In this paper, a fretting damage model based on fractal theory is proposed. The Weierstrass–Mandelbrot function of fractal theory is used to represent the rough contact surface, and a corresponding contact parameter analysis method is also established. Based on neural network algorithm, the values of fractal parameters are fitted, and the fitting accuracy has been greatly improved compared with traditional methods. According to the fractal parameters of the actual surface, the fretting wear process of the rough contact surface is analyzed based on theory of adhesive and three-body abrasive wear. A generic program for the analysis of three-dimensional fretting wear problems is also proposed. Compared with material tests, the prediction error of the fretting wear simulation model is 13.4% for wear depth and 16.7% and 3.9% for width and length of wear scar in stable wear stage. The prediction results show that the model can be applied to the prediction of the actual three-dimensional fretting wear model.

This paper reports the optimization of base oils composition involving oleate-based bio-lubricant that results in minimal wear-scar diameter (WSD) and coefficient of friction (COF) using mixture technique (MT) with simplex-lattice design (SLD). The lubricants used were neopenthylglycol dioleate (NPGDO), trimethylolpropane trioleate (TMPTO), and pentaerythritol etraoleate (PETO), which all are products of transesterification process between oleic acid and different types of alcohols becoming oleate ester. Fourball tester (FBT) was used to evaluate the resulting COF under ASTM-D4172 B testing procedure, while WSD was measured under an optical wear-scar measuring device. A second-order polynomial mathematical model was built and able to statistically predict the resulting WSD and COF of lubricant mixtures. In pure form, PETO exhibited the lowest COF with 0.06555 followed by NPGDO (+5.25%) and TMPTO (+16.97%). Meanwhile, NPGDO recorded the smallest WSD with 0.451 mm, followed by PETO (+4.04%) and TMPTO (+8.89%). Under SLD optimization technique, pure PETO was shown to give out the lowest COF; however, the lowest WSD was recorded by a mixture of 80.661 wt% PETO with 11.603 wt% TMPTO, and 7.736 wt% NPGDO resulting in 0.444 mm WSD; 5.53% lower wear than pure NPGDO.

Friction and wear behaviors of hybrid aluminum matrix self-lubricating nanocomposite, containing varying amount of nano-aluminum oxide (Al 2 O 3 ) and graphene nanoplatelet (GNP) particles were investigated under dry and boundary lubrication sliding conditions. All the specimens were prepared by ultrasonic probe mixing followed by high-energy mechanical ball milling and spark plasma sintering fabrication route. The objective of this present study is to determine the tribological behavior of GNP as nanoreinforcement under dry and wet lubricating conditions. The wear test was carried out at room temperature on a ball-on-disc reciprocating tribometer with a contact load of 5 N, a frequency of 30 Hz, a stroke of 2 mm, and a sliding distance of 120 m. The chromium-plated chrome steel ball is used as the counter body for tribo-testing. From the results, it has been observed that GNP, as the solid lubricant reinforcement, reduces the friction by 25.33% and 68.14% under dry and wet lubricating conditions, respectively, for the hybrid composite. Reduction in wear volume by 91.15% and 90.50% is observed under dry and wet lubricating conditions, respectively, for the hybrid composite in comparison to the base eutectic Al–Si alloy. The reduction in the coefficient of friction and wear volume for the hybrid composite is attributed to the multilayer two-dimensional GNP nanoparticles that cause easy shearing by forming a conformal protective film layer on the sliding interface. Ultra-mild to severe wear regime was obtained for different composition samples including base composition to hybrid composition.

In this study, the tribological performances of the colloidal suspensions with the additives of nano-silver and nano-gold were examined via wear experiments of AA7075-T6 material. The nanoparticles were penetrated in the wear region using suspensions prepared in distilled water and ethylene glycol environment. The wear experiments were performed under 30 N load and 20 rpm speed condition in 1000 m wear distance using the ball-on-plate method. The worn surfaces were analyzed with a three-dimensional profilometer, scanning electron microscope/energy-dispersive X-ray (EDX), and atomic force microscope (AFM) methods. According to the results, the colloidal dispersed nano-gold particles in ethylene glycol performed 28.85% better on reducing the surface roughness, 2.32% on reducing the weight loss, 4.85% on increasing the heat transfer, and 1.22% on reducing the friction coefficient than the nano-silver particles.

Nowadays, the titanium alloys observe broad applicability in aerospace, marine, automobile, and bio-medical industries due to their lightweight, bio-compatibility, good fatigue strength, and corrosion resistance. However, it possesses poor tribological behavior characterized by a high coefficient of friction (CoF) and the specific wear rate (SWR). In this paper, the impact of the electrical discharge machining on the tribological properties of Ti6Al4V (Ti64) was compared before and after electrical discharge machining (EDM) using a pin-on-disk tribometer under un-lubricated and ambient temperature. Besides, ex-situ analysis was performed on the distinct pin surfaces using (i) scanning electron microscopy (SEM), (ii) energy-dispersive X-ray spectroscopy (EDX), and (iii) X-ray diffraction spectroscopy (XRD) techniques to elucidate the associated wear mechanisms. The mechanical properties such as nano-hardness and elastic modulus of the test surfaces were also determined using a nano-indenter. Significant improvement in SWR (65.44% reduction) with a passable compromise for CoF (22.5% increment) occurred during experimentation (before and after EDM) at 100 N. Besides, the wear behavior of the electrical discharge alloyed Ti64 (ETi64) was evaluated at 200 °C, 400 °C, and 600 °C under the applied loads of 50–150 N. At 400 °C and 600 °C, the SWR initially decreased and then increased with variation in load from 50–100 N and 100–150 N, respectively. The enhanced tribo-behavior at 100 N was due to the protective influence of tribo-oxides, viz., TiO 2 and Ti 8 O 15 assisted by the hard Ti 24 C 15 carbides in the recast layer (RL).

Wear and surface damage of tools (die materials) in the hot metal forming industry is a critical problem observed and is producing an adverse effect on the process economy. The problem occurs when tool and workpiece interact at higher temperatures. However, the research related to the wear and friction of dies is still lacking. In the present investigation, tribological (wear and friction) studies were conducted with an aim to explore the potential of Cr 3 C 2 –NiCr surface coating. The high-velocity oxy-fuel (HVOF) spray technique was used to formulate the coatings. The microhardness, surface roughness, bond strength, and porosity of the coated specimens were found and analyzed. Subsequently, elevated-temperature wear and friction study of the uncoated and coated specimens were done in the laboratory. The study was conducted at 25 N and 50 N loads. The coated specimens showed an increase in wear resistance at all test parameters. The lowest value of coefficient of friction (COF) and the specific wear-rate for the coated specimens were observed at 400 °C. Wear mechanisms were studied by the scanning electron microscopy (SEM) technique. The wear mechanisms were observed to be adhesive in nature at room temperatures and the combination of abrasive/oxidative/adhesive in nature at higher temperatures for the Cr 3 C 2 –NiCr-coated specimens.

The tribological behavior of the 10%, 20%, 30%, and 40% cenosphere-filled epoxy syntactic foams in terms of the wear rate and the friction coefficient of the foams were reported using a pin on disc tribometer in the present study. The influence of the wear parameters like applied pressure, sliding speed, and the sliding distance on the tribological performance of syntactic foams was reported. Syntactic foams with 40% cenosphere volume fraction exhibit better tribological properties over the other syntactic foams. The worn surface examination shows the adhesive dominant wear mechanism and the wear debris with broken cenosphere particles.

Electroless Ni–B–W coating is deposited on low carbon steel in an alkaline sodium borohydride-reduced electroless bath. The mechanical and tribological properties of such coatings are much necessary to be assessed to carry out application-based studies. The present work focuses mainly on the evaluation of hardness and fracture toughness of electroless Ni–B–W coatings using a scratch tester. Coating's response toward scratching is also studied thoroughly. The characteristic short-range order present in its lattice structure causes the generation of a specific behavioral pattern. Furthermore, a linear sliding wear test is carried out on coatings' surface to analyze the wear behavior at different loading conditions. The specific wear rate is observed to be minimum at a normal load of 22.5 N against Si 3 N 4 counterbody. The patterns of tribological behavior of the coating at different load values are examined from the worn surface morphologies. But before embarking on the scratch and sliding wear tests, the synthesized coatings are characterized under field emission scanning electron microscope and X-ray diffraction in an exhaustive manner. The growth rates with respect to time and the changes in morphological aspects of the coating are also evaluated. The present study establishes electroless Ni–B–W deposits as a suitable option for protecting mechanical components against wear.

Hybrid metal matrix composites play a key role in the selection of advanced materials for automotive and aircraft structures in order to ensure the superior tribological properties. This research work highlighted the significance of Si 3 N 4 nanoparticles and premixing of reinforcement with metal powder in steady-state wear behavior of AA6061/Al 2 O 3 /Si 3 N 4 /Gr hybrid nanocomposites. The dry sliding wear test using Pin-on-Disc apparatus was conducted by following ASTM G99 standard. This research work also reported the influence of normal load on wear loss and coefficient of friction for the sliding distances up to 12 km. Si 3 N 4 nanoparticles significantly influenced the wear resistance of the hybrid nanocomposites by forming a well compacted tribo layer and the layer was retained at longer sliding distances. The composite with single ceramic reinforcement Al 2 O 3 , premixed with metal powder, showed abrasive wear. The composites with single ceramic reinforcement Al 2 O 3 , without premixing, showed delamination and third body wear during wear process.

Hydrophobic and self-cleaning photocatalytic ceramics and concrete with potential for the superhydrophobicity are promising novel materials for civil engineering applications including buildings, bridges, road pavements, and airport runways. Due to embedded liquid-repellent properties, such materials have low water and salt absorption and, therefore, enhanced durability. However, in applications requiring high traction (e.g., tire and pavement), there is a concern that reduced adhesion may compromise the friction. This paper reports on wetting, dry friction, and roughness properties of TiO 2 coated (hydrophilic) and polymethyl hydrogen siloxane (PMHS) coated (hydrophobic) self-cleaning ceramic tiles. The coefficient of friction values of the tile–rubber interface do not change significantly with the applications of the coatings up to 0.67 for hydrophilic TiO 2 based and up to 0.46 for hydrophobic TiO 2 + PMHS coatings versus 0.45 for uncoated reference. Friction has adhesion and roughness-related components and this response can be attributed to the roughness component of friction due to TiO 2 coating. The challenges related to hydrophobic coatings, including the durability and future research, are also discussed.

In this study, friction and evolution of cohesive failures (cracks and spallations) in CoB/Co 2 B layers were analyzed. Thermochemical treatment was carried out at 950, 975, and 1000 °C during 6, 8, and 10 h of exposure time, respectively. The characterization techniques include scanning electron microscopy (SEM) for morphology inspection of layers and thickness measurement, X-ray diffraction for the investigation of phases formed, and instrumented indention to obtain hardness, Young’s modulus, and residual stresses. The practical adhesion of the boride layers was evaluated by a progressive load scratch test (PLST), and the critical loads of cracking, chipping, and spallation were calculated. Later, unidirectional multipass scratch tests (MPSTs) were performed by applying subcritical loads selected from the lower spallation load (54 N); these tests were conducted for a different number of scratch passes. The results show that the coefficient of friction (COF) and coating damage depend on the applied load, the number of passes, and coating thickness. In multipass scratch, the mechanical properties, residual stress state, and thickness play a significant role in the evolution of the coating damage that manifests in the form of cracks and cohesive spallations. Considering the scratch and multipass scratch results, it was found that the sample with 10 h of exposure time presents a better performance among the samples.

To achieve thermoplastics-based composites with high tribological performances, molybdenum disulfide (MoS 2 ) and graphite (Gr) were incorporated separately to a polyamide 66 (PA66) matrix. Two different development methodologies of composites were used. The morphological features and the micro-mechanical properties of composites were investigated to stress the influence of the filler surface treatment and its dispersion. The friction coefficient was evaluated using a ball on a flat micro-tribometer. The wear mechanisms were also characterized. The best tribological performance was exhibited by 10 wt% of graphite. The surface treatment of the filler inclusions by 3-aminopropyltriethoxysilane (AMPTES) showed an improvement in the morphological aspects of adhesion at the filler/matrix interface.

A deterministic adhesive model for the contact between an elastic layered medium with surface roughness and a smooth elastic microsphere was developed on the basis of the Lennard–Jones surface force law. Through numerical simulations, the adhesive contact behavior of the layered medium with the measured three-dimensional (3D) surface topography was comparatively analyzed with that of the homogeneous medium. Furthermore, the contact characteristics of the layered medium with pre-assigned roughness parameters were investigated with the aid of a computer-generated technique for simulating surface roughness. Results showed that the pull-off force for the contact problem involving rough surfaces was influenced by the contact location, and the average value for the contact between an alumina (SiO 2 ) microsphere and a diamond-like carbon/silicon (DLC/Si)-layered medium was smaller than that for the contact between a SiO 2 microsphere and a Si homogeneous half-space. In addition, the effect of the diamond-like carbon (DLC) layer on reducing adhesion was smaller than that of the surface roughness. Finally, the average pull-off force for a DLC/Si-layered medium with computer-generated surface roughness rapidly decreased; however, it eventually became almost unchangeable with the increase in the root-mean-square (RMS) deviation.

The effect of Mn modification on the tribological properties of Al-15Mg 2 Si-(0.5-2)Fe composites was investigated. The sliding wear tests were conducted under the applied pressures of 0.25, 0.5, and 1.0 MPa at the constant sliding speed of 0.13 m/s. According to the results, the behavior of FeMn-rich intermetallics against the strains induced by sliding wear has an important role in the wear behavior of composites. In low-Fe composites (0.5–1 wt % Fe), Mn promotes the formation of Chinese script α -Al 15 (Fe,Mn) 3 Si 2 phases instead of harmful β -Al 5 FeSi platelets. The formation of these compounds strengthens the substrate and decreases its microcracking tendency giving rise to a more stable tribolayer and improved wear properties. At the higher Fe contents, Mn modification leads to the formation of primary polyhedral or star-like α -Al 15 (Fe,Mn) 3 Si 2 compounds in the microstructure and substantially neutralizes the harmful effect of the primary β -Fe crystals on the wear behavior. However, when subjected to the friction-induced surface plastic strains, the near-surface α -FeMn particles fracture and incorporate into the tribolayer making it unstable and less protective. The tribolayer stability in Mn-modified composites decreases the chance of adhesion between contacting surfaces, and, under low applied pressures, lowers the average friction coefficient (AFC) and its fluctuation. At higher applied pressures, however, the nonmodified composites exhibit lower AFC, which is probably due to the negative impact of β -Fe fragments on the tribolayer shear strength.

The objective of this research work is to synthesize functionally graded Cu-11Ni-4Si/10 wt % SiC, Cu-11Ni-4Si/10 wt % Si 3 N 4 composite using horizontal centrifugal casting method and to analyze its mechanical and adhesive wear behavior. The cast samples with dimension of Ø out 100 × Ø in 70 × 100 mm were synthesized and variation in volume of SiC and Si 3 N 4 particles on inner (1 mm), middle (8 mm), and outer surfaces (15 mm) along radial direction of the composites was analyzed. Microstructural images revealed that inner zone of the both composites had highest distribution of reinforcement particles. Tensile tests on inner (1–7 mm) and outer (8–15 mm) zones of composites revealed that the inner zones had highest tensile and yield strength. Fractography test was conducted for both composites at inner and outer zones to observe the mode of failure. Hardness tests taken along radial direction of the composites revealed that, the inner surface had better hardness and it reduced toward outer periphery. The outer and inner surfaces of Cu/SiC were compared with Cu/Si 3 N 4 composites and results revealed that inner surface of Cu/SiC had highest wear resistance among all surfaces of composites. It was also observed that, while increasing load, wear rate increased with it for all composites. Wear rate of composites majorly decreased while increasing the sliding velocity due to formation of tribolayer. Scanning electron microscopy (SEM) analysis carried out on worn surfaces of Cu/SiC and Cu/Si 3 N 4 composite revealed that, plastic deformation, and plowing were the dominant wear mechanism for varied parameters.

This paper primarily focused on the dynamic tribology properties of one certain nonasbestos organic (NAO) friction material by using an approximate in situ method. This study was performed through a pad-on-disk type friction tester under different temperature conditions. Results showed that temperature has a significant effect on the dynamic tribology performance. At 100 °C, friction coefficient and wear rate after the running-in stage varied little with time. At 250 °C, friction coefficient after the running-in stage increased gradually and then tended to be stable, while wear rate decreased gradually. From 100 to 350 °C, friction coefficient increased first as a function of temperature, but decreased sharply when the temperature was over 250 °C. Simultaneously, wear rate also increased sharply over 250 °C. Additionally, three dynamic evolution models of worn surfaces corresponding to different cases were established.

The present study includes the investigation on the frictional dynamics of hard and soft solid interface using low velocity linear tribometer. The effects of gelatin concentration, nanoparticles concentration, normal stress, and sliding velocity on the static and dynamic frictional shear stresses acting on the sliding gel block are studied using response surface methodology (RSM). The shear sliding experiments are conducted in steady sliding regime, well above the critical velocity. L 31 orthogonal array consisting of five levels for each factor is selected for the experimentation and second-order quadratic model has been generated for both the responses. The mathematic models are validated with the available trends mentioned in the literature.

A functionally graded Cu–10Sn–5Ni metal matrix composite (MMC) reinforced with 10 wt % of Al 2 O 3 particles was fabricated using the centrifugal casting process with dimension Φ out 100 × Φ in 85 × 100 mm. The mechanical and wear resistance of the composite has been enhanced through heat treatment. Samples from of the inner zone (9–15 mm) were considered for heat treatment, as this zone has higher concentration of less dense hard reinforcement particles. The samples were solutionized (620 °C/60 min) and water quenched followed by aging at different temperatures (400, 450, and 550 °C) and time (1–3 h). Optimum parametric combination (450 °C, 3 h) with maximum hardness (269 HV) was considered for further analysis. Dry sliding wear experiments were conducted based on Taguchi's L 27 array using parameters such as applied loads (10, 20, and 30 N), sliding distances (500, 1000, and 1500 m), and sliding velocities (1, 2, and 3 m/s). Results revealed that the wear rate increased with load and distance whereas it decreased initially and then increased with velocity. Optimum condition for maximum wear resistance was determined using signal-to-noise (S/N) ratio. Analysis of variance (ANOVA) predicted the major influential parameter as load, followed by velocity and distance. Scanning electron microscope (SEM) analysis of worn surfaces predicted the wear mechanism, observing more delamination due to increase in contact patch when applied load increased. Results infer 8% increase in hardness after heat treatment, making it suitable for load bearing applications.

AA2218–Al 2 O 3 (TiO 2 ) composites are synthesized by stirring 2, 5, and 7 wt % of 1:2 mixture of Al 2 O 3 :TiO 2 powders in molten AA2218 alloy. T61 heat-treated composites characterized for microstructure and hardness. Dry sliding wear tests conducted on pin-on-disk setup at available loads 4.91–13.24 N, sliding speed of 1.26 m/s up to sliding distance of 3770 m. Stir cast AA2218 alloy (unreinforced, 0 wt % composite) wears quickly by adhesion, following Archard's law. Aged alloy exhibits lesser wear rate than unaged (solutionized). Mathematical relationship between wear rate and load proposed for solutionized and peak aged alloy. Volume loss in wear increases linearly with sliding distance but drops with the increase in particle wt % at a given load, attributed to the increase in hardness due to matrix reinforcement. Minimum wear rate is recorded in 5 wt % composite due to increased particles retention, lesser porosity, and uniform particle distribution. In composites, wear phenomenon is complex, combination of adhesive and abrasive wear which includes the effect of shear rate, due to sliding action in composite, and abrasive effect (three body wear) of particles. General mathematical relationship for wear rate of T61 aged composite as a function of particle wt % load is suggested. Fe content on worn surface increases with the increase in particle content and counterface temperature increases with the increase in load. Coefficient of friction decreases with particle addition but increases in 7 wt % composite due to change in microstructure.

In a discharge reed valve for compressors, the oil stiction by the oil film between the reed and the valve seat is investigated experimentally, and a simulation model is developed. Through a model experiment, the initial oil film thickness is measured by an interferometry method, and the valve displacement and the bore pressure are measured from the stiction to the valve opening. The opening delay time together with the initial oil film thickness is measured while changing the contact area and the oil species. In the simulation model, the deformation of the reed and the pressure of the oil film as a result of cavitation are coupled. In order to take into account the tensile stress in the oil film, a cavitation model directly simulating the expansion of cavitation bubbles is developed (herein, dynamic cavitation model). In the experiment, a smaller contact area, a larger initial film thickness, and a smaller oil viscosity yield a shorter delay. In the simulation, the dynamic cavitation model is advantageous in representing the experimental delay time. In particular, with respect to the relationship between the initial film thickness and the delay time, the dynamic cavitation model with an initial bubble radius that depends on the oil film thickness yields results similar to the experimental results.