Search

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.

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 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

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.

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.

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.

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.

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.

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.

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 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.

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

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.

The historical development on the discoveries of lubrication regimes for lubricated sliding contacts has been reviewed from the very beginning. It was found that the functional relationship between the coefficient of friction and the product of sliding speed and viscosity divided by the normal load well known as the Stribeck curve has been experimentally explored much earlier by Adolf Martens in 1888 long before Richard Stribeck did his pioneering measurements in 1902. However, basic work in this field of experimental hydrodynamics was done and results were published even earlier than that back in 1854 by Gustave A. Hirn, in 1879 by Robert H. Thurston and in 1883 by Beauchamp Tower.

Transition between mild and severe wear has been observed in Al-8090 aluminium alloy and Al-8090–SiC composite. The transition is characterized by an abrupt increase in the wear rate and a change in the size, morphology and composition of the wear debris. In addition, mechanically mixed layers were formed during the wear process on the top of the worn surface. Critical sliding velocity and temperature has been determined as a function of normal load. A single transition diagram was determined including the effect of load, temperature and sliding speed using a unified parameter.

The abrasive wear behaviors of aluminum alloyed Hadfield steel at the high and low stress wear conditions were studied and compared with non-Al alloyed Hadfield steel. The wear tests were done with the pin on disc method using the abrasive wheel. The main parameters such as alloy compositions, normal load, sliding speed and sliding distance were evaluated. It is shown that at the low stress condition, the aluminum alloyed Hadfield steel has higher wear resistance than the non-Al alloyed Hadfield steel. But at the high stress wear conditions, the non-Al alloyed Hadfield steel is more resistant than the Al alloyed.

Self-mated wear and friction of Alloy 600 superalloy was studied in a water-submersed ring-on-rod configuration, loading the side of a 6.35 mm diameter rod across the flat surface of a rotating annular ring of 100 mm outer diameter and 70 mm inner diameter producing two sliding contacts along the ring. Tests were conducted at sliding speeds of 0.178 and 0.330 m/s for sliding distances of 100 m. Normal loads of 51 and 204 N were applied, and initial Ra surface roughnesses of the rings along the sliding direction were either smooth (∼0.2 μm) or rough (∼7.5 μm). Increased initial ring roughness caused a ∼20-fold increase in rod wear at the lighter load, whereas at the heavier load increased initial roughness only caused a ∼4-fold increase in wear. At lower initial ring roughness the 4-fold decrease in normal load caused a large (one order-of-magnitude) decrease in rod wear, whereas for rings of higher initial roughness the 4-fold decrease in normal load caused only minor (2-fold or less) decreases in rod wear. Wear during this 100 m sliding distance only experienced a minor effect from the 1.8-fold change in sliding speed, as did friction. In all cases friction coefficient rapidly settled into the range 0.6–0.7, except in the cases of lower load on rings of lower initial roughness where friction coefficient remained above 1 for most of this sliding duration. At this lower load the initial ∼0.2 μm rod roughnesses increased to nearly 0.8 μm by the 100 m sliding distance, whereas at the higher load this same sliding distance resulted in roughnesses returning near to the initial 0.2 μm. It was hypothesized more highly loaded cases also went through initial roughening prior to smoothening back to 0.2 μm roughness within the 100 m sliding distance, and given additional sliding the more lightly loaded cases would also experience subsequent smoothening. Increasing sliding distance to 400 m, roughnesses indicated a smoothening back to 0.2 μm level during those lightly loaded tests, with friction coefficient correspondingly dropping from 1 into the 0.6–0.7 range observed in all other cases. Extended sliding to 400 m at light loading against rings of lower initial roughness also allowed a rod wear rate which increased with increased sliding distance to be observed, approaching the same rate observed against initially rough rings within the 100 m sliding distance.

Friction and wear behaviors of SUS 304 austenitic stainless steel (ASS) disc against Al 2 O 3 ceramic ball and GCr15 bearing steel ball, respectively, were studied using a Cameron-Plint TE67 pin-on-disc tester. The tests were performed under 5–50 N loads and 0.06–0.19 m/s sliding speed. Results showed that there was a gestating period before the friction coefficient increased rapidly as the normal load was increased beyond 30 N. They also showed that the specific wear rate of SUS 304 austenitic stainless steel decreased with the increasing of the sliding speed. As a result of the breaking of Al 2 O 3 particles and/or the possible transformation of friction-induced meta-stable austenite γ to martensite α′ that led to the generation of harder debris, the wear of SUS 304 austenitic stainless steel was a mixing mode of both adhesion and plough processes.

Many biomaterials are being developed to repair or replace articular cartilage. One of these materials, poly(vinyl alcohol) (PVA) hydrogel prepared from aqueous solution of the polymer by freezing and thawing method may exhibit the mechanical properties required to withstand the harsh environment of diarthrodial joints. To better understand how PVA hydrogel friction is affected by different variable factors, a three-factor, three-level designed orthogonal experiment was developed. Factors include lubricant, sliding speed, and normal load. Friction coefficient of the PVA hydrogel was found to depend significantly on load and sliding speed. Lubricant had little effects on the friction coefficient. Friction coefficient of the PVA hydrogel decreased with the increase of sliding speed and the friction coefficient approximately increased linearly with the increasing load. Average friction coefficient decreased from 0.0447 to 0.0379 while the sliding speed increased from 0.06 to 0.22 m/s. Average friction coefficient increased from 0.0276 to 0.0546, almost increasing one time, while the load increased from 5 to 15 N.

This work examines how wear rates are affected by frequency of vibration in conjunction with relative humidity. Variation of wear rate with the variation of frequency of vibration and relative humidity is investigated experimentally on a mild steel disc using specially designed pin-on-disc apparatus having facility of vibrating the disc at different frequency of vibration and amplitude. During the experiment, the effect of normal load, speed and relative humidity on wear rate were also investigated. The surface conditions of the mild steel base plate were ‘as-turned’ and ‘as-ground’. Studies have shown that wear rate under no vibration condition is higher than that under vibration condition. The values of wear rate decrease with the increase of frequency of vibration. Similarly, the wear rate decreases with the increase of relative humidity within the observed range. In this study, it is also observed that the rate of reduction of wear rate has a particular relationship on the frequency of vibration and the relative humidity. The experimental results are compared with those available in the literature and simple physical explanations are provided.

Traction and curving are the principal causes of high tangential forces between railway rails and wheels. The magnitude and direction of these forces are calculated for equilibrium curving of a conventional two-axle bogie in curves of 600–1800 m radius, both without traction and for a level of tractive effort of 0.28 times the normal load of the vehicle. For a non-powered bogie, the tangential force is greatest at the high wheel of the leading axle and least at the high wheel of the trailing axle. At high traction levels, the tangential force is high at both leading and trailing high rail wheels. The ability of a bogie to steer deteriorates as tractive effort increases. Whereas a low inter-axle yaw stiffness helps a non-powered bogie to steer better, steering of a bogie with low yaw stiffness is poorer under traction. Cant deficiency both redistributes tangential loads between the four wheels of a bogie in a desirable way and reduces the maximum of the four loads for all levels of applied traction.

Diamond-like carbon (DLC) films were deposited on Si wafers using a plasma CVD apparatus with two different types of precursors. A friction and wear test was conducted under dry and wet air conditions. In wet air, friction was higher and the wear rate was smaller than that experienced in dry air. The rupture load of DLC films, were a normal load was increased stepwise, was larger with wet air than dry air. Many folds, perpendicular to the sliding direction, were seen on the friction surfaces under wet air conditions, although the friction surfaces in dry air seemed very smooth. There were no pits on the friction surface in wet air, although some pits existed on surfaces exposed to dry air. Even with the endurance test, there were no pits and clacks on the friction surface in wet air, in contrast to the friction surface in dry air. Many of the wear fragments obtained in wet air had a flattened-shape, while many granular wear fragments were scattered on the friction surface in dry air. These observations suggest that the friction surface obtained under wet air conditions has the property that can deform plastically. This property translates to a smaller wear and a greater film toughness.

In this paper the friction and sliding wear of WC–Co cemented carbides are studied. Friction and wear tests were carried out using six different WC–Co alloys (Co ranging from 6 to 20 wt.%) under unlubricated conditions against steel (0.45 wt.% C) disk. Tests were performed at sliding velocity of 2.2 m s −1 and normal load of 40 and 180 N. Sliding wear tests were carried out using moderated block-on-ring equipment. It is shown that wear resistance depends on the chemical composition and hardness of cemented carbides. The wear rate of cemented carbides decreases with an increase in hardness and decrease in binder content. Means, standard deviations (S.D.) and COV of wear data were calculated. The morphological analysis of the worn surface and wear debris were made by SEM. The wear mechanism has a complicated character and depends on the applied load and material composition. The wear of WC–Co cemented carbides under dry conditions is caused mainly by removal of the cobalt binder followed by fracture of intergranular boundaries and fragmentation of carbide grains.

This study was conducted to systematically investigate the wear behaviour of electrolytic hard chrome and arc-PVD coatings under lubricated reciprocating conditions. Experiments were conducted in unformulated base oil and the effects of normal load (5, 10 and 30 N) and temperature (room and 60 °C) on wear behaviour of both electrolytic hard chrome and arc-PVD CrN coatings are investigated. The results indicated that CrN performed better than hard chrome plating under lubricated reciprocating wear conditions used in this study. This effect became more pronounced by the increase of temperature and normal load. Profilometric wear depths on both coatings could not be determined after the tests conducted at room temperature. However, at 60 °C, wear depths as deep as 3.5 μm (at 30 N load) on EHC coating could be recorded by profilometer. Profilometric depth on CrN coated discs could not be detected. The reciprocating sliding tests on brushed CrN coated discs clearly demonstrated the important role of droplets on tribological behaviour of arc-PVD coatings.

Subsurface damage in scratch tests has been investigated to highlight the relationship between damage characteristics and mechanical response of materials, such as the tangential force F t . A progressive loading tester with a spherical indenter, on which the normal load F n was increased with increasing sliding distance, was utilized for tests on a commercially available hot-pressed silicon nitride. The damage was visualized using a plasma etching procedure previously developed. The trend of F t was categorized into three stages associated with the damage characteristics. In the first stage, the scratch track was barely perceptible but the presence of subsurface damage was confirmed, demonstrating that damage formation occurs prior to scratch track formation. Then, in the second stage, the scratch track was distinctly observed as the consequence of quasi plastic deformation, the presence of which was inferred from the continuous groove-like damage zone. Further increase in F n results in both high fluctuation of F t and significant variation in damage depth, suggesting the correlation between them.

Models for oxidation-modified wear in two phase materials have been proposed extending the earlier models of Archard and Quinn, for predicting the oxidative wear in homogeneous materials. Three distinct possibilities have been considered—(a) case A, both the phases having the same oxidation behaviour and also, the same critical thickness for oxidative wear; (b) case B, both the phases having the same oxidation behaviour but distinctly different critical thicknesses; and (c) case C, both the phases having different oxidation behaviour and also, different critical thicknesses. In all these cases the wear rate varies linearly with the real area of contact estimated as the ratio of normal load to the rule of mixture hardness. The oxidation-modified wear in dual phase steels, as observed experimentally appear to belong to case A but it may also belong to case B with small difference in critical thickness in both the phases of ferrite and martensite. The wear behaviour calculated for case B is similar to those observed experimentally but the calculated values of wear rates are lower. It is possible that the oxidation behaviour could also be different in different phases and case C could be more appropriate.

The effects of contact area and contact stress on the wear of ultrahigh molecular weight polyethylene (PE) articulating with a polished surface of cobalt–chromium alloy were evaluated using a pin-on-disk apparatus implementing bi-directional movement. Within a relevant range of contact stresses, volumetric wear rate increased with increasing contact area. Volumetric wear was found to be independent of normal load within this range. Mechanistic issues related to these findings are discussed.