Frequency effects in fretting wear

The effect of frequency of vibration on fretting wear has been investigated in the 10 – 1000 Hz range with additional experiments at 20 000 Hz. Fretting tests were performed with two materials, a low carbon steel (AISI 1018) and an austenitic stainless steel (AISI 304). The experiments showed that two cases of fretting contact can be distinguished and related to the displacement amplitude. If the amplitude is low, the contact situation is characterized by partial stick at the interface. At these conditions the wear rate (measured as the volume of material removed per cycle) is little affected by frequency. However, in low amplitude fretting material damage by surface degradation and fatigue crack initiation is usually of more concern than the actual wear itself. Both of these parameters are found to be greatly accelerated by an increase in frequency. In high amplitude fretting, in contrast, gross slip occurs at the interface and wear becomes the dominant damage mode. At these conditions variations in frequency appear to have little effect on fretting wear and related mechanisms. Therefore, in the case of fretting at high displacement amplitudes, it may be possible to apply high frequency fretting to obtain accelerated testing conditions.     

Wear mechanisms in oil-lubricated and dry fretting of silicon nitride against bearing steel contacts

The wear and friction behaviour of silicon nitride against bearing steel was investigated under lubricated and dry fretting conditions as a function of amplitude and test duration. Tests were performed on a high frequency fretting tester. Silicon nitride bearing balls were used as the upper oscillating specimens while the lower stationary flats were standard specimens of bearing steel. Amplitudes in the intermediate 5 to 50 μm range and a test duration from 10 to 360 min were studied. In lubricated conditions a commercial lubricant. ISO VG 220, was used. Light microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Auger spectroscopy (AES) and transmission electron microscopy (TEM) were employed to determine the wear mechanisms.

Under lubricated conditions transition from high to low wear volumes was recognised with increasing amplitude. At lower amplitudes and in the early stage of fretting tests at moderate amplitudes, mechanical wear dominated. Cracks on the stick-slip boundary and spalling of a thin tribolayer was observed. Under these conditions the highest wear in lubricated fretting was obtained. In the final stage of fretting tests at moderate amplitudes, and from the beginning at higher amplitude, tribochemical wear is suggested as the dominant wear form. A 0.2 μm thick tribolayer was observed on the contact, containing inclusions with different Fe and Si contents. A very high concentration of carbon, formed by oil degradation, was also determined in this layer, confirming the critical influence of oil on the wear behaviour.

Quite a different wear mechanism is proposed for dry fretting conditions. Results of AES analysis showed a layer an order of magnitude thicker than in lubricated fretting, also having a remarkably different chemical composition. TEM analysis confirmed that the reaction layer consisted of a silica-rich amorphous phase containing small inclusions of Fe₂O₃ and Fe₃O₄. In contrast to lubricated conditions, where the layer created was ductile, in the case of dry fretting the layer was brittle. The continuous process of forming and spalling the brittle tribolayer caused much higher wear rates and wear losses than under lubricated fretting conditions. No transition in wear behaviour was observed as was the case in lubricated fretting.     

Fretting of WC/a-C:H and Cr2N Coatings Under Grease-Lubricated and Unlubricated Conditions

The fretting phenomenon was investigated experimentally in contacts between coated and uncoated steel rod and ball specimens generating a circular Hertzian contact. A fretting wear test rig equipped with a video camera was used to observe the effects of fretting on coated steel surfaces in both grease-lubricated and unlubricated environments. Tungsten carbide reinforced amorphous hydrocarbon (WC/a-C:H) and chromium nitride (Cr₂N) coatings were tested and compared. Fretting wear volumes and surface profiles are presented for both grease-lubricated and unlubricated conditions. Videos of a coated ball fretting against a transparent sapphire flat were recorded and screen captures are presented. The role of normal load, lubrication, frequency, and amplitude of motion on the fretting wear of coatings is discussed. The lubricant released from the grease was observed to flow through channels in the stick zone of the fretting contacts. Both coatings were found to reduce fretting wear. WC/a-C:H was more effective at reducing wear under unlubricated conditions. WC/a-C:H decreased fretting wear more than Cr₂N when delamination was avoided in grease-lubricated contacts.     

Fretting of Hardened Steel in Oil

To determine the effect of hardness on fretting wear, tests of AISI 4340 steel were made in an oil bath using a new machine designed to make fretting corrosion tests with a wide range of parameters. Hardness values from 258 to 743 Vickers were tested, the hardest specimen having a nitrided surface. The fretting action used, 0.005 in. reciprocating motion at pressures from 430 psi to 5840 psi, produced much less fretting than similar tests in air, with little or no oxide products resulting. The galled areas were measured for depth of pit and height of deposit with the results indicating some small effects due to hardness up to 460 Vickers. The nitrided specimens, however, produced smaller fretted areas and the roughening of their surfaces was shallow.     

Fretting fatigue of zinc coated low carbon steel EN H320 M

The object of the present study was to investigate the influence of zinc coatings on steel sheets during fretting fatigue and fatigue tests. The influence of the fatigue stress range, normal pressure and amplitude of slip, on the fracture life was studied for both coated and uncoated EN H320 M steel. The wear produced by fretting was measured and compared with the fracture life evolution for different values of slip amplitude. The wear scars and the fracture surfaces were examined by scanning electron microscopy to identify the degradation mechanism. Although zinc films do not influence the fatigue life of the tested steel, when fretting is superposed on to a fatigue stress the coating markedly improves the fracture life.     

Influence of high-power diode laser heat treatment on wear resistance of a mold steel

The effect of hardness on wear loss and wear behavior during fretting was studied. A high-power diode laser was used to achieve the surface hardening of a mold steel (AISI P20-improved) at temperatures of 1000 and 1200 °C. A hardness increment was detected in laser heat-treated specimens, which may be attributed to phase transformation from ferrite to martensite, influencing wear loss and fretting wear behavior. In the fretting test results, smaller wear scars and less wear loss were observed for laser heat-treated specimens in comparison to those of base metal. Moreover, relatively more stable friction coefficient profiles were obtained for the laser heat-treated specimens due to uniform contact characteristics at two contacting surfaces. The effectiveness of the proposed technique was verified by the morphology of the wear scars of the treated specimens, which had a smooth appearance and minor abrasion grooves.

     

An investigation of fretting behaviour of several metallic materials under grease lubrication

Fretting wear tests under grease lubrication have been carried out on an aluminium alloy, 52100 steel and low-alloy steel. The sphere–flat contact configuration is used. The influence of the displacement amplitude and normal load is investigated. Comparison between dry and lubricated contact of aluminium alloy, between 52100/52100 steel and 52100/low-alloy steel contact with grease lubrication has been carried out. Results show that grease lubrication strongly affects fretting behaviour. Base oil that separated from the grease during friction may result in accelerated contact wear by fretting.     

不锈钢焊接区金属微动磨损行为研究

以1Cr18Ni9Ti不锈钢材料为母材,采用焊条电弧焊方法制备焊件。在焊接检验合格的焊态试件上从焊缝区、熔合区和焊接热影响区金属中分别截取并制备微动磨损试验用试样。将制备好的焊接区不同位置金属试样在相同条件下进行微动磨损试验,研究焊接区金属微动磨损行为。研究结果表明,在选定的微动磨损试验参数下,微动处在完全滑移区;焊接区不同部位金属的微动磨痕形貌存在差异,具有不同的微动磨损行为。焊缝区金属磨痕最大深度差异不明显,但磨痕平面投影面积差异显著。焊接热影响区金属磨痕最大深度差异显著,而磨痕平面投影面积差异不明显。     

An experimental study torsional fretting behaviors of LZ50 steel

Four simple fretting modes are defined according to relative motion: tangential, radial, rotational, and torsional fretting. This paper presents a new test rig that was developed from a low-speed reciprocating rotary system to show torsional fretting wear under ball-on-flat contact. Torsional fretting behavior was investigated for LZ50 steel flats against AISI52100 steel balls under various angular displacement amplitudes and normal loads. The friction torques and dissipation energy were analyzed in detail. Two types of T–θ curves in the shape of quasi-parallelograms and ellipticals were found that correspond to gross and partial slips, respectively. The experimental results showed that the dynamic behavior and damage processes depend strongly on the normal loads, angular displacement amplitudes, and cycles. In this paper, the debris and oxidation behaviors and detachment of particles in partial and gross slip regimes are also discussed. Debris and oxidation are shown to have important roles during the torsional fretting processes. The wear mechanism of torsional fretting was a combination of abrasive and oxidative wear and delamination before third-body bed formation. The mechanism was then transformed into third-body wear after a great amount of debris formed.     

Characterization of fretting wear behavior of Cu–Al coating on Ti–6Al–4V substrate

Fretting wear and fretting fatigue are two commonly observed material damages when two contacting bodies with a clamping load are under the oscillatory motion. In this study, fretting wear damage of Cu–Al coating on titanium alloy, Ti–6Al–4V substrate was investigated using the dissipated energy approach. Fretting tests were conducted with either no fatigue load or the maximum fatigue load of 300 MPa and stress ratio of 0.1 on the substrate (specimen). In order to investigate the effect of contact load and contact size, different pad sizes and contact loads were used in the tests. Accumulated dissipated energy versus wear volume data showed a linear relationship regardless of fatigue loading condition on specimen with the smaller pad size. However, two separate linear relationships were observed based on the fatigue loading condition with the larger pad size, such that a relatively more dissipated energy was required for a certain amount of wear with fatigue load on the specimen. The linear relationship between the accumulated dissipated energy and wear volume for both pad sizes extended from partial to gross slip regimes and was not affected by the applied contact load. Further, fretting tests with and without fatigue load resulted in different shapes of fretting loops when the larger pad size was used.     

Elevated Temperature Fretting Evaluations Using a Flat-on-Flat Configuration

Traditional fretting tests rely on the high Hertzian stress contacts between a cylinder or sphere and a flat surface to generate oxide particles and an eventual wear scar. However, this configuration does not always match the stresses and wear mechanism associated with parallel surfaces where fretting may only initiate in limited regions of contacting asperities. To simulate these conditions at 175°F, fretting wear tests were used to evaluate the performance of High Velocity Oxy-Fuel (HVOF) and Plasma-sprayed Cu Ni In coatings for the reduction of gross-slip fretting (relative displacements of 100 μm) experienced between mating beta-c titanium bosses and 4340 steel lugs. Scanning electron microscopy was then used to compare the frequency and severity of fretting wear on the titanium blocks. Results of the analysis indicated the viability of the lubricious coatings for eliminating the instances of fretting. Furthermore, the tests indicated the usefulness of the flat-on-flat testing configuration for illuminating the potentially random occurrences of fretting damage between parallel surfaces.     

Laboratory fretting tests with thin wire specimens

Wire ropes, due to their construction and application, are prone to fretting damages. In order to know the wear behaviour of individual wires under fretting conditions, laboratory tests are required. The present work describes the preliminary fretting tests accomplished with thin steel wires to optimise the testing procedure. The tests were carried out with ‘crossed‐cylinders’ configuration varying the stroke and normal load. Afterwards, the fretted surfaces were characterised by means of an optical and scanning electron microscope, and a diamond stylus. No significant influence of selected parameters was detected and a good correlation was proved for on‐line measured parameters and off‐line obtained values. Copyright © 2007 John Wiley & Sons, Ltd.     

Fretting wear behaviour of polymethylmethacrylate under linear motions and torsional contact conditions

The fretting wear behaviour of PMMA against a rigid counterface has been investigated under various contact zone kinematic conditions. A specific device has been used in order to achieve load axis spin or stationary rolling motions in a contact between a PMMA flat and a steel ball. Wear processes under such conditions have been investigated by means of laser profilometry and in-situ optical observations of the contact area during tests. Very different wear patterns were produced depending on the contact kinematics. For stationary rolling conditions, the progressive accumulation and compaction of debris induced the formation of a single ripple located in the middle of the contact. Very little debris was found to be eliminated from the contact and the resulting wear was quite low. On the other hand, little accumulation of debris was observed for torsional contact conditions and the wear was drastically enhanced. These results are analysed by considering the effects of contact zone kinematics on particle detachment and third body elimination.     

Study on transition between fretting and reciprocating sliding wear

An experimental investigation was conducted to find the associated changes in characteristics of wear before and after the transition between fretting and reciprocating sliding wear. A set of experiments were carried out using a AISI 52100 steel ball rubbing against a plate specimen made from the same steel under dry condition. Wear coefficient, wear volume, coefficient of friction, profile of the scars and wear debris were analyzed. The results displayed that there were significant differences in wear coefficient, wear volume, profile of the wear scars and wear debris before and after the transition. Wear coefficient and wear volume at a constant sliding distance were found to be the most appropriate for identifying the transition amplitude between fretting and reciprocating sliding wear.     

Tribological behaviour of AISI 316L stainless steel for biomedical applications

Abstract

The aim of this research is to study the tribological behaviour of AISI 316L stainless steel for surgical implants (total hip prosthesis). The tribological behaviour is evaluated by wear tests, using tribometers ball on disc and sphere on plane. These tests consisted of measuring the weight loss and the friction coefficient of stainless steel (SS) AISI 316L. The oscillating friction and wear tests have been carried out in ambient air with an oscillating tribotester in accord with standards ISO 7148, ASTM G99-95a and ASTM G133-95 under different conditions of normal applied load (3, 6 and 10 N) and sliding speed (1, 15 and 25 mm s^?1). A ball of 100Cr 6, 10 mm in diameter, is used as counter pairs. These tribological results are compared with those carried out with a tribometer type pin on disc under different conditions of normal load applied P (19·43, 28 and 44 N) and sliding speed (600 and 1020 rev min^?1). The behaviour observed for both samples suggests that the wear and friction mechanism during the tests is the same, and to increase the resistance to wear and friction of biomedical SS AISI 316L alloy used in total hip prosthesis (femoral stems), surface coating and treatment are necessary.     

An investigation of the fretting behaviour of low friction coatings on steel

Three different low friction coatings on steel (electrolytically deposited cadmium, PTFE solid lubricant in epoxy resin and PTFE solid lubricant in polyimide resin) were studied in order to relate their fretting behaviour with mechanical properties. Particular importance was given to adhesion which was measured using a scratch test. Fretting tests were carried out on the steel substrate and on the coatings under the same conditions. The major parameters of the tribological system were identified and then quantified. The values of the parameters obtained for each coating were compared with the corresponding values for uncoated steel. The mechanical characteristics of the coatings and their fretting parameters were plotted using a polar diagram in order to give an overview of the fretting behaviour of each coating. Differences were noted and the corresponding parameters were identified. The influence of the adherence of the coating and of the fretting test load on the lifetime of the coating was determined.     

Fretting wear behaviors of steel wires under friction-increasing grease conditions

Fretting wear tests were performed on the self-made fretting wear rig to investigate fretting wear behaviors of steel wires under friction-increasing grease conditions. The results demonstrated that the fretting regimes were dependent on displacement amplitudes and normal loads. The friction coefficient exhibited different variation trends in different fretting regimes. Friction-increasing grease changed the fretting running behavior and had a very good wear resistance for steel wires. Wear was slight in partial slip regime. Mixed regime was characterized by plastic deformation, fatigue cracks and abrasive wear. Slip regime presented main damage mechanisms of abrasive wear, fatigue wear and oxidation.     

Fretting wear and friction behaviour of engineering ceramics

Friction and wear characteristics of partially stabilized zirconia (PSZ) fretted against itself and against high carbon steel were investigated. The results for the transformation toughened PSZ ceramics are compared with the behaviour of more brittle alumina ceramic under the same test conditions. Fretting tests in air were carried out on a high frequency wear test rig at room temperature using a cross-cylinder configuration. It was found that both the oxide ceramics were more resistant to fretting wear than the steel. Surface cracking was observed on the alumina wear scars while microfracture and delamination dominated on the PSZ wear scars. When metallic samples were fretted against ceramics, metallic film transfer to the ceramic surfaces occurred.