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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.

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.

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.

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.

Nanoscale wear behaviour of copper-based nanocomposite with Al2O3 nanoparticles have been investigated with the help of the circular mode atomic force microscopy (CM-AFM). The occurrence of running-in and steady-state wear regimes is similar to macroscopic behaviour described by Barwell. Archard's macroscopic wear equation, which states that the wear value is proportional to the applied load and independent on the sliding speed, is also valid at the nanoscale, with the limitation that the normal load should reach a threshold value to generate wear. Eventually, it is shown that the wear value at the nanoscale is highly dependent on the nature of the counter-body (AFM tip) material.

Polyvinyl chloride (PVC) has been widely used in our daily life and industry because of its low cost, lightweight, chemical resistance and corrosion resistance. Tribological properties of soft PVC were studied in regard to sliding conditions of rotation speed and normal load. And the friction heating was observed with an infrared camera. The results indicated that the anti-wear performance of PVC specimens are improved under higher speed and normal load due to the increase of friction heating during sliding. It is attributed to the softening and mobility of the PVC polymer chains caused by the heating generated from the friction at the contact interfaces.

The fretting wear behavior of ultra-high molecular weight polyethylene (UHMWPE) against a GCr15 steel ball was investigated using an Optimal SRV-IV oscillating reciprocating friction and wear tester (Optimal Corp., Germany). The influence of temperature, stroke size and frequency was studied in detail under a normal load of 10 N. The results showed that the friction coefficients initially decreased and then increased afterward with the increasing of temperature, having the lowest value at 0°C. The wear loss of UHMWPE at a stroke of 100 µm showed a similar tendency as the friction coefficients, but monotonously increased with increasing of temperature for a stroke of 200 µm. According to an analysis of the worn surface, it was concluded that abrasive wear accompanied with local plastic deformation dominated the wear mechanism in the process of the fretting test at −30°C. The plastic deformation was slightly less at 0°C than that at −30°C. With the increasing of temperature, the hardness of UHMWPE d...

This work characterizes the wear behavior of pearlitic SAG Mill liner material for in-service and laboratory worn samples. The abrasion tests (Dry Sand/Rubber Wheel Abrasion Test – DSRW) were carried out on samples removed from the undeformed region of the same liner – applying different normal loads (from 22 N to 380 N). The electron microscopy techniques (FEG-SEM, FIB-SEM) were used to characterize the microstructural and wear micromechanisms. A cross sections analysis of both samples highlighted the presence of a deformed layer. The hardness of the original microstructure (undeformed pearlite) was 360 HV 10 , however, this work shows that the typical operational conditions in the mining process increased the hardness in a sub-superficial layer up to 580 HV 10 . The thickness of the deformed layer was determined to be approximately 300 µm and 3 µm in-service and laboratory worn samples, respectively. The in-service worn samples showed scratches and micro-indentations along the surface. For the laboratory tests, the predominant wear mechanisms were micro-cutting with and without micro-ploughing and micro-indentation. It was shown that the normal load in the laboratory abrasion tests did not significantly affect the deformed layer formation. For the various normal loads applied, the thickness of deformed layer remained practically constant, around 3 µm. On the other hand, regarding wear mechanisms, a change in the normal load affected the indentations/cutting ratio: for lower loads micro-indentations prevailed whereas increased loads (above 130 N) indicated the presence of micro-cutting. Therefore, on the basis of these observations, it was possible to conclude that the DSRW represented a suitable alternative to simulate the abrasion component occurring in liners for SAG Mills once a higher load was applied (200 N to 280 N).

Stick-slip, manifest as intermittent tangential motion between two solids, is a well-known friction instability that occurs in a number of natural and engineering systems. In the context of adhesive polymer interfaces, this phenomenon has often been solely associated with Schallamach waves, which are termed slow waves due to their low propagation speeds. We study the dynamics of a model polymer interface using coupled force measurements and high speed \emph{in situ} imaging, to explore the occurrence of stick-slip linked to other slow wave phenomena. Two new waves---slip pulse and separation pulse---both distinct from Schallamach waves, are described. The slip pulse is a sharp stress front that propagates in the same direction as the Schallamach wave, while the separation pulse involves local interface detachment and travels in the opposite direction. Transitions between these stick-slip modes are easily effected by changing the sliding velocity or normal load. The properties of these three waves, and their relation to stick-slip is elucidated. We also demonstrate the important role of adhesion in effecting wave propagation., Comment: 22 pages, 9 figures

When subjected to shear loading condition, a steel rock bolt will become bent in the field close to the loading point in situ. The bolt is deformed as the joint displacement increases, which can mobilize a normal load and a shear load on the bolt accordingly. In this work, the relationship analysis between the displacing angle and loading angle is carried out. By considering elastic and plastic states of rock bolt during shearing, the rotation of bolt extremity can be calculated analytically. Thus, the loading angle is obtained from displacing angle. The verification of analytical results and laboratory results from reference research implies that the analytical method is correct and working. In terms of in-situ condition, the direction of the load acting on steel bolt can be predicted well according to the direction of the deformed rock bolt with respect to original bolt axis.

Wear behaviour of ZE41A magnesium alloy coated with WC/Cu using electrical discharge coating (EDC) has been investigated in this study. The wear test was conducted with pin-on-disc machine using different conditions such as normal load of 1.5 kg, 2.5 kg, 3.5 kg and sliding speed of 100 rpm, 200 rpm, 300 rpm and sliding time of 3 min, 5 min, 7 min through L9 Taguchi orthogonal array to study the effect of sliding parameters on the wear characteristics. A wear transition map was constructed to describe the different wear conditions such as mild wear, severe wear and ultra severe wear. The main wear mechanisms for each wear regime were identified and classified through wear mechanism map. The worn-out specimens were characterized using scanning electron microscope (SEM) to identify the various wear mechanisms.

Scratch performance of thermoplastic olefins (TPOs) has been considered one of the required properties for automotive applications. The scratch resistance of TPOs can be enhanced by utilization of commonly used slip additives such as erucamide. When TPOs are injection molded, the mold temperature impacts the migration of the slip additive toward the surface and the surface crystallinity of the TPOs, which has been shown to influence scratch resistance. In order to evaluate the effect of the mold temperature and erucamide migration on scratch behavior at elevated temperatures, this research has adopted the ASTM D7027/ISO 19252 linearly increasing normal load scratch test methodology to investigate the scratch behavior of the model TPOs at 25 °C, 50 °C, and 75 °C. This study provides a comprehensive understanding on the effects of mold temperature, slip additive, elevated testing temperature, and thermal aging on scratch behavior of TPOs.

The tribological behavior of aged Al-Sn-Cu alloy rubbed in the presence of lubricant over a range of sliding velocities and normal loads was investigated. The results showed that peak-aged (PA) alloy had a better tribological behavior than under-aged (UA) and over-aged (OA) alloys, which could be attributed to the optimized strength-ductility matching and a better hardness under PA condition. Wear rate and friction coefficient showed great sensitivity to applied sliding velocity and normal load. The wear rate and friction coefficient of the alloy exhibited a reduction trend with the increase in sliding velocity. The low wear rate and friction coefficient of alloy at high velocities were due to the effectively protected film and homogeneous Sn on surface. However, an increase in normal load led to an obvious increment in wear rate. The friction coefficient exhibited a fluctuant trend with the increase of normal loads. The seriously destroyed film and abraded Sn resulted in poor tribological behavior at high normal loads. The Sn particles and lubricant film which includes low shear interfacial lubricating layer and oxide tribolayer are the key to the tribological behavior of Al-Sn-Cu alloy.

Little attention has been paid to the role of stacking fault energy (SFE) in the two-body abrasive wear of austenitic steels. Using a pin-abrasion test with 220 grit garnet paper as the counterbody, three austenitic steels of different SFEs were compared. The steels were: (i) FeMnAlC, (ii) Hadfield steel, and (iii) AISI 316 L steel. Following a pre-conditioning procedure, the normal loads on the 3 mm diameter test pins were 5 N, 10 N and 15 N, and the sliding speed along a spiral track of total length 430 m was 0.158 m/s. Data showed that the FeMnAlC steel had a higher wear resistance than AISI 316 L steel but lower wear resistance than the Hadfield steel. However, at the highest test load, all three steels had similar wear resistance. The steel with the lowest SFE had the highest abrasive wear resistance and the steel with the highest SFE had the lowest abrasive wear resistance. The main wear mechanisms were microcutting and microploughing. There was a transition from microploughing to microcutting as the normal load was increased.

Pure magnesium and its composites reinforced with 5, 10 and 15 vol% SiC particulates with a mean diameter of 7.8 µm were fabricated by a powder metallurgy process. The tribological behavior of the samples was investigated under normal loads of 5–60 N at sliding speed of 0.4 m/s and at wear temperatures of 25–200 °C. At the wear temperature of 25 °C, results showed almost close wear rates under normal loads of 5 and 20 N. However, under higher normal loads the composites showed lower wear rate than that of the unreinforced magnesium. At the higher wear temperatures of 100, 150 and 200 °C, a significant lower wear rate was observed for the composites compared to the pure magnesium. Increasing the normal load resulted in a transition from mild to severe wear at all wear temperatures. Below the transition load oxidation was a dominant wear mechanism, while above that severe plastic deformation and adhesion were the main wear mechanisms. The results also showed wear rate improvement of the composites with increasing SiC content. Finally, a wear map showing mild and severe wear regimes as a function of load and wear temperature was adopted for the composites.

The initial transient, or running-in, period during abrasive wear has been largely overlooked in the literature, with the focus instead being on steady-state conditions. However, the running-in period of abrasion might determine the evolution to steady-state wear behaviour, as is known to occur in sliding wear conditions. To this end, the running-in period during the abrasive wear of the austenitic stainless steel AISI 316L and Hadfield (15%Mn-1.5%C) steel was analysed through the testing pin (flat-ended)-abrasive paper wear configuration. The effects of the normal load, the size of the abrasive, and the type of material were evaluated, and the wear rate and the strain hardening of the matrix were recorded. The steady-state wear might be influenced by the phenomena occurring during the running-in period. Thus, the hardening, roughness, friction coefficient and wear micromechanisms were correlated with the wear rate to elucidate these possible relationships.

Maskless electrochemical texturing (MECT) is an inexpensive and fast technique with great potential to produce surface textures on metallic surfaces at industrial scale. This work used MECT to produce arrays of chevrons onto AISI 1045 steel surfaces. Block-on-ring tests using standard rings and textured blocks investigated the effects of full and partial texturing on friction and wear. Two normal loads (216.9 N and 315.0 N) were applied to investigate the effects of the textures under mixed and boundary lubrication regimes. Under the lower load, MECT increased friction and wear rates. This was attributed to the surface roughening of the areas outside the chevrons, which reduced the ratio between the average roughness of the asperities and the hydrodynamic film thickness (λ ratios), shifting the lubricant regime from mixed to boundary lubrication. Partial texturing performed better than full texturing, but no clear trend was found for the position of the textured potion either at the inlet or the outlet of the contact. On the other hand, for the higher normal load, both smooth and textured samples operated under boundary lubrication, so that the effect of the pockets to supply additional lubricant to the contact resulted in reduced friction and wear. Entrapment of wear debris within the chevrons was found for both normal loads, which avoids the presence of hard debris in the contact, thus also contributing to reduce friction and wear. The Kruskal-Wallis test was applied, and it was observed that the factors, load and surface, produced statistically significant effects on friction coefficient values.

Ti6Al4V coatings were made from spherical and irregular powders manufactured using plasma gas atomization and Armstrong processes, respectively. The coatings, made from the two different powders, were distinctly different in terms of porosity content and hardness. Sliding wear tests were performed at different normal loads on both Ti6Al4V coatings. Despite low porosity and high hardness, irregular powder (IP) deposited coatings showed higher wear rates compared to spherical powder (SP) deposited coatings. In case of IP coatings, abrasive ploughing by the wear debris led to high wear rates, whereas presence of porosity in SP coatings, entrapped the wear debris generated during sliding and decreased the wear rate. Increase in normal load led to a decrease in wear rate and CoF in both coatings. The decrease in wear rate was due to tribo-oxidation in IP coatings whereas the combined effect of entrapment of debris along with tribo-oxidation resulted in much lower wear rates in SP coatings. Transmission electron microscopy (TEM) analysis showed that the third bodies filled in the pores consisted of highly deformed material with ultrafine grain microstructure and micron sized particles from the counterface while the wear track had comparatively coarse grain microstructure. Results indicated that despite low hardness of SP Ti6Al4V coatings, presence of porosity facilitated for the entrapment of wear debris generated from first bodies which inhibited abrasive ploughing and contributed to low wear rates.

Electrical railways produce airborne wear particles (AWPs) in significant amounts from wheel–rail contact. Herein, the effects of wet conditions on the AWPs released from the wheel–rail contact under different normal loads were investigated using a twin-disk rig. A fast mobility particle sizer and an optical particle sizer were used to measure number concentrations (NCs) of AWPs. Analyses of NCs and particle size distribution were conducted. The findings suggest that significantly fewer AWPs are generated under wet conditions than under dry conditions. Marked differences were also seen in the size distribution peaks between wet and dry conditions: under dry conditions, the largest peak corresponded to fine particles, whereas under wet conditions, the largest peak corresponded to ultrafine particles. The generation trends of AWPs were different for dry and wet conditions: AWPs increased and then decreased after maximal NCs under dry condition; however, they increased and then remained nearly constant under wet conditions. The total amount of ultrafine, fine, and coarse particles increased with normal load under wet conditions, indicating that AWP generation is significantly influenced by the normal load. Furthermore, water can significantly reduce the amount of ultrafine, fine, and coarse particles generated from the wheel–rail contact.

Because of the low viscosity of high-water-based fluids, the intense wear and leakage of key friction pairs represent a bottleneck to the wide application of the high-water-based hydraulic motor in engineering machinery. In this work, based on the common characteristics of plane friction pairs, the friction experiments of a 316L stainless steel (316L)&ndash, polytetrafluoroethylene (PTFE) friction pair under various working condition were carried out by a self-designed friction experimental system with fluid lubrication. The influence of lubrication pressure and surface morphology on the 316L&ndash, PTFE friction pair was investigated both experimentally and theoretically. The experimental and numerical results indicated that increasing lubrication pressure reduced the surface wear of PTFE sample, but the leakage of 316L&ndash, PTFE friction pair also increased. It could not form an effective fluid lubrication film in the 316L&ndash, PTFE friction pair under low lubrication pressure, which caused the severe wear in friction pair interface. The smooth 316L surface could be conducive to the formation of high-water-based fluid lubrication film in 316L&ndash, PTFE friction interface. The pressure distribution of high-water-based fluid lubrication film in 316L&ndash, PTFE friction pair was also obtained in fluent. The PTFE surface was easily worn when the lubrication film in the friction pair was too thin or uneven. The friction and wear were obviously improved when the normal load was balanced by the bearing capacity of the high-water-based fluid lubrication film.

Coatings are normally employed to meet some functional requirements. There is a kind of self-generated coating during use, such as the transfer layer during sliding, which may greatly affect the tribological behavior. Although the transfer layer has aroused much attention recently, the formation of the transfer layer closely depends on the service conditions, which need to be further studied. In this paper, the effects of sliding speed, normal load, and duration of wear test on the transfer layer thickness during friction of Ni/PTFE (Polytetrafluoroethylene) composites were experimentally investigated. The formation mechanism of transfer layer and the relationships between tribological properties and transfer layer thickness were analyzed in detail. It was found that the transfer layer thickness increased with increases of sliding speed and normal load, and after a period of wear test, the transfer layer thickness remained stable. The transfer layer thickness correlates linearly with the friction coefficient and wear volume of the PTFE composites. With the increase of the transfer layer thickness, the friction coefficient decreased, while the wear volume increased, which means that a uniform, thin, and stable transfer layer is beneficial for the reduction of friction and wear of the polymeric composites.

International audience; The response of glass to a scratch experiment is first reviewed. Then the influence of the applied load on the microcracking pattern, the apparent friction coefficient, and the strength (post scratch test) are studied and discussed for a soda-lime-silica glass (standard window glass composition). As the normal load increases, the depth of the radial crack seems to stabilize at about 100 μm length. Correlatively it is observed that the residual strength of the scratched glass remains at about 40 MPa whatever the scratch load above 0.5 N. Generally, this work contributes theoretically in the understanding of the existing factor controlling scratch in glasses.

To investigate the effects of a developed friction film on clutch system performance, clutch samples tested in three different field conditions were characterized. The wear mechanisms identified were simulated in laboratory. For this, a commercial truck friction material and cast iron were tested in a pin-on-disc tribometer. Tribological tests were carried out at standard procedures and by cleaning the wear track of the counter-face. For both lab test conditions, the normal load ranged from 200 N to 450 N at constant sliding speed of 2.05 ms −1 and 3.27 ms −1 . These parameters correspond to PV values between 3.08 and 11.08 (MPa ms −1 ), which cover part of the power release in real clutch systems (between 1.3 and 20 MPa ms −1 ). The friction film simulated in laboratory showed similar characteristics with those observed in field and its development and morphology depend on the test severity. Standard tribometer tests presented a transition in the wear rate at temperatures of 250 °C. Removing the wear debris, the wear rate decreased almost 31% at the lowest level and 45% at the highest level of energy. The friction material tested traditionally revealed a stable friction film for tests performed to 7.88 (MPa ms −1 ) and a damaged film was found in severe wear regimes. When removing the wear debris under the same conditions, a stable friction film was observed and a less developed friction film was noted on the disc surfaces by eliminating the wear debris. The friction coefficient decreased with increasing testing temperature and cleaning the sliding surface increased the friction levels.

The WC particle-reinforced copper matrix composites with WC content in the range of 5 vol%–30 vol% were prepared and investigated by micro-scratch tests under the loads of 1–4 N. The influences of normal load and WC content on friction coefficient and wear volume of the composites were studied. The hardness and scratch resistance of the composites are greatly improved by the addition of WC. The penetrate depth and residual depth increase near-linearly with normal load increasing and decrease with WC content increasing, and the friction coefficient of the composites also shows the same variation trend. The valid material removal mechanism is found to transform from micro-plowing to micro-cutting as the normal load increases.

Under combined rolling and sliding materials can experience millions of cycles as well as complex loading and slip conditions, which can dramatically affect their friction and wear behaviour. It was shown that for a carbon black-filled natural rubber compound in combined rolling and sliding contact with a smooth alumina coated disk, the traction coefficient, as a function of slip percent, was dependent upon the normal load and independent of rolling velocity. The wear rate of this material pair was found to be independent of slip percentage as well as rolling velocity but dependent upon sliding distance. The wear rate was found to be approximately the same for all tested cases (K ~ 1 × 10−4 mm3·Nm−1). The worn profiles of the ball specimens showed that this wear occurred preferentially on the left side (inner radius) of the contacting area. Copyright © 2015 John Wiley & Sons, Ltd.

Reciprocating ball-on-disk tests were performed to investigate the effects of sliding velocity and ambient temperature on the tribological characteristics of a diamond-like carbon (DLC) coating under a boundary lubrication regime. The coating consisted of sequentially deposited gradient Cr/CrN, a-C:H:W, and a-C:H layers; the counter surface was an AISI 52100 steel ball. Average sliding velocities (range: 0.01–0.04 m/s), temperatures (range: 27–160 °C), and a normal load of 293 N were selected as the test conditions. One fully formulated motor oil containing a glycerol mono-oleate was used as a lubricant. Wear rates of the coatings increased with increasing temperature. As temperature increased from 27 to 55 °C, friction coefficients increased, but wear rates of the ball decreased. With an increase in temperature from 55 to 160 °C, friction coefficients decreased until 110 °C then slightly increased, and wear rates of the ball increased. Increasing sliding velocity led to a decrease in friction coefficients and wear rates of both friction surfaces. Through surface analyses and observations, it was confirmed that graphitization of the worn DLC coatings, reactive tribofilms on the worn ball specimens, portion of the surface asperities in dry sliding contact, and corrosive wear of the ball specimens affect tribological characteristics.

A model for interactions of a single large impurity particle with the optic and pad during pad-polishing has been developed to detailedly illustrate the scratch formation process. Equations for calculating the normal load applied on the optic by the impurity particle are provided, and the friction between the optic and impurity particle has also been considered in scratch formation. Initiation and evolution of the scratches under the combined effects of the normal and friction forces are illustrated in the model. The most important factors affecting the normal load and thus scratch formation have been analyzed and verified using published experimental results. Based on the model, the implications in reduction of scratch formed on optics during pad polishing have been analyzed.

In this work, polyvinylidene fluoride (PVDF)/polymethyl methacrylate (PMMA) alternating multilayered materials were fabricated. Firstly, the scratch damage behaviors of PVDF side was investigated experimentally. The results presented that the maximum of critical normal load of scratch damage (Fcr) was obtained by 32-layer material, which was 40% higher than that of pure PVDF and very close to that of pure PMMA. This indicated that the scratch resistance of PVDF could be significantly improved via multilayer assembly with PMMA. Furthermore, numerical modeling revealed that with the multiplication of layers, the decrease of tensile stress imposed on the first PVDF layer led to the delay of scratch damage, whereas the decrease of the distance between the first PMMA layer and the scratch tip promoted its early damage. Therefore, the optimum scratch performance was determined by the critical thickness of PVDF and PMMA layers, which was significant for designing scratch-resistant materials.

Although both wear and fatigue are inevitably associated with the wheel/rail contact, they are normally studied as different phenomena and both are commonly considered excluding. Wear of railway wheels and rails is usually studied by relating wear rate to the T γ or T γ / A parameters or by plotting the so called “wear maps”, where different rolling parameters are related to the wear rate. On the other hand, fatigue in wheel/rail contact is mainly studied from the surface and subsurface stress or deformation fields and from the crack growth rate. However, one of the main causes of wear in rolling contact is the loss of material due to delamination processes that have their origin in the presence of surface fatigue cracks. So, if wear and fatigue are related, it should be possible to study both of them using the same method. In this paper, the fatigue index, based on the shakedown theory and used to predict the surface initiated fatigue of railway wheels, is proposed as a means to study the wear rate in rolling contact. The fatigue index is directly related to the apparition and growth of fatigue cracks at the surface and, thus, directly related to the peeling and spalling processes that constitute the severe and catastrophic wear mechanisms. The data collected from a series of twin-disc tests show that the wear rate correlates with the fatigue index following an exponential evolution independently of the normal load. Furthermore, a fatigue index around 0 marks the onset of severe wear.

TaN–(Cu,Ag) nanocomposite films were deposited by reactive co-sputtering on Si(001) and M2 tool steels. The films were then annealed using RTA (Rapid Thermal Annealing) at 200 °C–400 °C to induce the nucleation and growth of metal particles in TaN matrix and on film surface. After deposition, structures, surface morphologies, and mechanical properties were analyzed, the samples were tested for their anti-wear and anti-bacterial behaviors against Gram-negative Escherichia coli. It is found that the antibacterial efficiency against E. coli can be much improved for TaN–(Cu,Ag), comparing with that of TaN–Ag or TaN–Cu films. This could be attributed to large number of surfaced Ag and Cu particles. The tribological properties could also be improved, and are similar to TaN–Ag under a normal load of 5 N. In general, the annealing temperature for TaN–(Cu,Ag) can be as low as 200 °C. Being annealed at this temperature, the film still shows good antibacterial and anti-wear behaviors.

We studied the effect of mating materials on the tribological properties of DLC film using mating materials of martensite stainless steels (hardened and annealed AISI440C), austenite stainless steel (AISI304), and bearing steels (hardened and annealed AISI52100). The reciprocating sliding tests were performed with ball-on-plate friction tester in dry air. Analyses of friction surface of specimens were carried out using optical microscopy and micro-laser Raman spectroscopy. With the exception of the annealed AISI52100 ball, the friction coefficient of DLC film decreased with increasing normal load. The friction coefficient for the annealed AISI52100 ball showed a high friction coefficient under wide normal load conditions. Analysis using micro-laser Raman spectroscopy showed that the difference between annealed AISI52100 and others materials appears mainly due to structural changes in the film. Tribological properties of DLC film may thus be affected by a property change in mating materials rather than by mating ball hardness.

The surfaces of fibrous materials like textiles are characterised by emergent superficial fibres forming hairiness. Hairiness is an important factor for the frictional and tactile properties of fabrics. In this study, we investigated the friction mechanisms of hairy fabrics by sliding probes with varying geometry over the textile surfaces. The total friction between a hairy fabric and a cuboid-shaped slider is given by two main contributions—one due to the contact of hairs with the front of the slider and the other one resulting from the hairiness underneath the slider. By changing the slider geometry, the relative importance of these two contributions can be systematically varied, so that conclusions about adhesion and deformation mechanisms involved in the friction of hairy fabrics can be drawn. For a given slider area and a given normal load, the force underneath the slider was found to be independent of the slider width while the force in front of the slider increased linearly with the slider width. The major contribution of the force underneath the slider is highlighted. This force is influenced by the material and surface roughness of the slider, indicating that adhesion mechanisms play a significant role in the friction.

A molecular dynamics simulation of confined n -alkanes has been conducted to investigate the effects of the chain length of lubricant molecule and normal load on friction and asperity contact. The density distribution and surface coverage of lubricant atoms were calculated. The simulation results indicate that longer chain n -alkanes can provide more atoms for the mono-layer in the asperity contact interface than shorter ones, which, as a result, significantly reduce the friction force when the asperity contact occurs. C64-alkanes molecules can form a mono-layer of lubricant to avoid direct asperity contact at pressures up to 1000 MPa.

The surfaces of materials differ in topography and compatibility with human skin. Those differences were distinguished by measuring the friction coefficients between a human finger and different types of surfaces. Sample groups used in these tests were glass, plastic, and fabric. In the case of fabric, the following materials were used: linen, canvas, felt, silk, velvet, and cotton. Experiments were conducted using a specially-designed apparatus under constant temperature and relative humidity. Two factors were identified using the finger friction measurements. First was the friction level and second was the variance in friction. In Particular, it was found that different surfaces show significantly different variance in their friction coefficients. Fitting parameters from a linear regression of the relationship between friction coefficient and normal load were used to map materials' responses.

This paper investigates the effect that contact geometry on fretting wear rates and mechanisms for non-conforming contacts. Tests have been conducted in the gross sliding regime under a constant normal load in a cylinder-on-flat configuration with a high strength steel for a range of cylinder radii. Two distinct damage mechanisms have been identified, with the operative mechanism depending upon contact geometry. Fretting of less conforming contacts results in higher wear rates compared to that associated with more conforming contacts where the wear rate is significantly lower (between 20% and 50% of that of the less conforming contacts) in addition, much higher levels of adhesive transfer are observed in more conforming contacts, with beds of metallic debris particles being evident. It is proposed that the dependence of wear rate and mechanism on the contact geometry is not associated with differences in contact pressure (although these do exist), but is associated with the influence of contact geometry on debris flow out of the fretting contact and on the effectiveness of oxygen being excluded from the centre of the fretting contactpatch.

International audience; Cu and Cu-MoS2 coatings were fabricated by cold spray, and the fretting wear performance of the two coatings was compared. A mixture (95 wt.% Cu + 5 wt.% MoS2) was used as feedstock for the composite coating. Coatings were sprayed with identical gas flow conditions on the substrates pre-heated to approximately 170 degrees C. The morphology of coating top surface and polished cross sections was analyzed by scanning electron microscopy (SEM) and light optical microscopy (LOM). The influence of MoS2 on Cu deposition was examined. The local MoS2 concentration within the coating was found to affect the hardness. Fretting tests were carried out at two different normal loads, and the influence of MoS2 on friction and wear was studied. The morphology and elemental compositions of the wear scars and wear debris were observed by SEM and energy dispersive x-ray spectroscopy (EDS), respectively.

Two alloys commonly used for the steam generator components are under investigation to assess the effect of sliding regime on the fretting-corrosion damage in 3.5 wt% NaCl solution. Inconel-600 was forced to fret against stainless steel SS431S29 under variable applied load at constant displacement. A Modular Universal Surface Tester was employed to provide fretting motion and to control the applied normal load. The overall damage involved mechanical and corrosive wear and interactive effects between those two were generally observed. In situ electrochemical measurements were conducted during fretting including open circuit potential and potentiostatic current measurements. Fretting motion was found to cause the contact area to be more active and more prone to corrosion. Electrochemical analysis revealed the relationship between fretting sliding regime and corrosion behaviour of tested materials. The extent of surface damage as a function of different loads is discussed.

The dry sliding wear behavior of AA6061/ZrB2 in-situ composite prepared by the reaction of inorganic salts K2ZrF6 and KBF4 with molten aluminum was investigated. An attempt was made to develop a mathematical model to predict the wear rate of AA6061/(0–10%) ZrB2 in-situ composites. Four-factor, five-level central composite rotatable design was used to minimize the number of experiments. The factors considered are sliding velocity, sliding distance, normal load and mass fraction of ZrB2 particles. The effect of these factors on the wear rate of the fabricated composite was analyzed and the predicted trends were discussed by observing the wear surface morphologies. The in-situ formed ZrB2 particles enhance the wear performance of the composite. The wear rate of the composite bears a proportional relationship with the sliding velocity, sliding distance and normal load.

Scratch tests of polypropylene injection moldings were conducted with a progressive load scratch test according to ISO 19252. Effect of scratch velocity on scratch visibility and damage initiation was investigated. The results showed that the critical normal load for onset of scratch visibility was independent of scratch velocity in the range from 1 to 10 mm/s. However, the critical normal load decreased with increase of scratch velocity higher than 10 mm/s. The other scratch damage transitions such as onset of fish-scale and cutting pattern, the critical normal load also decreased with increase of scratch velocity. A correlation between scratch behavior and subsurface deformation was observed by polarized optical microscope. The formation of yielded zone under scratch groove was clearly observed at onset of scratch visibility. It was found that the yielded zone size becomes shallower at higher scratch velocity. The results suggested that localized stress was generated near the surface at higher scratch velocity. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

The scratch behavior of butyl-acrylate rubber-modified styrene-acrylonitrile (ASA) upon high temperature annealing is investigated following the ASTM D7027/ISO 19252 linearly increasing normal load test methodology. The critical normal loads at the onset of the major deformation transitions along the scratch path, such as groove formation, scratch visibility, microcrack formation, and plowing, are reported and quantitatively analyzed. It is found that the scratch resistance improves with high temperature annealing, i.e., 30 °C above T g , as compared to annealing below or around T g . Microscopic investigation suggests that the increase in scratch resistance is related to the changes in surface morphology of the polymer. It is concluded that performing high temperature annealing enhances the scratch performance without compromising ASA bulk properties. Implication of the present study for improving scratch resistance of polymers is discussed.

Prestress scratching tests have been performed on polished surface of SiC ceramics under a Rockwell diamond indenter moving with uniform speed and constant normal load. Combining with acoustic emission testing, the scratching depth and the surface/subsurface damage were investigated under the action of different prestress values. The results showed that the existence of prestress should shorten the depth of median cracks and reduce the subsurface damage, moreover, with increasing prestress in a proper range, the depth of median crack was decreased and the propagation length of lateral crack was limited.

Elevated-temperature wear tests under atmospheric conditions at 400 °C were performed for a hot working die steel H21 on a pin-on-disk wear tester. The phase and morphology of worn surfaces were examined using XRD and SEM, and the relation of wear resistance to tempered microstructures was studied for H21 steel. XRD patterns exhibit that oxidative wear is a predominated wear mechanism with Fe 3 O 4 and Fe 2 O 3 on worn surfaces. It is found that with increasing normal load, obvious plastic deformation of substrate appears on worn surfaces. Microstructures start to affect apparently wear resistance of the steel with an increase of load. Under loads of 50–100 N, wear losses of steel retain low values and relatively approach for steels with various microstructures. As loads are increased to 150 – 200 N, wear losses of steel start to increase obviously and present apparent difference for steel with various microstructures. Wear resistance is found to increase in the sequence as follows: tempered sorbite, tempered martensite, tempered troostite without secondary hardening and tempered troostite with secondary hardening or upcoming one. Higher strength and microstructural stability are required for steels with excellent wear resistance.

The paper presents asymptotic modeling of the local contact of crossed elastic cylinders in reciprocating sliding wear under a prescribed constant normal load. The wear contact problem is formulated within the framework of the three-dimensional theory of elasticity in conjunction with Archard's generalized wear equation. It is shown that the asymptotic modeling approach, which maintains the experimentally related feature of contact pressure in the steady-state regime, leads to simple but sufficiently accurate analytical approximations. In particular, closed-form approximations are derived for the volumetric wear, parameters of the contact area, and the wear scar profiles. The developed asymptotic modeling approach is not capable of handling the initial period of wear process, when the contact pressure distribution transforms from the initial Hertzian form to the uniform distribution appearing in the steady-state regime. The obtained analytical results have been compared with finite-element simulations and experimental results published in the literature.

In the present investigation Cu based composites have been developed through solidification processing by addition of a fixed amount of Cr and three different amounts of graphite viz. 2, 3 and 4 wt.%. All of the cast composites have been hot forged and annealed. Dry sliding friction and wear behavior of all the composites in as cast, hot forged and annealed conditions has been investigated by sliding against a counterface of SAE 4615 steel disc under ambient conditions using a pin-on-disc machine. The sliding wear tests have been conducted at four different normal loads 10, 20, 30, and 40 N and a constant sliding speed of 0.786 m/s. The primary focus of the study is to understand the effect of hot forging and annealing after hot forging, on the wear characteristics of these composites. For a given normal load, the cumulative volume loss increases linearly with increasing sliding distance for all materials. The wear rate has also been found to increases linearly with increasing normal load. Wear rate of Cu–4Cr–4G composite is significantly lower than that of all other materials either hot forged or annealed. Average coefficient of friction decreases with increasing the normal load and the graphite containing composite shows the lower average coefficient of friction than the other materials. Worn surface of the pin specimen show significant formation of transfer layer for hot forged and annealed Cu–4Cr–4G composite.

article i nfo The TiCN coatings were deposited on WC cemented carbides using enhanced cathodic arc magnetron sputtering. The topography of TiCN coatings were observed using scanning electron microscopy (SEM), the composition and structure of TiCN coatings were analyzed by energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The friction and wear properties of TiCN coatings sliding against SiC and steel balls in air and water were investigated using ball-on-disk tribometer. The results showed that the TiCN coatings had a strong (111) preferred orientation. The friction coefficient and the specific wear rates of the TiCN/SiC tribopairs in air were higher than those in water. When the TiCN coatings slid against SiC balls in water, the friction coefficient and the specific wear rates first decreased, and then increased with the normal load, but decreased linearly with the sliding velocity. The lowest friction coefficient of 0.171 was obtained at 3 N and 0.4 m/s, while the lowest specific wear rate of the TiCN coatings was 2.3 × 10 − 6 mm 3 /Nm at 6 N and 0.1 m/s. The TiCN coatings were worn out when the normal loads were higher than 6 N. When the TiCN coatings slid against the SUJ2 and SUS440C balls in water, the friction coefficient increased to 0.271 and 1.026 respectively. The EDS analysis showed that Fe and O elements existed on the wear track. This indicated that the tribochemical reaction occurred at the friction contact area.

A profound description of friction in wheel–rail contact plays an essential role for optimization of traction control strategies, as input quantity for railway simulations in general and for the estimation of wear and rolling contact fatigue. A multitude of wheel–rail contact models exists, however, traction–creepage curves obtained from measurements show quantitative and qualitative deviations. There are several phenomena which influence the traction–creepage characteristics: Mechanisms resulting from surface roughness, frictional heating or the presence of interfacial fluids can have a dominating influence on friction. In this paper, a new wheel–rail contact model, accounting for these influential parameters, will be presented. The presented model accounts for the interaction of an interfacial fluid model for combined boundary and mixed lubrication of rough surfaces with a wheel–rail contact model that additionally accounts for frictional heating. A quantitative comparison with measurements found in the literature is not conducted, since the exact conditions of the measurements are mostly unknown and parameters can easily be adjusted to fit the measurements. Emphasis is placed on the qualitative behavior of the model with respect to the measurements and good agreement is found. The dependence of the maximum traction coefficient on rolling velocity, surface roughness and normal load is studied under dry and water lubricated conditions.

Ti(C,N)-based cermets have been attracting much attention because of their good high temperature strength, perfect chemical stability, excellent wear resistance, and relatively better machinability. In this paper, the tribological performance of Ti(C,N)/Si 3 N 4 sliding pairs lubricated in water was investigated using a ball-on-disk tribometer at sliding speed of 200 mm/s. The normal loads are controlled at 2 and 5 N, respectively. The experimental results show that, at the normal load of 2 N, ultra-low friction coefficient ( μ

A novel procedure is proposed which improves the application of the knife-cutting method to estimate adhesion energy. The origin of a previously reported difficulty in determining the force exerted by the cutting blade to the specimen in removing the coatings is identified and a method to overcome this difficulty is developed. The essential point of the method is to detect the “critical normal load”. The value of this load and that of the parallel load are used to obtain the adhesion energy and the energy for the deformation of the removed part of the coating.

W–25 wt%Cu nanocomposite powder was prepared by thermochemical co-precipitation method. Consolidation procedure was performed at 1200 °C under hydrogen atmosphere and led to the densification up to 98% theoretical density. Wear test was carried out with a pin-on-disc apparatus under 5, 10, and 15 N normal loads. Volume of the lost material and also the wear rate increased by increasing the normal load while, friction coefficient showed a reverse record and decreased by increasing the load. Formation of mechanically mixed layers (MMLs) and their successive deformation and work hardening was found to be the origin of the friction coefficient decrease at increased normal loads. At low normal load just shallow scuffs and particle pull out were observed in the surface and sub-surface studies of the wear sample. But at higher normal loads large flakes of the matter were cut off and lost accompanying deep grooves and branched cracks. Continuous cyclic deformation at sufficiently high normal loads, could give rise to MML formation, sub-surface deformation, crack nucleation and propagation, and finally delamination of the composite.

In micro-positioning systems, friction is often the limiting factor for the positioning accuracy. The thorough understanding of the frictional phenomena in sliding contacts is therefore a challenging aim. When a tangential force is exerted to one of a pair of contacting bodies, before an object relatively slides, the pre-sliding regime is crossed. This paper is dedicated to the investigation of the relation between the normal load and the friction force in the pre-sliding regime up to gross sliding. A Maxwell–Slip model strategy is supplied with model parameters, determined by an existing physics-based model. The combination of both models results in frictional hysteresis loops, fully determined by their virgin curve. A sensitivity analysis is carried out to evaluate the influence parameters on the results.