含石墨转移层对铜－二氧化硅／ 钢摩擦磨损行为的影响

为探讨干摩擦磨损条件下含石墨转移层对摩擦磨损性能的影响,在45#钢表面覆盖含石墨润滑层,通过干滑动磨损试验,研究含石墨润滑层对钢/铜-二氧化硅摩擦副摩擦因数、磨损量及摩擦损（亚）表面的影响。结果表明：与无石墨润滑层的45#钢相比,含石墨润滑层的45#钢的摩擦因数、磨损率明显下降,且干滑动试验后磨损表面相对光滑平整,表明含石墨摩擦层起到了减摩降磨作用,抑制了金属的直接接触。     

表面渗铜铈合金钢在干摩擦条件下的摩擦磨损性能

为提高采煤机滑靴在干摩擦条件下的抗磨损性能，采用双层辉光离子渗金属技术对滑靴用18Cr2Ni4W合金钢表面进行渗铜铈处理，通过环-块摩擦磨损实验机在不同载荷和滑动速率下考察其干摩擦条件下的摩擦学性能，并与45#钢和18Cr2Ni4W合金钢的摩擦学性能和磨损机制进行比较。结果表明：表面渗铜铈的18Cr2Ni4W合金钢在不同载荷和滑动速率条件下表现出最低的摩擦因数和磨损率，45#钢呈现出最高的摩擦因数和磨损率，这表明通过表面渗铜铈改善了18Cr2Ni4W合金钢的减摩抗磨性能；摩擦过程中，45#钢的磨损机制为犁沟和黏着磨损，18Cr2Ni4W合金钢的磨损机制为犁沟和轻微的黏着磨损，表面渗铜铈的18Cr2Ni4W合金钢表现出犁沟和轻微的剥落磨损特征。     

等离子弧表面淬火钢件的摩擦特性及耐蚀性

采用等离子弧表面淬火方法对45#钢和38CrMoA lA合金结构钢进行表面硬化处理,硬化深度分别为0.311和0.388 mm。在球-盘式摩擦磨损实验机上研究不同速度和载荷条件下,上述两种钢件的摩擦磨损特性。采用SEM观测磨损后涂层的表面形貌,探讨涂层的摩擦磨损机制。研究发现:38CrMoA lA硬化层表面硬度比45#钢高,且淬硬带无明显的硬度梯度;38CrMoA lA的磨损率低于45#钢,且随载荷和速度的增加而增加;不同载荷条件下,磨粒磨损、塑性流动和黏着磨损控制摩擦过程;38CrMoA lA的耐蚀性优于45#钢。     

接触应力和相对滑动速度对金属表面自修复膜生成的影响及机制

采用羟基硅酸镁粉体作为润滑油添加剂,在MMU-5G材料端面摩擦磨损试验机上,研究了不同接触应力和相对滑动速度对45^#钢/45^#钢摩擦副磨损表面自修复膜生成的影响及其机制,借助SEM及EDS测试分析摩擦副的表面形貌及表面成分组成。结果表明,接触应力和相对滑动速度对羟基硅酸镁粉体添加剂在磨损表面形成自修复膜影响显著。在接触应力为1.53,3.06,4.59,7.64MPa和在相对滑动速度0.416m/s的工况条件下,试样磨损表面有自修复膜生成。接触应力为3.06MPa和相对滑动速度为0.416m/s时,易于在短时间内达到磨损-自修复动态平衡,自修复效果最为理想。自修复膜的生成过程包含磨粒磨损和摩擦化学反应2个阶段。自修复膜的生成使得试样摩擦磨损表面平整光滑,可以有效降低金属磨损。     

时间效应对45~#钢-铸铁摩擦副在自修复添加剂作用下摩擦磨损性能的影响

利用MMU-5G型端面摩擦磨损试验机,研究了在自修复添加剂作用下,时间对45#钢-铸铁摩擦副摩擦磨损性能的影响及其机制.验证了45#钢与铸铁匹配时摩擦表面形成自修复膜的能力,研究了铸铁的摩擦磨损性能及自修复膜形成情况,借助SEM和EDS观察分析摩擦表面形貌及成分组成.结果表明:时间效应对45#钢-铸铁摩擦副摩擦磨损性能的影响显著,铸铁试样的磨损失重损失低于45#钢,摩擦磨损时间为10 h时,45#钢试样表面生成自修复膜,而铸铁表面未观察有修复膜的生成,添加剂对铸铁的减摩和耐磨效应显著.     

聚酰亚胺复合材料与不同金属间干滑动时的摩擦学性能

采用MPX-2000型摩擦磨损试验机研究了聚四氟乙烯和二硫化钼填充聚酰亚胺复合材料在干滑动摩擦条件下与45钢、镍铬合金、铜和铝对磨时的摩擦磨损性能,并利用扫描电子显微镜和光学显微镜分析了复合材料及对偶件的磨损表面形貌。结果表明:复合材料与铝对磨时的摩擦因数和磨损率最低,分别约为与钢摩擦时的43%和49%;摩擦后铝表面形成均匀连续的转移膜,45钢、镍铬合金和铜的表面没有形成有效转移膜,因此复合材料的摩擦因数较大;复合材料与不同金属材料摩擦时的磨损机理主要是粘着磨损与疲劳磨损。     

硅酸盐粉体作为润滑油添加剂在金属磨损表面成膜机制

在润滑油中添加蛇纹石硅酸盐粉体,采用MM-200摩擦磨损试验机研究了45#钢-45#钢摩擦副磨损表面的自修复陶瓷膜层形成机制,借助SEM及EDAX测试分析自修复陶瓷膜层的表面形貌及表面成分组成。结果表明摩擦能量对硅酸盐添加剂在磨损表面形成自修复膜层有很大的影响:自修复膜层为氧化物陶瓷材料,主要成分来自于硅酸盐添加剂。在低载荷300 N时,摩擦因数减小,硅酸盐添加剂不能转移到磨损表面,不能形成自修复膜层,仅仅起到减磨作用。下试样的失重随磨损时间增加而增加;在试验时间为20 h时,试样失重达到最大值,随后试样的失重反而减小。在载荷为600 N、900 N,试验时间30 h摩擦磨损后,在金属表面形成自修复保护膜,磨损表面比较平整光滑,无明显的片层剥落和犁沟,摩擦发生在自修复陶瓷材料之间,摩擦因数增加。硅酸盐添加剂在机械剪切作用下变形,在金属的磨损表面上铺展,并且在摩擦磨损过程中不断向摩擦表面转移,形成了均匀光滑的自修复膜层。自修复膜层隔离了金属摩擦表面的直接接触,摩擦磨损发生在自修复膜层之间,有效地降低了金属的磨损。     

永磁场条件下45钢与GCr15钢摩擦磨损性能试验研究

基于HSR-2M高速往复摩擦磨损试验机,研究在永磁体磁场条件下滑动速度、载荷等参数对45#钢/GCr15钢摩擦副摩擦学性能的影响,通过磨痕形貌分析其磨损机制,并与无磁场条件下的试验结果进行对比。试验结果表明:磁场的引入可以在一定程度上减小摩擦因数和降低磨损率,证明磁场能够改善45#钢/GCr15钢摩擦副的摩擦学性能;增大滑动速度将降低摩擦因数和磨损率,增大载荷将降低摩擦因数,增加磨损率。无磁场时,摩擦副的摩擦磨损为典型的磨粒磨损,磨损系统的磨损率和摩擦因数较大;有磁场时,磨损形式主要为黏着磨损,摩擦因数和磨损率较小。     

多晶及单晶铜的磨损及腐蚀性能研究

对比研究多晶及单晶铜耐磨与耐腐蚀性能。在干摩擦条件不同载荷和速度下考察多晶及单晶铜的摩擦学性能;探讨多晶及单晶铜在3.5%NaCl溶液中的自然腐蚀及电化学腐蚀性能的差异。结果表明:在干摩擦及转速为100~400 r/min条件下,多晶铜的摩擦因数高于单晶铜,磨损量低于单晶铜;在干摩擦及载荷为20~35 N条件下,多晶铜摩擦因数高于单晶铜,磨损量无明显差异;单晶铜在NaCl溶液中比多晶铜具有较强的耐蚀性;多晶铜与45#钢磨损机制以黏着磨损为主,而单晶铜与45#钢的磨损机制以剥层磨损为主。接触表面塑性变形能力以及晶粒取向、晶界分布的差异是影响单晶铜和多晶铜磨损和腐蚀性能的主要原因;含有平直柱状晶晶界的单晶材料具有高取向性,有利于其大塑性变形;择优取向使单晶铜在晶胞尺度上的微观平面排列致密,同时晶界的减少抑制了腐蚀的扩展,从而提高了其耐蚀性。     

金属滑动干摩擦条件下高频噪声的测试与分析

基于面-面接触旋转式滑动干摩擦系统,选用A3&45#钢为摩擦副材料,研究相对滑动速度,表面压力对高频摩擦噪声的影响和规律。运用ABAQUS有限元模态分析高频摩擦噪声产生的原因与机理。通过实验与模态分析发现,摩擦高频噪声易于发生在相对滑动速度较低处。A3&45#摩擦副,在面-面接触旋转式滑动干摩擦条件下,产生的高频摩擦噪声能量集中分布在7950 Hz,9200 Hz。验证了干摩擦条件下,摩擦高频噪声是由于摩擦界面形成类似"锤击效应"的微凸体之间的运动,使得摩擦力高频成分和系统固有频率耦合引起的系统不稳定现象。     

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.     

Formation of Laminar Structure Under Unlubricated Friction of Cu–SiO2 Composite

A laminar-structured tribolayer on the worn surface of Cu?CSiO₂ composite in sliding against 1045 steel is observed by etching the longitudinal sections. In morphology, the tribolayer consists of many subunits with different lengths and heights. The subunits are curved or parallel to the contact surface at different depths from bulk to the worn surface. In microstructure, the tribolayer is unconsolidated after etching, and fine Cu grains, as well as few fractured SiO₂ particles, are observed. The main formation mechanism of the laminar-structured tribolayer is grain boundary sliding. Shear localization with large plastic strain is a prerequisite for the formation of laminar structure. The generation and accumulation of frictional heating promote the plastic deformation and decrease the activation energy for grain boundary sliding. The etching effect is contributed to the presentation of the laminar structure.     

铜基粉末冶金/Q235B摩擦副载流摩擦磨损性能*

磁浮列车中部分制动闸片在服役时一直处于受流状态,导致材料磨损加剧,影响闸片的服役寿命。为研究中低速磁悬浮列车制动闸片在受流工况下的摩擦磨损性能,以制动闸片使用的铜基粉末冶金材料和刹车盘使用的Q235B材料为摩擦副,研究不同制动速度下铜基粉末冶金/Q235B摩擦副的载流摩擦磨损行为。结果表明：无电流时随着滑动速度的增大,摩擦因数及磨损率整体呈现下降的趋势,载流时随着滑动速度的增大,摩擦因数整体呈现下降的趋势,而磨损率则整体呈现上升的趋势;无电流时磨损后的铜基粉末冶金材料表面覆盖着一层靛色的第三体层,该第三体层低速时主要以颗粒状为主,随着速度的增加逐渐被压实成连续致密状,高速时因黏着磨损加剧使得连续致密状第三体被破环,导致材料的摩擦因数和磨损率呈现反向增长的趋势;载流下磨损后的铜基粉末冶金材料表面出现了以机械磨损为主和以电弧烧蚀为主的2个区域,其中以机械磨损为主的区域依然是由靛色的第三体层组成,而以电弧烧蚀为主的区域表面则覆盖了一层金色熔融状物质,并且随着速度的增大,烧蚀区面积也逐渐增大。     

滑动速度对油润滑表面胶合磨损的影响

在油润滑条件下,钢对钢摩擦副的胶合摩损不仅取决于润滑油膜是否破裂,而且取决于在摩擦表面上化学反应膜的形成情况。本文研究了在油润滑条件下滑动速度对钢摩擦副胶合的影响。在低滑动速度下摩擦表面易于形成反应膜,油膜破裂后并不直接发生胶合。胶合发生在高温、高摩擦系数的恶劣条件下。在高滑动速度下油膜破裂后很容易发生胶合,发生胶合前的表面温度和摩擦系数都比较低。     

Teflon固体润滑膜摩擦学特性实验研究

用销－盘实验机研究了Teflon固体润滑涂层在高速（5.6m/s)、重载（初始接触应力400MPa)条件下的摩擦磨损性能。结果表明该涂层不仅具有很低的摩擦系数（0．08－0．09）,而且耐磨性也较好,磨损率与渗碳钢处在同一致量级。     

Wear reducing effects and temperature dependence of tribolayer formation in harsh environment

Certain materials show a tribolayer formation especially at enhanced temperatures in abrasive environment, building a wear protection layer with the abrasive on the surface. Three materials with different microstructures were tested in three-body abrasive and impact/abrasive environments at temperatures up to 700 °C to investigate tribolayer formation. Optical and electron microscopical methods were used for wear qualification. Furthermore, hot hardness tests were performed up to 700 °C to investigate the influence of hardness drop on tribolayer formation.It was shown that no significant tribolayer formation occurs on grey cast iron, whereas other materials form tribolayers. Generally, tribolayer formation increases with increasing testing temperature, especially for austenitic and ferritic materials. This entails a self-protecting effect and thus superior wear resistance in abrasive environment.     

Influence of sliding speed on modes of material transfer as steel slides against PVD tool coatings

An intermittent sliding test was used in order to study the formation and build-up of tribofilms during intermittent sliding of PVD coated HSS against case hardening steel (20NiCrMo2). Two cutting tool coatings were tested, TiN and AlCrN, and the influence of sliding speed was evaluated. With moderate speed, two tribofilms were formed separately, one consisting of Mn, Si, Al and O on an intermediate layer of Fe and one consisting of Fe, Mn, Cr and O on an intermediate layer of Cr and Mn. At low sliding speeds an uneven transfer of steel occured while high sliding speeds resulted in thermal softening of the substrate leading to coating failure. AlCrN provided better substrate protection at high speeds than TiN did.     

Influence of cutting condition on white layer induced by high speed machining of hardened steel

White layer formed on machined surface during dry and hard high speed machining has great influence on workpiece performance. Studying machined surface white layer is significant to improve the machinability and surface quality of workpiece. Experiments of dry and hard high speed machining of GCr15 bearing steel and 40CrNiMoA alloy steel were carried out with PCBN inserts, the phase composition and the thickness of white layer were studied experimentally; the formation mechanism of the white layer were studied; effects of cutting parameters, carbon content of substrate material on white layer thickness were analyzed; effects of cutting speed on retained austenite content in machined surface were also summarized. Results show that the microstructure of white layer consists of cryptocrystalline martensite, retained austenite and carbide; the white layer is formed by martensitic transformation; the white layer thickness and the retained austenite content of machined surface increase firstly and then decrease with cutting speed; the white layer thickness increases with flank wear and carbon content.     

The effect of air humidity on tribological behaviours of W–C:H coatings with different tungsten contents sliding against bearing steel

Friction and wear behaviors of W–C:H coatings with different tungsten contents sliding against bearing steel balls at different air humidities were investigated. The worn out surfaces of steel balls and coatings were analyzed with the aid of scanning electron microscopy (SEM) and Raman spectroscopy. A tribolayer composed of a graphite-like material mixed with tungsten and iron oxides was observed on the friction surfaces of the steel balls. The chemical and phase compositions of the tribolayer, which depend both on the tungsten content in coatings and air humidity, determine the tribological properties of the W–C:H coating in a frictional contact with bearing steel. At average air humidity (50%), those coatings that contain less than 10 at% of tungsten in a frictional contact with steel exhibit favorable tribological properties. The friction coefficient of frictional contacts under test reaches a low value (f～0.01) at a low air humidity and increases with humidity of up to ca. 0.2. The best tribological properties in a wide range of air humidity (5–90%) have been found for W–C:H coatings with the tungsten content between 2 and 5 at%.     

Effects of Normal Load,Sliding Speed,and Surface Roughness on Tribological Properties of Niobium under Dry and Wet Conditions

The effects of normal load, sliding speed, and surface roughness on the friction and wear of high-purity niobium (Nb) during sliding without and with an introduction of water were systematically investigated. Increasing the normal load or sliding speed decreased the friction of the Nb under the both dry and wet conditions because the increased wear of the Nb decreased the interfacial shear strength between the steel ball and Nb by promoting the surface roughening and the production of wear debris. However, the Nb tested at the lowest sliding speed under the lowest normal load with water exhibited the lowest friction and wear due to the formation of oxide layer on the wear track. The friction and wear of the Nb tested under the dry condition decreased with increased surface roughness because the higher interfacial shear strength between the steel ball and smoother Nb resulted in the earlier breakdown of the native oxide layer and direct contact between the steel ball and Nb. However, increasing the surface roughness of the Nb increased its friction and wear under wet conditions, probably due to the easier breakdown of the oxide layer that formed on the rougher surface during sliding. The tribological results clearly showed that the introduction of water during sliding had a significant influence on the tribological properties of the Nb.