Fretting wear behaviour of hypereutectic P/M Al–Si in oil environment

The fretting wear behaviour of forged hypereutectic P/M Al–Si in contact with hardened steel and Cu–Sn–Pb bearing material is investigated. Fretting tests are performed with a view to the movement in the contact between the small end of the connecting rod and the piston pin in a car engine. Therefore, the tests are carried out under engine oil lubrication at temperatures up to 150°C. The behaviour of the Al alloy is compared to that of steel, the current connecting rod material. Some tests under non-lubricated conditions are also performed. The correlation between the friction coefficient, the wear volume and the microscopic wear mechanisms is discussed. After the running-in wear, a stable wear condition is reached for the Al–Si/steel contact.     

不同水介质下GCr15/45#钢微动腐蚀行为研究

在洁净水、酸性水和海水3种不同水介质条件下，对GCr15／45^#钢进行了不同位移幅值的微动磨损试验。结果表明：洁净水和酸性水改变了微动区域，降低了摩擦系数和磨损量，具有润滑效果，磨损受水润滑和介质腐蚀双重作用影响,且润滑作用随位移幅值的增加而减弱；对海水，摩擦系数与干态相近,电化学腐蚀作用强烈，磨痕中可观察到大量点蚀坑。     

Differences in Mechanisms for Fretting Wear Reduction between Oil and Grease Lubrication

The different mechanisms of fretting wear in oil and grease lubrication and methods to reduce fretting wear were examined by means of thrust ball bearings in this study. Tests of fretting wear under oil lubrication were conducted. It was confirmed that high-viscosity oil can reduce fretting wear at high velocity (i.e., high frequency) through oil film formation. In the case of grease lubrication, the influence of velocity on fretting wear was significantly different for low- and high-viscosity greases. Grease with low-viscosity base oils could reduce fretting wear at high velocity. In contrast, grease with high-viscosity base oils could reduce fretting wear at low velocity. Grease thickeners were found to be effective in forming a layer that could prevent fretting wear. These results highlight the large differences in effective fretting wear reduction mechanisms between oil and grease lubrication.     

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.     

The Effect of FeS Solid Lubricant on the Tribological Properties of Bearing Steel under Grease Lubrication

In order to improve the tribological properties of 52100 steel under grease lubrication, FeS solid lubricant was used in two ways. Low-temperature ion-sulfurization technology was utilized to prepare solid lubricant iron sulfide (FeS) films on the surface of 52100 steel, and FeS particles were mixed into the lithium grease as additive. The friction and wear properties were examined systematically on a “ball-on-disc” testing machine. The results showed that the tribological properties of bearing steel under grease lubrication can be improved either by using ion-sulfurization technique or by adding FeS microparticles into the grease. The tribological performance of sulfurized surface lubricated by grease is better than that of a plain surface lubricated by grease containing FeS microparticles at lower load and speed. The plain surface lubricated by the grease containing FeS micropaticles possesses better antiwear property under harsher conditions. The mechanism of the experimental results is discussed in detail.     

An experimental study on bending fretting fatigue characteristics of 316L austenitic stainless steel

Bending fretting fatigue tests of 316L austenitic stainless steel plates against 52100 steel cylinders have been carried out under same normal load and varied bending loads. Tests of plain bending fatigue were carried out as a control group. The S-N curves of the bending fatigue were made. The results indicated that there was an obvious drop of life under the condition of bending fretting fatigue due to higher local contact stress. A dislocation model of micro-crack nucleation mechanism, as a manner of zig-zag mode, was created to explain the nucleation of fretting fatigue cracks.     

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.     

Friction and wear behaviour of an Al-Si alloy against steel lubricated with N- and O-containing organic compounds

The friction and wear properties of an Al-Si alloy against AISI 52100 steel were investigated with a block-on-ring wear tester lubricated with a liquid paraffin base oil containing organic additive compounds, such as ethylenediamine, ethyleneglycol, ethanolamine, and N,N-dibutylethanolamine. The boundary film formed on the rubbed surface of the Al-Si alloy was then examined using FT-IR microscopy and XPS. The friction and wear tests revealed that ethylenediamine, ethanolamine and N,N-dibutylethanolamine additives provide good lubrication in the Al-Si alloy-on-steel system, especially N,N-dibutylethanolamine. FT-IR microscopy and XPS revealed the possible formation of a chemically stable five-ring complex of aluminium or silicon with diamine and ethanolamine.     

Fretting wear behavior of TiB2-based materials against bearing steel under water and oil lubrication

Lubricated fretting tests in water and paraffin oil were performed with a monolithic TiB₂, a TiB₂-based cermet with 16 vol.% Ni₃(Al, Ti) binder, a sialon–TiB₂ (60/40) composite and a ZrO₂–TiB₂ (70/30) composite against ball bearing grade steel. Based on the measured friction and wear data, the ranking of the investigated fretting couples was evaluated. Furthermore, the morphological investigations of the worn surfaces and transfer layers are carried out and the wear mechanisms for the investigated friction couples are elucidated. While fretting in water, experiments revealed that tribochemical reactions, coupled with mild abrasion, played a major role in the wear behavior of the studied material combinations. ZrO₂–TiB₂ (70/30)/steel wear couple has been found to have the highest fretting wear resistance among the different tribocouples under water lubrication. Under oil lubrication, extensive cracking of the paraffin oil at the fretting contacts, caused by tribodegradation, leads to the deposition of a carbon-rich lubricating layer, which significantly reduced friction and wear of all the investigated tribosystems.     

The influence of oxygen and water vapour on the friction and wear of an aluminium alloy under fretting conditions

An investigation was conducted to determine the effect of oxygen and water vapour on the friction and wear behaviour of an Al-Zn-Mg alloy under fretting conditions. Fretting wear experiments were carried out in wet air, dry air and in dry argon. In this case the peak-to-peak relative slip amplitude was varied from 20 to 260 μm to determine the critical slip amplitude of fretting wear in these environments.The experimental results indicated that the wear rates in dry air and in dry argon under macroslip conditions were almost the same and quite lower than the wear rate in wet air. This revealed that the effect of oxygen on fretting wear was not large but that water vapour accelerated the fretting wear of the aluminium alloy. The cyclically softened material due to overaging was observed below the contact surface during fretting in wet air. The mechanism involved rapid fretting wear in wet air which caused the removal of a heavily work-hardened layer as it was formed but the softened material below it was not removed.     

润滑剂减缓微动磨损研究进展

综述了油、脂润滑减缓微动磨损的条件、作用机制,以及油、脂性能对微动磨损的影响等基础研究的进展.介绍了油、脂润滑减缓微动磨损的工业应用研究现状,以期为工业正确使用润滑油、脂降低微动磨损指明方向.     

Friction and Wear Behavior of Steels under Different Reciprocating Sliding Conditions

The friction and wear behavior of ISO 100Cr6 steel ball sliding against conventionally hardened carbon and low-alloy steels was studied. The effect of hardness, hardening capacity, normal load, and sliding speed on the coefficient of friction and friction energy was investigated. Friction tests were carried out, without lubrication and under ambient conditions, on a reciprocating friction tester in which a ball-on-flat contact configuration was adopted. The results showed that there is a relative tendency for the friction properties to decrease with increased hardening capacity and decreased hardness. The results showed that increasing normal load decreases the coefficient of friction for the two steel nuances. However, increasing sliding speed increases the coefficient of friction of low-alloy steel and decreases the coefficient of friction of carbon steel. The oxidation of wear debris influences the wear mechanisms and friction behavior.     

On the behaviour of an oil lubricated fretting contact

Although many engineering situations involving fretting damage are lubricated, comparatively little has been reported on this aspect of fretting wear. The viscosity of the lubricating oil and its boundary layer performance are expected to influence fretting behaviour, in addition to the normal fretting parameters, such as stroke and contact force.

This paper examines the effect of lubrication regime, oil viscosity and stroke on the behaviour of a ball-against-flat specimen arrangement. Ball and flat specimens were both manufactured from a bearing steel (SUJ2). Polybutane oils, without additives, covering a range of viscosities from 1 to 10 000 cSt, and fretting strokes up to 35 μm were investigated. The lubricating oil was added to the fretting interface after 0, 3 and 2000 fretting cycles had been completed. Lubrication regime, oil viscosity and stroke were all found to affect fretting behaviour in terms of both coefficient of friction (or traction coefficient) and wear. For strokes less than 9 μm, i.e. for conditions approaching almost complete ‘stick’, coefficient of friction values under oil lubrication were well in excess of double those observed without it. These high values suggest that the oil was unable to penetrate into the fretting contact region, but did maintain a shield around it, so that metal-on-metal contact was maintained under oxygen deprived conditions. The lowest values of steady state coefficient of friction (≈ 0.2) were observed when oil lubrication was applied after 2000 cycles had been completed, indicating that surface roughening and the presence of oxide films and oxidised debris assisted penetration of the lubricant into the fretting contact zone.     

往复冲击对脂润滑成膜性能影响的试验研究

冲击现象广泛存在于工业链、滚动轴承等机械零部件中,严重的情况下会引起冲击磨损。为探究冲击载荷对脂润滑条件下成膜性能的影响,在点接触光干涉弹流试验台上对锂基脂润滑条件下的膜厚演化进行冲击试验研究。试验时钢球和玻璃盘的初始间隙设置为0,冲击载荷按三角波往复变化。结果发现：在第一个冲击周期内,接触区存在大块的增稠剂纤维团,该纤维团造成接触区内的脂膜凹陷;随着冲击周期的增加,接触区内的大块增稠剂纤维团消失,脂膜厚度逐渐降低,润滑状态进入到薄膜润滑状态,最后发生了表面损伤;在任何一个冲击周期内,中心膜厚和最小膜厚大部分的时间都呈现固定值;中心膜厚随着冲击周期数的增加而减小,最小膜厚在最初的100个周期内变化很小,此后逐渐降低,最后为0。     

Fretting corrosion of lubricated tin plated copper alloy contacts: Effect of temperature

The fretting corrosion behaviour of lubricated tin plated copper alloy contacts at ambient and elevated temperatures is addressed in this paper. At 27 °C, lubrication is very effective and the contact resistance remains stable for several thousand fretting cycles whereas at elevated temperatures (155 °C) the performance of lubricated contact is not appreciable. Surface profile and surface roughness confirm that the lubricated contacts have a smoother profile and experience a lesser damage at the contact zone at ambient as well as at elevated temperatures. The mechanism of fretting corrosion of tin plated contacts appears to be similar with and without lubrication at all the temperatures studied. The difference in performance of the lubricated contacts at ambient and elevated temperatures is due to the faster wear rate of tin coating at elevated temperatures. Oxidation of the contact zone of the lubricated contacts is prevented at all temperatures studied. The study concludes that lubrication is effective in improving the life of the tin plated copper alloy contacts under fretting conditions at ambient temperatures whereas at elevated temperatures lubrication provides only a marginal improvement in performance. The decrease in performance of lubricated tin plated contacts at elevated temperatures is due to the higher wear rate of tin coating and not due to evaporation of the lubricant.     

System18牙科支架合金在人工唾液下的微动磨损性能研究

为研究牙科支架合金的微动磨损性能,采用PLINT高精度液压伺服式微动磨损试验机,在法向载荷50N、频率2Hz、位移幅值3-30μm,在大气和人工唾液2种介质条件下,对System18牙科合金进行了微动磨损实验。分析了其微动磨损的动力学特性,并结合光镜（OM）、扫描电子显微镜（SEM）对磨痕及磨屑的成分进行了分析。结果表明：人工唾液对微动运行区域有明显改变;人工唾液明显减轻了System18牙科合金的微动损伤;其主要磨损机制为磨粒磨损和剥层磨损。     

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 behaviour of W-Si coated steels in vacuum environments

This study was focused on the effects of stroke on the fretting behaviour of sputtered W-Si coatings under room and vacuum environments. Fretting tests were carried out with AISI 52100 steel hemispherical ended pin against W-Si coated AISI M2 steel. The tangential force and the applied strokes were monitored during the tests in order to build up the fretting loops. The surface morphology of the wear scars was analysed by optical and scanning electron microscopy (SEM) in order to identify the wear modes and the fretting mechanisms. The shape of the fretting loops was used to characterise the fretting regimes. The formation of adherent films is determinant on the fretting behaviour and depends on the test environment. Electron probe microanalysis (EPMA) was used to analyse the composition of the adherent material and the role of oxides on the formation of the transferred layers. The influence of the coating on the fretting characteristics was discussed comparing coated and uncoated specimens.     

Radial fretting fatigue damage of surface coatings

Radial fretting tests with a 52100 steel ball-on-flat contact have been carried out under different normal loads. TiN, MoS₂ and TiN+MoS₂ coatings on a 1045 steel flat were examined. The normal loads amplitude used were 200, 400 and 800 N at speeds of 12 and 1.2 mm/min. Dynamic analysis in combination with microscopic examinations by SEM and EDX have been performed. It was observed that the vertical stiffness increased with the increase of loading speed and number of cycles. The metallographic examinations showed that little damage was observed for the MoS₂ coating, which exhibited excellent radial fretting fatigue resistance. For the TiN coating, micro-cracks appeared at the lower load while delamination occurred at the higher load. For the TiN+MoS₂ composite coating, the vertical stiffness increased but accompanied by some micro-cracks. As a result of the study, the radial fretting test is proposed as one possible new method to evaluate coating life.     

Boundary Lubrication with Tricresylphosphate (TCP). Importance of Corrosive Wear

The wear of 52100 steel in boundary lubrication condition is controlled by the formation of nonhomogeneous, thin films. When tricresylphosphate is used as an antiwear additive, the buildup of the film is due to a chemical reaction process involving the bearing surface and the lubrication on or near the bearing surface.

A plane-on-plane-type tribometer using a 52100 steel specimen was used to determine the rate of wear and to follow the development of films by the use of the electrical contact resistance method. The results are correlated with the chemical analysis of the additive (polarographic method), with surface analysis of the film (AES and XPS spectroscopies) and finally with the surface topography (surface replicas and electron transmission spectroscopy).

During the mild wear test, several phases of wear are evidenced and the observed relation with TCP decomposition suggests a corrosive wear model proposed in the discussion. Explanations of observed phenomena are offered. (ECR increase, wear reduction, film formation).