Wear Behavior of Aluminum Alloys at Slow Sliding Speeds

The investigated slow sliding speeds presented in this work enable the understanding of the wear behavior on aluminum alloys and could possibly facilitate the completion of the previously proposed wear mechanism map for aluminum at this slow sliding speed range. Dry sliding block-on-ring wear tests were carried out on aluminum alloys, AA5754 (Al-Mg), AA6082 (Al-Mg-Si), and AA7075 (Al-Zn-Cu), at a very slow sliding speed range (<0.01 m/s). A bearing steel ring of AISI 52100 was used as the counterbody. Tests were performed at varying contact pressures, 20, 100, and 140 MPa, and sliding speeds ranging from 0.001 to 1.5 m/s. The wear tracks and debris collected were examined by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD), with the aim of analyzing their morphology and composition. At relatively slow sliding speeds (>0.01 m/s), the specimens exhibited a wear process placed at the mild wear regime, characterized by oxidation and delamination mechanisms of both the aluminum specimen and the steel ring. However, at very slow speed range (<0.01 m/s), an increase in the wear rate and the friction coefficient is observed for all of the aluminum alloys, thus suggesting that an alternative wear mechanism could be taking place.     

高温下轴向柱塞泵滑靴副干滑动摩擦磨损性能*

采用Rtec摩擦磨损试验机模拟不同温度、载荷和转速等工况,研究轴向柱塞泵滑靴副在高温下干滑动的摩擦学规律。通过试验测得的摩擦因数、磨损体积和借助白光干涉三维表面轮廓仪所测得的表面形貌以及磨痕截面曲线,分析其润滑行为及摩擦磨损规律。结果表明：高温下滑靴副的摩擦因数随温度和转速的增大逐渐减小,随载荷的增大而增大;磨损体积随温度的升高先增大后减小,随载荷的增大逐渐增大,随转速的增大先减小后增大;温度和载荷对高温下磨痕的深度影响显著,转速对磨痕的深度和宽度都有影响。研究表明：在高温条件下,在温度为300 ℃、载荷为50 N、转速为75 r/min工况下滑靴副的减摩抗磨效果最好。     

Tribological Behavior of Ceramics at High Sliding Speeds in Steam

Three sets of tests were conducted using a pin-on-disk tribometer to determine the tribological behavior of ceramics at high sliding speeds in steam. In the first set, the speed was increased from 4000rpm to 10,000rpm in 1000 rpm increments. Constant rotational speeds of 4000rpm, 6000rpm, 8000 rpm and 10,000 rpm were used in the second test series. In the third series of tests, the rotational speed was slowly increased to 10,000rpm and allowed to coast down to zero. While the coefficient of friction for silicon nitride/YTZP pair varied between 0.2 and 0.4 without a clear pattern as the speed was increased in the first two test series, it decreased from about 0.6 to 0.2 when the speed was raised to 10,000 rpm in the third test series. This behavior is attributed to the general phenomena of powder lubrication as the wear debris provides an interfacial layer leading to reduced friction at high speeds. The coefficient of friction for silicon nitride/silicon carbide pair was substantially reduced to about 0.02 as the speed was raised. The low coefficient of friction, however, increased to a high level as the speed was further increased. The drop in friction is explained based on analysis of elasto-hydrodynamic lubrication assuming that a water film containing solid particles exists at the interface. Several possible mechanisms are suggested for the transition to a higher friction as the speed is raised: thermal effects at high flash temperatures, low residence times (for water adsorption on surface), collapse of the lubricant film and starvation effects.     

基于摩擦功原理的高副滑动磨损的研究

针对现有的摩擦磨损计算公式不能全面反映磨损机理的问题,根据摩擦功原理,推导了基于磨损功的高副滑动磨损计算公式;在考虑刚度变化将引起齿间载荷动态变化的情况下,进行了机车齿轮副磨损的计算仿真分析,计算结果与实际磨损情况相符。研究表明,该公式为滑动摩擦副磨损计算提供了一种原理清晰、使用简便的新方法,为齿轮副与凸轮副等复杂曲面的高副磨损状态评估提供了可靠依据。     

青铜-石墨复合粉末热喷涂层的干滑动摩擦磨损性能

研究了石墨含量和载荷等对青铜-石墨复合粉末热喷涂自润滑涂层干滑动摩擦磨损性能的影响。结果表明：青铜-石墨热喷涂层有很好的自润滑性能，石墨含量为6％的涂层抗磨损性能最优。     

Sliding Friction and Wear Characteristics of Novel Graphitic Foam Materials

While the use of ORNL developed high-thermal-conductivity graphitic foam materials has been focused on thermal management applications, recent experiments have revealed their potential as bearing surfaces as well. The three primary tribological advantages are: (1) they can efficiently remove frictional heat, (2) their natural porosity can trap wear debris, and (3) their porosity can serve as a lubricant reservoir for the contact surface. A series of pin-on-disk experiments were conducted at both room temperature and 400 °C to compare the sliding friction and wear characteristics of the densified graphitic foam (mated against M-50 tool steel or against alumina) to those of conventional bearing materials like graphite, bearing bronze, poly- tetrafluoroethylene, bearing steel, and a Co-based superalloy. At room temperature and under low contact pressure, the tribological behavior of the densified graphitic foam material was comparable to that of graphite and better than that of other bearing materials. At 400 °C, traditional graphite exhibited a dusting wear regime accompanied by a high friction coefficient. In contrast, the graphitic foam demonstrated an ability to maintain low friction and wear at that temperature.     

巴氏合金干滑动摩擦磨损机制分析

以巴氏合金(ZChSnSb11-6)和45*钢为摩擦副,在SST-ST销盘式摩擦试验机下进行干摩擦试验,采用超景深三维显微镜、SEM、XRD对巴氏合金试样的摩擦表面进行表征,探讨其磨损机制.结果表明:干摩擦条件下,巴氏合金的摩擦因数较大,且波动较大;干摩擦条件下巴氏合金试样表面的物相发生明显变化,且试样表面同时存在磨粒磨损、氧化磨损和应变疲劳剥落.     

铜碲硒铁合金的干摩擦磨损性能

利用环-盘式摩擦磨损试验机研究了铜碲硒铁合金的干摩擦磨损行为,分析了载荷和摩擦速度等参数对该合金摩擦磨损性能的影响,并用扫描电子显微镜对磨损形貌进行了观察.结果表明:铜碲硒铁合金的摩擦因数随载荷的增加变化不大,但随摩擦速度的增加而明显增大;合金的磨损率随载荷和摩擦速度的增加均增大;在轻载低速条件下,合金的磨损机制以犁削磨损和粘着磨损为主;在重载高速条件下,磨粒磨损和粘着磨损加剧.     

干滑动条件下45CrNi材料摩擦磨损规律研究

以某自行火炮底座传动箱摩擦副所用材料45CrNi为研究对象,考察了该材料在不同热处理状态下（530℃回火、380℃回火、830℃淬火及原始状态）组成摩擦副时的干滑动摩擦磨损特性。试验结果表明：530℃回火盘和摩始销组成摩擦配副时结合最好,具有较好的摩擦磨损性能,销试样磨损率最小;在较低速度下载荷是影响材料摩擦因数的主要因素,而速度对摩擦因数的影响较小;粘着磨损是材料配副磨损的主要形式。     

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.     

Origin of Friction in Running-in Sliding Wear of Nitride Coatings

To investigate the origin of running-in friction in unlubricated sliding wear, a magnetron sputtered multilayer coating TiAlN/VN was tested on a ball-on-disc tribometer for a series of sliding durations from 10 to 1000 cycles, followed by careful observation of the obtained worn surfaces using an field-emission gun scanning electron microscope. Three steps of friction variation were found: (1) prior to wear particle generation, low initial friction coefficient was around 0.2–0.25 purely attributed to the asperity contact; (2) then it increased steeply to a range of 0.4–0.5 in the first 100 cycles following the generation, breaking and agglomeration of wear particles, and in particular the scaling-up of fish-scale-like tribofilm; (3) eventually it approached to a steady-state value around 0.5 when the friction was governed by the viscous shearing of the tribofilm. It is concluded that, under unlubricated sliding wear, the friction behaviour of transition metal nitride hard coating is dominated by the viscous shearing of tribofilm adhesively bonding to the parent nitride coating.     

Acoustic Emission and Its Relationship with Friction and Wear for Sliding Contact

Further investigation of the relationships between friction and wear properties and the characteristics of acoustic emission was conducted in the case of dry and grease-lubricated sliding contact using a ball-on-cylinder testing apparatus. The effect of contamination simulated by the inclusion of glass bead particles was also explored. Experiments were performed at sliding speeds ranging from 0.09 m/s to 1.47 m/s, while maintaining a fixed load and duration. As a first observation and contrary to what could be expected, the higher speed did not contribute to the decrease in friction interpreted by a worsening of the starved regime that had a consequence of increasing wear. However, the results revealed a good correlation between the friction coefficient and acoustic emission (AE) rms voltage for dry sliding. Such a relationship may allow the prediction of a reasonable friction coefficient μ from an AE signal. It was also determined that the friction work correlated well with the corresponding integrated AE voltage over time, intRMS. The detection of the sliding speed threshold beyond which accelerated wear would occur was possible from the intRMS variation. Proportionality between the theoretically determined grease film thickness and the intRMS was observed.     

SiCp/AI有机摩擦材料摩擦磨损特性研究

对20%Vol SiCp/AI复合材料与有机摩擦材料组成的摩擦副的摩擦磨损特性进行了试验研究.试验表明:该摩擦副在不同的速度情况下都具有平稳的摩擦系数.摩擦系数在一定速度范围内随速度增加而减小,而在超过一定速度后随速度增加而增大.对摩擦系数随速度变化的机理进行了讨论.     

Dry Sliding Friction and Wear Characteristics of Cu-Sn Alloy Containing Molybdenum Disulfide

The wear and sliding friction response of a hybrid copper metal matrix composite reinforced with 10 wt% of tin (Sn) and soft solid lubricant (1, 5, and 7 wt% of MoS₂) fabricated by a powder metallurgy route was investigated. The influence of the percentages of reinforcement, load, sliding speed, and sliding distance on both the wear and friction coefficient were studied. The wear test with an experimental plan of six loads (5–30 N) and five sliding speeds (0.5–2.5 m/s) was conducted on a pin-on-disc machine to record loss in mass due to wear for two total sliding distances of 1,000 and 2,000 m. The results showed that the specific wear rate of the composites increased at room temperature with sliding distance and decreased with load. The wear resistance of the hybrid composite containing 7 wt% MoS₂ was superior to that of the other composites. It was also observed that the specific wear rates of the composites decreased with the addition of MoS₂. The 7 wt% MoS₂ composites exhibited a very low coefficient of friction of 0.35. The hardness of the composite increased as the weight percentage of MoS₂ increased. The wear and friction coefficient were mainly influenced by both the percentage of reinforcement and the load applied. Wear morphology was also studied using scanning electron microscopy and energy-dispersive X-ray analysis.     

Wear,Friction, and Electrical Noise Phenomena in Severe Sliding Systems

The sliding mechanisms of unlubricated gold and palladium are described. Transfer, roughening, wear, friction, and contact resistance phenomena involve the same discrete events.

With rider-flat geometry, severely Worked transfer particles form a prow-shaped wedge which adheres to the smaller member. Even when rider and flat are different, prow material comes from the larger part. Loss of prow occurs by adhesive weld-back transfer and, to form loose debris, by shearing or fatigue fracture.

Friction rises in the early stages of sliding as prows grow. Soon, back transfer increases hardness of the larger member and friction falls to an equilibrium level. Friction also falls when prows are kneaded into rollers and become loose debris. During these stages, wear rate diminishes.

Contact resistance noise originates in stick-slip, roller formation, surface hardening, and changing composition at the sliding interface when dissimilar contact metals are involved.     

Transitions in the Friction and Wear of Carbons and Graphites Sliding Against Themselves

The friction and wear properties of various carbons and graphites have been measured during sliding against themselves in air. Many materials exhibit sudden and large increases in both friction and wear at a critical combination of load, speed, and temperature, and the effects are most pronounced for electrographites and natural graphites. The sliding conditions at the transition are associated with a critical temperature of the contacting asperities, and the magnitude of this temperature, approximately 150–185 C for graphitic materials, has been estimated both directly and by application of flash-temperature theory. The phenomena accompanying the transitions are very similar to those occurring during dusting of carbon brushes at high altitudes, and a similar explanation is invoked in terms of the adsorption of water vapor and oxygen. The critical combinations of loads and speeds required to initiate the transition are much more severe than those normally encountered during the operation of carbon brushes and bearings.     

不同介质下ER8车轮钢滑动摩擦磨损性能

为探讨车轮在不同环境下服役时摩擦因数的变化机制,通过滑动摩擦试验机考察不同载荷下,ER8车轮钢分别在干燥空气、纯水、3.5%氯化钠溶液3种环境下的摩擦磨损性能。利用光学显微镜、扫描电子显微镜、非接触三维表面轮廓仪、X射线衍射仪对磨痕及元素组成进行了分析,探讨不同环境下ER8车轮钢的摩擦磨损机制。结果表明：随着载荷的增大,ER8车轮钢的摩擦因数明显增大;列车的服役环境对车轮的摩擦磨损性能有较大影响,在干燥空气环境下,ER8车轮钢无腐蚀状况,磨痕宽度最小,但摩擦因数最大,可达0.503;在盐水环境下,ER8车轮钢出现腐蚀现象,磨痕宽度最大,但摩擦因数最小;干摩擦下ER8车轮钢的磨损机制为黏着磨损、磨粒磨损和氧化磨损,纯水摩擦和3.5%NaCl溶液环境下的磨损机制为磨粒磨损和氧化磨损。     

Friction and Wear Behavior of Irradiated Polyethylene Sliding Against a Rough Steel Surface

The aim of this study was to evaluate the tribological behavior of polyethylene crosslinked by gamma radiation sliding against a steel surface. Two high-density polyethylenes were irradiated to a total dose in the range of 2?20 Mrad under vacuum and at room temperature. After irradiation, the materials were annealed at 423 K and then cooled slowly to room temperature. The same thermal treatment was applied to the non-irradiated polymer. The wear behavior of the polymers was determined under controlled ambient temperature of 298 and 333 K using a homemade tribometer. Sheet-shaped specimens were loaded against the surface of a steel disc with different normal loads to generate nominal contact pressures in the range of 0.25–1.5 MPa. The tests were performed under dry conditions using a disc rotation to produce an average sliding speed of 0.6 m/s and during a period of time to provide an average sliding distance of 1,080 m. The wear rate was obtained as the mass loss by the sample divided by the sliding distance, and the friction coefficient was determined by measuring the friction force. The results indicate that the wear rate increases with load in the case of non-irradiated polyethylene and low-dose irradiated polymers, while the wear rate reaches a maximum value with the load in the case of the irradiated samples with high doses. The samples irradiated with a dose of 10 Mrad showed the lowest wear. The coefficient of friction (COF) increases slightly with the load in all the cases. Most irradiated polymers show higher COF than the non-irradiated material when compared at a given load. The results show that the irradiation dose applied to the polyethylenes produced no noticeable effect on the COF values when a comparison was made at a given applied load.     

不同滑动速度下干接触体瞬态温度场计算

工程实际中,由于摩擦力的存在,接触副的运动将导致接触区内产生大量的摩擦热,使接触副温度升高;由此产生的瞬时高温会使接触副更易发生弹塑性变形、引起表层下裂纹的萌生及扩展,甚至使接触副表面发生化学变化。建立了不同滑动速度下干接触体的滑动接触模型,利用快速傅立叶变换,通过求解拉普拉斯热传导方程,获得光滑及粗糙表面接触副的瞬时温升以及接触体内部各离散点的温度分布,即半无限体干接触的温度场。结果表明,相同载荷及摩擦因数条件下,相对滑动速度对接触体的温升及其温度分布有重要影响;粗糙峰表面接触处的瞬时温升远高于光滑表面接触处的瞬时温升。     

Friction and Wear Characteristics of BaCr2O4 Ceramics at Elevated Temperatures in Sliding Against Sintered Alumina Ball

In this article, friction and wear characteristics of BaCr₂O₄ ceramics have been investigated using a high-temperature friction and wear tester from room temperature to 800?°C in dry sliding against sintered alumina ball. At room temperature, the friction coefficient and wear rate of BaCr₂O₄ ceramics are quite high. BaCr₂O₄ ceramics exhibit low friction coefficients and small wear rates with temperature increasing up to 400?C600?°C. The oxidation reaction of BaCr₂O₄ during high-temperature wear tests is responsible for the tribological properties. The oxidized product of BaCr₂O₄ is BaCrO₄, which forms a smooth self-lubricating film on the worn surface to effectively reduce friction and wear. However, at 800?°C, severe oxidation reduces the relative density of sintered BaCr₂O₄ ceramics, and further expedites the materials removal process.