Change In Wear Rate Research Articles

A quantitative analysis of the influence of carbides size distributions on wear behaviour of high-speed steel in dry rolling/sliding contact

The wear resistance of steels arises largely through the incorporation of a significant volume fraction of hard second-phase particles, usually carbides. While there is considerable understanding of the effect of chemical composition on carbide fraction and size distribution, the understanding of the effect of carbide size distribution on wear resistance, for constant composition, is poor. In the current work, wear tests on high-speed steels of the same chemical composition but different carbide distributions induced by different manufacturing routes are considered. For the investigated range of carbide size distributions wear rates can differ by 40%, indicating that the manufacturing route of the steel plays a major roll on its wear performance. We demonstrate that cumulative frequency plots of carbide sizes can be used to quantitatively predict changes in wear rate for materials of constant chemical composition but different carbide distributions, provided the critical thickness of the wear debris is measured.

Abrasive wear of 2124Al–SiC composites in the temperature range 20–200 °C

The main aim of this research was to investigate the influence of temperature (in the range 20–200 °C) on the abrasive wear behaviour of a 2124 Al/SiC composite produced by powder metallurgy techniques. Abrasive wear tests were conducted at constant distance and 10 N load using pin-on-disk apparatus. Some specimen taken from the composite materials were artificially aged (T6) to determine ageing effects. At the last stage of the study, worn surfaces and the subsurfaces were examined by using SEM, EDS and optical microscopy. Wear test results obtained at all test temperatures showed that the weight loss of the aged specimens was less than that of the non-aged specimens. It was also observed that the better wear resistance was seen for specimens worn at RT both the aged and non-aged specimens. There was no (or little) net change in wear rate for the test temperature above 50 °C both the aged and non-aged specimens. Because of contact between SiC particles in the composite material and abrasive paper, broken or loosened hard SiC particulates embedded to the soft layer under worn surface which observed at 50–200 °C, caused an increase in strength of surface of the composite specimens and so resulted little change in wear rate.

Abrasion resistance as a function of substructural changes in steel

It is known that there are three different stages of wear rate as a function of the abrasive grit diameter. The first shows only a modest increase in wear rate when the grit diameter increases. Then, in the second stage as the grit diameter further increases, the wear rate rises rapidly. In the third stage, the wear rate becomes independent of the grit diameter or increases only slightly. The main objective of this work is to explain these dramatic changes in wear rate. For this purpose, two-body abrasive wear tests were performed in order to study the structural changes in different steels, depending on the abrasive grit diameter. Special attention was paid to the correlation between the size of the fragments (subgrains) formed in the surface layers and the variations in the wear rate. The former determines work hardening of the metal, and therefore, its wear resistance. X-ray investigation showed that the size of the fragments formed in the surface layers of steels during the wear process is dependent on the abrasive grit and corresponding wear rate. In the first stage, the size of the fragments is relatively small. Then, it becomes larger, and therefore, work hardening of the surface layers decreases by comparison to those under wear with a smaller grit diameter. The dimensions of fragments are maximal and change only slightly in the third stage when we used abrasive paper of a greater grit size. Therefore, in these cases, work hardening of surface layers is minimal and it is expected that wear resistance will also be minimal.

Assessing the pattern of femoral head penetration after total hip arthroplasty

We evaluated temporal changes in wear rates among 205 primary cementless total hip arthroplasties that had minimum 10-year follow-up and at least 6 follow-up x-rays. Using the pelvic anteroposterior x-rays from each hip, two-dimensional head penetration was measured and wear rates were calculated using several techniques. The average wear rate for the study population did not demonstrate evidence of accelerated wear at 10- to 18-year follow-up. As an increasing number of follow-up x-rays were included in the least-squares linear regression used to calculate the wear rate, the 95% confidence interval associated with the wear rate for an individual hip tended to progressively decrease. These results indicate that a constant wear rate is a reasonable assumption for modeling clinical wear data. Although we cannot quantify the effects of polyethylene oxidation, femoral head roughening, debris accumulation, or activity level changes, the combination of these factors is not leading to clinically perceptible accelerated wear at intermediate to long-term follow-up in this heterogeneous population of cups representing our institutional experience.

Relation between strain hardening and wear resistance of polymers

AbstractThe friction and abrasive wear of blends of polystyrene (PS) and poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) were measured. The coefficient of friction decreases only slightly with an increasing PPO fraction, while the abrasive wear decreases largely upon the introduction of increasing amounts of PPO. It is clearly shown that the abrasive wear resistance of the PS/PPO blends increases with an increasing strain hardening modulus of the blend. The wear rate change between 20 and 40 wt % PPO is ascribed to a transition in the failure mechanism from predominantly brittle to predominantly tough. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2689–2692, 2004

Friction and Wear of Spheroidal Graphite Cast Iron in the State of Thermal Wear

To clarify the dry friction and wear characteristics of spheroidal graphite cast iron under high sliding speed and high contact pressure, especially those in the state of thermal wear, the wear tests of sliding a cast iron pin on a mild steel disk were carried out by using the pin-on-disk type test rig. The variations of the friction force, the wear rate and the temperature rise with the sliding distance were experimentally measured and the relations among them were clarified. The friction and wear of spheroidal graphite cast iron pin are strongly influenced with the friction-induced tempera ture rise. Its wear rate changes in three steps as the increment of sliding distance because of the changes of its hardness by temperature rise (the first, the second and the third wear regions in order). The thermal conductivity and the hardness change by temperature rise of spheroidal graphite cast iron give the effects on thses three step changes of wear. Meanwhile, the coefficient of friction decreases in the first and the second wear regions as the sliding distance increases, and it finally converges to some constant value in the third wear region. From the experimental results, some empirical formulae giving the relations between the coefficient of friction and the wear rate versus the sliding conditions were derived.

Nano-Scale Fatigue Wear of Carbon Nitride Coatings: Part I—Wear Properties

This paper, the first of two companion papers, reports empirical data on wear properties in carbon nitride coatings by a spherical diamond counter-face in repeated sliding contacts through in situ examination and post-sliding observation, with an emphasis on the effects of friction cycles and normal load. In the repeated sliding, a specific wear amount of about 10−9mm3/Nm was observed on the wear track of the carbon nitride coating when no wear particles were detected. On the other hand, a specific wear amount of about 10−6mm3/Nm was observed on the wear track of the carbon nitride coating, where wear particles were generated after a certain number of friction cycles. Wear rate change corresponds to a wear mode change. From in situ examination, the critical number of friction cycles, Nc, for wear particle generation is proven to be related to a wear mode change.

The Effect of Heat Treatment on Sliding Wear Behaviour of a Zinc-Based Alloy Containing Nickel and Silicon

This investigation deals with the observations made pertaining to the sliding wear behaviour of a zinc-based alloy containing nickel and silicon in partially lubricated condition. Wear tests were conducted over a range of applied pressures and sliding speeds. The effect of microstructural changes brought about through T6 heat treatment involving solutionizing followed by artificial ageing on wear behaviour was also investigated. The wear rate increased with pressure. The slope of the wear rate versus pressure plots was low initially up to a specific pressure. This was followed by a higher slope beyond the (specific) pressure. In some cases, the rate of change in wear rate, i.e. the slope, decreased at still higher pressures. Moreover, the (specific) pressure decreased with sliding speed in general. Increasing sliding speed caused the wear rate of the as-cast zinc-based alloy to increase up to a sliding speed of 2.68 m/s. The trend reversed at a still higher speed of 4.60 m/s. However, increasing wear rate with speed was noted for the heat-treated alloy over the entire speed range. Heat treatment led to reduced wear rate up to a sliding speed of 2.68 m/s. An opposite trend was observed at a higher speed of 4.60 m/s in this case. Specimen seizure was noted at speeds above 2.68 m/s in the case of the as-cast alloy whereas seizure took place only at 4.60 m/s for the heat-treated alloy samples. Frictional heating increased with pressure and speed. The specific response and changing mode of distribution of various phases were thought to be responsible for the typical wear behaviour of the alloy in specific material and test conditions. The predominance of parameters like thermal stability and cracking tendency over each other is suggested to lead to the varying wear behaviour of the alloy in different (material and sliding) conditions. The wear response of the samples has been substantiated through characteristics of their wear surfaces, subsurface regions and debris.

Investigation of sub-surface damage during sliding wear of alumina using focused ion-beam milling

In this work contact pressure and sliding distance-induced changes in wear rate and mechanism, and friction behaviour of alumina are investigated by consideration of sub-surface damage. Sub-surface cracking and the formation of tribochemical reaction products are observed through the use of a novel sectioning technique; focused ion-beam milling. Initially wear rate experiments with three different grain sizes and different contact loads were undertaken. These were followed by extensive sub-surface microscopic investigations. Wear experiments, undertaken on a pin-on-disc tribometer over a range of contact pressures, revealed that wear mechanisms changed as contact pressure decreased. Both wear rate and friction were monitored. Debris and surface layers which formed were characterised using X-ray photoelectron spectroscopy (XPS). This identified an oxide/hydroxide layer which formed during wear and which was found to significantly affect friction. The nature of this layer varied significantly with contact pressure and sliding distance. It was found that mild wear of alumina in air involves the continual formation and removal of a surface layer at differing rates.

The tribological characteristics of the Al-20Si-3Cu-1Mg alloy reinforced with Al2O3 particles in relation to the hardness of a mating steel

The application of aluminium in automotive engines requires the material to be strong, stiff and, more importantly, wear resistant, which calls for reinforcement with hard ceramic particles. The resultant wear resistance of an aluminium matrix composite is affected not only by the intrinsic properties of the material but also by extrinsic factors involved in the wear process. Few studies have been conducted on the influence of mating material on the wear resistance of aluminium matrix composites and that of the whole friction couple as a system. This paper presents the results of the pin-on-disk wear tests of a potential piston material, the Al-20Si-3Cu-1Mg alloy reinforced with 10 vol.% Al2O3 particles, with the variation of the hardness of a steel counterface from 28 to 58 HRC. The work shows that the wear rate of the composite is significantly affected by the hardness of the counter-specimen. For a higher wear resistance of the composite, the mating steel should also be harder. A soft steel counterface would result in increased wear of both the composite and the steel, and thus increased total wear of the friction couple. The observed change in wear rate with the hardness of the counter-specimen is associated with the predominant wear mechanism. The work also shows that the friction coefficient of the composite specimen is also affected by the hardness of the counter-specimen, in addition to the pressure applied in the wear tests.

Measurements and Correlations of Slider Vibrations and Wear

Studies have shown that micro-vibrations (10–100 μm amplitude, 10 to 100 Hz) of a slider can reduce sliding wear 50 percent, especially rigid body rocking motions that continuously realign the slider face with respect to the counter surface. In this article, clearances between a carbon sample and its holder were varied while sliding over a slightly wavy (8 to 20 μm) steel surface. Undulations on the counter surface induced rigid body vibrations of the slider. Clearances between sample and holder kinematically restricted rigid body rocking motions of the slider: larger clearances permitted more rocking. Measured were motions of the slider, including translations normal to the counter surface, and rotations about axes parallel to the counter surface. Time traces of these displacements were plotted at different sliding speeds. Frequency content and kinetic energies for each measured degree of freedom and the total were extracted. We sought correlations between measured wear and vibration data. Fractional changes in wear rate versus fractional changes in total kinetic energy clustered about a straight line. From these measurements, we found a quantitative relationship between amount of wear and total kinetic energy of vibration. [S0742-4787(00)05001-3]

Study of fretting wear behaviors of FEP

The fretting wear behaviors of perfluorinated ethylene–propylene copolymer (FEP) were studied on an SRV fretting wear tester with the plane contact of FEP against a bearing steel at room temperature of about 15°C. In our tests, the product of load (L) and total sliding distance (S) was preset to be a constant as the wear coefficient Kω can be expressed as Kω = W · Pm/(L · S), where W is the volume of material loss, Pm is the flow pressure of the softer material (FEP), L and S are the load and the total sliding distance, respectively. Under our test conditions, no wear of the bearing steel was observed when fretted against FEP. The sudden change of wear rate of FEP or its wear weight was governed by the critical PV value, an important parameter for polymers and polymer composites under sliding friction, which was the product of normal stress and average sliding speed. The critical PV value of FEP under study was 3 × 104 Pa · m/s. It was also found that the topography of wear trace formed on FEP were fairly well corresponding with that of their transferred films on steel surface. Both on worn surface of FEP and on metal surface, three sharply defined regions, wear debris formation region, high-stress region, and slightly sliding wear region, can be distinguished. It indicated that the higher the normal stress, the more difficult the formation of thick transfer film. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1119–1125, 1998

An approximate generalized experimental model for dry sliding adhesive wear of some single-phase copper-base alloys

Dry sliding adhesive wear of some copper-base alloys (CuZn, CuAl, CuSn and CuNi) is studied with a typical experimental plan of simultaneous variation of load and sliding speed in a selected range. Experimental response data is analyzed by formulating dimensional equations. The condition of plastic instability is considered as the criterion to evaluate the wear. The approach known as experimentation methodology is adopted to provide a new tool for material characterization for wear behaviour in practical situations. The sensitivity of the alloy systems to wear rate changes is analysed. The concept of a space curve is proposed for a relationship between dimensional constants that emerge from this study and Archard's wear constant. The approximate generalized experimental model proposed through this attempt helps in quantifying the combined and interactive effect of several significant parameters on the wear phenomenon.

Microwear mechanisms of coatings

Microwear mechanisms of coatings are studied by focusing attention on mechanical wear. Wear rates and wear modes of chemically vapour-deposited TiN and Al 2 O 3 coatings in abrasive sliding are observed experimentally with a scanning electron microscope which has a videotape recording system and a tribosystem. It is shown that the wear rate changes by factors of 3–5 orders of magnitude depending on load and friction cycle. Wear modes of ploughing, powder formation, flake formation and coating delamination are observed and their transitions are related to the change of load and friction cycle. For the prediction of possible wear modes, a new local yield map is proposed by taking into account the stress analysis at the contact region with the finite element method.

Microwear mechanisms of coatings

Microwear mechanisms of coatings are studied by focusing attention on mechanical wear. Wear rates and wear modes of chemically vapour-deposited TiN and Al 2O 3 coatings in abrasive sliding are observed experimentally with a scanning electron microscope which has a videotape recording system and a tribosystem. It is shown that the wear rate changes by factors of 3–5 orders of magnitude depending on load and friction cycle. Wear modes of ploughing, powder formation, flake formation and coating delamination are observed and their transitions are related to the change of load and friction cycle. For the prediction of possible wear modes, a new local yield map is proposed by taking into account the stress analysis at the contact region with the finite element method.

Mathematical modelling of wear of cemented carbide tools in cutting brittle materials

This paper presents a theoretical investigation dealing with the wear of cemented carbide tools in cutting brittle materials. The dependence of the rate of tool wear on the structure and properties of the hard alloy is determined with the use of fatigue concept of tool wear. A mathematical model of redistribution of contact stress in tool wear and the changes in wear rate due to the changes in tool geometry is developed on the basis of the theory of dynamic systems. The influence of variations of the cutting force and the tool-to-work vibrations on the tool wear is studied. The model indicates that the wear rate in approach cutting increases with time. When the cutting force is constant the wear rate decreases.

The effect of transfer film and surface roughness on the wear of lubricated ultra-high molecular weight polyethylene

Ultra-high molecular weight polyethylene (UHMWPE) wear debris is now recognised as one of the major contributing factors of the loosening and failure of total artificial joints. In water-lubricated laboratory tests the volume of UHMWPE wear debris generated is highly dependent on changes in counterface topography caused by polymer transfer film and the subsequent changes in wear rate have been determined under different conditions. In tests with deionised water as a lubricant, initially smooth surfaces became rougher and increased the wear rate of the UHMWPE, while there was some smoothing of the initially rough counterfaces. A change in the effective surface roughness, R A, of 0·02–0·04 μm caused by polymer transfer produced a seven-fold increase in the wear rate of UHMWPE. The use of protein-containing lubricants greatly reduced the amount of polymer transfer film, the counterface roughness remained constant and there was little change in the average wear rate throughout the tests. This was considered more representative of conditions in the body. It is more appropriate to use protein-containing lubricants in laboratory tests, which inhibit polymer transfer film formation and produce more consistent and reliable wear results.

Influence of shearing action of food on contact stress and subsequent wear of stress-bearing composites.

The influence of sliding action of the antagonist on occlusal three-body wear of composites and an amalgam was investigated in vitro by gradual change in the distance between the opposing substrates. When the distance was decreased from 10 microns to approximately 3 microns, wear increased significantly by a factor of two to three and was exclusively of erosive nature. At a slurry-film thickness of approximately 1 micron, direct contacts between the antagonist and protruding composite filler particles started to occur. This consequently slowed the erosive wear. Ultimately, direct contact phenomena predominated, decreasing the wear rate of the various materials to different degrees. Loss of material due to subsurface fatigue could not be demonstrated with a contact pressure of 45 MPa at which the experiments were performed. From this study, it can be concluded that minor alterations of the food-film thickness at the contact areas result in considerable changes in wear rates and wear-rate ranking of composite materials, which may partly explain inconsistencies among clinical trials.

Acoustic emission monitoring of the wear process

Acoustic emissions are generated at the sites of the fundamental processes resulting in material wear and so are an attractive possibility for continuously monitoring wear and for basic studies of the wear process. Changes in wear rate and acoustic emission activity were measured across the mild-severe wear transition in the sliding of metals. The intent was to characterize these changes in wear behavior in terms of acoustic emission characteristics and to determine the usefulness of acoustic emission measurements for the study of wear. Experimental results showed that changes in acoustic emission count rates correspond to changing wear rate. Acoustic emission amplitude distributions as well as acoustic emission energy measurements indicated a strong potential for the use of these two parameters in the identification of different modes of failure during the wear process.

Polishing wear resistance of ion-implanted 304 steel

Steel (AISI-304) disks, polished to a 3 μm diamond finish, were implanted to doses of about 2 × 1017/cm2 with N+, Ni+ or, Ne+, ions. Polishing wear rates, measured to a depth resolution of about 20 nm, showed that each of the implanted disks wore 20% to 40% faster than nonimplanted layers. Auger analysis showed (1) Gaussian-like profiles of the N-implanted layer, but with somewhat enhanced oxidation of the surface, and (2) a sputter-limited implantation profile in the Ni-implantcd layer, with some vacuum carburization. Transmission electron microscope analysis indicated that polishing produced an α′-martensite layer in the mainly austenitic 304 surface, but that implantation of N transformed the martensite to austenite at the outermost layers and produced iron nitrides below. In addition. Nimplantation stabilized the austenite against martensite transformation during subsequent wear. Martensite vanished after Ni implantation because of sputter removal, not phase transformation, during Ni bombardment. The Ne-implanted layer remained predominantly martensite. Changes in wear rates and microstructures were confined to depths commensurate with the range of ions in the implanted layer. Several hypotheses on the effects of ion implantation on microstructureand wear are discussed.