SiO2对铜基摩擦材料摩擦磨损性能的影响

为了提高铜基摩擦材料在高速干摩擦条件下的耐磨性能和具有稳定的摩擦系数,通过粉末冶金方法,制备了铜-SiO2摩擦材料.在摩擦速度为1.6～47.1 m/s条件下,研究了SiO2含量、粒度及摩擦方式对材料摩擦磨损性能的影响.研究表明:材料的摩擦系数和磨损率随着SiO2含量的增加而略有增大;SiO2颗粒尺寸的变化,对摩擦系数影响不显著;摩擦方式对材料的摩擦磨损性能的影响明显.SiO2含量增加有利于提高摩擦系数归因于增加了摩擦面高硬度质点的数量.干摩擦条件下影响材料摩擦磨损性能的一个重要因素是摩擦方式.在高速摩擦条件下,形成的第三体组织致密而连续,这种致密而连续的第三体有利于降低磨损量,并明显降低由于摩擦速度不同而导致的摩擦系数的波动程度.     

Sliding behaviour of nanophased AISI M2 tool steel obtained by mechanomaking and hot isostatic pressing

Abstract

The friction and wear behaviour of a nanophased AISI grade M2 tool steel was studied under dry sliding conditions and compared with that of a conventional AISI M2 steel. The nanocrystalline steel was produced by mechanosynthesis followed by cold and hot isostatic pressing. Slider-on-cylinder tests were performed against a ceramic coated countermaterial under loads of 10, 20, and 30 N and sliding speeds of 0.3 and 1.2 m s^-1 up to 10 km sliding distance. The nanocrystalline material underwent mild wear with low coefficient of friction under all testing conditions. The commercial M2 steel displayed distance dependent transitions from a regime of mild wear with low coefficient of friction, to a regime of severe wear with high coefficient of friction. The first tribological regime was due to the formation of a layer of iron oxides on the worn surfaces. In this regime, the wear resistance of both steels is mainly dominated by the mechanical properties of the carbides which have high load carrying capability. The second tribological regime, observed in the commercial steel, was due to the formation of cracks both on the mechanically mixed layer and at a depth beneath this layer, which also led to the detachment of carbides from the matrix. This abrasive ‘third body’ produced high wear damage of the commercial steel under high applied loads.     

Eine auf der Systemanalyse von Reibungs- und Verschleißvorgängen aufbauende Methodik zur Auswahl von tribotechnischen Werkstoffen

A method for the selection of tribotechnical materials based on a system analysis of friction and wear processes . The tribological behaviour of materials cannot be specified by their physical, chemical and mechanical properties only. Besides these ?system-independant”? properties ?system-dependant”? data are important. This is demonstrated by applying the methods of systems analysis to friction and wear processes. Based on systems thicking a method for the selection of tribotechnical materials is outlined.     

Analysis of increasing torque with recurrent slip in interference-fits

Previous research associated with interference-fitted assemblies has shown that as recurring slip occurs (i.e. load to total slip, unloading and reload to total slip) there is an observed increase in the holding torque after each loading cycle. The aim of this work was to identify the reasons for this ‘torque strengthening’ phenomenon. The work also has industrial relevance in the optimum design of interference-fitted rolls used for the hot rolling of steel sections. Previous work has shown that the major contributors to the overall holding torque were the interface pressure, material properties and the coefficient of friction between component materials. In this work, neutron diffraction tests and crack compliance tests showed no correlation between the interface pressure and increased holding torque. Meanwhile, experimental holding torque tests on sample interference-fits showed that for each recurring holding torque failure (slip) in a test cycle, the holding torque increased. Subsequent wear investigations showed that the wear of the surfaces increased throughout the testing and once a specific type of wear had occurred through a ‘ploughing’ mechanism, significant damage could be done to the more expensive shaft component. These observations suggest that an effective increase in the coefficient of friction between shaft and hub is responsible for the increase in holding torque, while the same level of interface pressure is maintained throughout slipping. The research provides a basis for the optimisation of interference-fit design in order that the working lives of expensive shafts, which are prone to damage through ploughing, and brittle hubs, which are prone to sudden fracture, are maximised when experiencing recurrent slipping.     

树脂粘结剂对汽车摩擦材料性能的影响

制备了不同树脂基体和不同树脂含量的汽车摩擦材料,研究了树脂种类与含量对汽车摩擦材料的机械性能和摩擦磨损性能的影响。结果表明,腰果壳油改性酚醛树脂为基体的摩擦材料的摩擦、耐热和力学性能,均优于纯酚醛树脂基摩擦材料。树脂-丁腈橡胶共混改性摩擦材料具有更好的力学性能和耐磨性,摩擦系数稳定。随着树脂粘结剂含量的增加,摩擦材料的力学性能提高。树脂粘结剂的含量在9%~12%时,摩擦材料具有优异的摩擦磨损性能;树脂粘结剂的含量小于6%时,摩擦系数较低且不稳定;树脂粘结剂的含量大于15%时,材料发生热衰退现象。      

Friction and Wear Behavior of Resin/Graphite Composite under Dry Sliding

The friction and wear behavior of resin/graphite composite has been investigated using a pin-on-disc configuration under dry sliding condition. The results showed that the resin/graphite composite exhibited much better mechanical and tribological properties compared with the unimpregnated graphite. The friction coefficient was reduced by addition of furan resin, which could also prevent the"dusting" wear at loads more than 15 MPa. The steady and lubricated transfer film was easily formed on the counterpart surface due to the interaction of furan resin and wear debris of graphite, which was useful to reduce the wear rate of the resin/graphite composite. The composite is highly promising for mechanical sealing application and can be used at high load for long time sliding.     

Friction and Wear Behaviors of Nanostructured Metals

Nanostructured （ns） materials, i.e., polycrystalline materials with grain sizes in the nanometer regime （typically below 100 nm）, have drawn considerable attention in the past decades due to their unique properties such as high strength and hardness. Wear resistance of ns materials, one of the most important properties for engineering materials, has been extensively investigated in the past decades. Obvious differences have been identified in friction and wear behaviors Between the ns materials and their corresponding coarse-grained （cg） counterparts, consistently correlating with their unique structure characteristics and mechanical properties. On the other hand, the superior tribological properties of ns materials illustrate their potential applications under contact loads. The present overview will summarize the important progresses achieved on friction and wear behaviors of ns metallic materials, including ultrafine-grained （ufg） materials in recent years. Tribological properties and effects on friction and wear behaviors of ns materials will be discussed under different wear conditions including abrasive wear, sliding wear, and fretting wear. Their correlations with mechanical properties will be analyzed. Perspectives on development of this field will be highlighted as well.     

Impact of post-curing duration on mechanical,thermal and tribological behavior of an organic friction material

This paper aimed to study the influence of post curing duration on mechanical, thermal and tribological behavior of friction materials elaborated with simplified formulation. Surface mechanical properties and thermal conductivity were analyzed and tribological behavior was studied for various thermal severities of sliding conditions. Results indicated that post curing for long duration allowed to reduce thermal conductivity and to homogenize the surface mechanical properties of the friction material. Concerning tribological behavior, it was shown that a longer post curing duration permitted to reduce the level of friction and to increase wear resistance. Worn surface morphology investigation using SEM revealed that wear and friction mechanisms involved in the contact were sensitive to post curing duration.     

铜基复合材料干湿条件下的摩擦学行为

采用粉末冶金技术制备铜基复合材料,在制动压力0. 5～1. 2 MPa 范围内,通过定速摩擦试验机研究了干、湿条件下,速度、压力与材料摩擦磨损性能的关系,结果表明:影响摩擦磨损性能的重要因素在于载荷性质和第三体状态。在干摩擦条件下,处于低摩擦速度范围时,摩擦力的静载荷性质使第三体呈疏松状态,这增加了微凸体间的啮合程度而使摩擦系数处于较高值。随第三体致密性增加,其润滑作用增强,微凸体间的机械啮合程度减弱,使材料的摩擦系数和磨损量降低。在高速摩擦时,微凸体间的冲击作用使处于摩擦表层的硬质颗粒容易发生粉碎性破损而弥散分布,这强化了表面强度而使摩擦系数有所增加。摩擦压力对高速摩擦性能影响明显,原因在于高负荷加剧了摩擦面的变形和损伤程度。湿摩擦条件下,水膜的润滑和流动具有降低摩擦系数和增加磨损率的作用主要体现在低速低压条件下。在高摩擦速度和高压力条件下,水分的高温蒸发与离心作用明显,破坏了水膜的存在条件,从而使材料的摩擦磨损性能与干摩擦状态相近。      

三种机械密封材料的摩擦磨损性能研究

研究了3种核主泵用机械密封陶瓷材料(氮化硅、氧化铝和碳化硅)在室温干摩擦条件下及水润滑条件下分别与氮化硅陶瓷球对磨的摩擦磨损性能。研究结果表明,在与氮化硅球干摩擦的3种材料中氧化铝陶瓷具有最大的摩擦系数和最小的磨损质量,氮化硅具有最小的摩擦系数。在氮化硅陶瓷自配对摩擦副摩擦磨损试验中,水润滑条件下氮化硅摩擦系数及摩擦质量损失都有很大程度的减小,且摩擦系数随转速增加而减小。综合考虑力学性能和摩擦磨损性能,选择氮化硅陶瓷作为核主泵机械密封材料更合适。     

Tribologisches Verhalten von Kunststoffen bei tiefen Temperaturen

Tribological Behaviour of Thermoplastics at low Temperatures The lubrication of sliding bearings for application to low temperatures is difficult, caused by the special failure after long standing of the most lubricants. An alternative is given by so-called „self-lubricated”︁ thermoplastic materials. Thermoplastic based composites with different filler materials have a good mechanical and thermal load capacity up to temperatures T = 200°C. The addition of sliding modifiers gives low friction coefficient and wear. Unknown is the behaviour of these materials at low temperatures. The aim of this work is to develope a test facility to estimation the tribological behaviour of materials at temperatures up to T = – 196°C and to investigate the application of different thermoplastic materials in friction with a steel of typ 100Cr6 as the counterbody under dry wear condition. Advanced thermoplastics, e.g. PPS, PAEK, PES or PI and PTFE with different fillers using for the investigations at temperatures T = − 40°C, room temperature and T = 160°C. The typical failure mechanism depending on the proof temperature are discussed.     

含Nb高碳钢的组织及耐磨性能

采用金相显微镜、扫描电镜表征了含Nb高碳钢的显微组织,并采用MFT-3000型摩擦磨损试验机,在室温下研究了摩擦载荷、滑动速度及滑动时间对铸态高碳钢的摩擦性能的影响。结果表明,铸钢组织由莱氏体和珠光体组成,洛氏硬度为37.3HRC。随施加载荷、滑动速度的增加,磨损失重量增加;摩擦系数随载荷增加而降低,随滑动速度增加而增加,随滑动时间的延长先增加后趋于稳定。磨损机制是以粘着磨损为主的粘着与磨粒磨损的混合磨损,高速、长时间滑动时,还存在明显的氧化磨损。     

超高分子量聚乙烯纤维/有机玻璃复合材料力学及摩擦磨损性能研究

用真空浸渍法制备出了超高分子量聚乙烯纤维／有机玻璃(即UHMWPE／PMMA)复合材料，并研究了其力学性能和摩擦磨损性能。实验证明，UHMWPE／PMMA复合材料具有优良的力学性能和摩擦磨损性能。纤维表面处理可以改善复合材料的力学性能。三维编织纤维增强的复合材料的磨损量远小于长纤维增强的复合材料的，但其摩擦系数没有显著变化。     

颗粒增强高熵基复合材料成形及其摩擦学性能研究进展

高熵合金是近十几年新发展起来的一种全新概念的多元合金,其在物理、化学性能和力学性能方面有很多优点,为了解决高熵合金在摩擦磨损应用方面的局限性,提高其综合力学性能,以高熵合金为基体加入增强相合成的复合材料(HEAMCs)成为金属领域研究的热点。基于此,根据研究现状综述了不同HEAMCs的制备成形方法,从制备方法的优缺点对粉末冶金法、熔炼法、激光熔覆法进行了详细的分析。归纳了HEAMCs中纳米细晶强化及第二相协同强化两个方面的强化机制,分别概括了室温和高温情况下HEAMCs的摩擦磨损性能的研究,最后对HEAMCs目前所面临的挑战及未来的发展进行了讨论和展望。     

Micro/nanomechanical characterization of ceramic films for microdevices

Microelectromechanical systems (MEMS) are currently fabricated using single-crystal silicon, various polysilicon films and other ceramic materials. Silicon carbide (SiC) film has recently been pursued as a material for use in MEMS devices owing to its excellent mechanical properties and high-temperature capabilities. Since physical and chemical properties, friction and wear are important issues in such small-scale devices, it is essential that the materials used in MEMS have good micro/nanomechanical and tribological properties. Micro/nanomechanical characterization of single-crystal 3C-SiC (cubic or β-SiC) films, undoped and doped (n⁺-type) polysilicon films have been carried out. For comparision, measurements on undoped single-crystal Si(100) have also been made. Hardness, elastic modulus and scratch resistance of these materials were measured by nanoindentation and microscratching using a nanoindenter. Fracture toughness was measured by microindentation using a microindenter. Friction and wear properties were measured using an accelerated ball-on-flat tribometer. It is found that the 3C-SiC film exhibits higher hardness, elastic modulus and scratch resistance as well as lower friction compared to other materials. These results show that the 3C-SiC film possesses desirable micro/nanomechanical properties that make it an ideal material for use in MEMS devices.     

Status of surface modification techniques for artificial hip implants

Surface modification techniques have been developed significantly in the last couple of decades for enhanced tribological performance of artificial hip implants. Surface modification techniques improve biological, chemical and mechanical properties of implant surfaces. Some of the most effective techniques, namely surface texturing, surface coating, and surface grafting, are applied to reduce the friction and wear of artificial implants. This article reviews the status of the developments of surface modification techniques and their effects on commonly used artificial joint implants. This study focused only on artificial hip joint prostheses research of the last 10 years. A total of 27 articles were critically reviewed and categorized according to surface modification technique. The literature reveals that modified surfaces exhibit reduced friction and enhanced wear resistance of the contact surfaces. However, the wear rates are still noticeable in case of surface texturing and surface coating. The associated vortex flow aids to release entrapped wear debris and thus increase the wear particles generation in case of textured surfaces. The earlier delamination of coating materials due to poor adhesion and graphitization transformation has limited the use of coating techniques. Moreover, the produced wear debris has adverse effects on biological fluid. Conversely, the surface grafting technique provides phospholipid like layer that exhibited lower friction and almost zero wear rates even after a longer period of friction and wear test. The findings suggest that further investigations are required to identify the role of surface grafting on film formation and heat resistance ability under physiological hip joint conditions for improved performance and longevity of hip implants.     

Embedded strong discontinuity finite elements for fractured geomaterials with variable friction

The strong discontinuity approach to modelling strain localization, combined with an enhanced strain element, has been used for more than a decade to model strain localization in materials including geomaterials. Most implementations of enhanced strain elements in the post-localization regime use very simple constitutive formulations along the discontinuity, such as linear softening or a constant friction coefficient. However, the softening relations can be much more complex for geomaterials. For rocks this softening is induced by micro-fractures coalescing into macroscopic cracks during a narrow time interval called ‘slip weakening.’ During this interval the cohesive resistance on the nucleating crack decays to zero while the frictional resistance increases. Furthermore, research has shown that the coefficient of friction for these materials is not constant, but in fact is a function both of the slip speed and the state of the material, including wear, temperature, and other factors. In this paper we augment the modelling capabilities of an enhanced strain element by incorporating a cohesive softening law and a popular rate- and state-dependent friction model commonly used for describing the constitutive properties of rocks and rock-like materials sliding along the fractured surface. Copyright © 2007 John Wiley & Sons, Ltd.     

Tribological characteristics of thin films and applications of thin film technology for friction and wear reduction

Thin film deposition technologies based on chemical and physical vapor deposition are now well established to improve the wear resistance of cutting tools. Although severe tribological conditions occur here, coated tools perform exceptionally well. Despite this, the growth in use of thin film deposition technology is slow in the general mechanical industry. In part, this is due to lack of data on the tribological characteristics of bodies coated with thin films.In this paper, tribological test data gathered in a systematic program of sliding and rolling contact tests are presented to demonstrate the usefulness of thin film coatings for wear protection and friction reduction. Samples coated by reactive magnetron sputtering were tested in sliding and rolling contact tests at low and high speeds and at varying contact stresses. These results are presented and used to identify the primary consideration guiding the choice of coating materials, coating properties, film thickness needed etc. A newly developed film-to-substrate adhesion strength test is also briefly described and the results obtained are cited. It is shown that film material selection and coating process selection have a reasonable physical basis.     

Tribological investigation of diamond-like carbon coated micro-dimpled surface under bovine serum and osteoarthritis oriented synovial fluid

Abstract

Osteoarthritis-oriented synovial fluid (OASF), i.e., that typical of a patient with osteoarthritis, has different physical and biological characteristics than bovine serum (BS), a lubricant widely used in biotribological investigations. Micro-dimpled and diamond-like carbon- (DLC) coated surfaces are key emerging interfaces for orthopedic implants. In this study, tribological performances of dimpled surfaces, with and without DLC coating, have been investigated under both BS and OASF. The friction tests were performed utilizing a pin on a disk tribometer, whereas contact pressure, speed, and temperature were simulated to a ‘medium walking gait’ of hip joint conditions. The mechanical properties of the specimen and the physical properties of the lubricant were characterized before the friction test. Raman analysis was conducted to identify the coating condition both before and after the test. The DLC-coated dimpled surface showed maximum hardness and residual stress. A DLC-coated dimpled surface under an OASF lubricated condition yielded a lower friction coefficient and wear compared to those of plain and dimpled specimens. The higher graphitization of coated materials with increasing load was confirmed by Raman spectroscopy.     

Advances in nature-guided materials processing

The center of excellence (COE) titled ‘The Creation of Nature-Guided Materials Processing’ has been established in Nagoya University as the 21st Century COE Program supported by Ministry of Education, Culture, Sports, Science and Technology. In the Nature COE, various activities on the education and research are being performed through learning the laws of nature, namely, methods of attaining ‘appearance of the maximum function under the minimum substance and energy consumption’, which the nature and living organisms have acquired through their evolution in long period. Together with such educational programs for PhD students as research incentive, oversea training, and external evaluation programs, an ‘Open-Cluster Program’ was originated for promoting researches proposed by research groups consisting of young researchers in and out of the university and also for fostering them.

The researches are being advanced on materials used for living bodies, mimicking structures which nature or living bodies are forming, and producing materials by mimicking processes to form the structures observed in the nature or the living bodies. In this COE, these researches are conducted by four groups to extend the processes observed in the natural world to a new type of processing, that is, thoroughly examined and rationalized by plunging a scalpel of engineering and to establish a new academic field of materials science and engineering.