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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 purpose of this paper is to compare the influence of the normal load on the friction and wear behaviour of nickel-based alloys, which is use communally in the industry. We chose two samples of nickel-based alloys (NI-Cr-B-Si-C-W) elaborated by isostatic compression with a difference in their microstructure composition and quantity of micro constituent. The friction coefficient, the wear loss and the wear rate are evaluated using a tribometer (pin on disc) and a test bench created to reproduce the same industrial environment. Experiments showed that the applied normal load affects differently on the behaviour of the samples. The results conclude that the friction and wear resistance of the alloy do not just depend on the increase of the normal load but also on the distribution, the location and the morphology of the hard compounds formed in the alloys.

The pin-on-disc test model system was used to simulate contact wear between wheel flange and rail gauge corner. Pins were extracted from a class C cast steel wheel and discs were extracted from premium and intermediate steel grades rail, both hypereutectoid and with hardness between 321 and 392 HB. Rails are pearlitic and the bainitic wheel is in its first life. Dry and lubricated tests were performed with normal load variation (40, 80 and 120 N). Under dry condition, there was no influence of the pair hardness to mass loss of the tribosystem studied, contrary to what is stated by literature. For the lubricated tests, mass loss was significantly lower and regardless of both, hardness ratio and normal load, than in the other tests. This shows the technological importance of: (i) implementing wheel flange lubrication (locomotive embedded process); (ii) improving rail lubrication techniques (mobile or way side process) and/or friction coefficient measurement techniques and (iii) need for revision of wheel standards and/or specifications.

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.

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.

We developed a method to simulate the polytetrafluoroethylene (PTFE) tribology by estimating the molecular interaction parameters on the basis of experimental verification. We fitted the molecular interaction parameters between coarse-grained PTFE beads using the iterative Boltzmann inversion method and multi-centered Gaussian-based potentials. The fitting parameters were subsequently validated by comparing an all-atom PTFE model and its corresponding coarse-grained model. A two-layer PTFE friction model was then built on the basis of the estimated parameters to study the effect of normal load on the friction coefficient and wear depth of PTFE. The simulation results showed that the friction coefficient decreases and the wear depth increases as the normal load increases. Moreover, the reasonability of the simulation results was verified through experiments.

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.

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.

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.

The similarity in implied process zones, based on violations of the plastic yield condition, between the state of stress at the edge of an incomplete contact subject to reciprocating shear and tension and a crack suffering pure mode II loading are compared. This is done for both small and large amounts of edge slip, i.e. when the frictional slip region is either enveloped by the plastic region or envelops it. The results show that for realistic coefficients of friction strong agreement is unlikely to occur, so that attempting to analyse the nucleation of fretting cracks as a form of crack branching/turning is inappropriate and the effect of normal load on crack nucleation is an important consideration.

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.

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.

This paper presents the results of the tribological experiments conducted using an oscillating wear tester under lubricated conditions. Specimen from piston ring slid against counter-specimen from cylinder liner. Various surface textures of cylinder liners resulted from honing and/or plateau honing. Tests were carried out for two normal loads of 100 and 300 N at a temperature of 80 °C, the stroke was 3 mm, the frequency was 10 Hz. Each experiment was divided into four time intervals. During breaks between the particular parts of the test, the surface topography of cylinder liners was measured by a white light interferometer. It was found that an increase in the normal load led to an increase in changes of the liner surface textures.

To investigate the nano-scale scratch and friction behaviors of polycarbonate (PC), atomic force microscopy (AFM) was utilized to conduct the nano-scratch tests under different normal loads with a probe of 20 nm tip radius. Then a probe of 1 nm tip radius was employed for the scanning of scratched surface morphology. The stick-slip phenomena are found for all studied normal load levels. The nano-scratch deformation at different normal loads can be categorized into three modes: sliding on asperities, elastic deformed groove and permanent scratch groove. After the analysis of amplitude-frequency characteristics of friction force, a good correlation is found among scratch deformation, friction force and stick-slip. Those findings can be a good guidance to understand and improve the nano-scratch performance of polymers.

Many wear failures are caused by a combination of fretting wear and sliding wear. In this study, the torsional fretting and torsional sliding wear properties of CuNiAl against 42CrMo4 were comparatively investigated under dry condition using a flat on flat contact tester. Experimental results showed that the sliding friction coefficients declined more dramatically than the fretting friction coefficients when the normal load increased. The fretting wear rate was lower than the sliding wear rate, which was partly due to the solid lubrication effect of the wear debris and strain hardening of the worn surfaces. The dominant wear mechanisms for the fretting tests were oxidation, cracks and delamination, while for the sliding tests were abrasion combined with plastic deformation.

Fretting crevice corrosion has become a major concern in orthopedic medical devices when passivating alloys are used alone or in combination. In this work the fretting crevice corrosion response of 316 L stainless steel was investigated when the counterface consisted of different alloys and the effects of potential and normal load were investigated. Fretting initiated crevice corrosion was observed in all stainless steel containing couples, but not in the Ti6Al4V_CoCrMo combination. The coefficient of friction (COF) varied with the applied potential, reaching a maximum of about 0.6–0.7 and decreasing on either side. In summary, normal load and electrode potential have significant effects on fretting crevice corrosion and fretting initiated crevice corrosion of SS316L and its mix-alloy couples.

The effects of normal load and velocity on the friction and wear behavior of single-phase Fe2B bulk have been investigated by optical microscopy, X-ray diffraction, scanning electron microscopy, an...

Most previous studies on fretting fatigue have been accomplished under constant normal loading and less attention has been paid to cyclic normal loading. An innovative test apparatus was specially designed and manufactured for fretting fatigue tests under cyclic loading in this work and the fretting fatigue behavior of Al7075-T6 was investigated at different normal load frequencies. A finite element model was developed to study the effect of normal load frequency on the contact stress distribution. It was found that the cyclic normal load has a more damaging effect on fretting fatigue life compared to constant normal load, particularly at lower frequencies. The results showed that at the normal load frequency of f = 1 Hz, fatigue life decreased by 52% in the high cycle fatigue regime and 28% in the low cycle fatigue regime. The experimental results also indicated that at the normal load frequency of 80 Hz, the fretting fatigue life converged to its corresponding life under constant normal load con...

An effective and simple method is reported to enhance the property and economics of graphene lubricants, that is, 3D porous graphene and T161 are proposed as hybrid lubricant additives. Compared with PAO 6, 3D PG-T161 can reduce the friction coefficient of 316 ASS (Austenitic stainless steel) by about 4.0%, 26.1% and 73.1% respectively under the normal load of 5 N, 50 N and 100 N, and the wear rate is reduced by about 28.9%, 65.6% and 97.8% respectively. The excellent tribological performance is attributed to the formation of uniform protective lubricating film. These findings are of great significance for enhancing the tribological properties of ASS and expanding its application range.

Experiments were carried out using a pin-on-disc tester in conformal contact starved lubrication and unidirectional sliding with constant normal load of 20 N and sliding speed of 0.8 m/s. Different combinations of co-acted samples were studied: textured specimen and untextured counter-specimen, both samples textured and untextured. Samples with the following densities of dimples were tested: 2.25%, 5%, 9%, 14% and 20.25%. The best tribological performance was achieved for both surfaces textured with the smallest pit-area ratio. For large area densities tribological behaviors of sliding pairs with one sample textured were better than those with both samples textured.

In this study, we investigated the effect of temperature on the friction and wear of rice bran (RB) ceramics, a hard porous carbon material made from rice bran, sliding against alumina, stainless steel, and bearing steel balls under dry conditions. Friction tests were performed using a ball-on-disk-type friction tester wherein a ceramic heater was installed in the rotational stage. The surface temperature of the RB ceramic disk specimens was controlled at 20, 100, 150, or 200°C. The normal load was 1.96 N, sliding velocity was 0.1 m/s, and number of cycles was 20,000. The effect of surface temperature on the friction and wear of RB ceramics substantially differed among the ball material types. The friction coefficient for the RB ceramics sliding against an alumina ball decreased with increasing temperature and exhibited an extremely low value (0.045) at 200°C. The friction coefficient in the case of the RB ceramics sliding against a stainless steel ball exhibited a stable value as the temperature ...

This paper presents an investigation into the effect of unexpected overloading on scuffing initiation with a twin-disc test device. An existing twin-disc test device was modified to be suitable for applying overloading dynamically to the disc contact. Three test series including three pairs of discs in each series were subjected to combined normal force and rolling/sliding loading. First a base level for scuffing initiation was defined by increasing the normal load stepwise until failure, while keeping the rolling and sliding between the discs constant. In the subsequent test series, the overload cycles were applied at a significantly lower level in two different patterns leading to scuffing at both an earlier and later stage than was observed for the base level. acceptedVersion

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

This study is concern with tribocorrosion behaviour of Ti6Al4V-HA biocomposites. The Ti6Al4V composites reinforced with different contents of hydroxyapatite (HA) particles 5–15%, vol%) were produced by hot pressing technique. The tribocorrosion tests were performed by using a ball-on-plate configuration in artificial saliva at 37 °C. The tests were carried out under open circuit potential (OCP), with a sliding duration of 1800 s, 1 N normal load and 1 Hz frequency. The open circuit potential and wear mechanisms for all tested biocomposites are presented and discussed. The results suggest that HA plays a relevant role on tribocorrosion behaviour of Ti6Al4V-HA composites. All composites samples presented better wear resistance and also a relatively lower tendency to corrosion with increasing HA content.

The fretting wear behavior of the nuclear power material Incoloy 800 was investigated in this study. A PLINT high-temperature fretting tester was used on an Incoloy 800 cylinder against a 304SS cylinder at vertical cross contact under different temperatures (25, 300, and 400°C). During testing, a normal load of 80 N was applied, and the displacement amplitudes ranged from 2 to 40 µm. The fretting wear mechanism at high temperatures and the kinetic character of the materials of the Incoloy 800 steam generator tube were analyzed. Results showed that the fretting running regimes varied little with ncreasing temperature, and some microcracks were observed in both the mixed fretting regime (MFR) and the partial slip regime (PSR) at high temperatures. Slight abrasive wear and microcracks were the main wear mechanisms of the Incoloy 800 alloy in PSR, whereas those in the MFR and the gross slip regime were oxidative wear, abrasive wear, and delamination.

The vacancy-enhanced contact friction of graphene is mainly attributed to the vacancy-enhanced out-of-plane deformation flexibility of the graphene and the climbing of the tip out of the vacancy trap (which actually acts as a step edge). However, this mechanism does not apply for explaining the enhanced friction caused by small-sized vacancies that are unable to accommodate the tip, such as single vacancy and double vacancies, which also commonly exist in the graphene. In the present study, by performing a set of classic molecular dynamics simulations, we demonstrated that the double-vacancy defect in graphene substantially enhanced the contact friction when the tip slides over it and the pinning effect of the reconstructed lattice of the double-vacancy defect with atoms at the bottom of the tip dominated such an influence. The underlying mechanism of such an atomic pinning effect and the influence of the normal load, sliding direction, and the sliding velocity were unveiled by analyzing the obtained friction evolution and the atomic configuration and interaction between the tip and the graphene. We believe that the findings presented in this study complete the state-of-art understanding of the nanoscale friction behaviors of vacancy-defected graphene, which is essential for the implementation of their potential control.

[EN] In fatigue problems, an accurate estimation of the propagation direction is important for life prediction. We identify the most relevant factors that affect the crack orientation during the propagation stage of fretting fatigue cracks, arising from complete contacts. Contrary to what initially expected, parameters such as normal load, cyclic bulk load, etc. do not have a noticeable influence on the orientation. However the relative Young's moduli of indenter/specimen materials, the indenter width and the surface coefficient of friction are the most influencing factors. Analyses are performed through the extended finite element method (X-FEM) and an orientation criterion for non-proportional loading proposed by the authors. Experimental fretting fatigue tests confirm the predicted trends. An explanation of this behaviour is also given., The authors gratefully acknowledge the financial support given by the Spanish Ministry of Economy and Competitiveness and the FEDER program through the projects DPI2017-89197-C2-1-R and DPI2017-89197-C2-2-R. The support of the Generalitat Valenciana, Programme PROMETEO 2016/007, is also acknowledged. The authors thank the collaboration of Mr. Francisco Gelardo Rodriguez

Solution procedures for establishing the regimes of stick and slip for frictional contacts capable of idealisation within the framework of half-plane elasticity and subject to complex loading regimes are reviewed, starting with the well known fundamental problems and going on to more complicated ones. These include problems where the normal load, shear force, applied moment and differential remote tensions all vary with time. Transient and steady state solutions are discussed., Comment: 16 pages, 9 figures, Tribology International

In this work, we have investigated anisotropic frictional behaviour of patterned silver surfaces. Anisotropy in coefficient of friction (COF) is observed depending on the sliding direction on one-arm and two-arm columnar structures as a function of applied normal load. Anisotropy in COF values for one-arm Ag nanocolumnar surface was observed to be as large as 42% when measured between along and transverse to the columnar tilt direction. However, the percentage change in COF values were as high as 67% for two-arm (zig-zag) nanocolumnar surface along the tilt direction of the columns between trace-retrace directions. There was a significant variation in COF of about 149% by changing geometry from one-arm to two-arm (zig-zag) nanorods, which is explained through a force balance model.

A marker layer (Au80Pd20) combined with four different techniques was used in order to estimate the real contact area between static steel–steel contact pairing (substrate: AISI304 and ball: AISI 52100). The experiments were done with polished references (substrate and ball) and with substrates having a laser-patterned line-like surface topography using two loads (1 and 5 N) and two pattern periodicities (9 and 15 µm). Irrespective of the normal load, all techniques led to the same results within the standard deviation for the polished surfaces. For the laser-patterns, only the combination of foot-printing, scanning electron microscopy and image segmentation is capable to provide meaningful results, since the other techniques significantly overestimate the real contact area.

Biodiesel has become an increasingly significant alternative fuel to replace conventional diesel completely or partially. Although biodiesel has several advantages, such as environmental friendliness, renewability, and reduced emissions, it also has major drawbacks. Tribology is one of the major concerns for biodiesel usage, in which biodiesel lubricity deteriorates by usage and/or by storage because of its oxidative nature. The present study aims to investigate the lubrication behavior of oxidized and pure palm biodiesel blends by using a four-ball tribotester machine. Tests were carried out in diesel, pure biodiesel (B100), their blends (B10 [10% biodiesel in diesel], B20, B30, and B50), and oxidized biodiesel (Oxd B100) and its blends (Oxd B10, Oxd B20, Oxd B30, and Oxd B50). Tests were conducted at room temperature under a normal load of 40 kg for 1 h at 1,200 rpm. Surface analyses were carried out by scanning electron microscopy, energy-dispersive spectrometry, and optical microscopy, and fue...

To determine the effect of thermal aging on the scratch behavior of polymethyl methacrylate (PMMA), the scratch tests of PMMA at different aging time were conducted with the linear progression of the normal load. It was shown that the critical normal load corresponding to the surface crack decreases with the increase of aging time. The supplement indentation test and numerical simulation were conducted to identify the surface crack-initiation strength of the aged PMMA. A good correlation was found between the surface crack-initiation strength and the critical normal load. This implies that the surface crack-initiation strength could be a good criterion to measure the scratch damage of PMMA.

In many engineering environments tribocorrosion is combined with fatigue (multi-degradation). In the present work, the effect of static/cyclic bending and normal load on multi-degradation of austenitic and super duplex stainless steels has been studied. Investigating surface and subsurface characteristics by SEM/FIB, tribologically refined layers (TRL), crack matrices and pits were observed and their role on wear mechanisms was elucidated. Passive film thickness and composition was examined with XPS. Observations showed surface tensions increase the passive film thickness which can control pit and crack matrix formation thus wear loss mechanisms. Static and cyclic bending resulted in thicker oxide layer, enhanced pit formation and wear debris detachment while in the absence of 4-point bending larger subsurface cracks and TRL were observed.

Al-2.26% Mg alloy reinforced with Al3Zr particles was synthesised by Direct Melt Reaction in situ technique. Wear rate, wear rate/vol% Al3Zr (normalised with respect to amount of Al3Zr), normalised wear, and wear coefficient have been evaluated. At different combinations of normal load and sliding velocity two modes of wear i.e. mild/oxidative and severe/oxidative-metallic modes are observed. With increase in the amount of high hardness Al3Zr particles, composites can be used even at higher load and sliding velocity while still being in mild wear regime. Coefficient of friction (COF) has fluctuating tendency with sliding distance. COF shows a decreasing trend with load, whereas, with sliding velocity and composition trend is reversed. Low wear and high COF indicates its suitability in brake materials.

The aim of this work was to investigate the influence of the processing conditions on the tribocorrosion behavior of hot pressed CoCrMo biomedical alloys. Several samples were processed as a function of different processing temperatures (900, 1000 and 1100 °C) and times (10, 30 and 60 min). Tribocorrosion tests were carried out in artificial saliva at 37 °C, under 1 N normal load, 1 Hz frequency and 3 mm stroke length. Open circuit potential was measured. The worn surfaces were inspected by means of SEM/EDS. Results revealed a decrease of wear rate with increasing hot pressing time. The samples hot pressed at 1000 °C revealed the lowest wear rate. These findings showed that the processing conditions play a relevant role on tribocorrosion behavior of CoCrMo.

This article aims to study the friction and wear behavior of Ti3Al2.5V alloy sliding against EN-31 steel under dry condition using a multi-tribotester. The effect of variation in load and sliding velocity on wear rate, average coefficient of friction, and contact temperature has been studied and analysis of wear debris has been carried out. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were employed to study the morphology of the wear tracks and deduce microchemical information at the elemental level of worn samples, respectively. Results reveal that the wear rate of Ti-3Al-2.5V increases with increasing sliding velocity and increasing normal load with few exceptions. The average coefficient of friction decreases as the normal load increases with exceptions at some loads. SEM micrographs of worn samples obtained at different loads and sliding velocities show the formation of wear tracks on the surface due to ploughing and flaking of the matrix. The main mechanis...

The torsion tribological behavior of polytetrafluoroethylene (PTFE) composites was investigated under different dynamic normal loads. The difference between the shapes of T–θ curves under static and dynamic normal loads indicates that the torsion regime was affected by the dynamic normal loads. Dynamic loads not only produced new frequency components but also enhanced the amplitude of frequency components produced by the static load. The biaxial dynamic stress and transformation of the torsion regime under dynamic loads produce higher wear than that of a static load. The wear mechanisms under static and dynamic loads are abrasive wear and adhesive and fatigue wear, respectively.

In order to investigate the deformation characteristics and material removing mechanism of the single crystal silicon carbide at the nanoscale, the nanoscratching tests were conducted on the surface of 6H-SiC (0 0 0 1) by using Berkovich indenter. In this paper, a theoretical model for nanoscratching with Berkovich indenter is proposed to reveal the relationship between the applied normal load and the machined depth. The influences of the elastic recovery and the stress distribution of the material are considered in the developed theoretical model. Experimental and theoretical machined depths are compared when scratching in different directions. Results show that the effects of the elastic recovery of the material, the geometry of the tip and the stress distribution of the interface between the tip and sample have large influences on the machined depth which should be considered for this kind of hard brittle material of 6H-SiC.

This study was undertaken to investigate the effect of heat treatments on the high-temperature wear behavior of 60Nitinol. The samples were hot-worked, aged at two temperatures of 400 and 700°C for 1 h and then water quenched. The microstructure of the alloys was investigated by scanning electron microscopy and X-ray diffraction. Sliding wear tests were performed at two temperatures of 25 and 200°C using three types of 60Nitinol disks: hot-worked, aged at 400°C, and aged at 700°C. All wear tests were performed at a speed of 0.3 m/s under a normal load of 60 N for a total sliding distance of 1,000 m using WC-Co pins sliding against 60Nitinol disks. The worn surfaces and microstructure of the subsurfaces were studied by scanning electron microscopy. Compression and hardness tests were also performed to characterize the mechanical properties of the alloys. The highest fracture strain and lowest hardness were obtained for the sample aged at 700°C that contained Ni3Ti2 precipitants. This sample also sh...

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.

An innovative in-situ method of generating tungsten disulphide (WS2) tribofilms was proposed in this study. It was found that the WS2 tribofilms formed via a tribochemical reaction between tungsten carbide particles embedded in a steel surface and an extreme pressure lubricant additive led to low friction and significantly improved anti-wear properties in humid air. The presence of the WS2 tribofilms was detected by X-ray Photoelectron Spectroscopy and their chemical surface composition was discussed. The friction behaviour was influenced by the rate of WS2 tribofilms formation, EP additive concentration and normal load applied. Moreover, it was found that the WS2 tribofilms were crucial for significant reduction in friction and negligible wear of WC-functionalized steel surfaces.

The self-lubricating effects of metal matrix self-lubricating composites are based on migrating solid lubricant from matrix to worn surface, which results in the formation of transferred film mainly containing solid lubricant. To explore the migration mechanism of solid lubricant and calculate the thickness of transferred film, an approximate model is developed. The influence of normal load, friction coefficient, volume fraction of solid lubricant and yield strength of solid lubricant are investigated based on the model. A comparison of theoretical and experimental data suggests that theoretical data is in qualitative agreement with experimental data, implying that the model can be expected to give recommendations for designing metal matrix self-lubricating composites.

This study focused on the normal load dependence of the friction coefficient for the sliding friction of a rubber material with a rough surface. A developed friction tester was used to visualize the real contact regions distributed within the transparent contact interface between poly-dimethyl siloxane (PDMS) and glass surfaces. Based on experimental results, an adhesion friction model was developed to explain the normal load dependence of the friction coefficient. This model provides a simple technique that can roughly but easily estimate the real contact area and shear stress without in situ observation of the contact interface.

Rail grinding is of vital importance for high-speed railway with safe, reliable and comfortable operation. Here, a self-design grinding machine was applied to evaluate the performance of as-prepared grinding stone (GS) vs Rail under normal loads and grinding speeds. Results illustrate that the increase in normal load leads to the wider and thicker wear debris, but the increasing grinding speed is opposite. Friction-induced heat regulated by working parameters determines the grinding properties of the GSs/Rail contact, high grinding-heat causes the plastic deformation and accelerates the wear. The finite element analysis verifies the source/distribution of grinding-heat and heat flux, thereby revealing the material removal mechanism. It is of great significance for long-term safe and reliable operation of rail via grinding regulation.

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.

This paper studies the friction and wear of Hadfield steel single crystals with the normal load/friction force orientations [ 1 ‾ 1 ‾ 0 ] / [ 1 ‾ 10 ] and [ 1 ‾ 1 ‾ 0 ] /[001]. Due to the different friction force orientation, deformation occurs by twinning in the first case and by slip in the second case. The shear stresses were estimated and correlated with the observed slip band systems. Changes in the orientation of the worn surface were examined by EBSD analysis. TEM studies were performed to investigate the dislocation structure evolution near the worn surface.