Friction and wear properties of two types of copper — Graphite brushes under severe sliding conditions

High speed dry friction experiments using two copper-graphite brushes against an AISI 4340 steel rotor were conducted at sliding velocities up to 230 m s⁻¹ and at current densities up to 526 A cm⁻². One brush was a commercial powder metallurgy (PM) specimen and the other was a graphite fiber-Cu/Sn matrix composite material. The composite brush was prepared by a proprietary process of liquid-metal infiltration and was run with the graphite fibers perpendicular to the rotor surface. The coefficient of friction was determined as a function of velocity, the wear rates were determined as a function of velocity and the voltage drop was determined as a function of velocity and current. The results show that the coefficient of friction exhibited by the PM brush is lower than that of the composite material at any velocity tested. The wear rates without current are much higher for the PM than for the composite brush, but they are of the same order when a current of 600 A is passed through. The voltage drop at the brush-rotor interface shows a similar variation with velocity for the two brushes, but the variation of the voltage drop as a function of current is different for the two specimens. The voltage drop increases almost linearly with increasing current for the PM brush. For the composite brush it exhibits a sharp increase up to about 50 A and then varies very little up to the maximum current of about 600 A. The damage done to the rotor surface in the case of heavy sparking is more pronounced with the PM brush than with the composite brush. It appears that the difference between the high temperature mechanical properties of the two types of brushes is responsible for their different behavior under severe sliding conditions.     

Effects of SEBS-g-MA on tribological behaviour of nylon 66/organoclay nanocomposites

The tribological behaviour of nylon 66, nylon 66/organoclay nanocomposites and nylon 66/(SEBS-g-MA+organoclay) nanocomposites was studied by means of a pin-on-disk apparatus. The morphologies of the transfer films and the worn surfaces of specimens were observed with an optical microscope and a scanning electron microscopy (SEM). Wear of all of the specimens increases with increasing load; meanwhile the coefficient of friction almost linearly decreases. Wear of nylon 66/organoclay is larger than that of nylon 66. Adding SEBS-g-MA to the nylon 66/organoclay improves the wear resistance. The coefficient of friction of nylon 66/organoclay is slightly less than that of nylon 66 at various loads. The coefficient of friction of nylon 66/(SEBS-g-MA+organoclay) is the lowest at every load. If the transfer film is thin, uniform and continuous, the wear loss and the coefficient of friction are low.     

Wear and Friction of Filled Polytetrafluoroethylene Compositions in Liquid Nitrogen

Wear and friction behavior of slider materials at cryogenic temperature is important to the development of seals and bearings for missile powerplants. Data were obtained in liquid nitrogen (?320°F) with a series of molded and extruded polytetrafluoroethylene (PTFE) compositions containing various filler materials. A 3/16-in. radius rider specimen (PTFE materials) was caused to slide in a circumferential path on the flat surface of a rotating 2½-in. diameter disk specimen (usually type 304 stainless steel). The sliding velocity was usually 2300 ft per min and the load was 1000 grams.

As compared with reference steels and carbons used in conventional seals and bearings, the filled PTFE compositions gave low wear and friction (friction coefficients from 0.06 to 0.13) in liquid nitrogen. Several extruded compositions have particular promise for seal and bearing materials. An extruded glass-filled material gave wear and friction that was essentially unaffected by sliding velocities to 6000 ft per min.     

短切玻璃纤维增强尼龙材料的摩擦与磨损

在环块式磨损试验机上研究了载荷、速度以及润滑介质等因素对自制短切玻璃纤维增强尼龙材料摩擦学行为的影响 ,利用扫描电镜对其磨损机理进行分析。发现 :材料的摩擦系数随载荷的增加而下降 ,达到最小值后 ,又随载荷的增加而持续上升 ,随着速度的增加 ,材料的摩擦系数增加 ;材料的磨损量则随载荷、速度的增加而持续增加 ;材料的磨损以粘着、疲劳为主。在润滑条件下 ,复合材料的摩擦系数大大降低 ;油润滑条件下 ,材料基本无磨损 ,但水润滑条件下 ,材料的磨损量反而比干摩擦条件下大。     

纳米SiO2对火焰喷涂尼龙1010涂层干摩擦磨损性能的影响

为了探讨纳米SiO2(n-SiO2)对火焰喷涂尼龙(PA)1010涂层干摩擦磨损性能的影响,采用MRH-3型环-块摩擦磨损试验机对不同n-SiO2含量的尼龙1010涂层的干摩擦磨损性能进行了测试;并利用扫描电子显微镜(SEM)对复合涂层的磨损表面进行观察,以探讨n-S iO2对火焰喷涂尼龙1010涂层摩擦磨损性能的影响机制。结果表明:n-SiO2的加入能明显提高尼龙涂层的耐磨性,降低摩擦因数,疲劳磨损、粘附磨损及犁切现象明显减轻;当n-SiO2含量为1.5%(质量分数)时,复合涂层摩擦磨损性能最佳,试验条件下磨损量降低近4倍,摩擦因数降低23%,跑合期降低44%,复合涂层与GCr15钢环对磨时的磨损机制主要为疲劳磨损和轻微的粘附磨损。     

Friction and wear properties of Ni–Cr–W–Al–Ti–MoS2 at elevated temperatures and self-consumption phenomena

The composites of Ni–Cr–W–Al–Ti–MoS₂ with different adding amount of molybdenum disulfide (6–20 wt.%) were prepared by powder metallurgy (P/M) method. Their mechanical properties and tribological properties from room temperature to 600 °C were tested by a pin-on-disk tribometer. The effects of amounts of molybdenum disulfide, temperature, load, and speed on the friction and wear properties of composite were discussed. Besides, the tribological properties against different counterface materials, such as alumina, silicon nitride and nickel-iron-sulfide alloys were also investigated. Results indicated that the molybdenum disulfide was decomposed during the hot-press process and the eutectic sulfides of chromium were formed. The hardness and anti-bending strength can be improved by adding 6 wt.% molybdenum disulfide due to reinforcement of molybdenum. The friction coefficients and wear rates of composites decrease with the increase of adding amount of molybdenum disulfide until a critical value of 12 wt.%. The composite with 12% MoS₂ shows the optimum friction and wear properties over the temperature range of RT 600 °C. The friction coefficients of composite with 12% MoS₂ decrease with the increase of temperature, load, and sliding speed, while the wear rates increase with the increasing temperature and are insensitive to the sliding speed and load. The friction coefficients of less than 0.20 at 600 °C and mean wear rates of 10⁻⁵ mm³/N m are obtained when rubbing against alumina due to the lubrication of sulfide films and glaze layer formed on the friction surface at high temperature, while a relatively low wear rate of around 10⁻⁶ mm³/N m presents when rubbing against nickel-iron-sulfide alloys. At high temperature, wear rates of composite containing sulfide are inversely proportional to friction coefficients approximately.     

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.     

Friction coefficient and wear rate of sputter-deposited thin films and plasma-sprayed thick coatings at high temperatures in room air

Silver, calcium fluoride (CaF_x with x = 1.85) and chromium-carbon (Cr₃C₂) thin films were deposited onto various tribological test specimens by sputtering. The friction properties of sputter-deposited Ag and CaF_x single layers as well as Ag/CaF_x multilayer films were determined by ball-on-disk tribological tests conducted in room air under various experimental conditions. The tribological properties (friction coefficient and wear rate) of sputter-deposited CaF_x films were also determined at 500°C by pin-on-disk tribological tests performed with pin specimens made of cobalt-based alloy (alacrite). Chromium-carbon films sputter-deposited onto alacrite disk and counterfaces were found to be of interest for reducing the formation of alacrite wear debris in the wear tracks; thus reduced friction coefficient and wear rate values were obtained. The friction behavior of sputter-deposited CaF_x/Cr₃C₂ thin bilayer structures and plasma-sprayed (PS) chromium carbide/Ag/BaF₂-CaF₂ eutectic composite coatings (PS-212 type coatings) was investigated by plane-on-plane tribological tests conducted in room air at 500°C and 700°C. The friction performance of solid lubricant thin bilayer films was compared with that of thick PS-212 type coatings similar to coatings developed by NASA.     

碳纤维改性热塑性聚酰亚胺材料摩擦磨损性能

通过正交实验设计和方差分析,系统考察了工况（温度、速度及载荷）对碳纤维改性热塑性聚酰亚胺（TPI）摩擦磨损行为的影响。用电子显微镜（SEM）观察其磨损面形貌分析材料磨损机制。研究表明：随着温度升高,分子链相对滑移增强,体现出良好的自润滑特性,材料的摩擦因数和磨损率均有所下降;排除摩擦热的干扰,方差分析表明载荷、速度及其交互作用对材料摩擦磨损行为影响不显著。根据粘着摩擦理论,载荷的改变对材料抗剪切强度无明显作用,表现为材料摩擦磨损性能稳定。随速度的增加,材料抗剪切强度呈现下降趋势,同时考虑到受力中的塑形硬化现象,摩擦因数出现先增后减的变化。     

PTFE对纤维增强尼龙66材料摩擦学性能的影响

考察了玻璃纤维（GF）增强尼龙66复合材料的摩擦磨损性能,以及PTFE对复合材料摩擦学性能的影响,利用扫描电镜分析了磨损形貌。结果表明：15％GF增强尼龙复合材料的摩擦学性能改善不明显,而且磨损量高于纯尼龙;加入PTFE在摩擦过程中形成了转移膜,降低了玻璃纤维增强尼龙复合材料的摩擦磨损,改善了其摩擦学性能。     

低摩擦速度下CT80油管摩擦磨损性能

研究采油过程中CT80油管与电缆在0.01～0.13 m/s速度下对摩时的摩擦磨损行为及其对油管剩余强度的影响。采用扫描电子显微镜及金相显微镜对油管组织、磨损表面及截面特征进行表征。结果表明:CT80油管的磨损量、壁厚减薄量与摩擦因数随摩擦速度增加先增大,速度达到0.07 m/s后趋于平稳;磨损率随着摩擦速度增加先增大后降低,最大磨损率对应的摩擦速度为0.07 m/s;采油过程中磨粒磨损与腐蚀磨损共同作用于油管,随着摩擦速度升高磨粒磨损造成的损失降低,腐蚀磨损造成的损失升高;随着摩擦速度增加油管的剩余抗挤毁强度以及剩余抗内压强度先降低后趋于平稳。     

Tribological behaviour of sintered 316L stainless steel impregnated with MoS2 plain bearing

The mechanical and tribological properties of sintered 316L stainless steel impregnated with molybdenum disulfide (MoS₂) were investigated. Tests were carried out at room temperature for two specific ranges of PV value (1.1 and 1.8 MPa m/s). The results prove that the friction coefficient and the wear are strongly influenced by the addition level of MoS₂.

In this paper, MoS₂ powder was mixed with 316L powder before being processed via compacting and sintering steps. The microstructure, hardness, tensile strength and elongation at breaking point of the sintered specimens were evaluated. The friction and wear properties of the materials were examined by a partial plain bearing wear test rig under dry conditions at room temperature and in air. Although some of mechanical properties of the composite decreased with increasing MoS₂ amount, the MoS₂ was very effective in reducing the friction and wear of the composites. Particularly, the sintered 316L–15% MoS₂ materials at 1.1 PV value showed a reduction of friction coefficient by approximately 20–25% when compared to the sintered 316L specimen without addition of MoS₂. In addition, wear of specimen with addition of MoS₂ was also reduced to some extent (5–10% weight loss reduction) at this specific PV value.     

Comparison of tribological behavior of nylon composites filled with zinc oxide particles and whiskers

Mechanical properties and tribological behavior of nylon composites filled with zinc oxides were investigated in this paper. Different effects of ZnO particles and ZnO whiskers filling on the friction and wear behavior of nylon 1010 (PA1010) composites under dry friction condition were observed. The hardness, tensile strength and scratch coefficients of two kinds of nylon composites filled with the ZnO particles and whiskers were measured. Experimental results show that ZnO particles and ZnO whiskers improve the mechanical and tribological properties of nylon composites without affecting the crystallinity of nylon matrix. Hardness, tensile strength and scratch coefficient of composites are increased by the addition of ZnO particles and ZnO whiskers. Filler shape has little effect on the friction coefficients of nylon-based composites. These composites filled with particles and whiskers have nearly the same friction coefficients which locate between 0.4 and 0.45. The wear rates of composites are strongly dependent on filler shape and filler content. Particle-filled composites exhibit the lower wear rates than whisker-filled composites when the content of filler is lower than 10 wt.%. After that, the case is reversed. Ploughing and adhesion are the main wear mechanisms of composites with the addition of both ZnO particles and ZnO whiskers.     

The effect of surface temperature on chemical wear

The effect of surface temperature on the chemical wear of copper with n-hexadecane containing elementary sulfur was studied in the steel-copper sliding system using a pin-on-disk type friction machine. It was found that there is an optimum temperature at which wear rate and friction coefficient are a minimum.The wear of constantan in argon was high and the wear rate was independent of sliding velocity; in air wear increased with sliding velocity. This difference is due probably to the fact that in argon no chemical reaction takes place while in air chemical reactions take place. It was confirmed by microscopic examination that films were formed on the copper surface in air. The surface temperature generated by friction at various atmospheres was measured by dynamic thermocouples. The experimental results showed good agreement with Archard's theory as modified by Dayson. It was found experimentally that the surface temperature rise is independent of the presence of surface films.A correlation between wear rate and surface temperature in the region of film flaking was obtained and the apparent activation energy of chemical wear was calculated from the Arrhenius' equation, assuming wear rate to be proportional to the chemical reaction rate.     

渐开线直齿轮时变热弹流润滑模拟

齿轮的非稳态弹流润滑问题，由于啮合过程中滑滚比、曲率半径、卷吸速度和载荷变化范围较大，因此数值计算稳定性很差。而考虑热效应的齿轮非稳态弹流润滑问题，数值计算就更困难。文中应用多重网格技术，考虑时变和温度场的影响，求得齿轮非稳态热弹流润滑问题的完全数值解，结果更接近实际。数值解得到轮齿的摩擦因数、油膜最高温升沿啮合线的变化规律以及两轮齿接触点中心压力、中心膜厚、最小膜厚沿啮合线的变化规律，同时获得任意瞬时轮齿接触点的压力、膜厚和轮齿间油膜温度分布，对分析齿轮传动问题具有重要意义。     

Tribological Behavior of NiAl–1.5 wt% Graphene Composite Under Different Velocities

The progress in aerospace field requires a new NiAl matrix composite that can stand against wear and decrease the energy dissipation through decreasing friction. In this study, the tribological behavior of NiAl–1.5 wt% graphene composite is investigated at room temperature under a constant load of 12 N and different sliding velocities. The results show that the friction coefficient and wear rate increase with increasing sliding velocity from 0.2 to 0.4 m/s due to the adhesion between the sliding bodies and tearing of the graphene layer. The friction coefficient and wear rate tend to decrease at a sliding velocity of 0.6 m/s as a result of severe plastic deformation and grain refinement of the worn surface. However, at 0.8 m/s the friction coefficient reaches a minimum value and the wear rate increases and changes the wear mechanism to fatigue wear. It can be concluded that various wear mechanisms lead to different tribological performance of NiAl–1.5 wt% graphene composite.     

基于摩擦温升效应的地铁车轮磨耗特性研究

踏面制动引起车轮温度急剧上升,影响车轮材料性能和轮轨接触状态,加剧车轮磨耗。基于Archard磨耗模型,建立一个考虑摩擦温升效应的地铁车轮磨耗预测模型。模型中根据车轮材料属性与温度之间的关系,考虑摩擦温升对接触斑大小、黏滑区划分和磨耗深度的影响,可实现对高温下的车轮磨耗特性的研究。相对以往的车轮磨耗预测模型,该模型能反映温度对磨耗影响的物理本质,适合研究轮轨接触界面有较大温度(如踏面制动)时的车轮磨耗演化机理。用所建立的车轮磨耗数值预测模型,计算对比不同温度下的轮轨接触状态和车轮磨耗深度。结果表明,轮轨接触斑和滑动区面积随温度的升高而增加;温度升高使接触斑单元磨耗深度增加,当踏面温度从常温25℃增加到最高温度300℃时,最大磨耗深度0.4 nm,增幅为28.4%;车轮转动一圈后,其径向磨耗深度也随温度的升高而明显增加,最大径向磨耗深度15 nm,增幅为28.2%,同时,车轮横向位置的磨耗范围增加5.8%,为踏面制动形式的地铁车轮磨耗预测研究提供更加准确的理论模型。     

Testing of metal-fluoroplastic sheet antifriction materials at up to 3 mps sliding velocities

The results of comparative tribotests of DU materials and developed netted sheet antifriction polytetrafluoroethylene-based materials during dry friction against a steel counterbody are discussed. It is shown that the netted sheet antifriction material is capable of long operation under the aforementioned conditions at up to 3 mps sliding velocities. IR spectroscopy and thermogravimetry of wear debris show a great amount of low-melting polytetrafluoroethylene destruction products that cause a decrease in friction temperature after the specimen run-in. The sheet material having a low wear rate, designed for operation in dry friction at high sliding velocities, can only be produced with a large volumetric share of polytetrafluoroethylene, which is the main condition for the formation of the antifriction layer. The Sharpy rule for sheet material friction at low wear rate is observed when the share of solid inclusions on the friction surface, the bronze frame in our case, is an order of magnitude lower that that of the softer and pliant matrix.     

Study on dynamic friction characteristics in reciprocating friction drive system

The dynamic friction characteristics of a reciprocating friction drive system are investigated under conditions of dry contact using 0·45% carbon steel pair. Three friction modes are found during the operation, i.e. stick-slip, sticking and a transition region. The critical operating conditions in classifying these three modes are examined under various driver speeds, normal loads and spring constants. The critical values of driver speed and normal load increase with increasing spring constant. Generally, in the friction drive system the disappearance of the stick-slip results in smooth rolling. It is also found that the slope at the first period of slip on the traction force–relative slip velocity curve would have a transition from negative to positive value when the friction mode of stick-slip changes into sticking. Moreover, results show that the sticking mode gives the best positioning accuracy with the least wear on the contact surfaces. In addition, a transition from severe wear to mild wear is found when the friction mode is transferred from stick-slip to sticking only.     

Friction and wear properties of Kevlar pulp reinforced epoxy composites under dry sliding condition

In this work, the friction and wear properties of Kevlar pulp reinforced epoxy composites against GCr15 steel under dry sliding condition were evaluated on a reciprocating ball-on-block UMT-2MT tribometer. The effects of Kevlar pulp content on tribological properties of the composites were investigated. The worn surface morphologies of neat epoxy and its composites were examined by scanning electron microscopy (SEM) and the wear mechanisms discussed. The results show that the incorporation of Kevlar pulp into epoxy contributed to improve the friction and wear behavior considerably. The maximum wear reduction was obtained when the content of Kevlar pulp is 40 vol%. The friction coefficient of epoxy and its composites increased with load while increase in the sliding frequency induced a reverse effect. Fatigue wear and scuffing were notable for the neat epoxy. The fatigue cracks were greatly abated when the filler content was 40 vol%. The wear grooves appeared on the worn surface at higher filler content.