indeed, the thermoset polyester and epoxy organic powder were deposited onto aluminum substrates by an electrostatic spray coating process. The effect of MoS2 solid lubricant on the friction and wear behavior of both polyester and epoxy composite powder coatings were assessed via reciprocating tribometer under dry friction conditions. The micro-mechanical performance of the scratch resistance of the composite coatings was conducted using progressive load scratch tests. The experimental findings of the tribological analysis have proven a significant reduction of the friction coefficient and a higher anti-wear ability of the polyester composite coatings compared with the epoxy matrix to which the addition of MoS2 particles has a little effect on the friction-reducing mechanism. Finally, the investigation of the scratch resistance of the polyester or epoxy composite powder coatings filled with MoS2 confirms that the incorporation of MoS2 particles to either polyester or epoxy matrices leads to a significant decrease of the critical loads characterizing the coating damage. From the residual depth trends and contact pressure analyses, the epoxy composite coatings reinforced by 5 wt.% of MoS2 are found to have a great scratch resistance response compared to the polyester composite reinforced by the same wt.% of MoS2.

Improving the tribological properties of NiAl matrix composites via hybrid lubricants of silver and graphene nano platelets

This work presents a comprehensive study of the synergistic tribological effect of combined solid lubricants of silver and graphene nano platelets (GNPs).

The Effect of Adding Calcium Stearate on Wear-resistance of Ultra-high Molecular Weight Polyethylene

In order to find an effective solid lubrication filler for the composites based on ultra-high molecular weight polyethylene, tribotechnical properties of UHMWPE and its blends with calcium stearate (С36Н70СаО4, CS) under dry friction, boundary lubrication and abrasion were studied. It is demonstrated that wear rate of UHMWPE-CS compositions under dry sliding friction decreases by more than 4 times as compared to pure UHMWPE while the mechanicals properties do not change substantially. Under abrasion conditions the wear rate of the stated composites rises with the increased content of the filler. The optimal filler weight fraction is determined in terms of ensuring maximum wear resistance. The wear mechanisms of UHMWPE-based polymer compounds with a solid lubrication filler under dry sliding friction conditions and abrasion are discussed.

Friction and Wear Behavior of Bronze Matrix Composites for Seal in Antiwear Hydraulic Oil

New self-lubricating bronze matrix composites were prepared for seals and the tribological mechanisms in antiwear hydraulic oil were explored. The tribological behavior of bronze matrix composites tribotesting against an AISI 52100 steel ball was investigated with a ball-on-disc tribotester over a wide range of applied load and sliding speed. The obtained results showed that the tribological properties of composites were markedly improved. The alumina enhanced the strength and wear resistance of composites. However, the friction coefficient increased due to the addition of alumina. Silver was an effective solid lubricant. The tribological properties of the new self-lubricating composites were improved because of the synergistic effect of silver and Al2O3.

Effect of several solid lubricants on the mechanical and tribological properties of phenolic resin‐based composites

The flake graphite, polytetrafluoroethylene, and molybdenum disulfide (MoS2) filled phenolic resin‐based composites were prepared by hot press molding. The thermal, mechanical, and tribological properties of composites were studied systematically. The morphologies of the worn surfaces and the change of chemical compositions during the sliding process of the composites were analyzed by scanning electron microscopy and X‐ray photoelectron spectroscopy, respectively. It was found that the heat‐resisting performance and the hardness of the composites are less affected by solid lubricants, while the solid lubricants did harm to the flexural strength of the composites. The friction and wear behaviors of composites highly depended on the volume fractions of solid lubricants and the sliding conditions. The wear resistance increases and the coefficient of friction decreases when the filler load increases. In addition, the appropriate content of solid lubricants is beneficial to reducing the sensitivities of the composites to load and sliding speed. POLYM. COMPOS., 36:2203–2211, 2015. © 2014 Society of Plastics Engineers

Composite polymer-containing protective coatings on magnesium alloy MA8

The earlier developed approaches to the formation of composite polymer-containing coatings by plasma electrolytic oxidation (PEO) using various low-molecular fractions of superdispersed polytetrafluoroethylene (SPTFE) have been summarized. A unique method for the formation of a composite polymer-containing coating at the surface of magnesium alloy MA8 has been suggested. The improvement in the corrosion and tribological behavior of the polymer-containing coating can be attributed to the morphology and insulating properties of surface layers and solid lubrication effect of SPTFE particles. Such multifunctional coatings have high corrosion resistance (Rp=3.0×107Ωcm2) and low friction coefficient (0.04) under dry wear conditions.

Tribological properties of short carbon fibers reinforced epoxy composites

Abstract Short carbon fiber (SCF) reinforced epoxy composites with different SCF contents were developed to investigate their tribological properties. The friction coefficient and wear of the epoxy composites slid in a circular path against a steel pin inclined at 45° to a vertical axis and a steel ball significantly decreased with increased SCF content due to the solid lubricating effect of SCFs along with the improved mechanical strength of the composites. The scanning electron microscope (SEM) observation showed that the epoxy composites had less sensitive to surface fatigue caused by the repeated sliding of the counterparts than the epoxy. The tribological results clearly showed that the incorporation of SCFs was an effective way to improve the tribological properties of the epoxy composites.

Surface morphologies, tribological properties, and formation mechanism of the Ni–CeO2 nanocrystalline coatings on the modified surface of TA2 substrate

In order to remedy the poor tribological properties and low micro-hardness for pure titanium (TA2) materials, the Ni–CeO2 nanocrystalline coating was deposited from a Watts–Nickel electrolyte on the modified surface of TA2 substrate. In the present study, an available method of chemical activation was innovatively employed to make surface modification for TA2 substrate, in which the modified surface was characteristic of a rough surface and fully covered by the Ce-rich conducting phase for better electrodeposition. In order to study the effect of surface pretreatments on the modified TA2 surface, the surface roughness profiles and average roughness values were carried out using optical profilometry on the measured surfaces. A predictive modeling of TA2 surfaces before and after surface pretreatments was compared and successfully validated for better understanding of the formation mechanisms of electrodeposited Ni coatings reinforced with CeO2 nanoparticles. To clarify the beneficial effects of CeO2 addition on surface morphologies, phase composition, and textural evolution, the as-received nanocrystalline coatings were evaluated using various analytical techniques such as XRD, FE-SEM/EDX, and TEM. In addition, the scratch tests performed with an acoustic emission (AE) detector were conducted for the determination of interfacial adhesion between the as-deposited coating and the modified surface of TA2 substrate. Tribological properties and micro-hardness of investigated specimens were also examined. Experimental results revealed that this innovatively chemical activation was more favorable for increasing interfacial adhesion. The existence of well-distributed CeO2 phase that precipitated along the defective grain boundaries in the coating was contributed to make particulate reinforcement, thereby achieving better structural densification for Ni–CeO2 coatings. Meanwhile it exhibited superior tribological properties of the Ni–CeO2 coatings as compared to those of pure nickel and TA2 substrate, which was mainly attributed to the Ce-rich abrasive products that acted as a self-lubricating phase to make the effect of solid lubricants on worn surfaces.

ZnS薄膜的制备及摩擦学性能的研究

ZnS具有密排六方层状结构，层间剪切力较小，是一种有效的固体润滑剂。本文中我们采用水热法在金属锌基底上一步合成ZnS薄膜，这里锌基底既作为锌源参与反应，同时又为ZnS的生长提供基片。利用X-射线衍射和扫描电子显微镜对ZnS薄膜的结构组分和表面形貌进行了表征，同时采用往复式滑动摩擦磨损试验机，考察了干摩擦条件下ZnS薄膜的摩擦学性能。研究结果发现，金属锌经水热处理后，在表面上生成的ZnS薄膜由直径在~0.5μm的ZnS微纳米颗粒组成。在干摩擦条件下，ZnS薄膜可显著降低金属锌的减摩耐磨特性，同时对基底起到了保护作用。ZnS is an effective solid lubricant because its close-packed hexagonal layered structure and low interlayer shear force. In this paper, zinc sulfide films are directly fabricated on zinc substrate through a one-step hydrothermal method. Zinc is used as both zinc source involved in the hydro-thermal reaction and the support for zinc sulfide film. The structure and morphology of ZnS film on zinc substrate are characterized by X-ray diffraction and scanning electron microscopy. The friction properties of ZnS film in dry sliding were observed. The results showed that ZnS film is composed of micro/nano particles with 0.5 μm, providing effective friction-reducing for the zinc substrate under dry sliding contact.

Grain refinement: A mechanism for graphene nanoplatelets to reduce friction and wear of Ni3Al matrix self-lubricating composites

Investigations in graphene of controlling friction and wear of Ni3Al matrix self-lubricating composites (NMSC) are needed for moving mechanical assemblies. The friction and wear behaviors of NMSC with graphene nanoplatelets (GNPs) against Si3N4 ball are tested using a constant load of 10N and a constant speed of 0.2m/s from room temperature (RT) to 600°C. Tribological test results have revealed that small amounts of GNPs in the NMSC are able to drastically reduce the friction coefficients and wear rates over the effective operating range (RT-400°C). A possible explanation for these results is that the refinement of grains accompanying the slippage of laminated sheets between GNPs could provide a source of the stress dissipation and form the GNP protective layer during sliding process, leading to the reduction of wear rates as well as the friction coefficients. It is concluded that GNPs hold great potential applications as an effective solid lubricant for moderate loads and stress, and can be easily used for the preparation of the self-lubricating composites in the future.

Effect of graphene nanoplate addition on the tribological performance of Ni3Al matrix composites

The main objective of this work has been the characterization of wear behavior of the graphene nanoplates (GNPs) in Ni3Al matrix composites (NMC). The friction and wear behaviors of NMC with the addition of 1 wt.% GNPs against Si3N4 ball are tested under different loads using a constant speed of 0.2 m/s. Tribological test results have revealed that small amounts of GNPs are able to drastically improve the antifriction and antiwear properties of NMC. A possible explanation for these results is that, the GNPs not only provide an enhanced effect for NMC to produce better wear resistance, but also form a local protective layer on the contact surfaces to reduce the friction. The investigation shows that GNPs hold great potential applications as an effective solid lubricant for Ni3Al matrix composites and possibly other alloys.

Effects of solid lubricants on wire and arc additive manufactured structures

This article reports a systematic study which examines the use of solid lubricants in the sequential deposition and machining of wire and arc additive manufactured parts and characterises the effects of solid lubricants on the microstructure. This article also describes the microstructure developed and the effect on microhardness by manual cleaning of deposited layers with acetone. Mild steel wire consumable electrode G3Si1 with the diameter of 0.8 mm was used. The use of graphite and molybdenum disulphide as solid lubricants in machining was also studied and a scanning electron microscope was used in detecting any form of lubricant contamination. A systematic study shows that a significant amount of solid lubricant contamination can be found in the deposited material. Furthermore, the results indicate that even cleaning of the wire and arc additive manufactured surfaces with acetone prior to the weld deposition can affect the microstructure of the deposited material.