Tribology International

High performance disk drives require high spindle speed. The spindle speed of typical hard disk drives has increased in recent years. The increasing disk velocity leads to increasing disk acceleration and slider-disk interaction. The slider-disk interaction in CSS (contact-start-stop) mode is an important source of particle generation and tribocharge. Charge build-up in the slider-disk interface can cause ESD (electrostatic discharge) damage and lubricant decomposition. We measured the tribocurrent/voltage build-up generated at increasing disk acceleration. In addition, we examined the effects of relative humidity and dwell time on the tribocharge build-up. We found that the tribocurrent/voltage was generated during pico-slider/disk interaction and its level was about 3-16 pA and 0.1-0.3 V, respectively. Tribocurrent/voltage build-up was reduced with increasing disk acceleration. Higher humidity conditions (75 -80%) yielded lower levels of tribovoltage/current. Dwell time affected the charge build-up at the slider-disk interface. The degree of tribocharge build-up increased with increasing dwell time

Wear of the carbon layer of a magnetic recording disk is investigated during load/unload using a surface reflectance analyzer (SRA). Wear is determined as a function of the number of the load/unload (L/UL) cycles, the disk rotational speed, and the air bearing design. Two types of subambient pressure sliders are used in the experiments, the difference being related to the size and position of the subambient pressure region. The load/unload behavior of the two slider types is determined numerically using finite element air bearing simulation.

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The effect of waviness was investigated on the wear performance of 080 M40 and 817 M40 steels machined by the turning and surface grinding processes for a sliding wear situation. The wear was measured with a precision relocation technique using a Talysurf 4 and the frictional coefficient force was monitored using a load cell. The worn surface was examined using scanning electron microscopy. For both types of steel, contact was at the wave crests. The crests were progressively truncated and work-hardened during the wear cycle. Generally, friction increased during running-in and stabilized on complete removal of the waves. For dry wear regimes high interfacial temperatures were set up at the wave crests. Consequently, the pin material oxidized and the friction and wear behaviour of the surface altered. On running-in the turned 817 M40 specimens showed large scale redeposition due to adhesive wear at the wave crests whilst the valleys were relatively smooth due to an abrasive process. A white layer of untempered martensite was produced at the surface of the ground 817 M40 specimens. This hard layer initially resisted abrasion and reduced friction.

It has been shown that 1,3-propanediol compounds exhibit antimicrobial properties in cutting fluids, two of the most active compounds being 2-nitro-2-bromo-1, 3-propanediol and 2-nitro-2-ethyl-1, 3-propanediol (nepd). Since the former chemical is well known as an antimicrobial agent, nepd was selected for additional studies. It was found that the antimicrobial properties of nepd were increased by the presence of edta, that it did not markedly interfere with the antimicrobial properties of cutting fluid preservatives and that it combines well with certain amines — such as ethanol-amines, propanolamines, butanolamine and butylamines — to produce mixtures with improved inhibitory properties.

The tribological behaviour of three commercial self-mated Si3N4/Si3N4-sliding pairs in pin-on-disc configuration was studied for sliding velocities between 0.03 m s−1 and 3 m s−1, constant load of 10 N and ambient temperatures between 22°C and 1000°C. The wear rate of Si3N4 is dependent on the overlap ratio, the ambient temperature and the sliding velocity. An influence of the phase composition was for the three tested commercial Si3N4 materials not observed. The coefficient of friction lies for solid state friction under steady-state conditions between 0.5 and 1. The tribological behaviour for temperatures greater than or equal to 400°C is characterized by a high wear/low wear transition with increasing velocities. Wear mechanisms were studied with scanning electron microscopy, infra-red spectroscopy and X-ray diffraction.

This paper presents an original ultrasonic technique devoted to the early detection of sub-surface fatigue cracks in 100Cr6 bearing steels. Echographic experiments were carried out during interrupted rolling contact fatigue tests. Crack initiation and crack propagation stages were both investigated. Quantitative measurements of sub-surface crack position, depth and angle with respect to the bearing surface are presented. Experimental results are analysed and discussed in relation to rolling contact fatigue theories. Contrary to what is generally accepted the presented results show that the crack propagation stage could represent an important part of bearing life.

The effects of conventional heat treatment and boronizing on SAE 1010 and SAE 1040 structural steels, D2 tool steel, and 304 stainless steel were investigated. During this investigation, layer thicknesses, corrosion and wear strength were examined by applying carburisation, nitriding, transformation hardening and boronizing to the specimens. Abrasive wear tests were carried out in a wear cup model device. Sand of 1 mm diameter was used and the test duration was 40 hours with a velocity 0.157 m/s. Corrosion tests were undertaken in a 10% H2SO4 solution at a temperature of 56°C. Through metallographic analyses, hard layer thicknesses and Vickers hardness values were determined for each hardening treatment.

The friction and wear properties of steel rubbing pairs were investigated under dry and lubricated conditions by using a pin-on-disk tribometer. The selected speed range was 0.8 to 3.2 m/s and the load range was 58.8 to 235.2 N. Distilled water and a mineral oil (no additives) were used for lubrication, respectively. The wear of Ti(CN) ceramic under dry conditions was caused mainly by adhesion between the rubbing surfaces and the microfracture of Ti(CN). With the load and speed increasing, the adhesion and diffusion between rubbing surfaces increased and resulted in wear increasement of Ti(CN). Because of the brittleness of ceramics, the microfracture wear of Ti(CN) increased rapidly when the load was raised to some high values. The lubricating and cooling effects of the lubricants could improve the frict on and wear. Compared with water, oil was much better in improving the tribological properties. The analysis results obtained from XPS and AES examinations showed that ferrous oxide was produced on the wear scars, which could reduce the adhesion between the rubbing surfaces to some extent. The lubricating effects of the oil under boundary lubrication conditions were attributed to the formation of carbon films on the rubbing surfaces.

The tribological behavior of alumina (Al2O3) in CF3CH2F (HFC-134a) gas at pressures between 170 Pa and 105 Pa were investigated using a ball-on-disk type tribometer. For comparison, the friction test was also carried out in a vacuum (10−5 Pa) under the same experimental conditions. X-ray Photoelectron Spectroscopy (XPS) and Time of Flight Secondary Ions Mass Spectrometry (TOF-SIMS) were used to identify the formation of tribochemical products.It was found that the friction and wear properties of Al2O3 were strongly dependent on the pressure of HFC-134a gas. A higher pressure correlated to a lower friction coefficient. When the pressure exceeded 103 Pa, the wear strikingly decreased. The results of XPS and TOF-SIMS analyses identified that tribochemical films, mainly composed of fluorine-containing organic compounds and Al-oxyfluorides, were produced on the frictional surfaces. In addition, it was found that the amount of the fluorides correlated well to the friction and wear properties, that is, the more the fluorides were, the lower were the friction and wear. The results of research indicate that HFC-134a gas has a good lubricating effect for Al2O3 ceramic, which is attributed to the formation of the tribofilms at the frictional interface.

The modified IP 48 procedure was used for testing the oxidation stability of engine oils for ignition engines of the SAE 15W-40 and minimum API SG/CD specifications. Eight engine oils, such as Agip, BP, Esso, Mogul, ÖMV, Petro-Canada, Shell, and Total, were collected and oxidised. Oils were also fractionated by using chromatographic methods, and group composition of base oils, amount of VI improvers and other additives were determined. Several differences in the oxidation stability were found between the collected oils. Viscosity characteristics, carbon residue, acid number, amount of pentane insolubles and mass losses during the test were chosen as parameters for evaluation of the oxidation stability of the oils. The most stable engine oil was blended from a hydrocracked base oil whereas most of the other oils were based on the solvent refined oils.

The tribological properties of Ni-17.5Si-29.3Cr alloy against Si3N4 were studied on a ball-on-disc tribotester between room temperature and 1000 °C. The effects of temperature on the tribological properties of the alloy were investigated. The worn surfaces of the alloy were examined using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results indicated that the tribological behavior of the alloy expressed some differences with increase in testing temperature. At low and moderate temperatures (below 800 °C), the alloy showed excellent wear and oxidation resistances, and the wear rate of the alloy remained in the magnitude of 10−5 mm3/Nm; but at elevated temperature (800–1000 °C), the wear and oxidation resistances decreased, and the wear rate of the alloy increased up to 10−4 mm3/Nm. The friction coefficient decreased from 0.58 to 0.46 with the rising of testing temperature from 20 to 600 °C, and then remained nearly constant. The wear mechanism of the alloy was mainly fracture and delamination at low and moderate temperatures, and transformed to adhesive and oxidation at elevated temperatures.

The tribocorrosion property of a Ni-17.5Si-29.3Cr alloy against a Si3N4 ball was studied in comparison with AISI321 stainless steel using a ball-on-disk reciprocating tribotester in 1 M sulfuric acid (H2SO4) solution. The effects of load and sliding speed on the tribocorrosion properties of the alloy were investigated. The results indicated that the wear rate of the alloy increased while the friction coefficient decreased with increasing load. The wear rate of the alloy increased linearly with increasing sliding speed and the friction coefficient increased in the initial stages and then remained constant with increasing sliding speed. The wear mechanisms were mainly microploughing, uniform corrosion and pitting corrosion. Under the experimental conditions of the present study, the Ni-17.5Si-29.3Cr alloy showed excellent corrosion-resistence and anti-wear ability compared with AISI321 stainless steel.

Pin-on-disc dry sliding wear tests have been carried out to study the wear behaviour of 10 vol% TiC and (Ti,W)C-reinforced Fe–17Mn austenitic steel matrix composites. The composites have been synthesized in situ by means of conventional melting and casting route. It has been observed that the abrasive wear resistance of the composites is higher than that of their unreinforced Fe–17Mn austenitic steel. Compared with the TiC-reinforced composite, the abrasive wear resistance of the (Ti,W)C-reinforced composite is better. The abrasive wear resistance and coefficient of friction of both reinforced and unreinforced materials decrease as the load increases.

Protective coatings, deposited mainly by thermal spraying and diffusion techniques, are considered a solution to extend the lifetime of many components in the energy production sector, such as heat exchangers. In this paper, some results are presented for uncoated, aluminized and chromized-aluminized 9Cr–1Mo steel, subjected to air and to impacts by 200 μm silica particles at angles of 30° and 90° and speeds of 7.0–9.2 m s−1 at 550 –700 °C, in a laboratory fluidized-bed rig, to determine whether or not aluminized and chromized-aluminized diffusion coatings could protect the steel under such conditions. Erosion-oxidation damage was characterized by measurement of the mean thickness changes using a micrometer and examination of worn surfaces by scanning electron microscopy.Under most conditions, the coatings provided some protection to the substrate: under 30° impacts, up to 650 °C, and under 90° impacts, at 700 °C, both coatings were effective, whereas under 90° impacts, up to 650 °C, only the chromized-aluminized coating gave significant protection. However, for 30° at 700 °C, the oxide scale on the substrate was protective and the coatings were not needed. Explanations for these observations are presented in this paper, in terms of interactions between the erosion and oxidation processes for the materials.

The tribological properties of nitrogen implanted Ti-5Al-2Nb-1Ta orthopaedic alloy was studied by performing lubricated pin on disc tests against ultra high molecular weight polyethylene pins. The results were interpreted on the basis of friction coefficient, wear volume loss and by characterising the wear debris to understand the wear mechanism. The results indicated a decrease in wear rate for implanted samples. Detailed investigations of the dose dependence on wear performance were carried out. The friction and wear data show a clear transition in wear modes between implanted and unimplanted alloys. The wear debris confirms the presence of titanium oxide and titanium oxynitride phases for untreated and nitrogen implanted alloy.

The effect of load range of 30–100 N and speed range of 3–12 m/s on the wear and friction behavior of sand cast brake rotor made of A359-20 vol% SiC particle composites sliding against automobile friction material was investigated. Dry sliding frictional and wear behavior were investigated in a pin-on-disc type apparatus. Automobile friction material was used as pin, while the A359-20 vol% SiC particle composites formed the rotating disc. For comparison, the wear and friction behavior of commercially used cast iron brake rotor were studied. The results showed that the wear rate of the composite disc decreased with increasing the applied load from 30 to 50 N and increased with increasing the load from 50 to100 N. However, the wear rate of the composite disc decreased with increasing the sliding speed at all levels of load applied in the present work. For all sliding speeds, the friction coefficient of the composite disc decreased with applied load. The worn surfaces as well as wear debris were studied using scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analyzer and X-ray diffraction (XRD) technique. At load of 50 N and speed range of 3–12 m/s, the worn surface of the composite disc showed a dark adherent layer, which mostly consisted of constituents of the friction material. This layer acted as a protective coating and lubricant, resulting in an improvement in the wear resistance of the composite.

En steel, in untreated and thermal treated conditions, with and without shot peening, were tested in a back-to-back gear test rig. Their contact fatigue characteristics were studied and S–N curves have been established. Contact fatigue strength of shot peened gears for a given life showed an improvement in relation to unpeened gears.

The effects of heat treatment, involving solutionizing at temperature of 370 °C for a relatively short period of time (3 or 5 h), followed by quenching in water, on tribological behavior of ZA-27 alloys were examined.Dry sliding wear tests were conducted on as-cast and heat-treated ZA-27 samples using block-on-disk machine over a wide range of applied loads. To determine the wear mechanisms, the worn surfaces of the samples were examined by scanning electron microscopy (SEM). The tribological results were related to the microstructure and mechanical properties.The heat treatment resulted in reduction in the hardness and tensile strength but increase in elongation. The heat-treated alloy samples attained improved tribological behavior over the as-cast ones, both from the aspects of friction and wear. The improved tribological behavior of the heat-treated alloys, in spite of reduced hardness, could be the result of breaking the dendrite structure, when the fraction of interdendrite regions was considerably decreased and a very fine α and η mixture was formed at the same time. The wear response of the samples has been corroborated through characteristics of worn surfaces and dominant wear mechanisms.

In this work, four ingots of Zn–40Al–2Cu–2Si alloy were produced by permanent mould casting. Two of the ingots were subjected to quench-ageing treatment. After examining the microstructure and some mechanical properties of the alloy in both as-cast and heat treated conditions, its friction and wear behaviour were investigated over a range of pressure and sliding speed using a conforming block-on-ring type machine without oil supply which corresponds to “oil cut off”.It was observed that the heat treatment increased the hardness and tensile strength of the alloy. It was also observed that in the case of oil cut off the friction coefficient of the alloy decreased with increasing pressure up to approximately 3 MPa above which the trend reversed. However, the friction coefficient increased with increasing sliding speed after showing a small decrease with it, and the temperature of the wear sample increased with both pressure and sliding speed. It was shown that the wear loss of the alloy increased exponentially with pressure, but linearly with sliding speed. However, the increase in wear loss with sliding speed became exponential at pressures above 4 MPa.As a result of this work, it was concluded that the quench-ageing treatment does not increase only the hardness and tensile strength of Zn–40Al–2Cu–2Si alloy but also its wear resistance during running without oil supply.

A computational analysis is conducted on a solid–liquid–solid interface: a rough, elastic surface is brought into contact with rigid flat while being influenced by an intervening liquid film of fixed volume. The problem is solved (iteratively) by satisfying the equations of elasticity and capillarity, while conserving liquid volume and honoring the constraints of no surface interpenetration and no negative pressures at dry contact points. As the liquid volume is increased from low values, a critical condition is reached whereby there are sudden increases in the values of certain output parameters, such as tensile force and wetted length. For the smaller values of surface roughness, the critical point is associated with a near complete collapse of the surface topography.

The present study concerns development of a hard in situ boride-dispersed composite layer on the surface of AISI 304 stainless steel substrate to improve the wear resistance property. Laser processing was carried out by melting the surface of sand-blasted AISI 304 stainless steel substrate using a continuous wave CO2 laser and simultaneous deposition of a mixture of K2TiF6 (potassium titanium hexafluoride) and KBF6 (potassium hexafloroborate) (in the weight ratio of 2:1) using Ar as shrouding environment. Powder feed rate was maintained constant at 4 g/min. Irradiation results in dissociation of a pre-deposited mixture along with a part of the stainless steel substrate, intermixing and rapid solidification to form the composite layer on the surface. The micro-structure of composite layer consists of dispersion of titanium boride particles in AISI 304 stainless steel matrix. Volume fraction of particles is found to be uniform throughout the composite layer, though varied with laser parameters. The micro-hardness of the surface was improved 250–350 VHN as compared to 220 VHN of the AISI 304 stainless steel substrate with a significant improvement in wear resistance property. The mechanism of wear was found to be a combination of adhesive and abrasive in as-received stainless steel. However, it was predominantly abrasive for laser composite surfaced stainless steel.

Along with the extensive application of polymers for tribological purposes, the understanding of polymer tribology is becoming increasingly important. A broad overview of the general area of polymer tribology is presented in this paper. The progress in understanding the field over the past decade is reviewed under the three topics of rubber tribology, plastic tribology and tribology of polymer composites. It is hoped that this paper will serve as a valuable source of reference for future tribologists.

The friction and wear behaviour of 316 stainless steel in CO2 has been investigated in the load range 8–50 N from 20 to 600°C. Wear transitions occurred at all temperatures but were load-dependent. At and below 300°C, wear transitions only took place at low loads, whereas above 300°C transitions were observed at all loads. The low temperature wear transition, representing an order of magnitude decrease in wear rate, was associated with a change in friction behaviour. The friction force across the specimen was initially widely fluctuating but after a time, which did not necessarily coincide with the wear transition, became much smoother. The smoother sliding is thought to indicate a trend to oxide-oxide contacts. At higher temperatures wear transitions result in a two orders of magnitude reduction in wear. The corresponding friction transition was similar to the low temperature friction change but also included a marked temporary drop in the coefficient of friction.Pits or troughs up to 450 μm deep were seen in wear scars above 400°C. It is proposed that isolated sections of grooves formed during the initial stages of wear become back-filled with loosely adhering oxide particles. These troughs are then further deepened, possibly by abrasive fretting action of the semi-fluid oxide material.

The present study concerns development of SiC dispersed (5 and 20 wt%) AISI 316L stainless steel metal–matrix composites by direct laser cladding with a high power diode laser and evaluation of its mechanical properties (microhardness and wear resistance). A defect free and homogeneous composite layer is formed under optimum processing condition. The microstructure consists of partially dissociated SiC, Cr3C2 and Fe2Si in grain refined stainless steel matrix. The microhardness of the clad layer increases to a maximum of 340 VHN (for 5% SiC dispersed) and 800 VHN (for 20% SiC dispersed) as compared to 150 VHN of commercially available AISI 316L stainless steel. Direct laser clad SiC dispersed AISI 316L stainless steel has shown an improved wear resistance against diamond surface with a maximum improvement in 20% SiC dispersed AISI 316L stainless steel. The mechanism of wear was predominantly abrasive in nature.

A tribological analysis of deformations and stresses generated and their influence on crack generation and surface fracture in a coated surface loaded by a sliding sphere in dry conditions is presented. A three-dimensional finite element method (3D FEM) model has been developed for calculating the first principal stress distribution in the scratch tester contact of a diamond spherical tip with 200 μm radius sliding with increasing load on a 2 μm thick titanium nitride coated steel surface. The model is comprehensive in that sense that it considers elastic, plastic and fracture behaviour of the surfaces. The hard coating will be stretched and accumulates high tensile stresses. At the same time, it is carrying part of the load and thus reducing the compressional stresses in the substrate under the sliding tip. The first crack is initiated at the top of the coating from bending and pulling actions and it grows down through the coating. The fracture toughness of the coating is calculated by identifying from a scratch test experiment the location of the first cracks and the crack density and using this as input data.

A finite-element approach to thermoelastohydrodynamic lubrication analysis is developed by extending a previous mass- and energy-conserving algorithm to include wall-convection boundary conditions, groove-mixing theory, and thermo-mechanical deformations. To this end, the cross-film-averaged energy equation is coupled with the heat conduction equations relevant to the bearing sleeve and the journal by fitting the temperature profile across the film thickness with a fourth-order polynomial. A finite-element condensation technique is used to reduce the unknowns in heat conduction equations in the bush and in the journal to the temperatures of the sleeve surface and journal axis, respectively. Applied to the analysis of steadily loaded journal bearings, the proposed method shows good agreement with published experimental results and incurs low computational cost.

The multipass strip drawing tests of sheet metal car body parts in cylinder/sheet/cylinder contact geometry is particularly well adapted to the simulation of sheet/tool contact conditions during a stamping operation. Within this framework, a rough sheet rubs against a smooth tool. During the sliding contact, a modification in the average size of plateaus appears, the locations where the shear stress and normal pressures are transmitted. Owing to a profilometrical relocation technique between each tool passage, we use statistical parameters corresponding to the average width and length of the plateaus. The observed flattening of the plateaus and the quantity of free wear particles modifying the third body in the contact are particularly more important in the case of aluminum sheets than in those of mild steel sheets.

A global approach coupling experiments and numerical modeling is proposed to enhance crack prediction. Fretting tests have been conducted under conditions leading to crack formation. Three dimensional crack shapes have been reconstructed from metallographic cross-sections and described with level set functions. They are then used as input data in 3D two-scale X-FEM model detailed in this paper. Frictional contact conditions holding between the crack faces are accounting for. The methodology developed to describe those contact conditions at the pertinent scale is detailed.A 3D fretting fatigue test is modeled to illustrate the coupling between experiments and numerical modeling.

The scratch behavior of a thermoset solid polymer exhibiting brittle behavior in tension is investigated. The surfaces are scratched and an imaging system is used to record real time photographs. The 3D crack pattern is analyzed using fluorescence confocal laser scanning microscopy. A finite element simulation is performed to determine the indenter/specimen contact conditions. They are used as input data for the 3D crack network analysis based on combined 3D localized multigrid and X-FEM/level set techniques. The computed stress distributions within the 3D cracked specimen are of great interest to understand the crack network formation observed during the experiments.

The aim of this work is to propose a characterization method of dental enamel topography through quantitative analysis by 3D profilometry, to allow relating changes in enamel texture with active wear mechanisms. Four extracted teeth, including an intact third molar tooth, were evaluated. The bearing area ratio curve was obtained and the functional and spatial parameters Spk, Sk, Svk and Str were extracted. Abrasive wear mechanism tended to increase the amplitude of irregularities until a certain point, when the material removal was capable of reaching the central zone of enamel, where the hydroxyapatite prisms are randomly oriented. The action of chemical agents was also observed, even when the abrasive wear was predominant. A relationship may exist between the variation of the irregularities’ directional pattern and the wear mode. The study presents micrographs of the analyzed surfaces to support the discussion.

One binary Al–40Zn and five ternary Al–40Zn–Cu alloys with different copper contents were prepared by permanent mould casting. Their microstructure and mechanical properties were investigated in as-cast state. Friction and wear properties of the ternary alloys were studied using a conforming block-on-disc type tester. The results obtained were compared with those of SAE 65 bearing bronze.The microstructure of Al–40Zn–Cu alloys consisted of aluminium-rich α dendrites surrounded by eutectoid α+η phases and θ (CuAl2) particles. Hardness of the ternary alloys increased continuously with increasing copper content, but their tensile strength decreased above 3% Cu. Friction coefficient and temperature of the Al–40Zn–Cu alloys and bronze increased in the initial period of run. This was followed by a reduction in the properties and attainment of constant levels afterwards. However, volume loss of the alloys increased rapidly at the beginning of the test run and reached almost constant levels after a sliding distance of approximately 400 km. The Al–40Zn–Cu alloys were found to be much superior to the SAE 65 bronze, as far as their wear resistance is concerned. Among the alloys tested, highest strength and wear resistance were obtained with the Al–40Zn–3Cu alloy.

Sheet metal forming of tribologically difficult materials such as stainless steel, Al-alloys and Ti-alloys or forming in tribologically difficult operations like ironing, punching or deep drawing of thick plate requires often use of environmentally hazardous lubricants such as chlorinated paraffin oils in order to avoid galling. The present paper describes a systematic research in the development of new, environmentally harmless lubricants focusing on the lubricant testing aspects. A system of laboratory tests has been developed to study the lubricant performance under the very varied conditions appearing in different sheet forming operations such as stretch forming, deep drawing, ironing and punching. The laboratory tests have been especially designed to model the conditions in industrial production. Application of the tests for evaluating new lubricants before introducing them in production has proven successful and has in a number of examples assisted the substitution of environmentally hazardous lubricants by more friendly ones in industrial production.

Microstructural changes occurring during scuffing failure in hardened 4340 steel were studied with a block-on-ring test rig using a step-loading test protocol. Tests were interrupted before, during, and after scuffing. Both surface and sub-surface changes in the original tempered microstructure were characterized by scanning electron microscopy. Results of our study showed that scuffing occurred by severe and sudden plastic deformation of near-surface material in a sub-second time frame. Based on this observation and other previously observed microstructural changes, i.e. formation of a large fraction of retained austenite during scuffing, a scuffing mechanism based on adiabatic shear instability is proposed. The proposed scuffing mechanism can effectively explain most of the phenomenological observations associated with scuffing failure.

This paper presents a study concerning the influence of the amount of metallic nanoparticles on the wear behaviour of Fe0.5–Cr0.5–alumina nanocomposites rubbing on Ti–6Al–4V in fretting. Due to the elaboration process (metal–oxide nanopowder prepared by selective reduction in hydrogen of oxide solid solution and densified by spark plasma sintering), these materials generally own two sorts of nanoparticles: the intragranulars (size: ) located within the alumina grains and the intergranulars (size: ) located at the grain boundaries. This paper focuses on the role of each sort of nanoparticles with respect to the wear of the nanocomposite. Results show that the presence of intergranular nanoparticles is crucial for improving the wear resistance of nanocomposites whereas the intragranulars rather improve the mechanical properties of matrix grains. The lowest wear rate of the nanocomposite is obtained when the amount of intergranulars is about 3.5 wt%. Finally, the fretting wear mechanism of nanocomposites and the mechanism enabling to prevent it by using nanoparticles are both identified and discussed.

A study was conducted to quantify fretting fatigue damage and to evaluate the residual fatigue strength of specimens subjected to a range of fretting fatigue test conditions. Flat Ti–6Al–4V specimens were tested against flat Ti–6Al–4V fretting pads with blending radii at the edges of contact. Fretting fatigue damage for two combinations of static average clamping stress and applied axial stress was investigated for two percentages of total life. Accumulated damage was characterized using full field surface roughness evaluation and scanning electron microscopy (SEM). The effect of fretting fatigue on uniaxial fatigue strength was quantified by interrupting fretting fatigue tests, and conducting uniaxial residual fatigue strength tests at R=0.5 at 300 Hz. Results from the residual fatigue strength tests were correlated with characterization results.While surface roughness measurements, evaluated in terms of asperity height and asperity spacing, reflected changes in the specimen surfaces as a result of fretting fatigue cycling, those changes did not correspond to decreases in residual fatigue strength. Neither means of evaluating surface roughness was able to identify cracks observed during SEM characterization. Residual fatigue strength decreased only in the presence of fretting fatigue cracks with surface lengths of 150 μm or greater, regardless of contact condition or number of applied fretting fatigue cycles. No cracks were observed on specimens tested at the lower stress condition. Threshold stress intensity factors were calculated for cracks identified during SEM characterization. The resulting values were consistent with the threshold identified for naturally initiated cracks that were stress relieved to remove load history effects.

The wear behavior of low-cost, lightweight 10 wt% titanium carbide (TiC)-particulate-reinforced Ti–6Al–4V matrix composite (TiC/Ti–6Al–4V) was examined under fretting at 296, 423, and 523 K in air. Bare 10 wt% TiC/Ti–6Al–4V hemispherical pins were used in contact with dispersed multiwalled carbon nanotubes (MWNTs), magnetron-sputtered diamond-like carbon/chromium (DLC/Cr), magnetron-sputtered graphite-like carbon/chromium (GLC/Cr), and magnetron-sputtered molybdenum disulfide/titanium (MoS2/Ti) deposited on Ti–6Al–4V, Ti–48Al–2Cr–2Nb, and nickel-based superalloy 718. When TiC/Ti–6Al–4V was brought into contact with bare Ti–6Al–4V, bare Ti–48Al–2Cr–2Nb, and bare nickel-based superalloy 718, strong adhesion, severe galling, and severe wear occurred. However, when TiC/Ti–6Al–4V was brought into contact with MWNT, DLC/Cr, GLC/Cr, and MoS2/Ti coatings, no galling occurred in the contact, and relatively minor wear was observed regardless of the coating. All the MWNT, DLC/Cr, GLC/Cr, and MoS2/Ti coatings on Ti–6Al–4V were effective from 296 to 523 K, but the effectiveness of the MWNT, DLC/Cr, GLC/Cr, and MoS2/Ti coatings decreased as temperature increased.

A study has been made of the sliding wear behaviour of untreated and ion implanted ultra high molecular weight polyethylene (UHMWPE) against a surface modified titanium alloy (Ti-6Al-4V) using a pin on disc apparatus. It was found that the presence of water lubrication and a very smooth counterface was necessary to maintain low wear rates of the UHMWPE. A ‘zero wear’ effect was observed when nitrogen implanted UHMWPE was tested against very smooth counterfaces (Ra ≈ 0.03 μm) of either surface oxidized or nitrogen implanted Ti-6Al-4V under water lubrication. The enhanced mechanical and physical properties of the surface treated materials are believed to be responsible for the improved wear performance.

A novel method to increase the adhesion strength of pure carbon coatings on Ti-6Al-4V biomaterials is reported. In the early stage of the experiment, ion implantation of carbon was carried out by metal vapour vacuum arc (MEVVA) in order to create a gradient composition interlayer in the Ti-6Al-4V substrate for subsequent coating depositions. The pure carbon coatings were deposited in a closed-field unbalanced magnetron sputtering system. It was found that the coatings prepared on the carbon-implanted substrates could provide a significant enhancement of adhesion strength, impact and wear resistance. The greatly increased performance could be explained by the increase in hardness of the carbon-implanted substrate and the formation of Ti–C bonds.

This paper describes testing of Ti–6Al–4V coupons in fretting fatigue and compares the effects of mechanical surface treatments on performance. Fretting fatigue tests were performed using a proving ring for fretting load, bridge-type fretting pads, and applied tension–tension cyclic fatigue stress. As-machined (AM), shot peened (SP), and laser peened (LP) coupons were evaluated, and data generated to compare residual stress, surface condition, lifetime, and fractographic detail encountered for each. Near-surface residual stress in SP and LP coupons was similar. The layer of compressive residual stress was far deeper in LP coupons than in SP coupons and, consequently, subsurface tensile residual stress was significantly greater in LP coupons than in SP coupons. SP coupons exhibited a rough surface and had the greatest volume of fretting-induced wear. LP coupons exhibited a wavy surface and had a small volume of wear localized at wave peaks. SP coupons had the greatest fretting fatigue lifetime, with significant improvement over AM coupons. Lifetimes of LP coupons were similar to those for SP coupons at high fatigue stress, but fell between AM and SP coupons at lower fatigue stress. Fractographic evaluation showed that fractures of AM samples were preceded by initiation of fretting-induced cracks, transition of a lead fretting crack to mode-I fatigue crack growth, and crack growth to failure. SP and LP samples exhibited behavior similar to AM samples at high fatigue stress, but in coupons tested at low stress the lead crack initiated subsurface, near the measured depth of maximum tensile residual stress, despite the presence of fretting-induced cracks. The level of fatigue stress above which lead cracks were initiated by fretting was higher for LP than for SP, and was predicted with good accuracy using an analysis based on linear elastic fracture mechanics, the fatigue crack growth threshold stress intensity factor range, and superposition of measured residual stress and applied fatigue stress.

Wear behaviour of 52100 low alloy steel has been studied on a pin on disc wear machine at disc temperatures ranging from room temperature to 500°C. Transitions occur in the wear rate versus load curves at certain critical loads, the magnitude of which increase with temperature. These transitions were found to be associated with change in surface oxide, lower wear rates being recorded when the predominant oxide was the spinel Fe3O4 for all temperatures. At disc temperatures above 300°C out of contact oxidation appears to be the most important wear limiting factor. A surface model was developed enabling contact temperature, numbers and size of contacts and critical oxide film thickness to be deduced. Remarkable agreement was found between oxide thicknesses estimated from this model and measured values using a scanning electron microscope

The friction and wear behaviors of (Ca, Mg)-sialon/SAE 52100 steel pair under the lubrication of water or various polyol aqueous solutions were investigated with an SRV friction and wear tester in a ball-on-disc configuration. This was conducted to simulate the effect of polyols as aqueous additive in machining sialon ceramic. The morphologies of and elemental distributions in the worn surfaces of the lubricated sialon ceramics and counterpart steel were observed and determined with scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). All solutions of the tested polyols decreased the friction coefficient of (Ca, Mg)-sialon/SAE 52100 steel effectively and increased the wear volume loss of (Ca, Mg)-sialon to some extent as compared with dry sliding. The friction coefficients under the lubrication of distilled water and various polyols aqueous solutions of polyols showed almost no difference, and propanetriol was found to be the most effective for machining (Ca, Mg)-sialon with the concentration of polyols in water fixed as 5 wt%. The friction coefficients under the lubrication of propanetriol aqueous solutions in varied concentrations are closely related with the concentration, which came to the lowest value of 0.04 at a concentration of 75%. The friction-reducing performance of the polyols as additives in water was roughly correlated with their wetting behaviors on the sialon ceramic surface. In other words, the higher the wetting ability is, the lower the friction coefficients will be. Moreover, the wear volume losses of (Ca, Mg)-sialon also varied with the variation in the concentration of propanetriol in water. Accounting for the friction-reduction and wear behavior, 20% concentration of propanetriol in water could be recommended for machining (Ca, Mg)-sialon. Electron microscopic analysis indicates that polyols as additives in water enhanced the corrosive wear of sialon ceramic, which could be beneficial for increasing the machining efficiency. There existed interactions among water, polyols and sialon surfaces, which were dependent on the compositions of the lubricant solution. This accounts for the variations in the friction and wear behaviors with the concentration of polyols in water.

The objective of this study was to analyse the erosion of API 5L X65 pipe steel whose microstructure consisted of ferrite and martensite obtained by quenching from intercritical temperature (770°C). Jet impingement tests with sand–water slurry were used. The changes in mechanical properties, caused by heat treatment carried out, did not induce changes in either the mechanism or erosion resistance. The erosion rate increased with angle of attack until 30° and later decreased until 90°. The microtexture of the eroded surfaces, at angles of attack of 30° and 90°, were similar for both conditions and were composed of craters and platelets at several stages of evolution. The erosion mechanism was by extrusion with the forming and forging of platelets.

An experimental setup has been developed to conduct fretting fatigue tests at 610 °C and fretting fatigue lives are characterized for the contacting pair of IN100 and single crystal nickel subjected to a range of loading conditions. A well characterized set of experiments have been conducted to obtain the friction coefficient in the slip zone. A robust quasi-analytical approach, based on solution to singular integral equations, has been used to analyze the contact stresses. Different multi-axial fatigue parameters have been investigated for their ability to predict the initiation life of the specimens. An estimation of crack propagation life was made using conventional fracture mechanics approaches, after making certain assumptions to simplify the problem. Total life was predicted using nucleation life from different parameters and propagation life from conventional fracture mechanics approach. These predicted lives were compared with experimentally observed failure lives. The quality of the comparison provides confidence in the notion that conventional life prediction tools can be used to assess fretting fatigue at elevated temperatures.

The friction and wear behavior of Inconel 600 against AISI 52100 steel have been studied in the presence of three ionic liquid (IL) lubricants, two imidazolium derivatives, 1-methyl-3-octylimidazolium tetrafluoroborate (L108) and 1-methyl-3-hexylimidazolium hexafluorophosphate (L-P106), and the quaternary ammonium chloride AMMOENG™101 (AM-101), and compared with a mineral base oil at room temperature. The IL lubricants have been studied at high temperature. While the ammonium derivative has been used at 100 and 200 °C, the higher thermal stability of the imidazolium derivatives allows them to be used up to 300 °C. The results show that the imidazolium derivatives are the best lubricants at all temperatures. A temperature increase from 100 to 200 °C reduces wear rates for all ILs due to a transition form abrasive to adhesive wear and formation of a tribolayer on the Inconel wear track. At 300 °C, the hexafluorophosphate derivative produces tribocorrosion attack on the steel ball and severe wear of Inconel 600 due to decomposition of the IL. The wear mechanisms and surface interactions are discussed in terms of IL-metal surface interactions from SEM, EDX and XPS data.

An investigation was performed to determine the influence of water vapour, oxygen and water in various environments on the friction and wear of a brass in contact with itself during fretting corrosion. A cylinder- against-flat type of fretting test rig was used and fretting experiments were carried out in various environments: wet air of various humidity levels, dry air, wet argon, dry argon and ion-exchanged water. In this study, a larger amplitude of relative slip was used to expose sufficiently the fretting surfaces to the surrounding environment. Oxygen, water vapour and water reduced the coefficient of friction during fretting. Wear debris showed a tendency to egress from the contact area with the increasing content of water vapour in air. Thus the wear rates increased with absolute humidity along the same curve at three room temperatures. When oxygen or water vapour existed alone in the environment, the effect of oxygen on wear was greater than that of water vapour. When both oxygen and water vapour existed simultaneously in the environment, as in wet air, the combined effect of them on wear was observed resulting in a marked increase in wear rate.

This article describes the dry sliding wear of 6061 aluminium alloy and composites containing up to 14 vol.% of graphite particle dispersions prepared by a power metallurgy route. Experiments were carried out with pin specimens against an EN25 steel disc using a pin-on-disc apparatus. The effects of varying sliding speed and distance, applied pressure and material characteristics, as well as the amount of graphite, on the dry sliding behaviour have been evaluated. The wear rates of the composites increased with increasing amounts of graphite. This anomalous behaviour has been attributed to the increased porosity (interconnected and interfacial) in the composites. SEM examination of the worn surfaces did not reveal the presence of graphite film on them. Most of the wear debris were flaky in nature.

The tribocorrosion behaviour of overlay welded Ni–Cr 625 alloy sliding against alumina in 0.5 M H2SO4 and 0.5 M HNO3 solutions under potentiostatic conditions was investigated. The passivation of the samples in the two electrolytes at different potentials (−1.5, −0.3 and +0.3 VMSE) was studied by means of potentiodynamic polarization curves and XPS. The tribocorrosion behaviour of the alloy in sulphuric acid was similar to the behaviour of stainless steels found in other studies, with much lower wear at cathodic potential compared to passive conditions. However, the behaviour in nitric acid was highly influenced by the reduction of nitric acid at the electrode–electrolyte interface. This reaction leads to the oxidation of the alloy even at cathodic potential. This feature influenced the tribocorrosion properties of the alloy in nitric acid, the wear rate at cathodic potential being in the same range as at passive potentials.

An investigation into the effect of fibre reinforcement on the friction and wear of PA66 in rolling–sliding contact is reported. Three types of short fibre—aramid, carbon and glass—were examined with the composites running against identical materials in a twin disc machine. It was found that the aramid-fibre reinforcement did not significantly alter the friction of the matrix material. However, both the carbon-fibre and glass-fibre reinforcement reduced the coefficient of friction substantially. Wear of the aramid- and carbon-fibre composites was essentially linear with time and generally around ten times greater than that of the unreinforced material. The wear of the glass-fibre composite was complex with an initial period where the wear rate was similar to that of the unreinforced material. After a significant depth of wear had occurred the wear rate changed to a value similar to, but slightly higher than, that of the other reinforced materials.It appears that one of the major benefits of introducing fibre reinforcement, particularly glass, is that it reduces the coefficient of friction and hence allows the material to be used for higher duties without exceeding the softening point of the matrix. This increase in duty is, however, at the expense of an increased wear rate and shorter component life.

Cobalt-based alloys are often used for bearing applications, especially at elevated temperatures. One of the newly developed 700 series cobalt-based alloys, Stellite 712, has been demonstrated to possess high resistance to wear and corrosion in aggressive environments. Continuous efforts have been made to further improve this alloy for enhanced resistance to high-temperature wear involving oxidation. Recent studies showed that the improvement of the oxide scale on Co-base alloys by alloying with yttrium was an effective way to diminish wear of the alloys at elevated temperatures.In this work, sliding wear performances of yttrium-free and yttrium-containing Stellite 712 samples at elevated temperatures were evaluated. The mechanism responsible for changes in its wear performance was investigated by studying the effects of alloying yttrium on microstructure and mechanical properties of the bulk alloy and its oxide scale, employing various experimental methods including micro- and nano-mechanical probing, XRD, SEM-EDS, AFM and high-temperature pin-on-disc wear testing. The research demonstrated that alloying a small amount of yttrium (e.g. less than 1%Y) rendered the oxide scale on Stellite 712 stronger with higher adherence to the substrate, which was largely beneficial to the wear performance of the alloy at elevated temperatures. Mechanisms involved are discussed in this article.