Tribological Effects Research Articles

Controlling high-speed dry friction through the geometry of micro-patterned asperities

Advances in manufacturing technologies have provided means to create surface textures with regular patterns of uniform asperities, leading to the potential for improved control of friction. In order to design surface topologies that induce desirable tribological effects, an understanding of the influences of the geometric features of asperities on measures of frictional resistance is required. Dynamic elastic-plastic finite element modeling methods, which included material damage and failure, were used to study the interactions of directly modeled 100 micron rib-like asperities on two deformable aluminum blocks. The relationships between the mechanics of the deformation and failure of five unique asperity geometries, the coefficients of static and kinetic friction, and the system energy stored and dissipated were studied under dry, high-load rate conditions, where motion was initiated in under 1 ms and acceleration approached 100 kG. Influences of the geometric features of the asperities were explored using semi-circular, triangular, and square-shaped cross-sectional profiles and evaluated for complex geometries created by combinations of these basic shapes. Static coefficients of friction were found to vary more than two-fold with asperity geometry based on the contact area normal direction. The study found that it was also possible to maintain the static friction coefficient but more than triple the force to initiation motion simply by changing the asperity shape. While kinetic friction coefficients were less influenced by asperity shape for the high-speed conditions studied, the geometric characteristics directed the way an asperity deformed under load and the extent of the material failure during sliding. A more than four-fold variation in energy stored within the system and over an order of magnitude variation in energy dissipated by the system was found for the geometries examined. This study demonstrates the importance of understanding the mechanical behavior of the asperity when designing surface textures to tailor dry, high-speed friction.

Tribological properties of vanadium oxides investigated with reactive molecular dynamics

We present a reactive molecular dynamics study on tribological properties of five vanadium oxides (V2O3,V3O5,V8O15,V9O17,VO2) under elevated temperatures and pressures. All considered stoichiometries provide lubrication with a comparatively low coefficient of friction (COF∼0.2 at 600 K, COF<0.2 at 800 and 1000 K) which is a valuable information relevant for the design of coatings containing vanadium as a lubricious agent. An overall tendency of the decrease of friction coefficient with the increase of temperature represents a tribological effect useful for self-adjusting lubrication. We observed the increasing trend of adhesion-related offset of the friction force with the decrease of oxygen content in vanadium oxides.

Investigation of Tribological Properties of Graphene Nanoplatelets in Synthetic Oil

Lubricants are commonly utilized in industry to minimize friction and wear for tools and components, and additives play indispensable roles in lubricants to attain overall enhanced tribological properties. Because of environmental concerns, the introduction of nanoparticles is regarded as a promising lubricant additive capable of replacing conventional additives and improving lubricant tribological properties. This study investigated the tribological behaviour of 5W30 PAO+ester fully synthetic oil (SO) with and without the addition of graphene nanoplatelets. Besides, this study also focuses on the tribological effect of graphene's concentration (0.01, 0.02, 0.05, 0.1 and 0.2 wt%). The experiments were conducted using a four-ball tester according to ASTM D4172 and surface analysis was done on the worn surfaces using scanning electron microscopy and energy-dispersive x-ray spectroscopy. The results show that the presence of graphene significantly improves the tribological properties. SO enriched 0.05 wt% graphene exhibits the lowest coefficient of friction and wear scar diameter, and the friction and wear were reduced by 33.78% and 34.42%, respectively. The protective film formed on the worn surface is responsible for friction and wear reduction. In addition, the worn surface becomes smoother after being lubricated by nanolubricants, which can be observed through the SEM analysis. EDX analysis revealed the presence of element carbon on the worn surface, implying that nanoparticles had deposited on the worn surface.

Effect of sulfur on the hydrolytic stability and tribological properties of N-containing borate ester

Two borate esters, one with benzotriazole (BTB) and another with 2-mercaptobenzothiazole (BMB) were synthesized and used as additives in mineral oil. BMB showed better hydrolysis stability, probably because S atoms in BMB provided negative charges to the N to enhance B←N coordination. Moreover, BMB was superior in terms of improving PB value, anti-wear and friction-reducing properties of mineral oil. XPS spectra revealed that h-BN, B2O3 and FexOy were detected in BTB-tribofilm, while additional FeSO4, FeS and B2S3 were found in BMB-tribofilm. The possible triple effects of S atoms in BMB can be summarized as: enhancing the B←N coordination; improving the adsorption ability of BMB on the metal surface; and generating tribochemical reaction products with tribological effects.

Future directions for active matter on ordered substrates

Active matter is a term encompassing particle-based assemblies with some form of self-propulsion, including certain biological systems as well as synthetic systems such as artificial colloidal swimmers, all of which can exhibit a remarkable variety of new kinds of nonequilibrium phenomena. A wealth of non-active condensed matter systems can be described in terms of a collection of particles coupled to periodic substrates, leading to the emergence of commensurate-incommensurate effects, Mott phases, tribology effects, and pattern formation. It is natural to ask how such phases are modified when the system is active. Here we provide an overview and future directions for studying individual and collectively interacting active matter particles coupled to periodic substrates, where new types of commensuration effects, directional locking, and active phases can occur. Further directions for exploration include directional locking effects, the realization of active solitons or active defects in incommensurate phases, active Mott phases, active artificial spin ice, active doping transitions, active floating phases, active surface physics, active matter time crystals, and active tribology.

Effect of heat treatment on microhardness of electroless Ni-YSZ cermet coating

The paper discussed the effect of heat treatment on electroless nickel-yttria-stabilised zirconia (Ni-YSZ) cermet coating. Ni-YSZ cermet coating has potential applications such as cutting tools, thermal barriers, solid oxide fuel anode, and various others. The compatibility of ceramic YSZ and metallic nickel in terms of the mechanical properties such as hardness by varying the heating temperature, time and ceramic particle size is highlighted. Ni-YSZ cermet coating was deposited onto a high-speed steel substrate using the electroless nickel co-deposition method. The temperature and time were varied in a range of 300-400°C and 1-2 hours, respectively. The microhardness measurements were carried out using a Vickers microhardness tester (Shimadzu) according to ISO 6507-4. The surface characterisation of the cermet coating was carried out using JOEL Scanning Electron Microscope (SEM) coupled with Energy Dispersive X-ray (EDX) JSM 7800F. The crystallographic structure of materials was analysed by X-ray diffraction (XRD) Bruker D8 Advance instrument. It was found that the microhardness of Ni-YSZ cermet coating with the ratio of 70:30, respectively, is directly proportional to the heating temperature and time. Heating the Ni-YSZ cermet coating at 300°C from room temperature (rtp) to 1 hour shows a 12% microhardness increment, while from 1 to 2 hours gives a 19% increment. Compared to heating at 350°C and 400°C, the increment is more significant at 33% and 49% for rtp to 1 hour and 8% and 16% for 1 to 2 hours, respectively. In addition, the effect of varying YSZ particle size in the Ni-YSZ cermet gave response differently for heating temperature and heating time. The paper is only limited to the discussion of the heat treatment effect on Ni-YSZ cermet coating hardness property. The tribological effect will be in future work. The microhardness data may vary due to the Vickers microhardness force applied and the amount of ceramic particle incorporation and phosphorus content in the nickel matrix. The value of this work is the compatibility of the ceramic YSZ and metallic nickel matrix in terms of mechanical properties, such as hardness, upon heat treatment.

On the function of lead (Pb) in machining brass alloys

Lead has traditionally been added to brass alloys to achieve high machinability, but the exact mechanisms at work are still debated. Lead-free brass alternatives could be developed if these mechanisms were better understood. Accordingly, machinability characteristics were investigated for two brass alloys with similar mechanical properties and phase composition, but with very different machining characteristics because one has 3 wt.% lead (CuZn38Pb3) while the other has only 0.1 wt.% (CuZn42). The effect of the lead was investigated using infrared temperature measurement, electron microscopy, secondary ion mass spectroscopy, quick-stop methods, and high-speed filming. Neither melting of lead nor its deposition on the tool rake surface takes place during machining thus confirming its limited lubrication and tribological effects. Instead, the main role of lead is to promote discontinuous chip formation. Lead deforms to flake-like shapes that act as crack initiation points when the workpiece material passes through the primary deformation zone. This effect prevents the development of stable tool–chip contact, thus lowering cutting forces, friction, and process temperature.

High-throughput screening of tribological properties of monolayer films using molecular dynamics and machine learning

Monolayer films have shown promise as a lubricating layer to reduce friction and wear of mechanical devices with separations on the nanoscale. These films have a vast design space with many tunable properties that can affect their tribological effectiveness. For example, terminal group chemistry, film composition, and backbone chemistry can all lead to films with significantly different tribological properties. This design space, however, is very difficult to explore without a combinatorial approach and an automatable, reproducible, and extensible workflow to screen for promising candidate films. Using the Molecular Simulation Design Framework (MoSDeF), a combinatorial screening study was performed to explore 9747 unique monolayer films (116964 total simulations) and a machine learning (ML) model using a random forest regressor, an ensemble learning technique, to explore the role of terminal group chemistry and its effect on tribological effectiveness. The most promising films were found to contain small terminal groups such as cyano and ethylene. The ML model was subsequently applied to screen terminal group candidates identified from the ChEMBL small molecule library. Approximately 193131 unique film candidates were screened with approximately a five order of magnitude speed-up in analysis compared to simulation alone. The ML model was thus able to be used as a predictive tool to greatly speed up the initial screening of promising candidate films for future simulation studies, suggesting that computational screening in combination with ML can greatly increase the throughput in combinatorial approaches to generate in silico data and then train ML models in a controlled, self-consistent fashion.

Explore the Tribological Effects of Two N-Containing Functional Groups on O/W Emulsion

Two water-soluble N-containing additives without sulfur and phosphorus, hexanamide with tetraethylenepentamine (EEHA) and benzotriazole amide with diethylenetriamine (BTAA), were synthesized and used as additives in the oil-in-water emulsion to investigate the effect of amino and benzotriazole ring on the tribological properties of the emulsion. The results showed that EEHA/BTAA exhibited wear resistance under all tested conditions. This may be attributed to the basic amino-functional groups in the additives which reduce the corrosive wear of the base emulsion. BTAA-emulsion showed the best friction-reducing and anti-wear performance under the 3 N loading condition, which may be attributed to its benzotriazole ring, which cannot be easily decomposed and could form self-assembled layers through π–π stacking. This π–π stacking may effectively compensate for the low chemical reactivity of the benzotriazole ring, and serve as a better protective film to exert tribological properties.

Tribological Wear Effects of Laser Texture Design on AISI 630 Stainless Steel under Lubricated Conditions

Surface texturing is used in many applications to control the friction and wear behaviour of mechanical components. The benefits of texture design on the tribological behaviour of conformal surfaces are well known. However, there is a big dependency between the geometrical features of the texture and the texture’s performance. In this paper, the effect of laser texturing parameters on textured geometrical features is studied, as well as its role in the tribological behaviour of AISI 630 steel under lubrication and high-contact pressure conditions. The results show a linear impact of the energy density on the surface quality, whereas the scanning speed influences the homogeneity of the sample. Nevertheless, the surface integrity is also affected by the laser parameters, reducing the micro-hardness on the textured area by up to 33%. Friction coefficient average values and stability presented high variations depending on the sample parameters. Finally, the wear mechanisms were analysed, detecting abrasion for the disc and adhesion for the pin.

Strong interfacial modified aramid fabric reinforced degradable thermosetting composites: reinforcing and tribological effects

In this work, dense molybdenum disulfide (MoS2) nanosheets were grown onto polydopamine (PDA) functionalized aramid fabric (AF) surface via a simple hydrothermal method to improve the wettability between AF surface and polyhexahydrotriazine (PHT) resin, thus resulting in stronger AF/resin interfacial bonding. The PDA-assisted surface modification on AF generated a high active interface allowing the nucleation and subsequent growth of MoS2. Moreover, this nanosheet-coated reinforcement fiber enabled the viscous liquid of resin precursor to spread over and form intimate contact with its surface, which eventually promoted the formation of strong interfacial bonding between AF-MoS2 and cured resin matrix. In addition, the enhanced interfacial bonding between the reinforcement and matrix generated stable mechanical interlock within the resulting AF-MoS2/PHT composites, and thus, contributed better thermal stability, higher tensile strength, and tribological properties. Compared with AF/PHT composites, the tensile strength and elongation at break of the AF-MoS2/PHT composites increased by 32.5% and 50%, and the average friction coefficient and wear rate of AF-MoS2/PHT composites decreased by 43.9% and 86.3%, respectively. Furthermore, the composites realized the non-destructive recovery of expensive AF at 25 °C. Overall, our study demonstrates a dependable strategy to construct the recyclable AF-MoS2/PHT composites, which exhibit valuable applications in tribology.

Investigation on the Influence of the Tribological System on Cold Forging and Ejection of Hollow Components with Helical Internal Geometry

This paper describes the tribological investigation of the cold forming and ejection process during ironing of hollow components with helical internal geometry. The experimental tests on a test tool are intended to evaluate the tribological system by varying the surface pretreatment of the blanks and the lubricant. For the evaluation of the tribological effects the ironing and ejection force are measured. In addition, the die filling as well as the surface quality of the pressed parts are determined, allowing the correlation of the test results with the tribological conditions. Furthermore, a numerical investigation of the process was performed. The numerical results are presented and compared with the experimental results.

Tribological effects of loose alumina abrasive assisted sapphire lapping by a fixed agglomerated diamond abrasive pad (FADAP)

The tribological effects between a fixed abrasive pad (FAP) and a workpiece can effectively maintain the self-conditioning process of the FAP in real time. However, the FAP is easy to be glazed along with the long-term lapping processes of hard-to-process ceramic materials. This paper proposed a novel method of loose abrasive assisted fixed agglomerated diamond abrasive lapping (LA-FADAL) to achieve efficient and stable lapping processes of sapphire. LA-FADAL tests with a fixed agglomerated diamond abrasive pad (FADAP) were carried out by changing the particle size and volume fraction of loose alumina abrasives in lapping slurries. The influences of the different alumina abrasives on the processing performance of the FADAP were discussed. Material removal mechanisms in the LA-FADAL processes were proposed based on the tribological effects of loose alumina abrasive assisted sapphire lapping by the FADAP. The loose alumina abrasives with the similar size as the diamond grains embed in the surface of the fixed AD abrasive could not remove sapphire materials directly and effectively by mechanical actions, mainly played a role of dressing the FADAP to enhanced the self-sharpening ability of AD abrasives, and further improved the self-conditioning ability of FADAPs.

Tribological investigation and process optimization of dry sliding wear behavior for WS2 solid lubricant layer deposition on Al 6061-T6 surface

PurposeThis tribological investigation aims to identify the effect of WS2 deposition on the Al 6061 surface and optimize the dry sliding conditions to enhance the friction and abrasion wear behavior.Design/methodology/approachWS2-deposited Al 6061-T6 surface was considered for this tribological investigation. The design of the experiment was based on the Box–Behnken design of the response surface methodology approach, which is used to evaluate the interaction effect of input parameters on friction coefficient (COF) and specific wear rate (SWR). The abrasive wear behavior of WS2 deposition against SiC emery sheet was explored through pin-on-disc experimentation by varying applied load (L), sliding velocity (V) and distance (D). Using analysis of variance and regression model, COF and SWR were predicted.FindingsBased on composite desirability criteria, multi-objective optimization was performed to minimize the COF and SWR. The obtained optimal sliding conditions are L = 10 N, V = 2 m/s and D = 949.49 m. The validation test results indicate that the experimental and predicted data are in good conformance. For optimized conditions, worn surface characterization was done using a scanning electron microscope with energy dispersive spectroscopy, and X-ray diffraction analysis was performed to ensure the formation of WS2 phases on worn-out surfaces. Furthermore, a counter body surface with collected wear debris has been analyzed.Originality/valueAlmost the industries are now focused on a new surface modification technique, which improves the surface and tribological characteristics. This research work specifically relates the tribological effect of WS2 deposition on an Al 6061-T6 surface through a novel electrical discharge deposition approach and optimizes the dry sliding conditions to improve the frictional and abrasive wear resistance.

Investigation of tribological properties of environmentally friendly ionic liquids as a potential lubricity improving additives for water-based lubricants

PurposeThis paper aims to investigate the tribological properties of two protic ionic liquids used as lubricity-improving additives in the water. Their concentration was optimized for different metal friction pairs including bearing steel, stainless steel and aluminum alloy.Design/methodology/approachIn this study tribological properties were investigated by using a ball-on-plate reciprocating tribometer. Three different friction pairs were selected: bearing steel-bearing steel; bearing steel-stainless steel; bearing steel-aluminum alloy. To optimize the concentration of investigated protic ionic liquids four concentrations were selected. Wettability was investigated using the droplet method. The corrosiveness of additive-loaded water was investigated using the iron chip method.FindingsThe results show that by using protic ionic liquids the lubricity of water could be greatly improved. However, the friction pair material and additive concentration play a significant role. The positive tribological effect was attributed to the polarity of the additive molecule which tends to form an adsorption layer. The polarity of molecules also leads to better surface wettability. It was also found that both investigated protic ionic liquids can improve the anticorrosion properties of water.Originality/valueTo the best of the authors’ knowledge, this is the first study to present a complex investigation of tribological properties of two protic ionic liquids as additives in the water. In this case, three different metal friction pairs and four additive concentrations were investigated. The results could be interesting to those who are working in the field of water-based lubricants and luck for multipurpose lubricity-improving additives.

Effects of Laser Surface Texturing and Lubrication on the Vibrational and Tribological Performance of Sliding Contact

Various textures are fabricated by a picosecond laser machine on the surfaces of circular stainless steel specimens. Vibrational and tribological effects of laser surface textures are investigated by means of a tribometer and a data acquisition and signal processing (DASP) system. Experimental results show that surface textures can reduce the coefficients of friction (COFs), enhance the wear resistance, and improve the dynamical performance of frictional surfaces. In this study, the surface with micro circular dimples in diameter of 150 μm or textured area density of 25% has the best tribological and dynamical performance. Compared with the non-textured surface, the surface with circular dimples in diameter of 150 μm and 15% textured area density has 27% reduction of COFs, 95% reduction of frictional vibrations, and 66% reduction of frictional noise. The frictional vibrations and noise in the sliding contacts can be effectively reduced by adding graphene to the lubrication oil, and the surface textures enhance the frictional noise reduction performance of lubrication.

Methodology, validation & signal processing of acoustic emissions for selected lubricated tribological contacts

Acoustic emission in the ultrasonic range in tribology and from friction-based events in general are an interesting field of study, because it provides information classical parameters can’t. Therefore, it is very important to develop good working and unified methodologies for recording the acoustic signals. In this work two methodologies for recording acoustic emissions for sliding contacts are presented. The validation of the signals from the sensor to the digital data in the computer is shown. To gain good information it is necessary to reduce noise and disturbances in the data as much as technically feasible. Electrical insulation, shielding, cable management, filtering and blind-testing are introduced. Signal processing of the data happens via various methods, such as Root-mean-square (RMS), filtering (band-pass, filter bank), short-time-Fourier-transformation (STFT), wavelet-transformation and combined techniques. Gathered information with these methods is shown for an example of a plain sliding surface Ring-on-disc test. The RMS works good as overall running indicator, while the spectral methods give insights in the different tribological effects and changes on the surface of the sample over the course of the test.[copyright information to be updated in production process]

Microstructural and tribo-mechanical investigation of as-cast Ti-Zr binary alloys

Titanium and its alloys are proved to be very successful in manufacturing of various types of automotive and aircraft parts. It is also used in manufacturing of some sophisticated medical instruments and medical implants purposes. Investigated titanium binary alloys in this research were Ti-5Zr and Ti-20Zr respectively. The casting process was used in an electric arc furnace to produce titanium alloys with addition of zirconium content (5% and 20%) in two different proportions separately. The primary aim of this research work was to evaluation of microstructural characterization and investigation of tribo-mechanical properties. XRD method was used to analyze present phases and both alloys showed martensitic hcp α' Ti structures complied with α Ti structures. FESEM was engaged to study microstructures and EDS showed that analyzed alloys have identical chemical compositions. Microhardness property was improved with the increment in Zr concentration. Resulted hardness for Ti-5Zr alloy was 305HV, while hardness was increased to 316HV for Ti-20Zr alloy. Tribological properties of binary Ti-Zr alloys were assessed with the help of a typical ball on plate set under the dry condition and at room temperature. In this case also higher Zr contain Ti binary alloy favored better tribological effects and this can be attributed from resulted COF values of Ti-Zr binary alloys. At the low load (15 N), COF values were 0.35 and 0.29 for Ti-5Zr and Ti-20Zr alloys respectively. Whereas at the high load (30 N), COF values were 0.36 and 0.34 for Ti-5Zr and Ti-20Zr alloys respectively. However, it was quite evident that adhesive wear was dominant for these Ti-Zr binary alloys.

Molybdenum disulfide nanosheet/polyimide composites with improved tribological performances, surface properties, antibacterial effects and osteogenesis for facilitating osseointegration.

Polymeric biocomposites display some advantages over metal or ceramic biomaterials, and are regarded as a promising candidate for artificial joint application. Herein, molybdenum disulfide (MD) nanosheets were prepared and incorporated into polyimide (PI) to form MD/PI composites with a MD content of 20 wt% (PM20) and 40 wt% (PM40). The results revealed that incorporation of MD nanosheets obviously improved the tribological performances, surface properties (e.g., roughness, wettability and surface energy) and protein absorption of the composites, which enhanced with the increase of MD content. In addition, the composites containing MD nanosheets exhibited antibacterial effects, and the antibacterial effects of PM40 were higher than those of PM20 and PI. PM40 significantly stimulated the cellular responses of rat bone mesenchymal stem cells in vitro, which was better than PM20 and PI. Furthermore, PM40 remarkably accelerated osteogenesis and osseointegration in vivo, which was better than PM20 and PI. In summary, the MD content in composites played pivotal roles in improving not only tribological performances, surface properties, antibacterial effects and cellular response in vitro but also osteogenesis and osseointegration in vivo. As a result, PM40 with high MD content exhibited excellent osteogenic bioactivity and antibacterial effects, which would have great potential for artificial joint applications.

TRIBOLOGICAL ASPECT OF ASSESSMENT OF EFFICIENCY OF FILTRATION USING MULTI-LAYER MATERIALS

This study presents the results of testing for the efficiency and effectiveness of filtration using multi-layer filter materials, and briefly presents a new technology for manufacturing filter media using these materials. The first part of the article describes the causes of the formation of impurities in operating fluids and the tribological effects of their impact. The second part is dedicated to testing for filtration efficiency and effectiveness for different filter materials. The third part of the article briefly describes the technology for manufacturing filter media using efficient but difficult-to-form materials. The testing results showed significant differences in filtering efficiency and effectiveness between the cellulose samples and the samples of filter materials based on glass microfibre layers. All of the tested multi-layer materials allow filtration effectiveness of over 90% to be achieved over the entire range of impurity sizes included in the experiment. The results of a comparative test for pressure change during filtration also indicate that glass microfibre materials have a considerably longer operating life than cellulose materials. The time after which a sharp increase in pressure occurs (due to the filter layer being filled with impurities) is nearly four times longer for multi-layer materials than for cellulose materials. The methods for cutting, forming, and joining filter materials have been developed by the author of this article and implemented at the EXMOT company.