A study on the formation of wear debris during abrasion

A set of five material specimens have been tested on five abrasives, some of which are harder, some softer than the materials, using the dynamic abrasive wear tester. Characteristics of selected wear debris have been observed by sem and wear debris of 9Cr2Mo steel analysed by Mossbauer spectroscopy. The test results show three wear mechanisms operating during abrasion: microcutting, plougging deformation and brittle fragmentation. Different abrasives formed different constituents of wear debris due to dissimilar wear conditions. Softer abrasive tended to form more ploughing debris, although some typical microcutting chips were produced. Crushing strength of abrasive may be an important factor in addition to hardness of abrasive. The microstructure of 9Cr2Mo steel wear debris has been changed by abrasion heat; this temperature could be estimated by Mossbauer spectroscopy.     

A model for the friction of multiphase materials in abrasion

A model is presented for the sliding friction of multiphase materials in abrasion. The friction is described in terms of the load distribution between the phases. Different load distribution modes are used with Amontons' first law of friction to derive both the friction force and the coefficient of friction as functions of the area fractions of the phases, their individual coefficients of friction and their wear resistance. It is shown that the coefficient of friction of a multiphase material should depend on the load distribution mode and that the upper and lower limits for the coefficient of friction expected from composites or multiphase materials can be identified. For most pressure distribution modes, the friction depends on the wear resistance of the phases. The model is compared with results from abrasion tests on a silicon carbide reinforced aluminium alloy (AlSi7Mg) over a wide range of loads and with different fixed abrasive particles. The experimental results are described and interpreted in terms of the model.     

Abrasive wear characteristics of a zinc-based alloy and zinc-alloy/SiC composite

An attempt has been made in this investigation to assess the contribution of various parameters towards governing the abrasive wear response of a zinc-based alloy under the conditions of varying applied loads and sliding distances. The factors whose contribution has been examined include deterioration in the cutting efficiency of the abrasive medium, role played by the SiC particles (dispersed in the alloy matrix) in terms of their degradation and resistance offered by them against the destructive action of the abrasive, subsurface hardening of the matrix and such other related aspects. Four types of abrasion tests were conducted on the samples to achieve the goal. The (abrasion) tests involved the use of (i) fresh as well as preworn surfaces of the samples and (ii) fresh and degraded abrasive media in four different combinations.The study suggests that the mentioned factors contribute to a varying degree towards controlling the (high-stress) abrasive wear behaviour of the specimens. However, degradation in the cutting efficiency of the abrasive medium (through capping, clogging, attrition and shelling) dominates over the influence of other parameters such as abrasion induced subsurface hardening of the matrix. Reinforcement of the SiC particles in the alloy matrix offered improved wear resistance (inverse of wear rate) under less severe conditions such as at low applied loads, wherein the dispersoid (SiC) particles could be retained by the matrix due to low cutting depths made by the abrasive particles. The dispersoid particles deteriorated the wear response of the matrix under more severe conditions of abrasion, such as at high loads, because of larger cutting depths causing fracturing and partial removal of the reinforcement (SiC) particles. The observed wear response of the samples has further been substantiated through the characteristics of wear surfaces, debris particles and abrasive medium after testing the matrix alloy and composite in a typical test condition expected to affect the abrasive medium and test specimens to the largest extent.     

Study of abrasive wear phenomena in dry and slurry 3-body conditions

Machinery and equipment used in abrasive environments, such as the mining industry, suffer from severe wear. In order to understand wear and to prolong the life time of the machinery, it is important to understand how materials respond to wear depending on the environmental and tribological conditions imposed.This paper exposes a comparative study between the influence of two abrasive environments (dry and slurry) on hard particle coatings and steels. To study this, the 3-body wear behaviour was evaluated in a dry environment using a continuous abrasion test (CAT) and in a slurry environment using a slurry steel wheel abrasion test (SSWAT) method. Both tests are capable of experimentally modelling the high stress wear at 45 N and 216 N, using quartz sand as an abrasive. The tests were performed on two types of coatings processed by sintering and hardfacing and martensitic steel was used as a reference. The wear was indicated as volume loss by measuring the samples before and after the tests. Furthermore, the specific wear energy was calculated in order to have a fundamental understanding about the material's response to wear. A correlation between the wear rate and the particle brakeage index (PBI) was done for the dry conditions using different loads, in order to explain the interdependence between the two parameters and the change in the wear mechanism between the two loads. The influence of load on the wear of the materials showed different wear mechanisms on coatings compared to the steel in the same environmental conditions. However, a change in wear mechanism at different load levels was observed, which might be directly dependent on the change of the particle's motion from sliding to rolling combined with the change in their shape and size. The results showed that the need to study the influence of different abrasive conditions on the material wear is crucial in order to improve the lifetime and the cost efficiency of the machinery used in such environments. The hard-particle coatings showed comparatively low wear rates promising a great potential in improving the lifetime of industrial equipments in different environments.     

Influence of hardness of the counterbody in three-body abrasive wear — an overlooked hardness effect

The resistance to three-body abrasion of some common metals, mainly a tool steel and an aluminum alloy, both heat treated to different hardnesses, has been evaluated in two different tribosystems. The different materials have been tested against each other in different combinations to study the influence of the relative hardness of the two bodies on the wear rate in three-body abrasion. In all tests the abrasives have been much harder than the metals. It was observed that the wear rate of asolid body in three-body abrasion strongly depends on the hardness of the counterbody. In three-body abrasion a material may, under some circumstances, be most strongly worn if the counterbody is softer than the metal to be worn. This is because the abrasive particles can be embedded in the softer surface and groove the harder one. However, many parameters of the tribosystem influence the embedding of particles and the wear rate in three-body abrasion. It is shown that the size of the area in which the abrasives are embedded compared to the size of the wear scar in the counterbody as well as the smoothness of the surfaces are of importance.     

高速切削Inconel 718刀具磨损形态和机理分析

利用涂层硬质合金刀具对Inconel 718进行了高速干切削试验,采用扫描电子显微镜SEM和能量分散光谱EDS扫描,对不同切削参数下刀具的损坏形态和损坏机理进行了研究。分析结果表明刀具损坏形式主要有前刀面磨损、后刀面磨损、剥落和崩刃。刀具损坏机理主要是粘结磨损、磨粒磨损、氧化磨损和扩散磨损等。     

Abrasive wear behavior of thermally sprayed diamond reinforced composite coating deposited with both oxy-acetylene and HVOF techniques

Diamond and diamond-based coatings have long been studied for their exceptional properties. Although a great deal of research has been carried out in this field, little is known about their tribological wear behavior. In the present work, diamond reinforced composite (DRC) coatings of varying diamond content was deposited on mild steel substrates using both oxy-acetylene (OA) and high velocity oxy fuel (HVOF) thermal spraying techniques. The high stress abrasive wear behavior of these coatings is studied by performing two body abrasion tests for varying experimental parameters. It is observed that the HVOF-sprayed coatings suffered abrasion at a relatively low wear rate. The reasons for variations observed in the wear rate as a function of displacement during abrasion and grit size could be attributed to the deterioration of abrasive particles and the particle size effect respectively. While the disparity in the wear rates with respect to composition of the coatings was primarily controlled by the diamond content in the coating. The abrasive wear mechanism was found to be the same in both the coatings except that the coating deposited by HVOF spray technique, offered better abrasion resistance and therefore abraded at a slower rate. This is possibly due to lower porosity in the coating and higher bond strength between reinforced diamond particulates and the bronze matrix in HVOF-sprayed specimens.     

The design of a finger wear simulator and preliminary results

A dual-cycle finger wear simulator has been designed, manufactured and commissioned. The simulator interspersed dynamic flexion-extension motion under light load with a heavier static 'pinch' load to a test prosthesis immersed in a lubricant heated to 37 degrees C. A validation test was undertaken on a size 2 Swanson prosthesis, leading to prosthesis failure in less than 1 million cycles. A second test was carried out on a Durham metacarpophalangeal prosthesis. After 4.8 million cycles a total wear factor for the joint of 0.60 x 10(-6) mm3/N m was calculated, with no cracks or damage visible. Both test results compare well with earlier tests undertaken on the Stokoe finger wear simulator.     

Analysis of the friction and wear mechanisms of multilayered plasma-sprayed ceramic coatings

Wear tests were conducted on a rotor-vane-disk adaptor where three rotating vanes were pressed against a disk. Vanes were coated by WC and used as the upper specimen while the disk was coated by Cr₂O₃ and used as the lower specimen. A buffer layer of various thicknesses and contents was placed between the top coating and the bulk steel of the disk to alleviate the effects of the large difference in thermal properties of the two materials. The experimental results reveal that correct placement of a buffer layer can indeed improve the wear resistance. Factors such as the temperature to which the specimen was heated before testing, the proportion by weight of each individual constituent in the buffer layer, and the thickness of each coating layer, were also important for the volume of wear of the lower specimen. As the specimens were heated to higher temperatures, the wear volume decreased with increasing proportions of Cr₂O₃ in the buffer layer. Elevating the preheating temperature of the specimens can diminish the wear volume but increases the friction coefficient. The steady-state wear rate is not much influenced by the constituents of the buffer layer and the coating thickness. Brittle fracture, abrasion, adhesion and oxidation were found to be the primary wear mechanisms in the tests.     

The effect of kinematic conditions on the wear of ultra-high molecular weight polyethylene (UHMWPE) in orthopaedic bearing applications

It is known that wear mechanisms differ between the ultra-high molecular weight polyethylene (UHMWPE) components of total hip replacement (THR) and total knee replacement (TKR). The difference in relative contact position or 'kinematic conditions of contact' between the metal and polymer components is thought to contribute to the contrast in observed wear mechanisms. A reciprocating wear tester was used to evaluate three basic kinematic contact conditions: sliding, in which the relative contact position on the polymer remains stationary; gliding, where the contact position on the polymer reciprocates; and rolling, where the contact position on the polymer varies and the relative velocities of both components are equal. All static load tests used cast Co-Cr alloy and irradiated Chirulen UHMWPE in a 37 degrees C environment lubricated with bovine serum albumin. UHMWPE test sample wear was measured gravimetrically at intervals of 600,000 cycles. The results indicated a difference in wear factor (volume lost due to wear per unit load per unit sliding distance) between the three groups with varying relative motion. The study indicates that screening tests which evaluate wear properties of new materials for total joint replacement should reflect the different kinematic contact conditions.     

Wear mechanisms in polymer matrix composites abraded by bulk solids

An experimental study of the wear of polymer matrix composite materials subjected to abrasion from bulk materials has been conducted. Three examples of vinyl ester resin systems were considered: (a) unreinforced, (b) reinforced with glass fibres, and (c) reinforced with particles of ultra high molecular weight polyethylene (UHWMPE). Soft and hard bulk materials used for abrasion were granular forms of coal and the mineral ignimbrite. The bulk material was presented to the wear surface on a conveyor belt in a novel wear tester. While UHWMPE reinforcement enhanced the wear resistance to both hard and soft abrasives, the situation for fibre reinforcement was more complicated. With coal as the abrasive, it was found that glass fibre reinforcement reduced the wear rate, whereas in the case of the harder ignimbrite, fibre reinforcement increased the wear rate. Microscopy indicated significant differences in the mechanism of wear in each surface/abrasive combination. Wear textures, consistent with both two and three-body wear, were observed with, respectively, soft and hard abrasive particles.     

Wear of low temperature nitrided steels under different wear processes

A programme of tests has been carried out to assess the wear resistance of three low temperature nitriding treatments when compared with the untreatedv steel and a standard cyanide case-hardening treatment, under conditions of scuffing, abrasion, fretting and corrosion. The main conclusion is that low temperature nitriding is most suited to applications where scuffing and corrosion are the main wear mechanisms and that the resistance to abrasion and fretting is poorer in general than that of traditional case-hardening. Therefore, care should be taken in assessing the wear process in any application in which these treatments are used. Reference is also made to the wear mechanisms in the different tests.     

Influence of precipitation and solution strengthening on abrasive wear resistance

The influence of precipitation and solution strengthening on gouging abrasion resistance has been studied using a 6061 aluminium alloy heat treated to obtain four different microstructures. Single-event abrasive grooves were generated using a modified Charpy impact tester and the specific energy consumption in grooving was recorded and used as a measure of wear resistance. In addition, the mechanisms of chip formation and material removal were studied by metallographic analysis of “quick-stop” specimens.The results of the grooving tests show that for small grooves precipitation strengthening yields higher energy values than solution strengthening, the wear resistance increasing with decreasing precipitate size. The ranking of the different heat treatments with respect to specific grooving energy depends, however, on the considered damage depth and the opposite order of ranking is found at the largest groove depths. On the basis of the results of the grooving tests, a discussion on the influence of groove depth and microstructure on chip formation and specific grooving energy is presented. In particular, the inhomogeneous nature of the plastic deformation involved in chip formation is discussed, and the resulting importance of the thermal stability of the material in determining wear resistance is emphasized.     

Wear of Chromium Carbide-Copper Composites with Continuous Phases

A tribological study has been carried out on a new type of carbide-metal composite, in which the two phases form a continuous skeleton microstructure interwoven throughout the body. The composites' resistance to two-body abrasion is evaluated in a pin-on-drum set-up with diamond and SiC abrasive papers. Also sliding wear and friction tests with steel and alumina as counter materials were undertaken. The composites show promising tribological properties, comparable to those of established wear resistant materials. Scanning electron microscopy was used to study the worn surfaces. The implications of the skeleton microstructure on the abrasive wear resistance are discussed on the basis of a wear model for multiphase materials.     

Abrasive wear resistance of some commercial abrasion resistant steels evaluated by laboratory test methods

The aim of the present study is to evaluate the abrasive wear resistance of some potential abrasion resistant steels exposed to different types of abrasive wear contact conditions typical of mining and transportation applications. The steels investigated, include a ferritic stainless steel, a medium alloyed ferritic carbon steel and a medium alloyed martensitic carbon steel.The abrasive wear resistance of the steels was evaluated using two different laboratory test methods, i.e. pin-on-disc testing and paddle wear testing that expose the materials to sliding abrasion and impact abrasion, respectively. All tests were performed under dry conditions in air at room temperature. In order to evaluate the tribological response of the different steels post-test characterization of the worn surfaces were performed using optical surface profilometry, scanning electron microscopy and energy dispersive X-ray spectroscopy. Besides, characterization of the wear induced sub-surface microstructure was performed using optical microscopy.The results show that depending on the abrasive conditions a combination of high hardness and toughness (fracture strain) is of importance in order to obtain a high wear resistance. In the pin-on-disc test (i.e. in sliding abrasion) these properties seem to be controlled by the as-rolled microstructure of the steels although a thin triboinduced sub-surface layer (5–10 μm in thickness) may influence the results. In contrast, in the paddle wear test (i.e. in impact abrasion), resulting in higher forces acting perpendicular to the surface by impacting stones, these properties are definitely controlled by the properties of the active sub-surface layer which also contains small imbedded stone fragments.     

Subsurface characteristics of an abraded low carbon steel

Ductile metals commonly exhibit plastic deformation at and near the worn surface and their flow behaviour at large strains has a clear effect on wear resistance. In this study, the characteristics of the near-surface region of a ferritic-pearlitic steel (0.2% C, 1.2% Mn), subjected to abrasive wear tests, were examined. Wear tests were performed under different loads by rubbing the specimens on sliding 60 mesh Al₂O₃ abrasive band. The metallographic technique used to determine the magnitude of plastic deformation was based on measurement of the displacements of pearlite bands. The hardness of the plastic deformation zone was determined by performing ultramicrohardness tests along ferrite bands with a Vickers indenter. Microscopic examinations of the near-surface regions revealed the wear mechanism to be ploughing and the deformation mechanism to be cross-slip. It was observed that plastic strain (more than 6) occurred on the abraded surface, and increased the hardness to about 1.5 times the original value. The strain and hardness gradient extended to a larger depth into the bulk with increasing wear test load. It is concluded that the wear resistance of the investigated steel increases by work hardening of the near-surface region which is required to consume high energy for abrasion, during sliding. Ultramicrohardness measurements performed on worn specimens revealed high hardness, as the indent size decreased. The indentation size-hardness relation was explained by a dislocation model incorporating geometrically necessary dislocations due to the presence of strain gradients in the deformation region around the indent.     

Simplified motion and loading compared to physiological motion and loading in a hip joint simulator

Two wear tests were conducted using the Durham Hip Joint Wear Simulator to investigate the effects of simplified motion and loading on ultra-high molecular weight polyethylene (UHMWPE) acetabular cup wear rates. Bovine serum was used as a lubricant and a gravimetric technique was used to measure wear. The first wear test duration was 7.1 x 10(6) cycles and investigated the effect of simplified loading. This was achieved by using full physiological motion and loading for the first 5 x 10(6) cycles of the test, then physiological motion with simplified loading for the final 2.1 x 10(6) cycles of the wear test. The UHMWPE acetabular cup wear rates using full physiological motion and loading were 32.2 and 51.7 mm3/10(6) cycles against zirconia and CoCrMo femoral heads respectively. Using simplified loading the cup wear rates were 30.1 and 49.2 mm3/10(6) cycles against zirconia and CoCrMo respectively which was not significantly different from wear rates with physiological loading. The effect of simplified motion was investigated in a second wear test of 5.0 x 10(6) cycles duration. Physiological loading was applied across the prosthesis with physiological motion in the flexion/extension plane only. Mean wear of the acetabular component dropped to 0.197 mm3/10(6) cycles. The surfaces of all the acetabular cups were subject to gross examination, optical microscopy and scanning electron microscopy. No notable difference was observed between the cups subjected to physiological motion and loading and those subjected to simplified loading. The cups worn with a single plane of motion had a much smaller worn area and a notable difference in surface features to the other cups. Simplifed loading is therefore an acceptable simplification in simulator testing but simplifying motion to the flexion/extension plane axis only is unacceptable.     

Cemented carbide and cermet tooling for film-perforating

The tools used to perforate a particular photographic film started to wear at an unacceptable rate when the film base was changed from cellulose triacetate to polyester (PET). A laboratory investigation was initiated to screen candidate tool materials and identify ones with potential for 10 times life improvement over cemented carbide (WC/10% Co).

The screening tests started with abrasion and corrosion tests on various grades of cemented carbide, cermets and selected ceramics. Concurrent production trials indicated that the laboratory corrosion tests were not correlating with production results. To address this problem, a “nibbler” test was developed which simulates perforating and material removal on a punch after 10⁶ perforations (nibbles) became the screening test metric.

It was determined that abrasion tests do not accurately predict tool material behavior when chemicals are present on or in the materials being perforated. Static corrosion tests do not predict tool response under production conditions. The rubbing of the film on the tool surfaces removes protective films and there can be a significant corrosion component in tool erosion. The nibbler simulates real tool conditions because erosion is produced by actual cutting of coated webs. Nibbler tests in this study indicated that alumina/zirconia resisted film erosion better than cemented carbide, even cemented carbide with PVD coatings. The nibbler tests also indicated that leaving recast layers from electrical discharge machining on cemented carbide greatly increases erosion rates. It should be removed.

Production tests conducted since completion of these laboratory studies suggests that nibbler results correlate with production results. Coated cemented carbides are providing 3 times the service life of uncoated cemented carbides as predicted by the nibbler test.     

Strain Hardening: Can it Affect Abrasion Resistance?

It has been largely reported in the literature that previous strain hardening has none or negligible effect on abrasive wear resistance. Those results are mainly obtained using sand rubber wheel tests and pin-on-disk tests, and have been attributed to the large strain hardening promoted by the abrasion phenomena themselves. The stresses involved in those tests are very high and the stress distributions spread toward subsurface regions at large depths. This work investigates the effects of strain hardening on low-severity (low stress at low depth) abrasive wear resistance. Microabrasion tests, normally regarded as lower stress tests, were used in order to impose low severity. Two types of stainless steels were tested: an austenitic AISI 304 steel and a ferritic AISI 430 steel. Strain hardening was obtained via thickness reduction (20%) of stainless steel sheets in a laboratory cold rolling mill. The microabrasion wear tests were carried out in a fixed-ball microabrasion tester with a three-axis load cell to continuously and simultaneously monitor the forces involved in the tests. Contrary to many findings so far in the literature, previous strain hardening increased abrasion wear resistance (55 and 63%, respectively) for both materials. Hertz calculations, simulations using Finite Element Program with explicit solution, conventional mechanical tests, microhardness profiles, microstructural analysis, and X-ray diffraction analysis were used to explain this paradigm shift for the case of microabrasion tests.     

Influence of heat and thermochemical treatment on abrasion resistance of structural and tool steels

Abrasive wear is responsible for intensive degradation of machine parts or tools. This process starts as an interaction between hard, mostly mineral, particles and the working surface. Methods of increasing the lifetime are based on application of abrasion resistant materials or creation of hard, wear-resistant surface layers or coatings on the surfaces of machine parts or tools. Carbon and low-alloy steels with different types of thermochemical treatment (case hardening, nitriding) are used in cases of low abrasion. Another method of increasing lifetime is the application of ledeburitic steels. The wear resistance of these steels depends on their chemical composition and heat treatment. The results of laboratory tests of thermochemically treated steels, heat-treated ledeburitic chromium steels and high-speed steels show the effect of the microstructure of these steels on their abrasion resistance. Abrasion resistance of carburized low-alloy steels is on the same level as in high-carbon structural and tool steels. In ledeburitic chromium steel maximum abrasion resistance was achieved by quenching from 1100 °C whilst in ledeburitic chromium–vanadium steel the optimum quenching temperature was 1150 °C. Growing abrasion resistance was caused by increasing amounts of retained austenite.