微型汽车离合器摩擦材料的热衰退现象

设计了适合研究树脂基汽车复合摩擦材料摩擦性能的小样试验,进行不同环境温度、不同滑动速度和定载荷下的摩擦试验。并通过扫描电子显微镜的分析手段,结合摩擦学原理分析了摩擦材料的热衰退机理,得出树脂基汽车复合摩擦材料热衰退的实质是树脂的高温热分解所生成的润滑层或气垫层的动力润滑而导致摩擦因数的明显下降,其机理是从典型的磨粒磨损和粘着磨损的干摩擦过渡到具有流体润滑磨粒磨损的润滑摩擦等结论。     

摩擦热加工技术及其应用

摩擦热加工是利用摩擦过程的能量转换原理使材料局部区处于热塑性状态而实现加工的方法,该项技术具有低耗能、无污染、高效率、加工质量好等优点,因而应用前景广泛。本文重点介绍了摩擦搅拌焊、耗材摩擦敷层等被称为是“科学摩擦（Ｓｃｉｅｎｃｅ Ｆｒｉｃｔｉｏｎ）”的先进摩擦焊接技术及摩擦热加工在其他方面的应用。     

GF/PTFE自润滑纤维复合材料磨损性能热衰退研究

针对高频摆动关节轴承摩擦热对自润滑纤维复合材料摩擦磨损性能的影响,研制了高频使用条件下的玻璃纤维增强聚四氟乙烯(GF/PTFE)自润滑纤维复合材料,利用MYB～500高频高载摆动摩擦磨损试验机,对其进行不同摩擦温度下的摩擦磨损性能测试,研究摩擦热作用下材料自润滑性能和磨损性能衰退特征,分析磨损产物和摩擦表面以及不同摩擦温度下材料的磨损机理。结果表明,摩擦热对材料自润滑性能影响显著,适当的摩擦温度范围能够保证材料的自润滑性能,摩擦温度和摩擦因数之间互为耦合作用,对材料的磨损性能具有一定的影响;高摩擦热作用于自润滑过程及机理的改变,造成材料的磨损性能衰退现象。因此,不同温度下材料的磨损特征具有明显的差异化,其中低摩擦温度下(60～120℃)材料自润滑性能优异,磨损率很低;140℃摩擦温度条件下材料摩擦磨损性能开始衰退;材料在高摩擦温度下(140～180℃)的磨损初期自润滑性能良好、磨损轻微,而中后期磨损严重。微观分析表明,低摩擦温度下材料的磨损机理以轻微粘着和疲劳磨损为主;高摩擦温度下材料的磨损以片状剥落、纤维剪切破坏为主,且磨损面局部损伤特征明显,磨损严重。     

摩擦过程中磨屑运动的分析

制动摩擦材料和铸铁摩擦盘在摩擦过程中产生磨屑。磨屑对摩擦层的形成、组成及其动态平衡、摩擦机制以及摩擦性能起着重要作用。为了理解磨屑对摩擦层形成的影响,以国家标准(GB5763-2008)中第4类盘式制动器用衬片规定的定速摩擦性能测定仪和测试条件,对四类磨屑(拖曳、跃迁、振动和碰撞)分别在摩擦材料和摩擦盘之间的三维空间运动的受力状态、运动轨迹和动力学行为进行了分析。结果表明,磨屑的运动轨迹是一个不规则运动,磨屑之间会发生碰撞。在摩擦过程中,磨屑可以飞离摩擦盘,也可以聚集在摩擦材料和摩擦盘表面形成摩擦层。     

苏联新型烧结减摩材料研究的进展

摩擦与磨损是一个非常复杂的过程,包括物理、化学和电化学的过程,摩擦表面材料间的相互作用,润滑剂与环境气氛,表面层的变形,摩擦材料的物质迁移等。现在,关于摩擦过程某些要素的试验数据表明,稳定的摩擦过程决定于工作表面上形成的二次结构(所谓工作层)的特性与性能。可将摩擦过程描述为表面层的机械与化学合金化,无定形化过程,这时发生的现象有,由于结合与分子相互作用区域性破坏;分散胶与以添加剂加入材料中的氧化物、石墨、类金属化合物及其它物质的一起研磨,造成的摩擦表面材料的弥散;和在某种程度上,由于局部高温与高压作用,摩擦副表面混合物烧结形成新物质,其特点与结构有点象弥散硬化材料的结构。在这方面,对摩擦表面的无定形层的性能研究是相当有趣的。文献证明,金属于无定形状态具有高的强度。含Si、B、C与一些其它元素的铁、镍和钴的合金,其最高强度为300～400公斤/毫米~2。     

木质素纤维增强摩擦材料的性能研究

制备一种木质素纤维增强摩擦材料,采用冲击试验机和硬度计分析其力学性能,采用摩擦磨损试验机考察其摩擦磨损性能,采用扫描电子显微镜(SEM)和X射线衍射仪分析其断面形貌及磨损表面形貌,并探讨其磨损机制。结果表明:与钢纤维相比,木质素纤维能够提高摩擦材料的抗冲击韧性和抗断裂韧性,降低摩擦材料的硬度;在摩擦过程中木质素纤维在摩擦材料表面形成一层致密的摩擦层和转移膜,使摩擦材料的摩擦因数比较稳定,且300℃高温时没有出现明显的热衰退现象,磨损量符合国家标准的范围;SEM和X射线衍射分析表明,木质素纤维与基体结合强度高,对摩擦材料增强效果显著,其在高温阶段的主要磨损机制为磨粒磨损和疲劳磨损。     

锡青铜-钢背双金属固体自润滑复合材料的摩擦性能研究

采用粉末冶金工艺制备含石墨固体润滑剂的锡青铜-钢背复合材料,研究了石墨含量对材料的硬度、显微组织和摩擦磨损性能的影响,并考察了摩擦磨损机制。结果表明:在含石墨的青铜-钢背双金属材料中,随着石墨含量的增加,材料的硬度逐渐降低,摩擦磨损性能逐渐改善,但是其显微组织的均匀性也逐渐变差;在石墨含量为3%～5%(质量分数)时,双金属材料既具有较好的摩擦磨损性能,同时表面铜合金层与钢背的黏结强度也很高;随着速度和负荷的增加,材料的摩擦因数降低,磨损增加;摩擦过程中,石墨在摩擦面上成膜是材料具有减摩自润滑性能的主要原因。     

第二讲 固体润滑膜的性能

第二讲固体润滑膜的性能常州牵引电机厂石淼森关键词固体润滑膜，摩擦，磨损，温度，性能，润滑固体润滑膜（以下简称膜）是指固体润滑涂（镀）层最表面的那层薄膜以及在对偶材料表面上形成的转移膜。固体润滑成功与否，取决于膜的形成能力。如果膜的生成与磨耗平衡，表明...     

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。     

CO_2激光表面改性处理对重载荷铜基粉末冶金摩擦片组织及性能的影响

针对重载荷铜基粉末冶金摩擦片对动态性能的更高要求,采用宽带激光束对摩擦片铜基粉末冶金摩擦材料层进行激光表面改性处理研究。采用扫描电镜、透射电镜、X射线衍射仪及硬度计等分析、测试仪器对粉末冶金摩擦材料层微观组织及性能进行表征,采用离合器摩擦元件动态性能试验台对摩擦片动态性能进行测试。结果表明,宽带激光表面改性处理后,铜基粉末冶金摩擦材料层的微观结构发生明显的变化,摩擦片的动态性能得到显著改善。聚合生长状态的α-Cu产生边缘溶解,大体积聚合态α-Cu细小化;在α-Cu相内部生成了大量的纳米晶体;铜基粉末冶金摩擦材料层密度提高了6%,表观硬度提高了12.7%,α-Cu相显微硬度提高了14%;摩擦片静摩擦因数提高了7.4%,动摩擦因数提高了9.2%,磨损量降低了33%,磨损率降低了49.6%,许用热负荷值提高了40%。     

Experimental Characterization of Micro-Friction on a Mica Surface Using the Lateral Motion and Force Measurement Capability of an Instrumented Indenter

An experimental characterization of friction forces between asymmetric surfaces in the micro-regime is presented. The lateral motion and force-measurement capability of an instrumented indenter (triboindenter) is characterized and explored for determining friction properties at low velocities. Friction experiments are performed using the triboindenter with high repeatability. It is observed that real-time depth measurements closely follow the Hertzian prediction. Friction spikes with magnitudes depending on the drive velocity input are observed with peak friction force increasing with the dwell time. Anisotropy is observed between surfaces of different materials with stick-slip occurring only at specific relative orientations. Directions for expanding the current range of the triboindenter to obtain data from the nano to the macro scale are also presented.     

材料干滑动摩擦磨损性能的研究进展

介绍高温、高速、载流、气氛、磁场等苛刻条件下材料的干滑动摩擦磨损特性的研究方法和研究结果。得到以下几点结论:材料的干摩擦磨损特性与速度、载荷之间存在着对应关系,当pv值超过临界值后,材料的摩擦因数和磨损率发生突变;摩擦面温度的升高会降低材料的干摩擦磨损性能;环境气氛的改变不影响金属摩擦副pv特性的基本规律,但显著影响其摩擦因数和磨损率数值的大小;电流的存在恶化材料的干摩擦性能;施加磁场可显著改善材料的摩擦磨损性能,并且磁场强度是影响材料干摩擦特性的主要因素。     

Influence of protein conformation on frictional properties of poly (vinyl alcohol) hydrogel for artificial cartilage

Poly (vinyl alcohol) (PVA) hydrogel is one of the anticipated materials for artificial cartilage. In our previous studies, wear of PVA hydrogel depended on content of proteins in lubricants. The secondary structures of bovine serum albumin (BSA) and human gamma globulin (HGG) were investigated in circular dichroism spectroscopy to clarify the influence of the proteins on frictional properties. BSA and HGG were mainly composed of the α-helix and the β-sheet, respectively. BSA containing the α-helix structure showed low friction compared to HGG composed of the β-sheet structure in mixed or boundary lubrication mode. The α-helix structure forms low shear layer because the α-helix structure is easily released from surfaces and low cohesive strength. HGG forms uniform adsorption layer, but showed higher friction than BSA in the rubbing with single protein. In the repeated rubbing with changing of lubricants from HGG to BSA, however, the final friction was reduced, because an optimum layered structure of proteins was formed. Hence, layered structure of proteins appears to play an important role to protect rubbing surfaces and to reduce friction. In heat treatment tests, heat-induced BSA showed very low friction because of reduction of the α-helix structure. Heat-induced HGG did not show large differences from native HGG, but could not bring low friction with heat-induced BSA. Thus it was shown that the protein conformation has effective influences on friction.     

Large friction anisotropy of a polydiacetylene monolayer

Friction force microscopy measurements of a polydiacetylene monolayer film reveal a 300% friction anisotropy that is correlated with the film structure. The film consists of a monolayer of the red form of N‐(2‐ethanol)‐10,12‐pentacosadiynamide, prepared on a Langmuir trough and deposited on a mica substrate. As confirmed by atomic force microscopy and fluorescence microscopy, the monolayer consists of domains of linearly oriented conjugated backbones with pendant hydrocarbon side chains above and below the backbones. Maximum friction occurs when the sliding direction is perpendicular to the backbones. We propose that this effect is due to anisotropic film stiffness, which is a result of anisotropic side chain packing and/or anisotropic stiffness of the backbone itself. Friction anisotropy is therefore a sensitive, optically‐independent indicator of polymer backbone direction and monolayer structural properties. This revised version was published online in September 2006 with corrections to the Cover Date.     

Speed‐ and topography‐dependent boundary friction characteristics of steel

A novel tribometer that undergoes significant changes at ultra‐slow (>5.0 µm s⁻¹) to moderate (<20 cm s⁻¹) sliding speeds was developed in order to study the friction‐speed characteristics of steel lubricated with oil. Three different surface topographies were applied to the specimens, and the friction characteristics with an additive‐free base oil (MO91) and a stearic acid‐formulated oil (StA/MO91) were studied to understand the effects of surface textures on the lubrication performance of an adsorbed molecular layer formed by StA. Friction reduction behaviour of the adsorbed layer observed in the transverse direction was attributed to microscopic hydrodynamic action that maintained the load‐carrying performance of the adsorbed layer. Copyright © 2010 John Wiley & Sons, Ltd.     

Friction force microscopy investigations of potassium halide surfaces in ultrahigh vacuum: structure,friction and surface modification

Friction force microscopy measurements on the vacuum‐cleaved (001) surfaces of KF, KCl and KBr have been carried out. All surfaces exhibit atomically flat terraces with monatomic steps aligned preferentially along low‐index lattice directions. Stick‐slip lateral forces with the lattice periodicity are observed on all surfaces. Tip‐sample contact creates higher friction domains on the terraces of all three materials. The structure, topography and degree of friction force contrast of these domains is material dependent. The dependence of friction upon load generally does not coincide with the behavior expected for an elastic contact. We propose that the observed domains result from surface structural changes created by low load tip‐sample contact on these relatively soft materials. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of two different rubbers as secondary binders on the friction and wear characteristics of non-asbestos organic (NAO) brake friction materials

Binder provides structural integrity by holding all ingredients in the composition of a brake friction material. The modified binders have played a major role in improving the frictional performance and thermal resistance of the friction material. The present research work evaluates the influence of secondary binders (Nitrile Butadiene rubber (NBR) and Styrene Butadiene rubber (SBR)) on the tribological performance of the friction material using a full-scale inertia brake dynamometer as per JASO C406 standard. Three brake pads were developed by varying the type and composition of secondary rubber binder (5%NBR, 5%SBR and 2.5%NBR + 2.5%SBR) with rest of the ingredients kept unaltered. It was found that the quantity of SBR rubber powder present as secondary binder improved dry and wet recovery. Friction coefficient (μ) exhibited better stability during the fade with the inclusion of both the rubber powders. The friction material with the inclusion of both the NBR and SBR rubber powders exhibited overall better performance than compared to the inclusion of only one secondary binder rubber in the composition. The worn-out surface of the developed friction materials and the counter discs were characterised using FESEM.     

Studies on friction and transfer layer: role of surface texture

Friction influences the nature of transfer layer formed at the interface between tool and metal during sliding. In the present investigation, experiments were conducted using “Inclined Scratch Tester” to understand the effect of surface texture of hard surfaces on coefficient of friction and transfer layer formation. EN8 steel flats were ground to attain surfaces of different textures with different roughness. Then super purity aluminium pins were scratched against the prepared steel flats. Scanning electron micrographs of the contact surfaces of pins and flats were used to reveal the morphology of transfer layer. It was observed that the coefficient of friction and the formation of transfer layer depend primarily on the texture of hard surfaces, but independent of surface roughness of hard surfaces. It was observed that on surfaces that promote plane strain conditions near the surface, the transfer of material takes place due to the plowing action of the asperities. But, on a surface that promotes plane stress conditions the transfer layer was more due to the adhesion component of friction. It was observed that the adhesion component increases for surfaces that have random texture but was constant for the other surfaces.     

惯性制动条件对铜-石墨材料摩擦性能及第三体的影响

采用粉末冶金技术制备铜-10%石墨烧结材料,通过GF150D型摩擦试验机,在干摩擦状态及制动压力为0.51 MPa的条件下,研究不同制动方式对材料摩擦磨损性能的影响。结果表明,采用从高速到低速分段制动方式(摩擦方式A)时,随着制动速度降低,摩擦表面形成的致密第三体破碎、剥落,机械啮合力增加,摩擦因数提高;同时,摩擦表面温度下降,基体强度提高,磨损率降低。采用从高速到低速连续制动方式(摩擦方式B)的摩擦因数和磨损量均大于摩擦方式A。     

Effects of ZrSiO4 in non-metallic brake friction materials on friction performance

The effects of ZrSiO₄ (zirconium silicate or zircon) as an abrasive on brake friction performance and friction layers of non-metallic brake friction materials were evaluated. The experimental results indicated that ZrSiO₄ enhances friction coefficient, but depresses wear rate. However, ZrSiO₄ can improve the negative wear rate of the friction materials. The formation and development of friction layers are complex so that the friction layers formed during friction process were carefully characterized using scanning electron microscopy (SEM), light microscopy (LM), and X-ray diffraction (XRD) methods. Following characteristics of friction layers were identified—(1) dynamic behavior: the structure of friction layers changes at the different surfacial positions and across sample's thickness; (2) friction condition dependence: formation of friction layers depends upon temperatures, time, and thermal history such as fade and recovery; and (3) compositional dependence: the compositions of friction surface and bulk differ, nevertheless the bulk's composition determine the friction layers. The phenomena as baryte films, altered layers, iron patches, and zircon loose areas formed on the friction surfaces were observed. Baryte films were detected on the friction surfaces of Zr-0 (sample without zircon). Baryte films have positive effect on wear property, but the films disappear in the presence of ZrSiO₄. The amount of carbonaceous materials decreases with the increase in ZrSiO₄. Only negligible thickness of altered layers was found on the friction surfaces of Zr-0 sample, while samples containing zircon show out relatively thick altered layers. Both iron-patches and zircon loose areas increase with the ZrSiO₄ contents. The relationships among formulation, friction performance, and friction surfaces were summarized.