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The wear behavior and mild–severe (M–S) wear transition of Mg–10Gd–1.5Y–0.4Zr alloy were investigated within a temperature range of 20–200 °C. The morphologies and compositions of worn surfaces were examined to identify the wear mechanisms using scanning electron microscope and energy dispersive X-ray spectrometer. The microstructure and hardness in the subsurfaces were analyzed to reveal the M–S wear transition mechanism. Under a constant loads of 20, 35 and 40 N, each wear rate–test temperature curve presented a turning point which corresponded to the M–S wear transition. In mild wear, the surface material was plastically deformed and hence was strain- hardened, whereas in severe wear, the surface material was dynamically recrystallized and consequently was softened. It has been found that the critical temperature for M–S wear transition decreases with increasing the normal load, and the normal load exhibits an almost linear relationship with critical temperature for M–S wear transition. This work reveals that the M–S wear transition of the studied alloy conforms to the surface DRX temperature criterion.

The present work investigates the effect of process parameters (normal load, sliding velocity, and sliding distance) on wear behaviour of Ti-3Al-2.5 V alloy under dry sliding condition. The wear te...

The work presented in this paper is to investigate the wear rate and wear mechanism of medium carbon steel with carbon contents of about 0,5 wt.% under the friction load with various contact surface temperatures. The wear test was performed by using the linear reciprocating ball-on-flat wear test machine. To develop the elevated temperature on the surface of the wear test specimen, the heater assembled into the wear test machine. The surface temperature of the wear specimen was set in the range of 30 ºC up to 250 ºC. The test was taken under 5000 cycles of friction loading with a maximum of the normal load of 25N. The experiment results show that the change in the contact surface temperature in the range of 30 ºC up to 250 ºC causes the wear rate to increase slightly. This is because the elevated temperature at the surface was not high enough to cause the hardness of the material to decrease significantly. The worn surface looks very thin scratches and slightly deformed layers, and the wear mechanism had identified as oxide wear.

The random distribution of graphene in epoxy matrix hinders the further applications of graphene-epoxy composites in the field of tribology. Hence, in order to fully utilize the anisotropic properties of graphene, highly aligned graphene-epoxy composites (AGEC) with horizontally oriented structure have been fabricated via an improved vacuum filtration freeze-drying method. The frictional tests results indicated that the wear rate of AGEC slowly increased from 5.19×10−6 mm3/(N·m) to 2.87×10−5 mm3/(N·m) with the increasing of the normal load from 2 to 10 N, whereas the friction coefficient (COF) remained a constant of 0.109. Compared to the neat epoxy and random graphene-epoxy composites (RGEC), the COF of AGEC was reduced by 87.5% and 71.2%, and the reduction of wear rate was 86.6% and 85.4% at most, respectively. Scanning electron microscope (SEM) observations illustrated that a compact graphene self-lubricant film was formed on the worn surface of AGEC, which enables AGEC to possess excellent tribological performance. Finally, in light of the excellent tribological properties of AGEC, this study highlights a pathway to expand the tribological applications of graphene-epoxy composites.

Tribological characteristics of AZ91/B4C surface composites were studied under air and argon gas environments. Tests were conducted under a constant normal load of 10 N, with a sliding velocity of 0.06 m/s using a linear reciprocating tribometer. Wear tracks and debris were analyzed using scanning electron microscopy, three-dimensional contour topography, and energy-dispersive X-ray spectroscopy in order to understand the wear mechanisms. The wear rate of the specimen tested under the argon environment was found to be lower (∼60%) in comparison with that of the specimen tested under the open-air environment. The value of the friction coefficient was found to be minimum under the argon environment compared with the air environment. In the air environment, the major material loss from the test specimen was attributed to oxidation wear; whereas under the argon environment, strain-hardening effect was dominant, and the material was found to be removed by delamination wear. In addition, the worn surface morphology of the wear tracks and counter surfaces showed the involvement of abrasion and adhesion wear mechanisms. The results of the study pave the pathway for the design of lightweight surface composite material systems such as AZ91/B4C toward an efficient and robust tribo-pair applicability for a controlled environment.

The tribological properties of carbide ceramics (SiC, B4C–SiC, and B4C) sliding against SiC balls in water at a normal load of 20 N in ambient conditions were investigated. Compared with traditiona...

Ceramic composites are extremely sensitive to the surrounding environment. Their tribological performance may degrade drastically if they are polluted by some external agent. The present article was aimed to investigate the unidirectional sliding characteristics of brake oil treated woven carbon-carbon (C/C), and carbon-carbon-silicon carbide (C/C-SiC) composites. The laminate orientation, surface conformity, normal load, and sliding velocity were varied. It was depicted that the quantity of oil absorbed by the composites depends on the laminate orientation. The decay rate in friction coefficient revealed that C/C composites are more prone to brake oil in comparison to C/C-SiC composites. The results showed that it is difficult to make an assumption regarding the wear and friction behavior of laminated composites in low conformity contacts concerning normal load and sliding velocity. However, friction coefficient increased with increment in sliding velocity and normal load, for non-conformal Hertzian contacts. The generation of friction film was arduous in the presence of absorbed oil. SEM analysis of worn surfaces revealed different surface morphology for low, and non-conformal contacts which depicted distinct tribological mechanisms.

A micromechanical experimental study is presented in this paper investigating the normal contact response of quartz sand grains under cyclic loading. Sand grains with clean surfaces, termed uncoate...

Nowadays, there are various types of techniques have been used to develop the composite material by using various types of reinforcement particles. In the present review article, different techniques have been discussed for the development of aluminum-based composite material. Furthermore, the percent utilization of different reinforcement particles has been also discussed. Mechanical properties of the developed composite were also discussed. It was identified from the literature that normal load, sliding velocity, sliding distance, and reinforcement weight percent also affect significantly the tribological behavior of composite material.

The usage of magnesium alloy has grown in the field of automotive, aviation, and marine sectors due to its significant characteristics of lightweight, high specific strength, impact, and wears resistance. The present investigation is to evaluate the wear characteristics of magnesium AZ91E alloy nanocomposite with SiCnp by pin-on-disc wear tester using dry sliding conditions. The dry sliding wear investigations were carried out on a 200 m constant sliding distance with a load of 10 N, 20 N, 30 N, and 40 N at various sliding speed (0.25 m/sec to 0.75 m/sec). The wear rate of nanocomposites significantly decreased with the normal load at a high sliding speed of 0.75 m/sec as compared to AZ91E alloy. The result showed that the coefficient of friction has gradually increased with increase in the load 10 N to 40 N at different sliding speed. It has varied from 0.307 to 0.472.

Two types of alloy (Steel and Kovar) were prepared and machined as half ring. Wear testing system was used to determine the wear rate of specimens without any lubrication, and after modified wear testing system which was used to test the specimen under lubricant condition. The wear rate wasdetermined by using weighing method and then calculated. The results shows the values of wear rate of kovar specimens are higher than the values of wear rate for steel specimens in both two cases with and without lubrication. The result of wear rates wereplotted as function of sliding time at a fixed normal load.

The shearing behaviour of reproduced flat LBS grains artificially bonded with ordinary Portland cement (OPC) and plaster of Paris (PP) was examined using micromechanical experiments. Monotonic shearing tests showed a distinct variation in the load–displacement relationship at low, medium and high normal loads, and a nonlinear shear strength envelope was proposed. For OPC-bonded sand grains, a brittle–ductile transition at 20–30 N normal load was observed and three breakage mechanisms in shearing (chipping, shear cracks and crushing) were distinguished in accordance with the changes in the load–displacement curves. OPC-bonded sands showed a predominant dilation at lower normal loads, whereas PP-bonded sands were highly compressive. Based on previously published works using element-scale tests, a new mechanism for dilation under micromechanical testing was proposed in the study. Cyclic shearing tests were conducted on OPC-bonded sands, and the effects of increased displacement amplitude and normal load were highlighted.

Alloys used as bearings in aircraft landing gear are required to reduce friction and wear as well as improve the load-carrying capability due to the increased aircraft weights. Cu-15Ni-8Sn-0.8Nb alloy is well known for possessing good mechanical and wear properties that satisfy such requirements. In this study, the microstructure, mechanical properties, and grease-lubricated sliding wear behavior of Cu-15Ni-8Sn-0.8Nb alloy with 0.8 wt% Nb are investigated. The nanoscale NbNi3 and NbNi2Sn compounds can strengthen the alloy through the Orowan strengthening mechanism. A Stribeck-like curve is plotted to illustrate the relationship among friction coefficient, normal load, and sliding velocity and to analyze the grease-lubricated mechanism. The wear rate increases with normal load and decreases with sliding velocity, except at 2.58 m/s. A wear mechanism map has been developed to exhibit the dominant wear mechanisms under various friction conditions. When the normal load is 700 N and the sliding velocity is 2.58 m/s, a chemical reaction between the lubricating grease and friction pairs occurs, resulting in the failure of lubricating grease and an increase in wear.

Knowledge of the rheological behavior of saturated particulate networks is crucial for every process in which a particulate network is built-up, dewatered, or transported, as in a decanter centrifuge. However, difficulties arise as to how to characterize the material properties. Thus far, no standardized method or measurement device has prevailed. In this work, the requirements for a useful device are discussed, followed by the design of a modified shear cell for a Schulze ring shear tester RST-01.pc and its measurement procedure. Shear experiments under normal load with different sediments consisting of inorganic and organic particles whose material properties strongly affect the rheological behavior were performed. The results demonstrate the potential of the modified shear cell. Furthermore, current challenges in characterization are discussed. The characterization possibilities of the developed shear cell are a further step toward understanding the rheological behavior of liquid-saturated particulate networks.

The effect of normal load on the frictional and wear behaviour of carbon fiber is investigated by simulating the tow-on-tool friction relevant to the beating-up motion of three-dimensional (3 D) weaving process. The true number of contact filaments over a range of normal loads is calculated by characterizing the cross-section parameters of carbon tow. The real contact area is calculated on the basis of the filaments amount by Hertzian contact model. The friction force values obtained from multiplying the real contact area with shear strength are closely with the measured results. The coefficient of friction increases with the increase of normal loads. When the normal load is 250, 400 and 600 mN, the tensile loss rate of the carbon tow after friction test is 6.3%, 23.2% and 42.4% respectively. The filaments reveal multiple fracture damage patterns which are caused by stretching, shearing and compression during the weaving process.

Dry sliding wear experiments were carried out at constant normal load and sliding speed on electrodeposited Ni and Ni-α-nano Al2O3 coatings. The coating surfaces were worn against EN-32 HRc hardene...

Solid-liquid separation aims to increase the solids concentration. The dewatering extent can be parameterized through the compressive yield stress, py(ϕ) whereby to further consolidate a suspension, higher stress has to be applied to the material. In a variety of dewatering devices, shear (in addition to unilateral compression) is applied to the material and is demonstrated to be of benefit to the process, albeit without a basis for optimisation. To address this fundamental issue, two novel measurement techniques, namely the Vane-in-a-Filter (ViaF) and the Vane-under-Compressional-Loading (VuCL), are presented, allowing measurement of the shear stress response with different normal loads under fixed solids concentrations. Furthermore, high solid concentration shear yield stress measurements are possible. The results demonstrate that the shear stress response increases with normal load (at a fixed state of compression) and the peak shear stress has a minimum at shear rates of 0.01–0.1 s−1.

Shearing behavior and failure mechanism of bolt-grout interface are of great significance for load transfer capacity and design of rock bolting system. In this paper, direct shear tests on bolt-grout interfaces under constant normal load (CNL) conditions were conducted to investigate the effects of bolt profile (i.e. rib spacing and rib height) and grout mixture on the bolt-grout interface in terms of mechanical behaviors and failure modes. Test results showed that the peak shear strength and the deformation capacity of the bolt-grout interface are highly dependent on the bolt profile and grout mixture, suggesting that bolt performances can be optimized, which were unfortunately ignored in the previous studies. A new interface failure mode, i.e. ‘sheared-crush’ mode, was proposed, which was characterized by progressive crush failure of the grout asperities between steel ribs during shearing. It was shown that the interface failure mode mainly depends on the normal stress level and rib spacing, compared with the rib height and grout mixture for the range of tested parameters in this study. Keywords: Bolt-grout interface, Direct shear test, Shear behavior, Failure mode, Bolt profiles

The aim of the present study is to investigate the influence of polymerization times, normal loads and titanium dioxide nanoparticles content on the wear of hybrid composite resin reinforced with titanium dioxide (TiO2) nanoparticle. The materials used are hybrid composite resin and titanium dioxide nanoparticles (TiO2nanoparticles). Four groups of composite resin samples are prepared; one as received and three groups reinforced with TiO2nanoparticles in contents of 0.1, 0.2 and 0.3 wt. %. Hybrid composites resin is manually mixed with TiO2 nanoparticles. The resulting blend is packed into plastic cylindrical bars. The samples are then cured from both sides for 10, 20, 40, 60 and 80 seconds using a visible light curing unit. To determine the wear, all samples are tested with two-body abrasion, reciprocating sliding apparatus at room temperature. The test conditions are; sliding velocity= 60 strokes/min, load= 6, 8, 10, 12 and 14 N, time= 60 seconds. Results show that the wear decreases with the increase of polymerization time at all normal loads. Results showed also that wear depends on the normal load. The wear initially decreased and reached a minimum at a concentration of 0.1 wt. % TiO2 nanoparticles, above 0.1 wt. % TiO2 nanoparticles, the aggregation of TiO2 nanoparticles led to increase of the wear. The present study suggests that in order to minimize wear, it is important to use relatively higher polymerization time, lower TiO2content and lower force of chewing.

Wear behaviors of a peak-aged Cu-15Ni-8Sn alloy fabricated by powder metallurgy were investigated. The results indicated that the friction coefficients and the wear rates of Cu-15Ni-8Sn alloy within a normal load range of 50-700 N and a sliding speed range of 0.05-2.58 m/s were less than 0.14 and 2.8×10−6 mm3/mm, respectively. Stribeck-like curve and wear map were developed to describe the oil-lubrication mechanism and wear behavior. The equation of the dividing line between zones of safe and unsafe wear life was determined. Lubricating oil was squeezed into micro-cracks under severe wear conditions. In addition, the lubricating oil reacted with Cu-15Ni-8Sn alloy to generate the corresponding sulfides, which hindered the repair of micro-cracks, promoted cracks growth, and led to delamination. This work has established guidelines for the application of the Cu-15Ni-8Sn alloy under oil-lubricated conditions through developing wear map.

The current research work addresses evolution of coefficient of friction over sliding distance. Friction and wear tests were conducted using pin on disk type tribometer. The stabilized friction coefficient values under normal load of 10 N and 15 N for Al 6061 were noted as 0.5 and 0.58 respectively. Corresponding friction coefficient values for Al 6082 were noted as 0.6 and 0.45 respectively. Equation to calculate wear volume was derived for cylinder on flat contact. The dominant wear mechanisms were justified with the images of the disk specimens captured using optical microscope. Increase in wear volume resulting from increase in normal load was observed for Al 6061 and Al 6082 alloys.

The wear characteristics of AZ91D Mg alloy was analyzed at elevated temperature and under different load conditions. Sliding wear tests was conducted for AZ91D Mg alloy against a harden steel disc under various normal load (10 N, 20 N, and 30 N) in a pin-on-disc type wear tester in dry condition at different temperatures (50 °C, 100 °C, 150 °C). The wear value was assessed in terms of height loss as well as weight loss of the pin shaped specimens. In addition, a cumulative wear value against the test time was also recorded through data acquisition arrangement equipped with the wear tester. The results indicated that the AZ91D alloy exhibited a lower wear rate at elevated temperature. However, the wear value increased with the enhancement of normal load applied during the wear test.

The present study focuses on understanding the variation of coefficient of friction over a period of time. At various sliding cycles, the coefficient of friction was noted from the well-controlled sliding experiments. Friction tests were conducted using Aluminium alloys (Al 6061 and Al 6082) with 10 N constant normal load and at sliding speed of 1.5 m/s. The detailed friction results have been presented and discussed to understand the influence of coefficient of friction on the contact tractions at the interface. The obtained friction results are compared with the results mentioned in literature, where reciprocating sliding experiments were conducted. From this comparison, it is concluded that the formation of oxide and nitride layers are dominant, when the friction tests are conducted using pin on disc setup.

In the present study, a mathematical model is proposed for the prediction of wear rate of Al-12.6Si alloy-based composites reinforced with in situ TiB2 (2, 3, 5 wt%) particles by halide salt reaction route. For deducing an empirical relationship for wear rate (pin-on-disc type wear), a multiple regression analysis has been performed to show its dependency on the TiB2 content of composite and various wear test parameters. From the regression statistics, it is inferred that the wear rate is strongly dependent on the rotating speed of the disc but moderately on the TiB2 content and applied normal load.

It has been observed that well designed parameters of surface texturing can enhance the tribological performance of lubricated surfaces under relative sliding motion. These micro-features develop hydrodynamic lift at the interface of sliding surfaces. These textures can be positive (protruded out of surface) and negative (recessed out of surface). This paper focused on the effects of positive texturing on reduction of friction and wear of piston ring/ cylinder liner (PR/CL) system under lubricated conditions by providing rotary sliding motion between textured ring and un-textured liner surfaces. The square shaped textures of different heights were produced by photo chemical etching method. The experiments were conducted on pin on disc friction and wear test rig to determine the effects of load, sliding speed and texture geometric parameters including texture height and area density. From the results obtained, it is reported that there existed a set of optimal parameters of texture height, area density, normal load and sliding speed to obtain reduction in friction and wear of PR/CL system.The maximum reductions in friction and wear rate were observed with the textured patternsat an optimal height and area density of 25 µm and 10% respectively.

Determination of food rheological and tribological behaviors is imperative for understanding both processing behaviors and texture attributes. The objective of this study was to determine wear behavior of Cheddar and Monterey Jack cheeses. Wear measurements were performed at 50 mm/s sliding speed, 1N normal load, and 25 °C. Cheese linear and nonlinear viscoelastic properties were also determined. Compared to Cheddar, Monterey Jack showed significantly greater small-strain storage and loss moduli values and lower extent of nonlinear viscoelastic behavior. Lissajous plots agreed with these results. Overall, Monterey Jack had lower penetration depth increase and lower mass loss during wear testing than Cheddar. The results of this study provided fundamental information on cheese rheology–wear relationships.

Bulk metallic glasses (BMGs) often offer excellent physical, chemical, and mechanical properties such as high strength, high hardness, and good wear/corrosion resistance, stemming from their unique atomic configuration. These properties enable them to be a potential engineering material in a range of industrial applications. However, the wear behaviors must be considered in structural applications. Here, the wear tests of a TiZrNiCuBe bulk metallic glass at high temperatures were carried out. As the testing temperature increases, the wear rate of the studied BMG sample gradually decreases and the sample surface becomes smoother. Meanwhile, a higher applied normal load causes a higher wear rate. The wear mechanism evolves from the abrasive to adhesive mode with increase in the testing temperature. The results obtained here could shed more insights into the deformation mechanism of BMGs and thus extend their industrial uses in high-temperature environments.

Surface texturing plays a significant role on the tribological performance of contact surfaces. The tribological characteristics are mostly dependent upon the different pattern and methods of surface texturing. This research works investigates lubricated wear behaviour on circular dimples textured EN-31 alloy steel materials using DUCOM linear reciprocating tribometer. The surface dimples are fabricated by micro-EDM and micro-drilling CNC methods. Initially plane surfaces are tested under different lubricants ISO-68 and ISO-220 oil on a couple of EN31 plates with EN8 steel pin. At loading conditions the results clearly shows that the ISO 68 oil gives better performance than ISO-220 oil in terms of frictional force and COF. The operation during test under ISO-220 oil observed is very noisy and wear rate is also more. Then after experiments under different load conditions on textured surfaces were investigated using optimized ISO-68 oil. An experimental results on m-EDM provides superior frictional characteristics with respect to m-CNC. Surface texturing may act as wear debris trapper, lubricant reservoirs, hydrodynamic lift, and retarding the lubricant molecules flow in a particular path where potential exists. Here micro-dimples EDM surface textures can enhance mixed lubrication and in mixed lubrication the friction is least and this may leads to decrement of wear loss.

In this article, we have studied experimentally the frictional behavior of dry multiwall carbon nanotubes (MWCNTs) nanoparticles between the metal–metal interface as function of areal concentration of the MWCNTs and normal load. The results show that critical velocity, at which stick–slip disappears, decreases with increase in areal concentrations of the nanoparticles. However, steady dynamic friction remains almost constant with the areal concentrations. These observations are explained on the basis of rolling and sliding motion the cylindrical carbon nanotubes. Future implications of the present study are also highlighted.

The viscosity of the ice premelting layer in contact with silica in the temperature range of -18 to -1 °C was studied by resonance shear measurement (RSM). The viscosity of the ice premelting layer was determined to be ∼5 orders of magnitude greater than that of the bulk liquid water and continuously decreased with the increasing sliding speed between the two surfaces over the temperature range employed in this study, which was the same behavior as for the typical confined liquids including water. On the other hand, the normal load and the contact pressure did not influence the viscosity, indicating that the premelting layer behaved differently from the typical confined liquids.

A constitutive model is developed that incorporates the wavy elastic response of an arc-shaped metallic glass (MG) ribbon subjected to applied progressive normal load. This model is based on the ev...

Tribological performances are significantly affected by the tribo-chemical reaction of the mating materials, while the effect on the B₄C film under high relative humidity conditions are poorly investigated. Therefore, fiction tests of three tribo-pairs (B₄C/WC, B₄C/steel and B₄C/Al₂O₃) under 85% RH with various normal loads and sliding frequencies were performed. The results show that the B₄C/WC tribo-pair exhibits excellent tribological properties, including very stable friction curves, minimum friction coefficients & wear rates, maximum carrying-load capacity and the smallest fluctuations with the change of the normal load. Similar results have been obtained for the B₄C/WC tribo-pair with the increase in the sliding frequency. This is mainly attributed to the oxidation of WC to form WO₃ that is conducive in enhancing the tribological performances. Therefore, the sliding contact of B4₄C/WC is the desirable design for engineering applications under high relative humidity.

The paper assesses and compares the friction and wear behavior of SAE-AISI 1055 steel and brass (CuZn39Pb2) under dry sliding condition. The tribological behavior was investigated and compared by conducting two different experiments, the first experiment conducted on a CSM tribometer, and the second experiment was carried out on a test bench in horizontal lathe machine where device holder pin is fabricated and mounted on a test bench and a rotating disc, varying the normal load exert on the disc by the pin and the rotation speed of the disc. These tests consisted of measuring friction coefficient and wear loss of samples. Experiments are carried out in normal load 5-10 N, sliding speed 0.24-0.35 and 0.48 m/s. Variations of coefficient of friction during sliding at different initial surface roughness, normal load and sliding speed are investigated. Results show that the two alloys had different friction and wear behavior, for steel friction coefficient increase slowly with the increase of normal load and sliding speed. For brass friction coefficient decreases with the increase of normal load and sliding speed. On the other hand, it is also found that wear loss increase with sliding distance. Microscopic of worn surfaces for each alloy were carried out and compared.

Pumice has a large potential to be used in structural and geotechnical engineering projects as a lightweight aggregate, and it is a material of unique characteristics. Gravel-sized pumice from Yunnan, China, was examined in the present study with a custom-built micromechanical apparatus investigating the properties of pairs of grains at their interfaces subjected to monotonic and cyclic tests under different saturation states. Based on interferometer measurements, the vesicular surface of the pumice was characterized to be very rough. From the interface micromechanical experiments, it was shown that the virgin surfaces appeared to be very soft under normal loading tests, during which micro-asperity breakage was caused. After preloading and preshearing, the normal load–displacement curves became much smoother and the Young’s moduli, which remained relatively low in magnitude compared with other geo-materials previously studied, could be quantified applying the Hertzian model. Large hysteretic loops were observed from cyclic normal load tests. Plastic displacements dominated the first normal loading cycle, while elastic displacements prevailed in the subsequent cycles. High values of the apparent coefficient of friction were observed from the monotonic shearing tests. A modification of the power value of the Mindlin and Deresiewicz model was necessary to be applied during the fitting of the experimental data so that theoretical and laboratory curves could match. It was shown that this power had a direct correlation with the coefficient of friction.

Two-body abrasive wear tests of Fe-B alloys with various matrix microstructures were performed using a pin-on-disc tribometer at a normal load of 3 N. The wear behavior was analyzed using s...

The paper investigates sliding friction of the α-Al2O3/α-Al2O3 and α-Fe2O3/α-Fe2O3 contacts by using the spring interfacial potential. It is found that at micronscale the friction properties of the oxides are almost independent of the coarse-graining and are the same in the different sliding directions. Even the hardness contacts friction coefficient shows a decrease with increasing intensity of the normal component of the interfacial interaction force. This result is as an implementation for the previous observations of sliding friction of various materials that showed that a drop of friction coefficient with increasing externally applied normal load has originated from deformation of interfaces or occurrence of debris at contact, indicating an unsteady contact.

An investigation was conducted to determine the extent to which the microstructure of NiCrSiBC alloy coatings influences micro-abrasive wear resistance. The wear performance of the complex microstructure in coatings is strongly dependent on nature of the strengthening particles. Processing conditions can be altered to manipulate these particles and therefore to design coatings to address specific service demands. The purpose of this investigation was to evaluate the relationship between microstructure and micro-abrasive wear performance of NiCrSiBC coatings. Differences in the microstructure of coatings were imposed by processing with Plasma Transferred Arc (PTA) and High-Power Diode Laser (HPDL). The microstructures of NiCrSiBC coatings were evaluated using EDX, XRD, SEM techniques and hardness measurements. Wear performance was assessed by micro-abrasive wear tests in which normal load, sliding distance and ball sliding speed were varied. A suspension of alumina in water was used as the abradant. The features of the strengthening particles were observed to depend on the imposed solidification/cooling rate. A faster cooling rate, produced by HPDL processing, displayed block shape chromium borides (CrB) in finer structure coatings. This contrasted with PTA-processed coatings which exhibited floret-shape chromium borides (Cr5B3) in a coarser microstructure. Higher hardness coatings with finer microstructure exhibited lower abrasive wear resistance than the coatings with coarser microstructure.

There have been insistent demands for effective lubricants as well as additives for reducing friction and wear in various applications. Recently, graphene oxide (GO) and nanodiamond (ND) have been observed to be promising materials to reduce friction and wear in tribological studies. Herein, a novel lubricant has been developed by using GO and ND together as lubricant additives in water in order to enhance tribological performance. The tribopairs employed were Si3N4 balls and Si wafers, and the applied normal load was 5–80 mN. The lowest friction coefficient of approximately 0.03 was obtained for water with 0.1 wt.% GO and 0.5 wt.% ND, while the corresponding depth of wear track was as low as about 5 nm. Analysis of the tribological mechanisms elucidated that the sliding-induced nanostructured tribofilm, the low shearing resistance between graphene sheets, and the possible ball bearing effect of ND all contributed to the remarkable tribological behaviors of the lubricant.

This study investigated the tooth friction force and transmission error (TE) of spur gears due to sliding friction under quasi-static condition. The sliding velocity and friction force of spur gears and mesh compliance during meshing were calculated. The load–deformation relations between the tooth normal load, tooth errors, and mesh compliance, and moment equilibrium equation, including friction force, were derived. The friction force, tooth load, and TE of unmodified and linear tip-relief modified spur gears were analyzed by using the derived equations. Results indicated that the friction force, tooth load, and TE increased during approach and decreased in recess regardless of tooth modification, particularly in the single-mesh region. Friction caused larger peak-to-peak change of TE than that without friction. Xu’s friction coefficient generated smooth TE and tooth load transitions near the pitch point, and BK’s friction coefficient remained approximately constant, except for the sharp increase in tooth load and TE near the pitch point.

To clarify the unconscious response actions to a friction stimulus applied to a finger, ten participants performed a friction test using their right index finger and a specimen on which a self-assembled monolayer was striped to intentionally change the shear strength. Drastic changes were observed in both normal load and shear strength when a finger slid across the striped surface. Because the rate of change under normal load was negligible as the sliding speed increased, the response action to the friction stimulus appeared to depend on sliding speed.

Tribological performance of Ti3Al0.8Si0.2Sn0.2C2 solid solution sliding against S45C steel disk was investigated using a block-on-disk type tester at sliding speeds of 5–30 m/s under normal loads of 20–80 N. Ti3Al0.8Si0.2Sn0.2C2 exhibited a friction coefficient of 0.17–0.53 during the sliding process. It was shown that the wear rate decreased linearly as normal loads increasing from 20 to 80 N at 5 m/s, while the wear rates increased faintly in the range of 1.78–5.6 × 10−6 mm3/Nm with an increase in normal load when at other sliding speeds of 10 m/s, 20 m/s and 30 m/s. Both the friction coefficient and wear rate were found closely related to the tribo-oxidation induced tribofilm. Friction surface morphology and cross-section analyses revealed the tribofilm coverage played an effective performance, and the percentage of that was confirmed to increase with the sliding speed and normal load increasing. Phase composition and chemical states analyses of frictional surface showed that the tribofilm formed was a combination of TiO2, Al2O3, SnO2, SiO2, and Fe2O3 mixtures. Microstructure and physical state of the wear debris were also investigated for deeply understanding the contribution of the tribofilm.

The present study deals with the wear characteristics of magnesium based metal matrix composites reinforced with alumina nano particles (50nm) under stir casting process. The wear test is conducted during dry sliding condition using pin on disc tester machine configuration with hardened steel counter-face, the load applied is 10N and 20N with different sliding speed (200,400,600 & 800 rpm) under the time intervals of 0-180 sec at room temperature. The wear decreases with addition of alumina nano particle under normal load at high sliding speed and also improves the co-efficient of friction from 0.095 to 0.55.

Surface topography is a critical parameter that can influence friction and wear in engineering applications. In this study, the influence of surface topography directionality on seizure and scuffing initiation during tribological interactions is explored. Hence, unidirectional sliding wear experiments were carried out in immersed lubrication conditions for various normal loads. The tribological interactions were studied using EN31-60 HRC flats and SAE52100-60 HRC pins in a sphere on flat configuration. The results show that, in some cases, the sliding interactions in the initial cycles lead to a high friction coefficient of up to ∼0.68 in lubricated conditions, which was termed as “peak friction”, and this was accompanied by scuffing. The existence of peak friction was found to be dependent on surface topography directionality, especially when the directionality in topography was parallel to the sliding direction. Continuous ratchetting was found to be the cause of peak friction, which was accompanied by seizure and scuffing. When the topography directionality was perpendicular or independent of the sliding direction, elastic shakedown occurred at earlier cycles and prevented peak friction initiation and scuffing and also facilitated for higher steady-state friction values.

Sliding wear performance of thermal spray WC-based coatings has been widely studied. However, there is no systematic investigation on the influence of test conditions on wear behaviour of these coatings. In order to have a good understanding of the effect of test parameters on sliding wear test performance of HVAF-sprayed WC–CoCr coatings, ball-on-disc tests were conducted under varying test conditions, including different angular velocities, loads and sliding distances. Under normal load of 20 N and sliding distance of 5 km (used as ‘reference’ conditions), it was shown that, despite changes in angular velocity (from 1333 rpm up to 2400 rpm), specific wear rate values experienced no major variation. No major change was observed in specific wear rate values even upon increasing the load from 20 N to 40 N and sliding distance from 5 km to 10 km, and no significant change was noted in the prevailing wear mechanism, either. Results suggest that no dramatic changes in applicable wear regime occur over the window of test parameters investigated. Consequently, the findings of this study inspire confidence in utilizing test conditions within the above range to rank different WC-based coatings.

Rails and wheels are one of the most expensive assets in the railways, and their life needs to be increased by existing methods such as using the optimum rail/wheel hardness ratio. This study aims to verify the synergistic effect of hardness ratio and normal load on the sliding wear resistance. For this, it was used as model system the test pin against disc. The pins were extracted from a class C steel cast wheel (AAR Standard) and the discs were extracted from premium and intermediate grade steel rails (AREMA Standard). Rails are pearlitic and the bainitic wheel is in its first life. Both are hypereutectoid steels with hardness between 321 and 392 HB. The results of the unlubricated sliding tests made possible to compare the sliding wear resistance as a function of the three normal loads (40, 80 and 120 N). The sliding wear behavior for some of the singly body wear rate cases here studied served to validate the field and laboratory tests presented in the literature. From a crossing between the results of the literature and the present study, it is recommended aiming reduction of the wear of rail and/or wheel in a unlubricated condition, to adopt the optimal hardness ratio between rail/wheel ROptimal ≥ 1.0, proposed in the field study (Steele and Reiff 1982), and/or 1.0 ≤ ROptimal ≤ 1.1 proposed by the laboratory test and mathematical model (Razhkovskiy et al. 2015).

The aluminium hybrid composite processed powder metallurgy and wear behaviour was experimentally investigated on aluminium with 0.5 wt% nano-BN reinforcement combined with nano-TiO2 weight per cent reinforcement of 0.3, 0.5 and 0.7% at different sliding velocities ranging from 1.5 to 2.5 m/s and different normal loads ranging from 5 to 15 N. The effect of specific wear rate and coefficient of friction was optimized using D-optimal method. The results predicted by the developed model are concurring well within the measured values. The correlation coefficient of model, regarding the specific wear rate and coefficient of friction, was about 0.9891 and 0.9805, respectively, with conform the degree of accuracy of the mathematical model. The optimal condition attained the minimum specific wear rate and coefficient of friction at sliding velocity 1.5 m/s at normal load 14.36 N for Al + 0.5 wt% BN + TiO2 0.3 wt% composite. The optimal predicted value of specific wear rate was 0.00043e-9 mm3/Nm and coefficient of friction 0.66, respectively.

The aluminum hybrid composite is prepared in powder metallurgy route aluminum with equal wt% nanoTiO2 and nanoGr reinforcements (5 wt% TiO2 + 5 wt% Gr). The wear behavior was experimentally investigated on three different specimens weight of same volume such as 4, 5, 6 g at different sliding velocities of 1.5, 2.0, 2.5 m/s and normal loads of 5, 10, 15 N were considered. The effect of specific wear rate and co-efficient of friction was optimized by D-Optimal method. The results predicted by the developed mathematical model are compatible well within the measured values. The correlation co-efficient of model, regarding the specific wear rate and co-efficient of friction, were about 0.9895 and 0.8468, respectively. The optimal condition of specific wear rate and co-efficient of friction is attained at sliding velocity 1.62 m/s and normal load 10 N with specimen weight of 5 g. The predicted value of specific wear rate is 5.5548e-6 mm3/Nm and co-efficient of friction is 0.23, respectively.

RESUMEN En el presente trabajo se realiza la caracterización del comportamiento ante el desgaste por deslizamiento en seco de un acero inoxidable súper dúplex. Los ensayos fueron desarrollados en un tribómetro tipo bola sobre anillo. Como material del anillo se empleó el acero inoxidable dúplex tipo SAF 2507 sin tratamiento térmico y como material para la bola se usó el acero AISI 52100. Los ensayos se realizaron sin lubricante en condiciones de ambiente (aire), temperatura y humedad estándar de laboratorio. Los parámetros seleccionados, a fin de estudiar sus efectos en el coeficiente desgaste por deslizamiento, fueron: velocidad de deslizamiento (0,9 m/s y 2 m/s), carga normal (9 N, 19 N y 29 N) y distancias de deslizamiento (500 m, 1000 m y 2000 m). Se empleó un diseño experimental de Taguchi con nueve tratamientos y dos réplicas. En la caracterización del acero SAF 2507 se obtuvo valores del coeficiente de desgaste en el intervalo desde 0,19588 x 1012 m2/N hasta 0,72381 x 1012 m2/N, para las condiciones evaluadas. El factor que más afecta el coeficiente de desgaste es la velocidad de deslizamiento. El mecanismo de desgaste identificado para el SAF 2507 es de adhesión y delaminación de alta velocidad. ABSTRACT In this paper the characterization of the behavior during dry sliding wear of a super duplex stainless steel was performed. The tests were developed in a ball on ring tribometer type. As material of the ring is used the duplex stainless steel type SAF 2507 without heat treatment and as material for the ball is used the steel AISI 52100. Tests were conducted without lubrication in ambient conditions (air), temperature and humidity laboratory standard was used. The parameters selected in order to study its effects on sliding wear coefficient were: sliding speed (0.9 m/s and 2 m/s), normal load (9 N, 19 N and 29 N) and distances slip (500 m, 1000 m and 2000 m). Taguchi experimental design with nine treatments and two replicates was used. In the characterization of steel SAF 2507 wear coefficient values was obtained in the range from 0.19588 x 10-12 m2/N to 0.72381 x 10-12 m2/N, for the conditions tested. The factor that most affects the wear coefficient is the sliding velocity. The wear mechanism identified for the SAF 2507 was adhesion and high speed delamination.

A multifunctional hypothesis of filler selection for PTFE suggests ultralow wear (10−7 mm3/Nm) depends on the filler’s ability to both support the normal load by being large in size and to induce favorable tribochemistry by being weak in aggregate strength. This study is the first to test the independent effects of preferential load support and tribochemistry on PTFE wear by studying the wear reducing properties of a porous GaN fiber, a fully dense SiO2 fiber and microsized GaN particles. The results found the only filler that induce ultralow wear is the GaN fiber which was microns in size and friable under shear stresses. This study reinforces the leading hypothesis that a mechanistic synergy is required for ultralow wear PTFE composites.