Shear-Induced Surface-to-Bulk Transport at Room Temperature in a Sliding Metal–Metal Interface

Predictions from molecular dynamics (MD) simulations, that sliding at a metal–metal interface causes vortices in the near-surface region that transport atoms from the surface into the subsurface region, is tested experimentally. This is accomplished by rubbing a methyl thiolate overlayer grown on a clean copper foil by exposure to dimethyl disulfide at room temperature. Repeatedly rubbing a 1.27 × 10⁻² m diameter pin over a thiolate-covered copper surface at an applied load of 0.44 N and sliding speed of 4 × 10⁻³ m/s in an ultrahigh vacuum tribometer, results in the removal of sulfur from the wear track as measured using spatially resolved Auger spectroscopy. Any remaining surface species, in particular, outside the wear track, are removed by argon ion bombardment. Since sulfur is more thermodynamically stable at the surface, heating the sample causes the sulfur to resegregate to the surface only inside the wear track, thereby directly confirming the predictions from MD simulations.     

Temperature-dependent contact phenomena of PVD- and CVD-deposited DLC films sliding on the thin aluminium foil

This paper reports on tribological properties of magnetron-sputtered WC–C and chemical vapour-deposited diamond-like carbon films coated onto hard-metal surfaces when sliding on aluminium foil (0.2 mm nominal thickness) at different temperatures. The study addresses the evolution of the coefficient of friction at the interfaces of the coated hard metal and the aluminium foil under dry-lubrication conditions, in a ball-on-disc configuration. The wear mechanisms of the aluminium foil and the damage produced on the coated surfaces due to the sticking of aluminium were evaluated as a function of the deposited coating and the temperature at their interfaces. Aluminium-transfer to WC–C coated hard-metal surfaces during the sliding operation seemed to be a non-continuous process, which appeared after a certain number of sliding cycles. Temperatures above 70°C accelerated the transfer of aluminium to the WC–C tool surfaces. Chemical vapour-deposited diamond-like carbon films hindered the transfer of aluminium to the hard metal even at temperatures of around 125°C. At greater temperatures, an aluminium–aluminium tribosurface is formed at the interface, which increases the wear rate of the foils and rapidly degrades the quality of coatings of the hard-metal surfaces.     

铜箔在渗硼处理中防渗作用的试验研究

通过试验研究了铜箔（copper foil）在渗硼处理中的防渗作用。结果表明在金属表面粘贴铜箔具有明显的防渗效果。     

镍箔中介法粘接铜与Al2O3陶瓷

采用镍箔中介法研究了铜与Al2O3陶瓷的粘接，重点考察了镍箔的厚度、粘接温度、压力对界面粘结强度的影响，在温度850℃，压力6.5MPa，粘接时间300s的条件下，获得最大粘结强度18.0MPa。     

激光诱导空化微孔冲裁试验研究

针对微尺度下金属箔模具冲孔存在模具挤压磨损、对中困难,激光打孔存在烧蚀、吸收层无法补偿等问题,提出通过激光诱导空泡对金属箔进行加载来实现冲裁小孔的方法。研究了不同激光焦点位置(H=0~4 mm)、激光能量(E=10.3~50.8 mJ)和铜箔厚度(T=20~70μm)对铜箔冲孔的影响,发现激光焦点位置影响明显,当铜箔变形平均深度达到147.0μm后,铜箔发生剪切断裂,可实现冲裁,并且制备的小孔边缘正表面无烧蚀、毛边、裂纹和卷边等缺陷。同时,利用高速摄影仪对激光诱导空化微孔冲裁过程进行研究,结果表明激光诱导空化微孔冲裁过程是激光等离子体冲击波、空泡溃灭冲击波和微射流共同加载的过程。     

Effect of temperature on the fretting corrosion of tin plated copper alloy contacts

The effect of temperature on the fretting corrosion behaviour of tin plated copper alloy contacts in the temperature range of 25–185 °C, is addressed in this paper. The change in contact resistance with fretting cycles at various temperatures was determined. The contact zone after fretting corrosion test was analyzed using laser scanning microscope, X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray spectrometry (EDX), to assess the surface profile, phase content, morphology and compositional changes across the interface. The study reveals that temperature has a greater influence on the extent of fretting corrosion of tin plated copper alloy contacts. The softening of tin is responsible for the extended region of low contact resistance observed at 85 °C. The increase in thickness and the resistance of Cu–Sn intermetallic compounds (IMCs) is responsible for the decrease in surface roughness and the drastic increase in the contact resistance at higher temperatures. The study suggests that the tin plated copper alloy contact system should be considered as copper alloy/IMC/Sn/SnO₂ instead tin plated copper alloy. During fretting corrosion test at elevated temperatures, once the top surface layers are worn out, the contact interface is transformed from tin versus tin-to-tin-intermetallic versus tin-intermetallic. The study concludes that tin plated copper alloy contacts are not suitable for high temperature applications.     

自补偿摩擦表面微观形貌分析

进行了钢－铜摩擦副的原始表面、常规润滑油和自补偿滑油润滑下的表面微观形貌测试和分析;对自补偿润滑下和常规润滑下钢、铜表面的粗糙度和表面轮廓特征参数进行了比较;研究了载荷、摩擦行程对自补偿润滑下钢、铜表面微观形貌的影响;得出了钢－铜摩擦副的磨损在一定范围内与载荷无关、其磨损不随摩擦行程线性增加、自补偿添加剂ＳＷ４更适应于重载工况和经过大的摩擦行程后仍起作用等结论。     

铝-铜层状复合材料热辅助超声波増材制造方法

为实现铝铜层状复合材料的优质固相増材制造,克服现有超声波功率器件和设备输出功率的限制,提出具有辅助热场的大功率超声波増材制造装备及方法,并分析热场对铝铜界面结合性能的影响。在不同辅热温度下使用T2铜箔和1060铝箔进行了多层叠加固结试验,对Al/Cu和Cu/Al两种界面形式进行了研究,剥离试验和断口形貌分析表明Cu/Al界面形式具有更高的剥离强度。采用SEM和EDS方法,分析了不同加热温度和压力下的铝-铜界面组织特征,结合金相分析和力学性能测试结果表明：Al/Cu界面力学强度随辅助加热温度的上升而提高,并在加热温度为100℃时铝铜界面在超声波作用下可以形成有效的固相连接接头,且最大力学强度达到26.23 N/mm,Al/Cu和Cu/Al两种焊接形式下界面处元素扩散层宽度均可达到4～6 μm;界面断口呈现准解理断裂的撕裂棱形貌特征。铝-铜复合材料超声増材制造过程中,辅助热场方式可明显提高铝-铜复合材料的加工质量和效率。     

单次扫描检测大表面痕量赖氨酸和黑索今的质谱分析方法

为了进一步提高大表面样品的分析速度,减少给定样品表面的扫描次数,建立了一种单次扫描即可检测分布于大表面样品上任意位置痕量待测物的质谱分析方法。以人造革表面（4 cm×4 cm）添加的赖氨酸和黑索今为代表性检测对象,用一块无毛刺等边三角形金属铜电极（边长为8.6 cm）紧贴在样品表面,将甲醇-水（3∶7,V/V）电离试剂涂洒在金属电极表面,让其与样品表面保持湿润接触,并使三角形电极尖端对准质谱仪的离子入口;然后在金属电极上施加+5.8 kV高压,在电场的驱动下,湿润表面的待测物朝着质谱入口移动,并在三角形电极尖端形成待测物离子进入质谱仪检测。结果表明,该方法可单次扫描检测随机分布在皮革样品表面上任意位置的非均匀分布的赖氨酸和黑索今,检测限可达6.2×10^-7 μg/cm²,分析单个样品表面的时间不到2 s;与采用电喷雾解吸电离质谱等顺次扫描检测（采样面积不到1 mm²）的方法相比,本方法的分析速度提高了1000倍。     

Various TEM methods for the study of metal matrix composites

We have investigated the applicability of a number of TEM techniques for the study of the metal/ceramic interface in a short fibre metal matrix composite (SFMMC). In particular, we found that dark field techniques were best suited to the study of any possible (0.4-2 nm) amorphous layer. High resolution imaging was found to be difficult to use because of the absence of well defined ‘edge-on’ interfaces, but EELS with parallel recording was found to be very useful for finding and identifying segregated particles at the fibre/matrix interface. It was also shown that micro-mechanisms of fracture such as voiding and fibre breakage could be readily examined by TEM using a foil preparation method which resulted in an ‘edge-on’ fracture surface and an observation region extending about 0.8 mm below it.     

Morphology and Nanomechanical Properties of ZDDP Antiwear Films as a Function of Tribological Contact Time

We have employed scanning force microscopy (SFM) and nanoindentation analysis to track the evolution of tribologically generated antiwear films derived from zinc dialkyldithiophosphate (ZDDP) as a function of rubbing time. The SFM images reveal that film morphology evolves with time through a growth mechanism consisting of three stages. In the first stage nucleation on active sites at the steel surface leads to the growth of distinct segregated islands. In the second stage the islands coalesce causing the film to spread over a larger fraction of the surface. In the final stage continuous rubbing induces the large islands to divide into smaller, densely packed structures. In contrast to the observed morphological changes, rubbing time does not strongly influence the nanomechanical properties of the films. This highlights the importance of film morphology in determining the effectiveness of ZDDP antiwear films. We also observe large variation in both the morphology and nanomechanical properties that are likely due to the heterogeneity in contact pressure at the pin-sample interface of the wear rig.     

Equipment for deposition of thin metallic films bombarded by fast argon atoms

Deposition of thin metallic films on dielectric substrates using a source of metal atom flow combined with a flow fast argon atoms has been investigated and the investigation results are presented. The fast atoms are produced due to charge-exchange collisions in a vacuum chamber of argon ions, which are accelerated by potential difference between the hollow-cathode glow-discharge plasma and an emissive grid and enter the chamber through the grid. The metal atoms produced due to ion sputtering of a metallic foil placed on the inner surface of the hollow cathode enter the chamber through the same grid. Substrate pretreatment and pulse-periodic bombardment of the growing film by ～1-keV argon atoms both ensure adhesion of copper to glass up to 2 × 10⁷ Pa. The use of a hollow substrate holder, whose inner surface is also covered with the same foil, makes it possible to exclude losses of the depositing metal and allows recommendation of the equipment for beam-assisted deposition of precious metal films.     

A procedure for obtaining complementary replicas of ultra-rapidly frozen sandwiched samples

Complementary replicas of samples prepared for electron microscopy by the freeze-fracture/etch technique are extremely valuable in the interpretation of the exposed surfaces, the nature and location of the membrane fracture plane, and as an aid in the recognition of the potential artefacts of this technique. This paper describes a procedure for the preparation of complementary replicas of thin samples sandwiched between copper foil strips and frozen ultra-rapidly in the absence of chemical pretreatments. In this procedure, the copper foil support bearing the replica is floated on the surface of a chromic acid solution, resulting in the controlled dissolution of the copper metal. The replica which remains at the surface of the chromic acid is then stabilized against fragmentation during subsequent cleaning and rinsing steps by placing a 50 mesh gold grid on top of the replica. To minimize agitation of the replica/grid, all cleaning steps are performed in a single depression plate well. The clean replica/grid is picked up from below on a thin Formvar film, dried, and then separated from the extra film. Careful placement of the gold grid on the replicas and low magnification electron micrograph montages of the complementary grids facilitate the location of complementary regions and simplify examination of complementary specimen areas at higher magnification.     

Investigation of mass transfer during tribological interaction of alloyed steels

Variations in the chemical composition of the surface layers of two alloyed steels are studied in a tribojoint operating according to the ??shaft-on-bush?? geometry (bushing test) where the shaft is copper electroplated. Complex interactions are observed during testing in the presence of a molten tin and lead-containing metal lubricant that separates the rubbing surfaces; wear, oxidation, adhesion, and diffusion phenomena are observed in all components of the joint, including the metal lubricant. Comparative studies are performed to study the changes in the surface layer composition of all elements of a ball bearing with a cage fractured due to misuse.     

Tribological Properties and Electrical Signal Transmission of Copper–Graphite Composites

The correlation between tribological properties of resin bonded copper–graphite composites and electrical signal transmission is investigated. Particular attention is given to the loss of electrical signal at the sliding interface and the amount of signal noise as a function of the composition in the composite. A custom designed slip-ring type tribotester with a copper ring has been used for this study. Results show that the tribological properties of the sliding couple, that is closely associated with morphology of sliding surfaces and the presence of transfer films, determine the amount of voltage drop at the interface and electrical signal noise. The change of the applied load during sliding experiment changes the coefficient of friction (COF) and energy loss at the sliding interface, suggesting that the effective contact area at the rubbing surface of the composite strongly affects the amount of voltage drop. It is also found that the electrical signal noise is directly related with the fluctuation of the friction coefficient caused by the variation of contacts at the sliding interface and by the transient patches of transfer films on the surface of the ring.     

地铁刚性弓网系统接触线磨损特性试验研究

为研究地铁刚性接触网系统接触线磨损的规律,以地铁刚性接触网系统常用的浸金属碳滑板/铜银合金接触线作为摩擦副,通过模拟地铁弓网系统运行参数,使用载流摩擦磨损试验机研究有、无电火花放电情况下,浸金属碳滑板与铜银合金接触线直流电滑动过程中磨损量、摩擦因数、载流效率随滑动距离的变化。试验结果表明：电火花放电会使得接触线与浸金属碳滑板磨损量显著上升,出现电火花放电时摩擦因数较小,弓网系统载流效率会明显降低同时出现大幅波动。试验后对碳滑板和接触线表面形貌的观察可知：电火花放电会使得浸金属碳滑板表面烧蚀坑数量和尺寸大小增加,同时会出现滑板材料大面积剥落和表面裂纹增多的问题,接触线表面形貌变得更加粗糙。     

The Kinetics of Shear-Induced Boundary Film Formation from Dimethyl Disulfide on Copper

The kinetics of the shear-induced surface-to-bulk transport of methyl thiolate species formed from dimethyl disulfide (DMDS) on a copper surface are explored. It is found that the loss of surface species as a function of the number of rubbing cycles can be modeled by assuming that the adsorbed layer penetrates the subsurface a distance of ~0.7 nm per scan. Adding wear to this model does not improve the fit to the experimental data providing an upper limit for the wear rate of ~0.06 nm/scan. This model is applied to analyzing the depth distribution of sulfur within the subsurface region as a function of the number of rubbing cycles, measured by Auger depth profiling when continually dosing the copper sample with DMDS. It is found that the shape of the experimental depth profile is in agreement with the model developed to analyze the surface-to-bulk transport kinetics of the adsorbed layer. However, the profiles are almost identical for surfaces that have been rubbed 130 and 360 times, so that the surface-to-bulk transport kinetics are self limiting.     

A comparison of specimen stage surface temperature and the GA-1 control unit reading in Balzer's Freeze fracture microtome cold stage

The cold stage specimen surface in our Balzer's 300 Freeze-etch instrument, averages 29–43°C warmer than the reading on the GA-1 stage temperature control unit. By introduction of Indium foil seals above and below the stainless steel plug in the stage tower, the specimen cold stage surface temperatures were still 9–10°C warmer than the GA-1 reading. After replacing the stainless steel plug with a copper plug and using Indium seals, the cold stage specimen surface was brought within 2.6°C of the GA-1 temperature reading. In addition, the copper plug, Indium seal modified stage cools about two times faster in going from –100°C to –150°C than the normal stainless steel stage modified with Indium seals.     

An investigation of the wear of abrasive grains by rubbing on diamond disks

In earlier wear studies¹ single abrasive grains were rubbed against the surfaces of metal disks under light loads. These studies have now been extended to include an examination of wear behaviour when using diamond-impregnated surfaces at lower sliding speeds and when using more accurately controlled test conditions. These wear tests provided values of wear resistance in the absence of chemical effects (i.e. at sufficiently low surface temperatures). The results are in excellent agreement with the conventional wear theory pertaining to lightly loaded sliders. The wear volumes are, however, two orders of magnitude greater than those obtained when rubbing tough grains against steel disks and three orders of magnitude greater than the results obtained when rubbing friable grains against similar metallic surfaces.     

The transfer of polytetrafluoroethylene studied by x-ray photoelectron spectroscopy

A polytetrafluoroethylene (PTFE) sphere of radius 4.8 mm was rubbed against nickel and S-Monel at speeds from 0.94 to 94 mm s^?1 and at loads from 0.19 to 3.9 N. The transfer film of PTFE on the metal was examined with X-ray photoelectron spectroscopy. In all cases the film was found to be indistinguishable from bulk PTFE. A trace of metal fluoride was observed whether the rubbing took place on oxidized or atomically clean metal. The film was of the order of a molecule thick for the entire range of loads and did not increase with repeated passes over the same rubbed area. An erratic increase in thickness at rubbing speeds above 10 mm s^?1 was taken as evidence of random transfer of bulk material.