Wear of polyethylene (UHMWPE) is dependent on cross-shear. The aim of the present study was: 1) to develop a theoretical description of cross-shear, 2) to experimentally determine the relationship between cross-shear motion and UHMWPE wear using a wheel-on-flat apparatus, and 3) to calculate the work it takes to remove a unit volume of wear for the use in advanced computational models of wear. The theoretical description of cross-shear has been based on the previously reported finding that cross-shear is maximal when movement occurs perpendicular to fibril orientation. Here, cross-shear is described with a double-sinusoidal function that uses the angle between fibril orientation and velocity vector as input, and maximum cross-shear occurs at 90° and 270°. In the experimental part of the study, friction and wear of polyethylene were plotted against increasing sliding velocity vector angles, i.e. increasing cross-shear. It was found that wear intensified with increasing cross-shear, and wear depth could be predicted well using the double-sinusoidal function for cross-shear (r(2)=0.983). The friction data were then used to calculate the work to remove a unit particle by integrating the frictional force over the directional sliding distance. Using the wear volumes, determined for both longitudinal and perpendicular motion directions, the work to remove a unit volume of material was qy = 8.473 × 10(8) J/mm(3) and qx = 1.321 × 10(8) J/mm(3), respectively. Hence, 6.4 times more work was necessary to remove a unit wear volume in the direction of principal motion (i.e. along the molecular fibril orientation) than 90° perpendicular to it. In the future, these findings will be implemented in computational models to assess wear.
Damping characteristics and frequency characteristics of ferro fluid bearing (FFB) spindles were measured using a high-frequency vibration base driven by a piezo actuator. Using the high-frequency vibration base, high-frequency excitation was added to ferro fluid bearing spindles mounted on the vibration base, and it was proved that ferro fluid bearing spindles have effective damping. And the damping effect became larger with higher spindle rotational speed. Also we have measured spindle runout of a ferro fluid bearing spindle using a lock-in amplifier to increase S/N ratio and succeeded to measure nano meter order displacements.
A modeling study with bench apparatus was conducted with connector
contact materials consisting of electroplated hard gold and gold flashed
palladium on nickel underplatings mated to a clad noble metal. The clad
metal contact was the “rider”, i.e., had the smaller surface
involved in sliding compared to the plated “flat” surface.
This configuration is consistent with good engineering practice in
commercial products. It was found that although a lubricant could reduce
friction significantly and virtually eliminate adhesive transfer of
metal, a requirement for negligible wear, i.e., the absence of loose
particles, was that the plated surface be very smooth. If this contact
was rough, such as might occur due to it having a nodular nickel
underplate, tool marks, or burrs, abrasive wear of the cladding occurred
in proportion to the magnitude of roughness, However, when both contacts
were plated, lubricated wear was low and surface roughness was not a
significant factor. Unlubricated plated contacts wore severely with high
friction by the prow formation adhesive wear mechanism regardless of
their surface roughness
The origin of fatigue cracks in fretting fatigue is the boundary between the slip and non-slip areas in the contact region. They arise at this boundary because of the high stress concentration. When a crack is formed it relieves the stress concentration at this point, and the boundary between the slip and non-slip areas moves inwards, resulting in the initiation of another crack which propagates more rapidly than the first crack because of the higher stress concentration. Crack formation can be prevented or retarded by ensuring that slip occurs over the entire contact region.
Sursulf-treated low carbon steel gears were tested in a back-to-back gear test rig. The failure of the gears is by pitting and the contact stress-pitting life curve has been established. Wear particle analysis of the lubricating oil was carried out to analyse the nature of the failure. The study reveals that Sursulf treatment on low carbon steel gears considerably improves their performance. The cumulative wear particle concentration at the pitting limit has been suggested as a basis for predicting the onset of failure of the gears.
Fretting wear was investigated to clarify its mechanism at high temperature. Two materials, 0.45% C steel and austenitic stainless steel, were examined and experiments were carried out in air under a load of 30 N using linear oscillations 150 μm in amplitude with a frequency of 16.6 Hz. The temperature was varied in the range 20 – 650 °C.It was found that wear decreased with increasing temperature up to 300 °C. The adhesive transfer of oxide, which was identified as Fe3O4 by X-ray microanalysis, was detected at high temperatures. The mechanisms of wear debris formation and transfer are discussed from the observations of wear scars and debris by scanning electron microscopy. A new model based on fracture mechanics is proposed for the formation of flake-like oxide debris.
The present investigation of a unidirectionally abraded pearlitic (0.4 wt%C) steel and the steel with vanadium addition (0.1 wt%V) elucidates the work hardening and the reorientation near the surface layer caused by abrasion, particularly its relation to the wear behavior. The abraded surfaces were examined with a nanoindentation apparatus to evaluate the variation of nanohardness and elastic modulus with depth below sliding contact on a nanometer scale. It has been found that the wear rate of each specimen was almost equal, although the nanohardness of the abraded surface of the vanadium addition steel was lower than that of the vanadium free one. The elastic modulus of the vanadium free steel increased with decreasing the indentation depth below the abraded surface to about 1.3 times the original value (∼200 GPa), while the vanadium addition steel was constant. The varying nature of influence of interlamellar spacing and the vanadium addition on the wear response of the pearlitic steel has been discussed in terms of the ratio between hardness and elastic modulus of the abraded surface which corresponds to a plasticity factor.
A plain carbon (0.5% C) steel was subjected to various heat treatment cycles to produce a variety of microstructures. Low stress abrasion tests were conducted using an ASTM standard rubber wheel abrasion test apparatus. Crushed silica sand particles were used as the abrasive medium. The wear loss decreased progressively with the number of test intervals until a steady state was reached. The steady state abrasion resistance was found to increase linearly with bulk hardness up to about 350 HV beyond which there was a marginal increase.Abrasion-induced changes were studied via metallographic examinations of transverse sections and hardness vs. depth (below the abraded surface) profiles. Abraded surfaces and wear debris were examined in a scanning electron microscope equipped with a wavelength-dispersive X-ray spectroscope. The hardened steel showed a large number of continuous and parallel grooves, while the annealed specimen revealed a considerable amount of micropitting in addition to the grooves. Wear debris from the annealed specimen was mainly of the flake type, while long micromachining chips of the “card-deck” type were observed in the case of the hardened steel. The results of this study revealed that the material removal mechanisms during abrasion of steels are controlled by the properties of a layer beneath the abraded surface. The properties of this layer are in turn governed by the bulk microstructure.
The sliding wear behavior of an iron-base NOREM 02 hardfacing alloy was investigated in the temperature range of 25–300°C under a contact stress of 103 MPa (15 ksi). The wear resistance of NOREM 02 was comparable to that of Stellite 6 at temperatures below 180°C, and the dominant wear mechanism was mild oxidative wear. With increasing temperature, however, the wear mode of NOREM 02 changed abruptly to severe adhesive wear at 190°C and galling occurred above 200°C. It was found from microhardness variations beneath the worn surfaces that the abrupt decrease of wear resistance is due to the loss of work hardening ability. X-ray diffraction and TEM analyses of the worn surfaces showed that a strain-induced phase transformation from austenite to a′ martensite took place below 180°C while not above 190°C. Thus, it was concluded the development of strain-induced a′ martensite plays an important role in the wear resistance of an iron-base NOREM 02 hardfacing alloy.
Surface texture of a harder mating surface has a great influence on frictional behavior during sliding against softer materials. In the present investigation, experiments were conducted using a Pin-on-Plate inclined sliding tester to study the effect of the surface texture of hard surfaces on the coefficient of friction and transfer layer formation. 080 M40 (EN8) steel plates were ground to attain surfaces of different texture with different roughness. Pure magnesium pins were then slid at a sliding speed of 2 mm/s against the prepared steel plates. Scanning electron micrographs of the contact surfaces of pins and plates were used to reveal the morphology of transfer layer. It was observed that the coefficient of friction, formation of transfer layer, and the presence of stick–slip motion depend primarily on the surface texture of hard surfaces, but independent of surface roughness of hard surfaces. The effect of surface texture on coefficient of friction was attributed to the variation of plowing component of friction for different surfaces.
The cavitation erosion (CE) behavior of two kinds of Cr–Mn–N stainless steels was investigated by means of an ultrasonic vibration processor and compared with that of 0Cr13Ni5Mo stainless steel, commonly used material for hydraulic turbines in China. The eroded surfaces after different CE duration were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Roughness (Ra) of the eroded surfaces was calculated from the measured profiles after different CE duration, and microhardness of cross-sections of the tested materials was also measured to indicate work-hardening ability. The results show that the CE resistance of austenitic single phase or austenite–ferrite duplex phase Cr–Mn–N steels is higher than that of the 0Cr13Ni5Mo martensitic stainless steel, which is mainly attributed to their high work-hardening ability. Different from 0Cr13Ni5Mo stainless steel, the cracks initiating in the eroded austenite of Cr–Mn–N stainless steels propagate nearly parallelly rather than normally to the surface, which is also beneficial to the resistance to CE. Low ferrite content is also found to be beneficial to improving the resistance to CE of duplex phase Cr–Mn–N stainless steels. It is supposed that in the case of Cr–Mn–N stainless steels the cavitation impingement energy could be absorbed and transferred into the inside of materials by the “forming and transferring” mode of the high hardness layer. Developing steel with high work-hardening ability and low ferrite volume content is possibly an important method to design steel with high CE resistance.
An unusual combination of wear and corrosion resistance has been developed in cobalt and nickel base alloys known as Tribaloy∗∗ intermetallic materials. These two-phase alloys depend on the unique properties of a Laves intermetallic phase to resist wear under poor or unlubricated conditions from cryogenic temperatures to about 1000°C. The constituent elements are partitioned so that both the Laves intermetallic and the solid solution phases have generally good resistance to corrosion also. At higher chromium content the corrosion resistance is excellent in most environments.Parts can be fabricated by powder metallurgy, plasma spray coating, casting or hardfacing. Several wear tests are used to demonstrate the qualities of Tribaloy. Wear resistance was excellent at 25°, 315°, 650° and 980°C in air. Another wear test compares several Tribaloy compositions with other commercial, corrosion resistant alloys in 5% hydrochloric acid. Some examples of applications are described.
Friction and wear of 13 different materials with silicon nitride (Si3N4) matrix were investigated under unlubricated conditions. Tests were performed in laboratory air at sliding velocities between 0.03 and 5 m s−1 and at temperatures in the range of 22 to 1000°C. These materials were tested in the same test rig by means of the pin-on-disc configuration with self-mated couples to evaluate tribological influences of composition, structure and other properties, which were varied to reach friction coefficients below 0.2 and wear coefficients below 1 × 10−6 mm3 N−1 m−1.
The aim of this paper is the study of the tribological behavior of DLC-coated 100C6 couple vs. temperature. The DLC coatings studied belong to amorphous hydrogenated carbon coatings. The goal of this study is to characterize the friction coefficient evolution after 1 h tests vs. sliding velocity and contact pressure for several test temperature values. Tests were carried out for the pin-on-disc configuration under three normal loads, three sliding velocities and for test temperatures between room temperature and 400 °C. Results have shown that the DLC-coated 100C6-steel discs should not be used at temperatures higher than 200 °C. Coating damage strongly increases with high test temperature mainly due to stiffness reduction of 100C6-steel substrate.
Nylon 1010 composite specimens were prepared with MoS2 filler and short carbon fiber as the reinforcement. The friction and wear behavior of composite materials was investigated on a ring-block wear tester where sliding occurred under dry friction condition at a speed of 0.42 ms−1 under various loads. The results showed that the addition of carbon fiber was effective in reducing friction and wear of pure nylon, but MoS2 filler increased its wear. Wear and friction reduction were more significant while the carbon fiber was used as reinforcement along with MoS2 filler. The tribochemical studies by XPS revealed that MoS2 particles decomposed and MoO3, FeS, FeSO4 and Fe2(SO4)3 were produced during sliding. It was concluded that FeS, FeSO4 and Fe2(SO4)3 compounds could increase the adhesion between the transfer film and the counterface surface. The ability of the synergistic fillers in helping the formation of thin, uniform and continuous transfer film would contribute to the increase in wear resistance of nylon composites.
In the present work a series of systematic erosion tests were carried out to investigate the influence of impingement angle on erosion mechanisms of 1017 steel and high-Cr white cast iron using a slurry whirling-arm test rig. Scanning electron microscopy (SEM), image analysis system, optical microscopy as well as gravimetric and microhardness measurements were utilized to identify the slurry erosion process. Test results showed that, the effect of impingement angle on erosion mechanisms of 1017 steel has three regions. In the first region (θ ≤ 15°) shallow ploughing and particle rolling were the dominant erosion mechanisms, microcutting and deep ploughing in the second region (15° < θ < 75°), while indentations and material extrusion prevailed in the third region (θ ≥ 75°). For high-Cr white cast iron the test results showed that, the erosion mechanisms involved both plastic deformation of the ductile matrix and brittle fracture of the carbides. At low impingement angles (up to 45°) observations of microphotographs of the impacted surfaces revealed that, plastic deformation of the ductile matrix was the dominant erosion mechanism and the carbides fracture was negligible which lead to small erosion rate. Whereas, at high impingement angles (greater than 45°) gross fracture and cracking of the carbides were the main erosion mechanisms in addition to indentation with extruded lips of the ductile matrix.
The abrasive wear properties of the alloys produced by the laser surface alloying of chromium onto AISI 1018 steel substrates were studied in the present paper. The low carbon steel samples were chromium electro-deposited using conventional electroplating techniques and a laser beam was used to melt the surfaces to produce the alloying effects. The chromium coating thickness, laser power and working speed were varied and their effects on the wear resistance of the alloying produced were investigated. The conducting dry sand-rubber wheel abrasion test was adopted and the weight loss measured to evaluate the wear properties. Scanning electron microscopy was used to characterize the worn surfaces of the alloyed specimens. The results show that the weight loss decreases with increasing chromium content, melted depth and hardness. The width and depth of the wear scratches decrease as the wear resistance properties increase.
The purpose of the present investigation is to evaluate the effect of Venturi throat velocity on the cavitation erosion of specimens for constant cavitation number, which is here based on Venturi discharge conditions. 1018 carbon steel and 1100-O aluminum were tested in the University of Michigan high speed cavitation tunnel with tap water at 27 °C (80 °F). Results of present tests are consistent with previous work done at the University of Michigan, showing that the velocity-damage exponent varies over the range ±1–5 for the velocity range 10–49 m s−1.
The resistance to sliding abrasion was determined for a 1040 steel. Specimens were either hardened and tempered or cooled to produce various ferrite-pearlite structures. For the hardened and tempered condition the abrasion resistance follows a Hall-Petch relation with the cementite particle spacing. For the ferrite-pearlite structures the abrasion resistance is proportional to the volume fraction of pearlite present.It is shown that the bulk hardness, the microhardness of the abraded surface and the abrasion resistance all are interrelated via the material's stress-strain curve. The strain corresponding to abrasion was found to be 4.8 and the portion of the cutting work which is directly involved in the chip formation to be 18.5%.
In all machining operations, tool wear is a natural phenomenon and it eventually leads to tool failure. The growing demands for high productivity of machining need use of high cutting velocity and feed rate. Such machining inherently produces high cutting temperature, which not only reduces tool life but also impairs the product quality particularly when the work piece is quite strong, hard and heat resistant. Conventional cooling methods are not only ineffective but also deteriorate the working environment by producing harmful gasses and smokes. Attempts have already been initiated to control the pollution problem by cryogenic cooling which also enables get rid of recycling and disposal of conventional fluids and possible damage of the machine parts by corrosion, etc.This paper deals with experimental investigation on the role of cryogenic cooling by liquid nitrogen jet on tool wear and product quality in plain turning of AISI 1040 and E4340C steel at industrial speed–feed combinations by two types of carbide inserts of different geometry. The encouraging results include significant reduction in tool wear rate, dimensional inaccuracy and surface roughness by cryogenic cooling application mainly through reduction in the cutting zone temperature and favourable change in the chip–tool and work–tool interaction.
Previous studies have demonstrated that the wear-corrosion synergism can be markedly affected by the loading speed. In this study, effects of the loading speed or strain rate on corrosion and corrosive wear of annealed, impact-fractured and slow bending-fractured surface layers of AISI 1045 steel in a 3.5% NaCl solution were investigated using electrochemical, scanning Kelvin probing and electrochemical scratching techniques. In order to understand the mechanism responsible for the effects of loading speed on corrosion and corrosive wear, SEM fractography, X-ray line profile analysis and micro-hardness testing were employed to investigate changes in microstructure and corresponding mechanical properties with respect to the loading speed. Results of the experiments are explained in terms of the effect of strain rate on surface microstructure and corresponding electrochemical and mechanical properties, and consequently the corrosive wear behaviour of the steel.
This paper reports on the influence of environment gas on the brass film and tribological behaviour of brass (Cu64Zn34)/steel (AISI 1045) couple. The friction coefficient and the wear rate of brass/steel were measured in ambient air, in pure oxygen at 105 Pa and in vacuum at 5 × 10−5 Pa. In this study, the mechanism of brass film transfer onto steel substrate has been studied with the scanning electronic microscope, the optical microscope and the interferential microscope. The analysis shows that the transfer film properties (roughness, hardness, thickness) depend on the atmospheric conditions. The brass film has an ellipsoidal surface in air and in oxygen with two different thicknesses.However, in vacuum, the transfer film is produced by discontinuous adhered particles on the disc. The largest wear rate is obtained, when using pure oxygen and the largest friction coefficient μ was measured in ambient air. The smallest friction coefficient and wear rate are obtained in vacuum due to the transition of a brass/steel contact to a brass/brass contact after nucleation of transfer particles.
The wear mechanisms of steel 1080 and the wear behaviour of various microstructures in the steel were systematically studied by wear testing, and by SEM and TEM observations of worn surface and wear particles. The experimental results show that three dominant wear mechanisms appeared in succession with increasing normal load and/or speed during unlubricated sliding. The transitions of the wear mechanisms depend mainly upon the conditions of testing, and changes in microstructure of the steel have no marked effect on the transitions. In the case of oxidation-dominated mild wear, no obvious differences in wear volume were found for the various microstructures. However, considerable differences in the wear volumes were observed under the condition of severe wear characterized by adhesion and delamination and the wear resistance of the different microstructures increased in the order: spheroidized carbide, martensite, bainite and lamellar pearlite.The experimental results also indicate that the differences in wear resistance of the various microstructures were caused by the differences in microstructural thermal stability, resistance to plastic deformation, resistance to nucleation and propagation of microcracks and especially by the differences in energy consumption in these layers during wear.
The effect of surface finishing method on near-surface residual stress, relative cold work and sliding friction and wear behavior of commercially available air hardening A2, D2, and CPM-10V tool steels was investigated. Microstructural characterization was accomplished using X-ray diffraction and scanning electron and optical microscopy combined with macrohardness measurements. The wear tests were performed using low load-slow speed reciprocating sliding conditions with tool steel flats in unlubricated contact with a 52100 steel spherical slider. The coefficient of friction and mass loss were measured during the course of wear testing and residual stress measurements were made before and after wear testing.Surface grinding and polishing conditions had a significant effect on surface residual stress but had little effect on tool flat sliding wear rates. Residual stress measurements performed after wear testing showed a decrease in compressive residual stresses as wear rate increased. Tool steel wear rates were a linear function of sliding distance except for the initial run-in period. The low wear rates, the run-in friction behavior, and the constancy of near-surface mechanical properties indicate that during run-in surface finish was wear rate controlling and that sample microstructure and composition controlled long-term sliding friction and wear behavior. The low wear rates and the post wear residual stress measurements also indicate that oxidative wear was the primary mechanism responsible for tool flat material attrition. CPM-10V steel flats exhibited the lowest coefficient of friction and the highest resistance to wear which can be attributed to the high volume fraction and homogeneity of V-Cr-C carbides.
The tribological behavior of nylon 11 reinforced with particulate inorganic fillers was studied. The fillers used were ZnS, PbS and ZnF2. The composite specimens with different filler proportions were made by compression molding. The friction and wear experiments were run under ambient conditions in a pin-on-disk machine with the composite pin riding on the flat surface of a steel disk at a sliding speed of 1 m s−1 and under a normal load of 19.6 N. The influence of the fillers on transfer film formation was studied by optical and scanning electron microscopy. X-ray photoelectron spectroscopy (XPS) analysis was performed to detect the chemical changes during the wear process. In the case of PbS-nylon composite the filler was found to dissociate during the wear process and thus provide a strong adherent transfer film which led to increased wear resistance of the composite as compared to that of unfilled nylon. On the other hand, when ZnS and ZnF2 were used as fillers in nylon, the wear rate of nylon increased. The reasons for this behavior have been investigated by transfer film studies and XPS analysis.
The tribological properties of polyamide 11 coated carbon steel injector tubulars are reported using a commercially available micro-abrasion tester, as a candidate method for assessing the abrasive wear of polymer coatings. Efforts have been made to reproduce the wear mechanisms found to predominate in field simulated conditions. The wireline-based tests produced severe grooving abrasion of the polyamide 11 coating resulting from contact between the spherical capped wireline asperities and the coating. Scanning electron microscopy (SEM) confirmed that grooving wear mechanisms were generated in the micro-abrasion tests and were due to micro-ploughing by the hard silicon carbide abrasives. To better reproduce wire-on-tubular contact conditions, a series of micro-abrasion tests using 6 μm spherical glass beads were also performed, but bead embedment complicated their interpretation. Test parameters such as load, sliding distance, sliding speed, abrasive morphology and type were found to significantly affect the wear rate of the coating. Comparison between the results of monolithic and coated polyamide 11 show that the coating generally out-performed the monolithic polyamide 11, possibly linked to enhanced coating properties induced during deposition. The wear rate of the coating was found to vary as a function of crater depth, increasing at a depth of 50 μm indicating the presence of a hard surface layer. Overall, the micro-abrasive wear test has reproduced a similar mechanism to that exhibited by wireline tests. Thus, the micro-abrasive test can be used as an accelerated wear test to investigate the tribological performance of coatings for tubulars.
Venturi cavitation erosion tests were performed and correlated with bubble collapse pulse height spectra measured by a microtransducer. The effects of the throat velocity and the cavitation number σ (referred to the downstream pressure and throat velocity) on the erosion rate (MDPR) were studied. The velocity damage exponent was 4.11 for 0.62 ⩽ σ ⩽ 0.80, while the MDPR is almost independent of velocity for σ = 0.85. The MDPR decreases with increased σ for 0.62 ⩽ σ ⩽ 0.85. The data were reduced to “acoustic power” (from pulse height spectra) and “erosion power” (the ultimate resilience multiplied by the MDPR). A near-linear relationship was found between these. Their reciprocal ratio ηcav ≈ 7 × 10−11. For σ = 0.62, the data deviated from the others, possibly because of the work hardening of the eroded surface.
Aluminum alloy 1100 was eroded by 70 μm and 210 μm silica spheresand by 210 μm angular quartz particles at a velocity of 122 m s−1 and at an impact angle of 90°. Extensive scanning electron microscopy examination of eroded surfaces, erosion debris and metallographiic sections, together with transmission electron microscopy examination of debris and eroded surfaces, was conducted. Hills and valleys were formed during the 'incubation period of erosion for all types of erodent. During steady state erosion small non-fragmenting erodent removed material by a flaking mechanism in valleys. For larger fragmenting erodent four additional mechanisms aiding erosion were identified. Furthermore, a threshold particle size for hill and valley formation is proposed. The implication of this on the magnitude of the erosion rate is discussed.
Sputter-coatings of carbon with 10% nitrogen incorporation grown to four different thicknesses of 10, 50, 100 and 200 nm were prepared by ion beam assisted depositing (IBAD) onto Si(111) substrates and then both surface characterized by an atomic force microscope (AFM) and nano-indented by a Thin Film Hardness Analyser. In sliding against a diamond pin at a relative humidity of 40%, CN0.1 coated Si(111) showed an increased friction with a decrease in coating thickness. And the friction was also found to reach the maximum value of 0.171 for the coating with a thickness of 10 nm when the normal load was consecutively changed until 300 mN at a sliding speed of 10 μm/s. The traditional Bowden–Tabor model and the theoretical contact model proposed by Halling and Sherbiney however, are still found to be useful to discuss the observed behavior of friction variations of nano-scale CN0.1 coated Si(111) from the viewpoints of coating thickness, adhesion and nano-indentation hardness, respectively.
Tribological performance of sub-nano to nanometer-thick Ag layers deposited on Si(1 1 1) have been examined to understand the effect of surface thin layers to the wear and friction characteristics. The slider was made of diamond sphere of 3 mm in diameter.Sliding tests were carried out in an ultra-high vacuum environment (lower than 2 × 10−8 Pa) and analyzed in situ by Auger electron spectroscopy (AES) for the quantitative thickness-measurements, by reflection high-energy electron diffraction (RHEED) to clarify the substrate cleanliness and crystallography of the Ag films, and by scanning probe microscopy (SPM) for the morphology of the deposited/slid film surfaces. The Ag and substrate surfaces were atomically clean during the tribological tests so that the chemical effect of the Ag and Si surfaces appeared directly on the friction and wear processes.Experimental results of the sliding tests indicated that the minimum coefficient of friction (μ) was 0.007 for the 1–5 nm thick as-deposited films of Ag on a Si(1 1 1) surface. Beyond the minimum thickness region, μ increased to 0.01 or higher. Observations of the slid surfaces showed that the Ag(1 1 1) sliding planes orientate parallel to the sliding direction, although the surface morphology of the deposited surface was totally deformed by the slider on the track. The Ag crystallites were not, therefore, destructed crystallographically by sliding but the fine Ag(1 1 1) sliding sheets were rotated, sheared, and displaced layer by layer, to orientate the Ag(1 1 1) plane parallel to the sliding direction by the reciprocal movement of the slider. After 100 cycles of the reciprocal movements, no worn particles were found around the sliding track and the low friction sliding lasted over 1000 cycles of the reciprocal sliding.The observed results indicated that the atomic force between surface atoms, especially diamond CAg chemical bond, Ag(1 1 1) interlayer bonding force, and also the orientation of the sliding planes strongly reflect to the friction force, in addition to the asperity of the surface. A sliding mechanism of very thin layers of Ag film of very low wear and friction is discussed.
An internal combustion engine made of Al–Si alloys should operate in ultra-mild wear (UMW) regime. The objective of this work was to understand the wear mechanisms operating in Al–12.6 wt.% Si alloys tested at 100 °C under boundary lubricated condition simulating UMW regime. The sliding tests were conducted on surfaces etched to protrude silicon above the aluminum surface and optical profilometery was used to analyze changes in Si morphology during sliding. Three different stages of UMW were identified. During UMW-I, formation of a discontinuous island-like tribofilm primarily consisting of zinc sulphide from lubricating oil on top of silicon particles was observed and silicon particles progressively became embedded in the matrix. A criterion for transition between UMW-I and UMW-II was developed in terms of the ratio of pile-up height to silicon height. In UMW-II, the piled-up aluminum started to wear and an approximately 100–150 nm thick continuous oil-residue layer (ORL) formed on the worn surface primarily consisting of smeared island-like tribofilm mixed with aluminum. The ORL was also supported by a sliding induced ultrafine grain aluminum layer, and consequently microstructure evolution led to a stabilized surface with lower wear loss in UMW-III compared to UMW-II. UMW-III wear rates at 100 °C were similar to those at 25 °C.
Planar-randomly oriented alumina short fiber (Saffil) reinforced AlSi (LM 13) alloy metal matrix composites (MMCs) were produced by a modified liquid infiltration technique. The wear and friction behavior of LM 13 alloys containing up to 30 vol % Al2O3 fiber were investigated in sliding against a hard steel counterface (63 HRC) by continuous loading experiments carried out in a pin-on-disk machine under dry conditions at room temperature in the transverse section of the composites. Sliding tests were conducted at five loads (5 N, 10 N, 20 N, 40 N and 60 N) and under a constant sliding speed of 1 m/s. The wear and coefficient of friction against sliding distance initially showed a short transient period and then reached a steady state behavior. The wear behavior of the composites was dependent on fiber volume and applied load. The wear rate decreased with increased volume fraction of fiber and increased with increasing load. The wear resistance of the composites over the range of loads and volume fraction of fibers studied was found to range from almost 1.2 to about 4.0 times that of unreinforced alloy. Coefficient of friction decreased with increased fiber volume percent and applied normal load. To analyze wear mechanisms, wear surfaces were examined by scanning electron microscopy and it was found that the wear of the unreinforced alloy and composites occurred by groove formation and its subsequent growth, the magnitude of which increased with increasing fiber volume and applied normal load.
The friction and wear properties of the ionic ceramics Al2O3 and ZrO2, and the covalent ceramics Si3N4 and SiC rubbing against an Al2O3 ball in vacuum (10−5 Pa) and in CF3CH2F (HFC-134a) gas at 104 Pa were investigated using a ball-on-disk type tribometer. Without exposure to air, the surface composition and chemical state of the wear tracks and debris on the disks were determined with X-ray photoelectron spectroscopy (XPS). It is found that HFC-134a gas significantly reduces the friction and wear of all the ceramic couples, and that the ionic ceramic pairs show lower friction and wear. On the other hand, metal fluorides and/or fluorine-containing organic compounds are detected on the sliding surfaces. The differences in the friction–wear behavior of the ceramics rubbing in HFC-134a gas may be due to the products of tribochemical reactions, which are dependent on the bond type of the ceramics.
Hydrofluorocarbons (HFCs) are transitional refrigerants being used in the wake of international agreements aimed at developing more environmentally acceptable refrigerants. An evaluation of the tribological characteristics relating to the conforming contact between the die-cast aluminium alloy connecting rod and the hardened steel gudgeon pin of a reciprocating compressor is presented. An experimental investigation was carried out on liquid/vapour refrigeration systems. Hermetic refrigerating compressors, working in an HFC-134a environment and at high compression ratios, were adopted. Three synthetic lubricants, characterised by viscosity, were used. Results indicated extensive surface damage, observed at the interfaces, depending on the viscosity of the lubricant/refrigerant combination used. Wear mechanisms were studied using scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis and light microscopy analysis. Evidence of adhesive wear and lubricant decomposition were observed. The significance of this study is to assist industry and related research work in the optimal design and selection of working fluid viscosities to be used in domestic refrigerating systems working in an HFC-134a environment.
The effect of heat treatment on the microstructure, hardness and sliding wear behavior of Ti–13Zr–13Nb has been investigated. The wear behavior was studied in dry as well as in wet conditions using Hank's solution and bovine serum as the lubricating media. The microstructure of the heat-treated alloy consisted of acicular and globular α, β and martensite. The hardness was found to depend on the volume fraction and distribution of α phase in the matrix. In dry condition, there was no significant variation of the wear rate with the heat-treatment conditions except for the sample deformed above the β transition temperature and aged after solution treatment at 800 °C. In Hank's solution, the wear rate of all the samples increased considerably. The rate of wear was the highest in bovine serum, possibly due to the presence of protein in the lubricant. The wear process is characterized by ridged wear scars parallel to the sliding direction with superficial plastic deformation along the direction of the sliding and smeared wear surface. The wear mechanism is mainly abrasive.
A β particle backscatter instrument has been developed to measure changes in surface profile due to wear. The response of the instrument to the backscatter of 147Pm β particles from metal and plastic surfaces is reported.The backscattered β particle intensity has an angular dependence which is approximately sinusoidal and use has been made of this phenomenon to measure the change in profile of a copper surface. A profile change involving a maximum depth of 15 μm was readily detected. A model has been developed which fits the data and predicts a simple proportionality between the area under the response curve and the volume of material removed from the surface. The data confirm this simple relationship and demonstrate the potential of the method for the measurement of small changes in surface profile.
A 147Pm β particle backscatter instrument has been developed and its applications to the measurement of changes in the surface profiles, due to wear, of dental restorations is described. The response of the β particle backscatter instrument to small changes in surface profile are adequately described by a model based on the known behaviour of backscattered electrons. The simulated wear of dental amalgam restorations, composite resin restorations and metal-coated replicas has been studied using this technique. The β particle backscatter instrument is capable of detecting changes of the order of 15 μm in the profile of irregularly shaped surfaces.
The sliding friction and wear behaviour of 15Cr–15Ni–2Mo titanium-modified austenitic stainless steel (alloy D9) was studied in high purity liquid sodium at high temperature viz. 473 and 823 K respectively using a reciprocating-type tribometer. Weight loss measured in specimens after the tests was negligible. Scar depth measurements on disc specimens were carried out by confocal laser scanning microscope, which revealed not much number of scratches tested at 473 and 823 K, respectively. Scanning electron microscopy on worn pin specimens revealed the presence of deformed zone in the rubbed area, and adherence of wear particles at few locations in both the cases. Damage is more in specimens tested at 823 K because of the softening of the rubbing surfaces at that temperature. Further, friction coefficient is lower at 473 K than at 823 K.Research highlights▶ Friction and wear studies of 20% cold-worked 15Cr-15Ni- 2Mo Titanium-modified austenitic stainless steel (alloy D9) in liquid sodium at high temperature. ▶ Low value of friction coefficients for this alloy is due to lubrication mechanism independent of oxygen content. ▶ Values well within the design criteria (as per fuel duct assembly for the Fast Flux Test Facility) for pads of wrapper material for FBRs.
A deformation-processed Cu-15vol.%Cr in situ composite was made by consumable arc melting and casting followed by extensive deformation. A superior combination of mechanical strength and electrical/thermal conductivity was achieved with the composite since Cr filaments existed in the nearly pure copper matrix. The effects of sliding speed and normal pressure on sliding wear behavior and microstructure of the composite were investigated, with a composite pin rubbing against a hardened AISI 52100 steel disk on a pin-on-disk wear tester. In the studied range of normal pressure and sliding speed, the wear rate increased with increased normal pressure, whereas the wear rate decreased with increased sliding speed. Sliding-induced subsurface deformation occurred not only in the sliding direction but also in the lateral directions perpendicular to the sliding direction. This lateral flow produced a twisting of the Cr filaments. The complex deformation mode was revealed clearly by the morphological change of the ribbon-like filaments. Both constituents of the composite were cooperatively deformed. The thickness of deformed subsurface layer increased with increasing normal pressure and sliding speed. Scanning electron micrographs showed plastic deformation flow on the wear surface.
A casting technique for assessing the extent of the penetration of femoral heads into polyethylene acetabular cups in explanted Charnley prostheses is described and the observed penetration rates are related to laboratory wear studies carried out in the Institute of Tribology at Leeds over some 16 years. Some 32 explanted high molecular weight polyethylene (RCH 1000) acetabular cups provided by Wrightington Hospital were examined, and 25 were found to be suitable for penetration measurements. Relevant patient details for the 25 explanted acetabular cups were provided and 15 of the subjects were male whilst 10 were female, with 14 of the cups coming from the right hip and 11 from the left. The ages of the subjects at the time of the removal of the prostheses ranged from 18 to 68 years, the average being 54.4 years. The average period of residence of the prosthesis in the body was 8 years 11 months.
This work analyses the wear behaviour under dry sliding contact of a titanium-alloyed high-chromium white cast iron (16%Cr). Wear behaviour is analysed as a function of the load in the range of 50–250 N as well as a function of the titanium additions (0–2.02%Ti). Such additions resulted in the precipitation of small hard titanium carbide particles in the proeutectic austenite promoting a strengthening of matrix, and thereby increased the bulk hardness of the alloy. A structural refinement, as measured by the secondary dendrite arm spacing, was also observed as the titanium amount increased. The wear behaviour was investigated for each alloy in the as-cast condition (austenitic matrix) using a pin-on-ring configuration in dry sliding for a distance of 50 km against a hardened M2 steel counterface. For loads between 50 and 100 N all the alloys showed similar wear rates (∼2.5 × 10−4 mm3/m) associated with the formation of debris composed by Fe2O3 as well as metallic particles. For the higher loads (150–250 N) wear showed a strong dependence on the titanium content (wear decreased with the increase in titanium) and was associated with the formation of Fe2O3, Fe3O4 and carbide particles as wear debris. Depths of deformation from ∼3 to 20 μm were observed. The depth of deformation had a direct correlation with the load and was inversely proportional to the titanium content. A linear relationship was observed between these depths of deformation and the wear rate. Results are discussed in terms of the microstructure and the best wear behaviour was observed for the iron with 2.02%Ti and was attributed to the presence of small, hard TiC particles reinforcing the matrix as well as to the structure refinement.
The effect of indenter shape on the transient current response of Fe-16 wt.%Cr-16 wt.%Ni alloy has been investigated in an 0.01 M H2SO4-0.01 M KCl electrolyte. Various Rockwell hardness indenters with C-Brale, Vickers, in and in balls at their tips have been used in this study to produce scratches of different shapes on the alloy when the specimen was being rotated at 1500 rev min−1 in the given electrolyte. The transient current increases linearly with increasing impact force of the stylus. The transient current response in itself indicates various stages corresponding to passivation, depassivation and repassivation kinetics of the samples. The details of the kinetics have been discussed in this paper. The scanning electron micrographs indicate that the area of the scratches increased with increasing applied load, and the morphologies of the scratches appear to be quite different in air and electrolyte. The scratches are usually more elongated in the electrolyte.
Variable feed machining has recently been proposed as a significant method to improve cutting tool life particularly for hard and diffucult to machine materials. This method, which is easy to apply in industry, has been shown to improve tool life in the order of 40% in certain cases. This paper presents a reliability model for the quantitative study of the effect of feed variation on tool wear and tool life. To better compare processes with two different wear modes, a reliability model taking simultaneously into account both flank and face wear has been developed. With this model, which is based on experiments, the tool life for the constant and variable feed cases was calculated from the reliability function. The mean time to failure, obtained from the reliability function, provides an accurate evaluation for any probabilistic distribution. The proposed method is therefore a general approach that can be used for analyzing cutting tool life under any conditions and for any equipment and material.
The surface evolution during dry sliding wear of 2009 Al-20vol.%SiCp on 17-4 PH with differing SiCp sizes (4, 10, 13 and 29 μm) was investigated. Surface profilometry indicated, independent of composite reinforcement size, that the roughness (Ra and Rq) increased throughout the entire sliding distance, the larger (29 μm) particulate-reinforced composite showing a tendency for Ra and Rq to increase at a higher rate with sliding distance. The larger (29 μm) particulate-reinforced composite also displayed an Rsk and Rku increase throughout the entire, 3600 m, sliding distance, while a decreasing Rsk and increasing Rku between 360 and 3600 m were observed for the smaller (4, 10 and 13 μm) particulate-reinforced composites. These results suggest that the lower roughness after 3600 m observed in the small reinforcement composite vis à vis the larger particulate-reinforced composite is the result of a higher degree of peak removal, the valleys not being differently affected between the composites. This difference was attributed to differing third body behavior and wear mechanism between the investigated composites. Scanning electron microscopy showed that the SiC particulate reinforcement debris in the 4 μm composite were crushed into very fine particles during sliding and acted as a polishing agent while in the 29 μm composite, the initially larger ceramic debris acted as abrasive particles. Similarly scanning electron microscopy showed that adhesion-induced tribofracture and microcutting were the predominant wear mechanisms at smaller (4, 10, and 13 μm) reinforcement, while particulate cracking-induced subsurface delamination occurred in the large ceramic (29 μm) reinforced composites.
In this article the author discusses the application of a lubricating process as described by Vitruvius about 25 B.C. He explains how there was a retrogression in machine-building from the decline and fall of the Roman Empire up till the Renaissance, when the work done by pre-Christian machine-builders became more generally known. Moreover, he shows that on mining-machines described by agricola in 1556, provision was made for an easy replacement of worn bearings, gear-teeth and chain-drums. He concludes his article by mentioning lathe-development up till 1701, which led to further improvement in the scientific design of machinery and tools.
Specimens of 18 Ni (250) maraging steel were solution treated and aged at 480, 590 and 650 °C for varying times up to a maximum of 24 h. Solutionannealed specimens were also cold rolled to varying amounts. The erosion behavior of these specimens was studied in a sand-blast type of test rig. The tests were conducted under ambient conditions with 125 μm angular SiC particles impacted with a velocity of 50 m s−1 and at an angle of 30° to the specimen surface.The variation in erosion has been related to the microstructural changes which occur during aging and which involve precipitation, reversion of austenite and precipitate particle growth. It has also been studied with respect to the mechanical properties. It was found that the erosion rate depends on both the hardness and the ductility. The erosion rate varies directly with hardness when the ductility remains constant and it varies inversely with the square of the per cent area reduction when the hardness remains constant.Scanning electron microscopy of the eroded surfaces and debris revealed that erosion was accompanied by a large amount of plastic deformation and that the eroded particles were in the form of small flakes. The flakes were detached because of a combination of cutting, ploughing and crack propagation mechanisms.
18 polymers were characterized with respect to their friction and wear behaviour in contact with steel in environments of air and water. These were six unfilled materials, i.e. polyamide 66 (PA 66), polyoxymethylene (POM), polyethyleneterephthalate (PETP), polyetheretherketone (PEEK), polyphenylenesulphide (PPS) and polyetherimide; also, the same base materials filled with polytetrafluoroethylene (PTFE) or PTFE plus glass fibre were used.Two types of experiments were performed, i.e. measurement of the coefficient of friction f as a function of the contact temperature Tc (“f;−), and measurements of friction and wear in 20 h tests. The f−Tc diagrams were obtained in air; the 20 h tests were performed in air and in water at a temperature of 20 °C. In air the polymers ran against rings of ball-bearing steel (AISI 52100); in water the rings were made of stainless steel (AISI 316).It turned out that in air addition of PTFE was generally beneficial; PA 66, POM, PETP and PEEK, all filled with PTFE, performed exceptionally well (specific wear rates k appreciably lower than 1×10−15 m3 N−1 m−1). In water, however, PTFE did not function at all. Now PA (with or without PTFE), unfilled POM and PETP filled with PTFE and glass fibre met the k<1× 10−15 m3 N−1 m−1 criterion. With a few exceptions, addition of glass fibre produced unfavourable effects, in air as well as in water.The observed phenomena are explained tentatively in terms of polymer structures and transfer and wear mechanisms, whereby special attention is paid to the ratio of friction over strength.
The mild wear regime of a cast Al-18.5% Si (A390), a lightweight alloy used in automotive components requiring wear resistance, was investigated in order to characterize the progression of the sliding wear processes. Block-on-ring (SAE 52100 steel) type sliding wear tests were conducted under a controlled dry air environment with 5% relative humidity. It was observed that the mild wear regime consisted of two sub-regimes: The first sub-regime of mild wear (MW-1) occurred at loads between 0.2 N and 35 N, and the second sub-regime of mild wear (MW-2) between 60 N and 150 N. A common characteristic of MW-1 and MW-2 was the attainment of steady-state wear conditions. The load (L) dependence of the steady-state wear rates (W) in both sub-regimes was expressed as W = C(L)n, where C1 = 1.08 × 10−4, n1 = 0.56 for MW-1 and C2 = 2.18 × 10−4, n2 = 0.67 for MW-2. A transition regime, where the wear rates of MW-1 increased by 270%, occurred in the 35–60 N load range. The transition between MW-1 and MW-2 was accompanied by a rapid increase (25%) in the amount of material transferred to the counterface.
This paper describes an experimental study on the temperature-dependent tribological behavior and oxidation of a carbon-carbon (C/C) composite material sliding against itself in ambient air up to 1800°C. Tribological experiments were conducted with a ring-on-ring type of apparatus using a wide range of load and speed conditions. As the specimen temperature gradually increased with frictional heating, the friction of C/C composites experienced two abrupt increases at 150–200°C and 650–700°C. The two transition temperatures divided the friction and wear of C/C composites in ambient air into three temperature-dependent regimes: the normal wear, the water-desorption dusting wear, and the oxygen-desorption dusting wear regimes. The friction and wear also depended on the load and speed conditions. In addition to the wear loss at the rubbing surface, the oxidation loss at the exterior of the specimen also contributed to the weight loss of the specimen, especially at elevated temperatures. The linear wear of C/C specimens amounted to less than 2% of the total weight loss when the maximum specimen temperature exceeded the failure temperature of the oxidation-inhibitor. The effect of specimen geometry on the wear and oxidation at the rubbing surface is also discussed.