Average Coefficient Of Friction Values Research Articles

Tribology Evaluation on a Four-Ball Tribometer Lubricated by Al2O3/PAG Nanolubricants

Nanolubricants can improve the tribological properties for application in automotive systems. By reducing the friction rate of the internal components with nanolubricants, the service life of a compressor used in automotive air conditioning (AAC) can be extended. The investigation aims to determine the optimal volume concentration of nanolubricants for achieving the highest performance in tribological properties. Al2O3 nanoparticles dispersed in a polyalkylene glycol (PAG ND12) base at volume concentrations of 0.01%, 0.03%, and 0.05% were investigated to improve the lubrication system in the AAC compressor. The stability investigations were carried out by comparing absorbance conditions using a UV-Vis Spectrophotometer at each volume concentration for 210 days. Koehler's four-ball tribometer was used to measure coefficient of friction (COF) and friction torque at a load of 40.0 kg and a speed of 1200 rpm. The stability study of nanolubricant yielded average absorbance values of 0.752, 0.755, and 0.684, respectively. The average COF values of the nanolubricants of 0.01%, 0.03%, and 0.05% were 0.104, 0.078, and 0.117, while the pure lubricant was 0.095. Further investigation on friction torque resulted in a decrease in the pure lubricant of 0.064%, and for nanolubricant Al2O3/PAG ND12, a decrease of 0.087%, 0.057%, and 0.092%, respectively. The results indicated that a concentration of 0.03% produced the greatest reduction in COF and torque, namely 0.0078% and 0.0578%, correspondingly. Therefore, it is recommended to use Al2O3/PAG ND12 nanolubricant at a volume concentration of 0.03% because it is the most optimal in terms of stability and has the highest COF and frictional torque reduction.

Surface modification of grey cast iron by laser cladding for automotive brake disc application

In this research, Laser Cladding (LC) of three different alloys powders, two iron-based (AISI 4140 and SS420) and a Cobalt-based (Stellite 6) was performed on a Grey Cast Iron (GCI) substrate. The Stellite 6, SS420, and AISI 4140 cladding samples were tested against a semi-metallic composite brake pin for friction and wear study using a pin-on-disc friction test rig (under dry-sliding conditions). The surface wettability tests were performed on GCI, and cladding discs showed Stellite 6 and AISI 4140 were hydrophobic while SS420 and GCI were hydrophilic. Stellite 6, SS420, and AISI 4140 had surface hardness values of 542.16 HV1, 689.56 HV1, and 719.50 HV1, respectively. The friction test indicated that AISI 4140 and Stellite 6 cladding discs could produce a stable Coefficient of Friction (CoF) and friction layer coverage. SS420 could not maintain a constant CoF for the entire test duration as the plowing effect of the wear particles damaged the friction layer created on its surface. Stellite 6's average CoF value was closest to that of the GCI disc, whereas AISI 4140 and SS420 were found to have a higher average CoF. The LC on grey cast iron reduced its wear rate, with AISI 4140 being the most wear-resistant cladding, followed by SS420 and Stellite 6, respectively. All three cladding layers exhibited three-body abrasive wear, with the rolling mechanism dominating the AISI 4140 surface and sliding on the remaining two.

Taguchi optimization of process parameters used for improving tribological behaviour of graphene nanoparticle dispersed nanolubricant

Graphene nanoparticle has gained much attention in recent years as a potential additive to base oil, used for lubrication. In this scenario, the current study is aimed at analyzing the influence of process parameters such as concentration of graphene nanoparticles in Polyolester (POE) oil, sliding velocity and applied load upon the tribological behavior of POE oils with graphene nanoparticle-based additive. A robust Taguchi method was applied to optimize the selected process parameters and identify the best combination of the chosen factors. XRD and SEM analyses were conducted to characterize the graphene nanoparticles. Taguchi method was applied and pin-on-disc type test was conducted to assess the friction and wear properties. Analysis of variance (ANOVA) was conducted to analyze the significance of control factors considered (R2 = 98%). The average coefficient of friction value was found to be around 0.051, whereas average S/N ratio value was calculated as 26.15. The current study found the optimum control factors to be 0.05% graphene nanoparticles, with 50 N applied load at a sliding velocity of 3.6 m s−1.

Inhibition of cold‐welding and adhesive wear occurring on surface of the 6061 aluminum alloy by graphene oxide/polyethylene glycol composite water‐based lubricant

In this paper, graphene oxide/polyethylene glycol (GO/PEG) composite water‐based lubricant was prepared by an ultrasonic dispersion method, and characterized and analyzed by Fourier transform infrared (FT‐IR), Raman spectroscopy, X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). The suspension performance of GO/PEG composite water‐based lubricant in water was verified by static sedimentation and centrifugation, and then, the prepared GO/PEG composite water‐based lubricant was added into 304 stainless steel and 6061 aluminum alloy, and the coefficient of friction (COF) curve, average COF value, average wear rate, corresponding photomicrographs of balls and disks after wear, and energy‐dispersive spectrometer (EDS) elemental analysis were used to illustrate the lubrication effect and lubrication mechanism. The results show that the GO/PEG composite water‐based lubricant possesses excellent suspension ability in water, and the average COF value and wear rate of GO/PEG composite water‐based lubricant are reduced by 78.8% and 88.8%, respectively, compared with water lubrication. The excellent lubrication effect of GO/PEG composite water‐based lubricant can effectively reduce the cold‐welding and adhesive wear phenomenon, mainly because GO/PEG composite water‐based lubricant first fills the uneven surface of friction mating to form a high‐quality lubricating film and then because of the special space structure of GO and the low shear between GO layers and the synergistic lubrication effect of GO/PEG.

Tribological and thermal behavior with wear identification in contact interaction of the Ti6Al4V-sintered carbide with AlTiN coatings pair

Due to high demand of titanium and its alloys in modern manufacturing sectors, the high reactivity, poor conductivity and its functionality with other materials is still cumbersome. Therefore, it’s very imperative to study the tribological, thermal and wear behavior of Ti6Al4V alloy against other effective materials like carbides etc. In this holistic work, the pin on disc tests were conducted on Ti6Al4V alloy against PVD-Al00.55 Ti 0.45 N coated carbide pin. Then, the contact temperature, surface topography and wear behavior of pin and material were studied with the help of Scanning Electron Microscope (SEM). The results reveal that the effect of sliding distance on friction coefficient value is very low. On the other hand, the micrographs of wear surface reveal that the sliding distance plays a major role in generation of abrasion marks with adhesive joints as well cold weld junctions. Further, the results of friction coefficient values and the interquartile range (IQR) confirmed the satisfactory range of 14%. Moreover, the average coefficient of friction values were obtained in the range of −7.2–4.6%.

A simple cornea model for the tribological performance assessment of the lubricating eye drops

Purpose Dry eye syndrome is one of the most common reasons for eye-related discomfort which, without treatment, in some cases may even lead to corneal damage. Blinking, baseline and reflex lachrymation and drainage compromise the topical application of therapeutics demanding repeated, often hourly applications of common lubricants. In contrast, topically administered chitosan-N-acetylcysteine-based eye drops were reported to sustain on the ocular surface for more than 24 h. The thiolated biopolymer can interact with the corneal mucin layer thereby forming covalent disulphide bridges, which may contribute to extended residence times. Design/methodology/approach In this study, the tribological characteristics of four different lubricants including hyaluronic acid and chitosan-N-acetylcysteine containing commercially available eye drops were investigated. For this purpose, a representative test setup was developed, which mimics the contact between the cornea and the eyelid wiper. Gels with different elastic properties coated with a mucin layer were used as a substrate to mimic the corneal surface. Tests were conducted with a micro-tribometer, and friction values were recorded. Contact zones were characterized by X-ray photoelectron spectroscopy to investigate wear and thiol bonding on the surface. Findings Results revealed the lowest average coefficient of friction values for chitosan-N-acetylcysteine-based eye drops and substrate dependence of the test setup. Originality/value In this study, the authors introduced an in vitro system to test different types of eye drops so that chemical interaction with the mucin layer can be observed. These interactions change the tribological performance significantly and must be considered to have results relevant to the actual application.

Studies on physical properties of pearl millet grains

The perception on the physical properties was helpful in developing food processing machines and equipment for processing, packaging, and storage. Size, geometric mean diameter, sphericity, aspect ratio, bulk density, true density, porosity, thousand seed weight, angle of repose, coefficient of static friction are some engineering attributes that are vital in manufacturing of an equipment were investigated in the present study. The grain length varied from 3.39 to 4.79 mm, with a breadth of 2.22 to 2.79 mm and a thickness of 2.02 to mm. The 1000 grain weight ranges from 14.0 to 15.3 g, an angle of repose of 31.5 to 35.5⁰, The average coefficient of friction values was 0.38 & 0.36 in plastic, 0.40 & 0.40 in glass, 0.42 & 0.46 in mild steel sheet, 0.47 & 0.45 in fibre, and 0.51 & 0.53 in plywood and a bulk density of 577.63 to 565.16 kgm-3, with a true density of 551 to 554 kgm-3 varieties were respectively.

Enhancing the tribological properties of boron nitride by bioinspired polydopamine modification

Boron nitride (BN) shows obvious anti-wear performance as additives in lubricants, ceramics and polymers, however, the strong interlayer interactions lead to the weak anti-friction effect compared to those of carbon-based materials. In this work, we obtained the hydroxylated BN (BNO) via annealing the bulk material in air at high temperature. Utilizing the self-polymerization reactions of dopamine (DA) on the hydroxyls of BNO, the polydopamine (PDA) modified BNO (BNO-PDA) was formed, which has a good dispersity in water. The tribological tests indicate that both the hydroxylation and PDA modification can effectively lower the coefficient of friction (COF) and wear rate of the BN as additives in water, but the letter seems to present lower COF values when the testing time is increased. We also studied the influence of polymerization time on the tribological behaviors of BNO-PDA, and it was concluded that the 6 h modification gained the lowest wear rate and the 24 h modification yielded the lowest average COF value. It is believed that the favorable tribological performance of BNO-PDA as additives in water lubrication is resulted from the improved dispersity and the formation of organic layers on the surface of BN.

Wear properties and synthesis of CrFeNiMoTi high entropy alloy coatings produced by TIG process

The aim of this study is to investigate wear and microstructure properties of CrFeNiMoTi high entropy alloy coating produced by using tungsten inert gas (TIG) process on the medium carbon steel. The coatings have been compared in terms of their phase composition, microstructure, and hardness. Phase compound and microstructure of coating layers have been examined by using X-ray diffractometer (XRD), scanning electron microscope (SEM), and optical microscope (OM). The images show that the coatings have consisted of the cladding zone, interface zone, and heat affected zone. Also, the microstructure of the coating has been mainly composed of dendrite and discontinuous interdendritic segregation. The surface microhardness of this high entropy alloys up to 450 HV0.3, has been about 2.5 times as the substrate. The wear behaviour of the specimens has been compared through dry sliding wear tests under the same conditions. Average coefficient of friction values of the high entropy alloy (HEA) coating has been obtained at relatively low levels.

Recent Developments and Trends in the Friction Testing for Conventional Sheet Metal Forming and Incremental Sheet Forming

Friction is the main phenomenon that has a huge influence on the flow behavior of deformed material in sheet metal forming operations. Sheet metal forming methods are one of the most popular processes of obtaining finished products, especially in aerospace, automobile, and defense industries. Methods of sheet forming are carried out at different temperatures. So, it requires tribological tests that suitably represent the contact phenomena related to the temperature. The knowledge of the friction properties of the sheet is required for the proper design of the conditions of manufacturing processes and tools. This paper summarizes the methods used to describe friction conditions in conventional sheet metal forming and incremental sheet forming that have been developed over a period of time. The following databases have been searched: WebofKowledge, Scopus, Baztool, Bielefield Academic Search Engine, DOAJ Directory of Open Access Journals, eLibrary.ru, FreeFullPdf, GoogleScholar, INGENTA, Polish Scientific Journals Database, ScienceDirect, Springer, WorldCat, WorldWideScience. The English language is selected as the main source of review. However, in a limited scope, databases in Polish and Russian languages are also used. Many methods of friction testing for tribological studies are selected and presented. Some of the methods are observed to have a huge potential in characterizing frictional resistance. The application of these methods and main results have also been provided. Parameters affecting the frictional phenomena and the role of friction have also been explained. The main disadvantages and limitations of the methods of modeling the friction phenomena in specific areas of material to be formed have been discussed. The main findings are as follows—The tribological tests can be classified into direct and indirect measurement tests of the coefficient of friction (COF). In indirect methods of determination, the COF is determined based on measuring other physical quantities. The disadvantage of this type of methods is that they allow the determination of the average COF values, but they do not allow measuring and determining the real friction resistance. In metal forming operations, there exist high local pressures that intensify the effects of adhesion and plowing in the friction resistance. In such conditions, due to the plastic deformation of the material tested, the usage of the formula for the determination of the COF based on the Coulomb friction model is limited. The applicability of the Coulomb friction model to determine the COF is also very limited in the description of contact phenomena in hot SMF due to the high shear of adhesion in total contact resistance.

Properties and High-Temperature Wear Behavior of Remelted NiCrBSi Coatings

Remelted NiCrBSi coatings were examined using optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, x-ray diffraction analysis, microhardness and wear testing. After wear tests, the surfaces of the worn samples were examined by 3D profilometry and scanning electron microscopy to investigate the effects of load and temperature on the coefficient of friction and wear resistance. In all the wear experiments, there was a momentary increase in the wear volume and a momentary decrease in the average coefficient of friction values at the elevated test temperatures. This behavior was caused by the stable oxide layer formed on the surface as a consequence of the elevated test temperature. Three dominant wear mechanisms were observed with the NiCrBSi coatings: delamination at room temperature, spalling and adhesion at 250°C, and oxidation at 450°C, whereas in the uncoated samples there was delamination at room temperature, and micro-cracking and oxidation, both at 250°C and 450°C. Remelted NiCrBSi coatings provided better wear resistance and lower coefficient of friction than uncoated STKM-13A steel, especially at higher temperatures.

Inferences of Slurry Bow Wave Width from Mean Coefficient of Friction and Directivity in Chemical Mechanical Planarization

Retaining rings with different slot designs (i.e. sharp and rounded) were exposed to identical polishing conditions, and at 2 different slurry flow rates, to study their tribological attributes and to see whether trends existed between frictional forces and previously reported bow wave width values. Two separate parameters, namely, coefficient of friction (COF) and directivity (Δ) were extracted and analyzed. Average COF values indicated that both rings operated in “boundary lubrication” regardless of slurry flow rate. A slight trend was observed between bow wave width and average COF such that higher bow wave widths (resulting from higher flow rates) were shown to cause a drop in COF. However, COF values in all cases were not far from the precision of our instruments. In contrast, the shape of the shear force and normal force data clusters were found to be markedly different for both ring designs and slurry flow rates, pointing to the utility of the directivity parameter (which captured the ratio of the variance of shear force to that of normal force) to provide information on bow wave characteristics. Here, wider bow waves caused a significant drop in directivity for both ring designs indicating significant differences in the stick-slip events for each case and paving the way for deducing bow wave characteristics through tribological studies alone.

Microstructural characterization and wear properties of silver and gold nanoparticle doped K-Mg-Al-Si-O-F glass-ceramics

In ascertaining the effects of silver (Ag) and gold (Au) nanoparticles on crystallization of boro-alumino-silicate system; the K2O-MgO-Al2O3-SiO2-B2O3-F glasses doped with/without 0.2 wt% Ag- and Au- content were melt-quenched at 1550 °C. Doping of nanoparticles considerably increased the glass-transition temperature and softening point but decreased the thermal expansion. A sharp crystallization exotherm in differential scanning calorimetry (DSC) is observed at 750 °C ( ± 1 °C) for glass without nanoparticle and that broadened to 800–855 °C when contains nanoparticle. Opaque glass-ceramics were derived from the glasses by controlled heat-treatment at 1050 °C with predominant crystalline phase fluorophlogopite (KMg3AlSi3O10F2) mica. Traces of Ag- and Au- particles were also identified from X-ray diffraction (XRD) technique. The activation energy (Ec) of crystallization (344 ± 17 kJ/mol) is decreased to 233 ( ± 12) and 307 ( ± 15) kJ/mol (Kissinger method) on doping with Ag- and Au- nanoparticles, respectively. Compact microstructure (FESEM) composed of rock like and plate-like mica crystals are developed in base glass-ceramic and that gets restructured to interlocked type morphology in presence of Ag- nanoparticle. Significant microstructural change induced by nanoparticle addition caused the decrease in microhardness (4.31–4.66 GPa) and increase in thermal expansion. Friction and wear testing under reciprocative sliding (using WC-Co ball) exposed that the average coefficient of friction (COF) is 0.60 ± 0.2 for all glass-ceramics at 20 N load and 10 Hz frequency. At a lower load of 5 N, the average COF value is increased from 0.69 to 0.92 on use of Au-nanoparticle. A Similar trend was also observed at 10 N load as COF increased from 0.62 to 0.78.

Wear Characteristics of FeW/FeW-B4C Coatings Produced by TIG Process

AbstractIn this study, wear properties of FeW-B4C coatings produced by tungsten inert gas (TIG) process on the AISI 1060 steel were investigated. TIG process was selected because it is a cost-effective approach for melting-based coatings. The treated surfaces were evaluated and characterized by means of scanning electron microscope (SEM), X-ray diffraction analysis, and electron dispersive spectrometry (EDS). The microhardness and wear experiment were also performed by using a microhardness machine and ball-on-disk tribometer. SEM observations showed that the obtained coating had a smooth and uniform surface. According to XRD analysis, borides and carbides phases formed in the coatings. The wear behavior of the coatings was compared with ball-on-disc configuration wear tests, at the same conditions. Average coefficient of friction values of the coatings were obtained at relatively low levels.

Microstructure and wear behaviour of plasma transferred arc (PTA)-deposited FeCrC composite coatings on AISI 5115 steel

Plasma transferred arc (PTA) cladding was used to produce composite coatings on the surface of AISI 5115 steel using five different energy inputs and ferrochromium (FeCrC) powder. The effects of different energy inputs and of ferrochromium powder on the microstructure, hardness, and wear behaviour were investigated. The dry-sliding wear properties of the samples were determined using the ball-on-disk wear test method. The alloyed surfaces exhibited increases in hardness and wear resistance and a decrease in the coefficient of friction. The increase in hardness was explained by the presence of hard phases, such as the martensitic phase, Cr7C3, C3Cr7, Fe23C6 and iron carbides, in the microstructure. The average coefficient of friction value of the substrate was determined to be 0.83, whereas these values for the composite layers varied between 0.62 and 0.73. The lowest wear rate (2.88×10−6mm3/N/m) was observed for the 100A PTA cladding sample. The industrial coating process was applied to an AISI 5115 steel rolling cylinder using the optimum parameters (100A), which were determined after experimental studies. The PTA cladding process on the rolling cylinder improved the useful life by approximately 2.5-fold compared to the actual rolling cylinder.

Mechanical and Tribological Properties of Zeolite-reinforced UHMWPE Composite for Implant Application

Ultra-high molecular weight polyethylene (UHMWPE) reinforced with different loadings of zeolite particles were prepared using hot compression molding. The effects of zeolite particles on the mechanical and tribological properties of the UHMWPE composites were studied. The tribological properties were investigated using a Ducom TR-20 pin-on-disc tester under different sliding speeds of 0.209 m/s, 0.419 m/s and 0.838 m/s with various applied loads of 10, 20, and 30N. The worn surfaces and transfer films of the zeolite/UHMWPE composites were observed under the scanning electron microscope (SEM). The results showed that the addition of zeolite into UHMWPE matrix has reduced the tensile strength and elongation at break, but increased the modulus. The 10wt.% zeolite/UHMWPE composites showed an increase of ∼25% in impact strength as compared to pure UHMWPE. The 20wt.% zeolite/UHMWPE composite exhibited lowest wear volume loss as compared to 10wt.% zeolite/UHMWPE and pure UHMWPE. In addition, the average coefficient of friction (COF) was also found to decrease with the addition of zeolite. The lowest average COF was also obtained with the 20wt.% zeolite/UHMWPE composite. The wear volume loss was found to increase with increasing applied loads for all samples. Meanwhile, the average COF values have decreased with increasing applied loads. Furthermore, shallower wear grooves and smoother worn surfaces were observed for zeolite/UHMWPE composites as compared to pure UHMWPE. In terms of the transfer film observation, the counterface of pure UHMWPE were partially covered, rough, and discontinuous. On the other hand, counterface of zeolite/UHMWPE composites were fully covered, smooth, and continuous. Overall, the tribological properties showed significant improvement with the reinforcement of zeolite in UHMWPE.

Dry Sliding Tribological Properties of Fe-Based Bulk Metallic Glass

The dry or unlubricated sliding friction and wear properties of as-cast and annealed BMG (bulk metallic glass) with nominal composition of Fe66.7C7.0Si3.3B5.5P8.7Cr2.3Al2.0Mo4.5 against Si3N4 ceramic ball was studied, along with a conventional material, using a ball-on-disk tribotester at room temperature. The overall average coefficient of friction value of the as-cast BMG was in the range of 0.26–0.42, which was better than the conventional material SUJ2 (0.36–0.46) and comparable with SUS304 (0.31–0.40). The wear mechanism of the Fe-based BMG changed with wear condition. The wear rate increased with increasing load. The hardness of the BMG increased during annealing, however, the wear resistance did not increase proportionally.

Sliding tribological characteristics of Zr-based bulk metallic glass under lubricated conditions

This paper presents the effect of lubricant, SAE EP 90, on tribological properties of Zr-based bulk metallic glass. The coefficient of friction and wear rate values were evaluated for the wide range of applied normal loads (5–40 N) and contact sliding speeds (0.15–1.60 m/s). Wear and friction properties of tribolayers were strongly affected by both parameters throughout the study. Overall average coefficient of friction values were less than 0.1 in the range of study. No sliding induced crystallization was detected by X-Ray analysis. The results of wear characteristics of BMG were also compared with well-known structural materials, AISI 6061-T6 and AISI 304.

Sliding tribological characteristics of Zr-based bulk metallic glass

Wear and friction characteristics of Zr-based bulk metallic glass under dry sliding conditions are investigated. This study demonstrates that load and sliding speed significantly affect the wear characteristics of bulk metallic glass material and sliding distance is less effective on wear. Critical sliding speed and normal force limits, 1 m/s and 10 N, respectively, are distinguished. Overall average coefficient of friction value was in the range of 0.35–0.45, better than that of conventional structural materials such as AISI 6061-T6 and AISI 304. Analysis of the worn surface revealed that the bulk metallic glass was exposed to inhomogeneous shear deformation, adhesive wear, and abrasive wear during sliding test. Three sizes of wear debris, oversize flakes, machining chips and powder-like debris, are collected. There was no change recorded in surface and cross-sectional hardness measurements after the sliding test. This study concludes that bulk metallic glass is better in general friction characteristics than conventional structural materials such as AISI 6061-T6 and AISI 304.

Investigation of high-pressure micro jet technology as an alternative to diamond disc conditioning in ILD CMP

The efficacy of an alternative to conventional diamond conditioning in chemical mechanical planarization (CMP) was evaluated in this study. The high pressure micro jet (HPMJ) system sprays ultra-pure water (UPW) at pressures ranging from 10 to 20 MPa onto a CMP pad to clean the pad of slurry residue, remove embedded slurry particles, and re-establish pad asperities. The system is employed in an ex situ fashion and is compared to in situ and ex situ diamond conditioning as well as using no conditioning. Real-time frictional force acquisition allows for coefficient of friction ( COF) analysis, which indicates the extent of pad wear. Removal rate analysis, SEM imagery, and pad surface profilometry are also used to evaluate HPMJ as an alternative conditioning technology. Removal rates significantly lower than those associated with diamond conditioning are obtained for the HPMJ system when UPW conditioning is directly followed by polishing. SEM imagery and pad profilimetry indicate these low HPMJ removal rates are due to differences in pad surface chemistry, not pad surface topography. Experiments including a 30 s silicon wafer polish with slurry following HPMJ conditioning to re-establish pad surface chemistry were performed and result in removal rates that are comparable to those obtained using ex situ conditioning. The removal rates obtained using HPMJ conditioning for relative wafer-platen velocities of 0.31 and 0.62 m/s are 8 and 1% higher than those obtained using ex situ diamond conditioning and 18% lower than those obtained using ex situ diamond conditioning for 0.93 m/s. The average COF values for HPMJ conditioning using the intermediate silicon wafer polishes are 15% lower than average COF values associated with ex situ diamond conditioning, suggesting a possible increase in pad life for the HPMJ system.