Improvement Of Tribological Properties Research Articles

Improvement of Tribological Properties of Steel Camshaft by Plasma Nitriding

Improvement of Tribological Properties of Steel Camshaft by Plasma Nitriding

Research on the Improvement Effect and Mechanism of Micro-Scale Structures Treated by Laser Micro-Engraving on 7075 Al Alloy Tribological Properties.

During various applications in aerospace, ships, autos, and aircraft, 7075 Al alloy will frequently contact other materials, and therefore suffer from slight abrasion. However, the poor tribological properties of 7075 Al alloy greatly affect its performance and life length, leading to limitations in its application. Preparing roughness structures on the surface is regarded as a promising method to improve the properties of materials. However, the tribological properties of 7075 Al alloy cannot be enhanced significantly by roughness structures in complex dynamic changeable environments, owing to the incomplete understanding of the effect of roughness structures. Given the above issues, in this paper, micro-scale structures (linear grooves, gridding grooves, and arc grooves) were designed and prepared on 7075 Al alloy surfaces by a surface treatment (laser micro-engraving), which provides excellent controllability of the morphology and dimensions of as-prepared roughness structures. The tribological properties of the as-prepared surfaces were investigated systemically. The effect of micro-scale structures on the tribological properties was studied. The wear mechanism and tribological properties improvement mechanism of the surfaces were clarified. Furthermore, the effect degree of the enhancement factors of the micro-scale structures on the tribological properties was explored under different conditions. The results indicate that the micro-scale structures play an important role in improving the tribological properties of Al alloy under different sliding speeds. The improvement mechanism can be summarized by four factors. However, the effect degrees of these factors on the tribological properties exhibit considerable differences. This study not only develops specific micro-scale structures that can dramatically improve the tribological properties of 7075 Al alloy under different conditions, but also offers guidance for the construction of appropriate roughness structures that can dramatically improve the tribological properties of Al alloy according to the friction conditions.

THE INFLUENCE OF SILICON-DOPED DIAMOND-LIKE CARBON COATING ON THE WEAR OF IONIC LIQUID LUBRICATED FRICTION PAIRS

This article reports the results of the study of an a-C:H:Si coating doped with silicon and produced by chemical deposition (PACVD). The effect of the coating on the tribological behaviour of IL-lubricated friction pairs was evaluated. The properties of the 100Cr6 steel specimens with and without the coating were compared. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis were used for imaging the morphology of the coating surfaces and cross-sections and for identifying the elements in the coating composition. The contact angle of the investigated surfaces was measured with an optical tensiometer. Friction tests were performed on a ball-on-disc tribometer under dry friction and when lubricated with trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl) amide ionic liquid. The geometrical structure of the surfaces before and after the tribological tests was measured using an optical profilometer. The ionic liquid used with the silicon-doped diamond-like coating under friction conditions reduced the coefficient of friction and wear. The results obtained from the tests and analysis allow for the conclusion that the use of DLC coatings a-C:H:Si lubricated with trihexyltetradecylphosphonium Bis(trifluoromethylsulfonyl) amide contributes towards the improvement of tribological properties of sliding surfaces under friction.

Solid/liquid lubrication behavior of nickel aluminum-silver alloy under seawater condition

The purpose of this work was to investigate whether a combination of solid lubrication with lubrication by seawater would be a feasible lubrication approach for marine applications such as propulsion system components, pumps, and other machinery. In particular, the friction and wear behavior of a high-strength, intermetallic-based solid-lubricating alloy (Ni3Al-Ag alloy) coupled with Al2O3 ceramic was investigated in simulated seawater. Under seawater conditions, the Ni3Al-Ag alloy exhibited a relatively low friction coefficient of 0.11–0.08 and a wear rate of about 1–2 × 10−7 mm3/Nm. It is proposed that the Ag alleviates plowing and adhesive actions of tribo-pair and retains chemical stability in seawater. Also, the seawater plays lubricating, cooling, and corrosive roles in the friction and wear response of the Ni3Al-Ag alloy. The improvement in tribological properties under seawater conditions is attributed to the synergistic action of solid and liquid lubrication.

Improved tribological property of VN film with the design of pre-oxidized layer

At room temperature, VN films often have a relatively high friction coefficient (COF), which vastly limits their industrial application. In this work, pre-oxidation thermal treatments with different oxygen concentration were applied to improve the room-temperature tribological properties of VN films. The results showed that the V2O5 and VO2 thin pre-oxide layer form under the high and low oxygen concentration, respectively, and after thermal treatment, the tribological properties of VN films are promoted greatly. The VN film with V2O5 thin pre-oxide layer has the lowest COF (~0.23) but the greatest wear rate ((11.41 ± 0.22)× 10–15 m3 N−1 m−1), while the VN film with VO2 thin pre-oxide layer has a relative lower COF (~0.46) as well as wear rate ((2.27 ± 0.14)× 10–15 m3 N−1 m−1) than VN film without a pre-oxide layer. By analysis, the initial existence of V-oxide seems to have a more positive effect than in-situ formation of V-oxide on the improvement of tribological property at room temperature, and the V2O5 plays a decisive role in the decrease of COF, and the VO2 can improve the properties of anti-friction and wear resistance simultaneously. Thus designing a thin pre-oxide layer on the V-based films seems to be a promising method to promote their room-temperature tribological property.

Tribological Properties of Spark Plasma Sintered NiCr–Cr2AlC Composites at Elevated Temperature

In this work, layered ternary Cr2AlC powders with high purity and a size of 0.5–1 μm were synthesized by solid-state reaction method. NiCr–Cr2AlC composites have been prepared by spark plasma sintering (SPS) process. The composites' tribological properties were evaluated against alumina ball under dry sliding condition from room temperature to 600 °C. Compared with unmodified NiCr alloy, Cr2AlC addition has an effect on reduction of friction coefficient of NiCr–Cr2AlC composites at the temperatures up to 400 °C. Especially, in comparison with NiCr alloy, the wear rates of NiCr–Cr2AlC composites significantly decrease from 10−4 mm3/(N·m) to 10−5–10−6 mm3/(N·m) from room temperature to 600 °C (except for 200 °C). The NiCr–20 wt % Cr2AlC composite exhibited excellent tribological properties with a friction coefficient of 0.3–0.4 and a wear rate of about 10−6 mm3/(N·m) from 400 °C to 600 °C. Through the analysis of scanning electron microscope (SEM) and X-ray photoelectron spectroscope (XPS), it is clarified that effective improvement of tribological properties of NiCr–Cr2AlC composites is attributed to a glaze layer consisting of NiO, Cr2O3, Al2O3, and NiCr2O4, which is formed by tribo-oxidation during wear process.

Modelling of elliptical dimples generated by five-axis milling for surface texturing

Abstract Surface texturing processes that improve workpiece surface properties such as the friction of textured surfaces, the lubrication of sliding surfaces and the adhesion of workpiece surfaces are of increasing interest in industry. The most frequently employed processes for surface texturing are based on laser methods and on chemical etching processes. A widespread application of surface texturing is the improvement of tribological properties in terms of friction and load capacity. In these applications, surface texturing usually consists of generating dimples that are uniformly distributed on the workpiece surface. Five-axis milling with a ball-end mill can be an effective and productive option for these processes in these applications, as it is able to generate surface texturing that consists of periodic elliptical dimples if the tool geometry and the cutting conditions (feed, depth of cut and yaw and tilt angles defining tool axis orientation) are appropriately selected. In this paper, a model that predicts the geometry (shape, dimensions and orientation) of elliptical dimples machined by five-axis milling on flat surfaces for given cutting conditions is developed. In order to achieve this, equations expressing the trajectory followed by the cutting edges in five-axis milling are derived. The model takes into account the effect of tool parallel axis offset on dimple geometry. Next, the influence of cutting conditions on dimple geometry is analysed in order to define the cutting conditions that generate a given dimple geometry. From this analysis, a significant influence of the tool's tilt angle on the elliptical shape of the dimples and a linear dependence of the yaw angle on dimple orientation are observed. In order to mill elliptical-shaped dimples, tilt angles larger than 30° and feed, step over and depth of cut values that avoid interference between the dimples generated by different cutting edges of the ball-end mill are required. Finally, a series of five-axis milling tests was carried out in order to validate model predictions. A low dispersion in the dimensions and area of milled dimples was obtained. The shape and dimensions of predicted and measured dimples are compared and good correspondence between them is observed, the largest error being 7%.

Effect of Size of Multiwalled Carbon Nanotubes Dispersed in Gear Oils for Improvement of Tribological Properties

The aim of the paper is to investigate the effect of size of multiwalled carbon nanotubes (MWCNTs) as additives for dispersion in gear oil to improve the tribological properties. Since long pristine MWCNTs tend to form clusters compromising dispersion stability, they are mildly processed in a ball mill to shorten the length and stabilized with a surfactant before dispersing in lubricant. Investigations are made to assess the effect of ball milling on the size and structure of MWCNTs using electron microscopy and Raman spectroscopy. The long and shortened MWCNTs are dispersed in EP 140 gear oil in 0.5% weight. The stability of the dispersed multiwalled carbon nanotubes is evaluated using light scattering techniques. The antiwear, antifriction, and extreme pressure properties of test oils are evaluated on a four-ball wear tester. It is found that ball milling of MWCNTs has a strong effect on the stability and tribological properties of the lubricant. From Raman spectroscopy, it is found that ball milling time of up to 10 hours did not produce any defects on the surface of MWCNTs. The stability of the lubricant and the antiwear, antifriction, and extreme pressure properties have improved significantly with dispersion shortened MWCNTs. Ball milling for longer periods produces defects on the surface of MWCNTs reducing their advantage as oil additives.

Microstructural and tribological properties of A356 based surface hybrid composite produced by friction stir processing

Fabrication of surface hybrid composite with reinforced particles has been developed in order to enhance tribological properties of aluminum alloys. Among the aluminum alloys, increasing of tribological properties of A356 casting aluminum alloys using different reinforced particles into the surface by FSP, as a surfacing technique, is of great interest, which should be considered. Friction stir processing was attempted in order to produce a surface hybrid composite for improvement of tribological properties with alumina (Al2O3) particles and graphite (Gr) as a lubricant particles. The FSP was carried out with tool rotational speed of 1000 rpm, tool travel speed of 100 mm min−1 and tilt angle of 2° through two passes. In the present work, the structural and tribological properties of surface hybrid composite of A356 Al alloy are investigated. Structural characterization is evaluated by optical and scanning electron microscopies. Hardness and wear tests are performed in order to investigate tribological behaviors of the FSPed composite samples. The obtained results showed that the composite reinforced by Al2O3 particles exhibits higher hardness value compared to hybrid composite of Al2O3/Gr-particles because of the good bonding between Al2O3 and aluminum matrix as well as higher hardness value of Al2O3 particle itself than the Gr- particle reinforcement. In addition, wear test results depicted that the wear resistance of A356/Al2O3/Gr sample is significantly decreased compared to that of A356 Al alloy. The wear mechanism of all composites were identified adhesive wear mechanism. The reduction friction coefficient of A356/Gr composite presented higher value as opposed to the other composites.

Improvement of tribological properties of niobium nitride films via copper addition

Niobium nitride and copper (NbN-Cu) composite films with different copper content (Cu/(Nb+Cu) = 0.6 at.%-24.8 at.%) were deposited using magnetron sputtering, and the microstructure and tribological properties of the films were investigated. The results showed that the films exhibited a mixture phase of face-centered cubic (fcc) NbN, hexagonal close-packed (hcp)NbN and fcc-Cu. The addition of copper below 6.0 at.% dropped both friction coefficient (μ) and wear rate (WR) sharply. A further increase in copper content decreased the μ furtherly, while the decreasing in μ took sacrifice of WR. The addition copper of 6.0 at.% into the niobium nitride matrix could broaden the niobium nitride film's effective service temperature to 400 °C. The lubricating copper (<200 °C) and the tribo-phases of copper oxide and niobium oxide remained the value of μ at ∼0.55 regardless of temperatures at the cost of the increase of WR.

Femtosecond laser nanostructuring of reinforcement bars surface for improvement of its interaction with concrete

Femtosecond laser nanostructuring of metal surfaces is a powerful tool for improvement of their various properties. Namely, increase of optical absorption (“black metals”), superhydrophobity, surface hardening, as well as improvement of tribological properties have been reported previously. Here we show the improvement of bond slip of nanostructured reinforcement bars with concrete. We demonstrate strong dependence of straining force and pulling force on the regime of surface nanostructuring. In particular, two-fold increase of straining force and pulling force can be achieved at the highest fluence in the regime of “black metal”. Our finding has high practical importance for advanced civil engineering.

Improvement of tribological properties of as-sprayed 8YSZ coatings by in-situ synthesis C/MoS2 composite lubricant

Abstract The 8YSZ-C/MoS2 composite coating was fabricated to improve its tribological properties by introducing a novel and simple method. The C/MoS2 composite lubricants were synthesized in defects of 8YSZ coating via hydrothermal reaction connect with vacuum pressure impregnation. Results indicate that the porous C/MoS2 flower-like microsphere powders consist of interconnected ultrathin nanoflakes. The C and MoS2 are uniformly attached to the defects of 8YSZ coating and unable to assemble into microspheres due to the limitation of the size of pores and cracks. The tribological behaviors of the composite coating are significantly improved, which are devoted to the formation of the lubricating film. This preparation technique provides a novel approach to establish self-lubricating ceramic composite coatings with temperature-sensitive solid lubricants.

Tribological properties of water-based drilling fluids with borate nanoparticles as lubricant additives

In this work, several nanostructured borates such as magnesium, zinc, aluminum and titanium borates were synthesized. These borates were added to drilling muds and their ability to improve tribological properties of water-based drilling fluids, was investigated. The tribological properties of the fluids containing these nano-additives were compared with those of a typical mud (containing bentonite and water) with and without a commercial lubricant additive (BitcLub, M − I SWACO) as reference samples. The results indicated that adding nano-additives to the drilling mud increased its extreme pressure property by more than five times compared to the reference samples. At the same time, these nano-additives decreased the coefficient of friction due to their good ability in producing a strong protective film (tribo-film) on the contacting surfaces being stable at extremely high pressure and temperature conditions. Among all the prepared nano-additives, titanium borate, which is biodegradable, showed a significant improvement in tribological properties of drilling fluid as compared to the other borates.

Investigation on surface morphology and tribological property generated by vibration assisted strengthening on aviation spherical plain bearings

The extreme and complex working conditions require aviation spherical plain bearings not only to have high machining accuracy and low surface roughness, but also to possess high surface microhardness and lubricant retaining capability. This paper presents a vibration assisted strengthening approach to achieving the synergistic effects of the surface property-improving and appearance-improving. The research attempts to answer how vibration assisted strengthening technique can improve the surface tribological properties of aviation spherical plain bearing components particularly in light of proposing the flat-headed asperity distribution model and the corresponding elastic–plastic contact modelling for the special processed surface morphology. Subsequently, the models are corroborated by the experimental results of characterizing the surface morphology produced by vibration assisted strengthening with different parameters such as rolling times and rolling static force. The surface tribological properties of spherical plain bearing specimens were studied by employing the UMT-TriboLab platform. The theoretical analysis and experimental results indicate that the surface asperities of spherical plain bearing components processed with repeated high frequency strikes present a flat-headed distribution but not Gauss distribution. It characterizes with a marked majority of produced small asperities with similar height, which is beneficial to frictional couple contacts and a lot of original valleys retaining lubricants. The processing technique contributes to increasing the surface microhardness by 20% and decreasing the surface roughness from about Ra 0.4 µm to below Ra 0.1 µm. The ball-on-flat friction tests demonstrate that both the special flat-headed surface structure and the elevated microhardness can attribute the improvement of tribological properties and wear resistance performance of spherical plain bearings.

New Boron-Nitrogen containing modified multifunctional alkylphenolate additives to motor oils

By carrying out condensation reactions for alkylphenols and methylene-bis-alkylphenols with amines, alkanolamines and formaldehyde, working with boric acid and the neutralization of the obtained product with calcium hydroxide, new boron-nitrogencontaining alkylphenolate, additives have been synthesized (AKI-114B, AKI-212B, AKI-115B, AKI-210B, AKI-214B, AKI-219B).The structure of the obtained - boron esters (derivatives of phenolate) has been studied through the use of the IR spectroscopy method. Simultaneously with studying the functional properties of the synthesized additives in motor oil, it has been established that their detergent, water, corrosion, oxidation and wear resistance properties greatly overbalance the same properties of their single nitrogen-containing and industrial analogues. Through thermoanalytic research conducted on OD-102T typed derivatograph, the high stability (through to 360ºC) of additives containing boron-nitrogen has been determined.On the basis of new boron, nitrogen-containing modifications AKI-210B and AKI-115B different motor oil compositions such as M-8B, M-10G2 and etc. have been prepared and tested. The creation of high-synergy efficiency upon interaction of synthesized additives with other ones (sulfonates, dithiophosphates) has been observed, particularly in the improvement of tribological properties, and the increase in the oxidation induction period.

Tribological behaviour of Fe3Al-Ba0.25Sr0.75SO4 self-lubricating composites in vacuum and air

The effect of Ba0.25Sr0.75SO4 on tribological properties of the Fe3Al-based composites were evaluated both in vacuum and air. The tribological properties of the composites were significantly improved by the addition of Ba0.25Sr0.75SO4, especially in vacuum. The Fe3Al alloy shows relative poor tribological performance in vacuum than in air. The main reason was the severe adhesion wear and deleterious contact surfaces in vacuum, but in air, the formation of the oxides film on the friction surface protected the Fe3Al alloy materials from wear. It is worth noting that the wear rate of the 30% self-lubricating composite reduced almost 3–7 times than that of Fe3Al alloy in vacuum, and the COF also lowered to about 2 times. The improvement of tribological properties of Fe3Al-based composites was attributed to that the Ba0.25Sr0.75SO4 was easily softened and formed lubricating film on the worn surfaces to effectively reduce friction and wear in vacuum. The dominant wear mechanism for Fe3Al alloy was surface fatigue wear and oxidative wear in air, but in vacuum was adhesive wear and plastic deformation. For Fe3Al-Ba0.25Sr0.75SO4 composites, mainly wear mechanism was adhesive wear and surface fatigue wear in air, while in vacuum that was abrasive wear and adhesive wear.

Friction reduction of steel by laser-induced periodic surface nanostructures with atomic layer deposited TiO2 coating

We report on the reduction of friction of steel treated by femtosecond laser pulses and subsequent atomic layer deposition. Uniform laser-induced periodic surface structures (LIPSS) are produced on the surfaces of stainless steel samples by an 800-nm femtosecond laser. These nano-textured surfaces are then deposited with TiO2 coating by means of atomic layer deposition (ALD). Friction tests show that the average friction coefficients of the treated samples have been greatly reduced. The improvement of tribological properties is attributed to the intact ripple structures reduce the contact area between friction pairs and act as reservoirs for wear particles. Moreover, the TiO2 coating further reduces adhesion and plastic deformation, which is beneficial to improving tribological properties. It is suggested that the synergistic effect of LIPSS and ALD TiO2 coating had a more marked potential for improving tribological properties.

The lubrication effectiveness of dialkylpentasulfide in synthetic ester and its emulsion

Abstract The application of dialkylpentasulfide (DPS) in synthetic ester (pentaerythritol tetraoleate known as PETO ester) and its emulsion is studied in this paper. PETO ester blended with DPS shows good antiwear, friction reducing and extreme pressure performance, while PETO emulsion doped with DPS exhibits only excellent extreme pressure properties. The above difference originates from the tribofilm formed on the worn surface by tribochemical reaction. SEM-EDS and XANES are applied to determine the relationship between tribochemical products and lubrication effectiveness. The tribofilm is composed of FeSO4, FeS, FeS2 and FeSO3. DPS in PETO ester and PETO emulsion undergoes tribochemical reaction dominated by sulfidation and thermal oxidation respectively, resulting in distinct tribological properties. This provides an essential explanation for the improvement of tribological properties of DPS in PETO ester and emulsion, and also indicates that sulfur is not fitted as antiwear, friction-reducing additive in water based system.

A Preliminary Study to Enhance the Tribological Performance of CoCrMo Alloy by Fibre Laser Remelting for Articular Joint Implant Applications

CoCrMo alloy has long been used as a pairing femoral head material for articular joint implant applications because of its biocompatibility and reliable tribological performance. However, friction and wear issues are still present for CoCrMo (metal)/CoCrMo (metal) or CoCrMo (metal)/ultrahigh molecular weight polyethylene (UHMWPE) (plastic) pairs in clinical observations. The particulate wear debris generated from the worn surfaces of CoCrMo or UHMWPE can pose a severe threat to human tissues, eventually resulting in the failure of implants and the need for revision surgeries. As a result, a further improvement in tribological properties of this alloy is still needed, and it is of great interest to both the implant manufacturers and clinical surgeons. In this study, the surface of CoCrMo alloy was laser-treated by a fibre laser system in an open-air condition (i.e., no gas chamber required). The CoCrMo surfaces before and after laser remelting were analysed and characterised by a range of mechanical tests (i.e., surface roughness measurement and Vickers micro-hardness test) and microstructural analysis (i.e., XRD phase detection). The tribological properties were assessed by pin-on-disk tribometry and dynamic light scattering (DLS). Our results indicate that the laser-treated surfaces demonstrated a friction-reducing effect for all the tribopairs (i.e., CoCrMo against CoCrMo and CoCrMo against UHHMWPE) and enhanced wear resistance for the CoCrMo/CoCrMo pair. Such beneficial effects are chiefly attributable to the presence of the laser-formed hard coating on the surface. Laser remelting possesses several competitive advantages of being a clean, non-contact, fast, highly accurate and automated process compared to other surface coating methods. The promising results of this study point to the possibility that laser remelting can be a practical and effective surface modification technique to further improve the tribological performance of CoCr-based orthopaedic implants.

Mechanical and tribological properties of NiAl/muscovite composites

To ascertain if muscovite act as a new type of filler for self-lubricating composites, NiAl/muscovite composites were successfully fabricated by spark plasma sintering. The mechanical and tribological properties of the composites were investigated. It was found that the relative density, microhardness and fracture toughness of the composites were inversely proportional to the muscovite content. The tribological results showed that both the friction coefficient and wear rate of the composites distinctly decreased with the incorporation of muscovite. The composite with 9 wt% muscovite had the best anti-friction and anti-wear performance. The improvement of tribological properties could be attributed to the formation of self-lubricating films consisting mainly of Si-Al oxides.