Optimum film thickness of thin metallic coatings on silicon substrates for low load sliding applications

The frictional behaviour of thin metallic films on silicon substrates sliding against 52100 steel balls is presented. The motivation of this work is to identify an optimum film thickness that will result in low friction under relatively low loads for various metallic films. Dry sliding friction experiments on silicon substrates with soft metallic coatings (silver, copper, tin and zinc) of various thickness (1–2000 nm) were conducted using a reciprocating pin-on-flat type apparatus under a controlled environment. A thermal vapour deposition technique was used to produce pure and smooth coatings. The morphology of the films was examined using an atomic force microscope, a non-contact optical profilometer and a scanning electron microscope. Following the sliding tests, the sliding tracks were examined by various surface characterization techniques and tools. The results indicate that the frictional characteristics of silicon are improved by coating the surface with a thin metallic film, and furthermore, an optimum film thickness can be identified for silver, copper and zinc coatings. In most cases ploughing marks could be found on the film which suggests that plastic deformation of the film is the dominant mode by which frictional energy dissipation occurred. Based on this observation, the frictional behaviour of thin metallic coatings under low loads is discussed and friction coefficients are correlated with an energy based friction model.     

The Influence of Methyl Group Content on Tribological Properties of Organo-Silica Thin Films

Solid thin films of lubricants are often used as protection coatings of working surfaces in frictional contacts. Usually, these films have to contain stable and tribologically active additives like, for example, molybdenum disulphide or graphite. In this work chemically modified silica was investigated as a potential matrix of nanocomposite lubrication films. The sol-gel technique was used with tetraethoxysilane (TEOS) and triethoxymethylsilane (TEMS) as precursors of organo-silica thin films. Dip coating was applied as the method of film formation. Introducing a methyl group into silica by adding TEMS during sol-gel synthesis of silica films strongly increases their adhesion to the coated materials, which gives possibilities for using them on steel surfaces. The chemical properties of films synthesised by the sol-gel technique were examined by FTIR spectroscopy with the use of the transmission method. The surface topography was imaged and frictional features of organo-silica films were examined by Atomic Force Microscopy (AFM).     

Assessment of adhesion between thin film and silicon based on a scratch test

Thin film coatings are commonly utilized to prevent wear, modify surface properties, and manipulate the frictional behavior of various mechanical systems. The behavior of a coating has a direct effect on the life as well as performance of the system. However, the coating itself is subject to damage, and the quality of the coating is related to the adhesion characteristics between the coating and the substrate. Therefore, a quantitative assessment of the adhesion properties of thin film is important to guarantee the reliability of not only the thin film but also the mechanical system. In this study, ramp loading scratch tests were performed to assess the adhesion characteristics of Ag and ZnO thin films coated on a silicon wafer. Silver thin film, deposited by sputtering, and ZnO thin film, fabricated by a sol-gel method, were used as scratch specimens. Scratch tests using a diamond tip were performed with a continuously increasing normal force. During the scratch test, the normal and frictional forces were monitored to assess the integrity of the film. The Benjamin and Weaver model commonly used for obtaining the horizontal force during the scratching of films coated on a substrate showed large discrepancies with the experimental results. In this work, the model was modified with a plowing term to minimize the difference between the experimental and theoretical results. Using the modified model, the experimental results could be predicted with an accuracy of about 10%.     

Holey carbon micro-arrays for transmission electron microscopy: a microcontact printing approach

We have used a microcontact printing approach to produce high quality and inexpensive holey carbon micro-arrays. Fabrication involves: (1) micromolding a poly(dimethylsiloxane) (PDMS) elastomer stamp from a microfabricated master that contains the desired array pattern; (2) using the PDMS stamp for microcontact printing a thin sacrificial plastic film that contains an array of holes; (3) floating the plastic film onto TEM grids; (4) evaporating carbon onto the plastic film and (5) removing the sacrificial plastic film. The final holey carbon micro-arrays are ready for use as support films in TEM applications with the fidelity of the original microfabricated pattern. This approach is cost effective as both the master and the stamps have long-term reusability. Arbitrary array patterns can be made with microfabricated masters made through a single-step photolithographic process.     

Comparison of friction measurements using the atomic force microscope and the surface forces apparatus: the issue of scale

Results are presented of lateral force measurements using the atomic force microscope (AFM) and the surface forces apparatus (SFA). Two different probes are used in the AFM measurements; a sharp silicon nitride tip (radius R20 nm) and a glass ball (R15 m). The lateral force is measured between the (silicon nitride or glass) probe and a mica surface which has been coated by a thin lubricant film. In the SFA, a thin lubricant film separates two molecularly smooth mica surfaces (R1 cm) which are slid relative to each other. Perfluoropolyether (PFPE) and polydimethylsiloxane (PDMS) were used as the lubricant films. In the SFA where the contact diameter is largest, the PFPE film shows much lower friction than PDMS. As the size of the probe decreases, the difference in the measured friction decreases. For sharp AFM tips, no clear distinction between the tribological properties of the films can be made. Hence, the measured coefficient of friction varies according to the length scale probed, at least for small dimensions.     

T10钢表面BN薄膜结合力改善及减摩性研究

采用射频磁控溅射法在T10碳素工具钢表面制备了氮化硼薄膜;研究了在基材和薄膜之间化学镀N i-P中间层对薄膜结合力的影响;使用摩擦试验机对基材和镀膜后的试样进行了摩擦性能检测;通过划痕试验进行了结合强度试验。结果表明在工具钢表面溅射镀BN薄膜后摩擦因数明显降低,从原来的0.8下降到0.6,具有良好的减摩效果;BN薄膜和T10钢基材之间有一定的结合强度,加入N i-P中间层以后膜基结合力有显著增加,能达到约30 N;采用射频磁控溅射法制备得到的薄膜内部的应力为压应力,这有利于薄膜的附着和立方相氮化硼的形成。     

Frictional modes of barrel shaped piston rings under flooded lubrication

A friction force measurement system using the floating liner method was developed to study the frictional behavior of piston rings. The measurement system was designed to control the effect of the secondary piston motion and to control temperatures of the cylinder wall and oil. The friction force between the barrel shaped piston ring and the cylinder liner was measured under flooded oil supply conditions. The measured friction forces were classified into five frictional modes with regard to the combination of predominant lubrication regimes (boundary, mixed and hydrodynamic lubrication) and stroke regions (mid-stroke and dead centers). The modes were identified on a Stribeck diagram, where the friction coefficients were evaluated both at mid-stroke and at the dead centers.     

口腔环境下巧克力摩擦性能影响的试验研究

为探讨口腔加工时间对典型高脂高糖食品的摩擦性能影响,开展口腔环境下巧克力摩擦性能的影响因素研究。以人工唾液和某品牌巧克力配制不同巧克力质量分数的混合溶液,改变聚二甲基硅氧烷(PDMS)基础液和固化剂的比例分别制备硬PDMS和含微凸体的软PDMS材料,基于陶瓷球对软PDMS和硬PDMS对软PDMS的两组摩擦副,在MFT-5000摩擦试验机上开展混合溶液在不同载荷和滑动速率的摩擦性能研究,讨论混合溶液与摩擦副的作用机制。结果表明:巧克力在口腔加工过程的摩擦性能与其质量分数、载荷、滑动速率和摩擦副等因素有关,随着巧克力质量分数的降低,巧克力的摩擦因数总体上是减小,这意味着消费者能够获得更好的丝滑感;载荷和滑动速率对巧克力摩擦性能的影响与摩擦副的选取有关,但滑动速率比载荷对其摩擦因数的影响更显著,研究结果为巧克力摩擦性能和口感的系统评价提供参考。     

Experimental testing for metrological traceability and accuracy of liquid microflows and microfluidics

Micro-flows are growing more important and useful for a wide variety of scientific and engineering fields such as bioanalysis, drug development and administration, Organ-on-a-Chip, etc, but accurate and reliable measurements traceable to the International System of Units can be challenging in micro-to-femto flow operating ranges. In this paper a gravimetric method has been used to quantify the measurement error of the volumetric flow rate of water from 1000 μL/h to 1 μL/h delivered by a syringe pump in different experimental conditions that replicate the current microfluidics setups. Several sources of error have been determined such as the mass measurement, the fluid evaporation dependent on the gravimetric methodology implemented and the repeatability, believed to be closely related to the operating mode of the stepper motor and drive screw pitch of the syringe pump. The elastic deformability of the medical grade 1 mL polypropylene syringes commonly used in micro-flows has greatly affected the volumetric flow rate, unlike the glass syringes tested. Finally, testing the gravimetric method while adding PDMS microfluidic channels to the flow circuit served to demonstrate that material, dimensions and shape of the microchannels did not show significant influence on the volumetric flow rate error for the flow rates imposed, important to establish well defined methodologies for microfluidics.     

Dependence of the friction process on the molecular structure and architecture of thin polymer films

The frictional properties of a homologous series of poly(n-alkyl methacrylates) (PnAMA) and a series of poly(methyl methacrylate) (PMMA) films, cast from a variety of solvents, are characterized. The choice of polymer film was driven by the consideration of the possible mechanisms for the accommodation of a macroscopically applied shear stress by molecular entities. Two possible mechanisms are proposed: (i) the relative flexibility of the polymer backbone chain. For this purpose the PnAMAs have been chosen. By varying the length of the substituent chain, the relative molecular freedom around the backbone chain is altered. These molecular differences are sensed in the frictional properties at the macroscopic level, and (ii) the molecular organization is also proposed to be a factor in determining the friction response of a particular polymer film. For this purpose, the frictional properties of PMMA films cast from different solvents are investigated. There is observed to be a strong influence of the molecular organization on the frictional properties of the solvent cast PMMA films. The molecular probe employed to characterize the molecular environment is vibrational spectroscopy. Conformationally sensitive vibrational modes are used to determine the relative flexibility of the backbone chain and the organization of the chain network.     

注塑机芯杆回料机械手的设计

介绍了生产医用注射器行业里自动抓取芯杆回料用的机械手及其中的夹取回料装置和模具光电检测装置,分析了电气自动化控制系统硬件和软件中PLC与触摸屏的应用设计。实践证明注塑机芯杆回料机械手是成功的,是一种创新设计。     

类金刚石薄膜微观摩擦性能的FFM评价——针尖尺度效应

采用等离子体增强气相沉积制备了类金刚石薄膜，利用原子力显微镜的轻敲模式观察了它们的形貌，并在考虑外加载荷和扫描速度的基础上，用摩擦力显微镜（FFM）对比考察了尖端探针和平头探针对类金刚石薄膜摩擦性能评价的影响。结果表明：类金刚石薄膜的表面粗糙度随基底负偏压的增加而减小；存在于探针和类金刚石薄膜之间的水膜对尖端探针的剪切阻力贡献较大，且尖端探针测得的摩擦力变化趋势受扫描速度影响显著；水膜对平头探针起着不同形式的润滑作用，从而导致平头探针和类金刚石薄膜之间摩擦性能的速度效应存在差异；利用摩擦力显微镜考察类金刚石薄膜的摩擦性能时，存在着明显的针尖尺寸效应。     

Application of Spectroscopic Reflectometry to Elastohydrodynamic Lubrication Films Study

Optical measurement techniques have been successfully used for elastohydrodynamic (EHD) lubricant films studies for several decades and have significantly helped to understand the lubrication mechanisms within highly loaded machine contacts. Nevertheless, there are still many phenomena waiting for the explanation and new experimental approaches and measurements techniques are developed. Recent studies have provided promising results as to the application of spectroscopic reflectometry to the study of EHD films. Nevertheless, some simplifications were introduced. The main aim of this study was to develop a physically correct approach that could provide the additional information about the properties of lubricant film within highly loaded contacts. The principal part of this article was devoted to the effort to develop and verify the optical design suitable for such applications. This verification was carried out within lubricated contact formed between a steel barrel and sapphire disc without any semi-reflective layer. This simplified optical arrangement has enabled to obtain the correct lubricant film data and verify the applicability of the spectroscopic reflectometry for EHD lubrication films study. It represents the first step in this application of spectroscopic reflectometry and further research in the field of the behavior of thin solid films under high contact pressures is necessary to enable thin film measurements.     

软包锂电池电芯封装铝塑膜外壳拉深工艺

通过拉深试验对铝塑膜材料特性进行分析,在DYNAFORM软件中定义铝塑膜材料属性并进行仿真试验。结合单因素试验和正交试验对影响铝塑膜拉深成形性能的各工艺参数进行显著性分析,采用响应曲面法、拉丁超立方试验设计和多目标粒子群优化算法相结合的方法对影响铝塑膜成形性能显著的参数（如压边力、模具圆角半径、摩擦因数和拉深速度）进行优化,优化后的铝塑膜拉深成形时,其壳体最薄处厚度为55 μm。试验验证了铝塑膜拉深成形工艺优化的结果可行。     

Nanotribology: an UHV-SFM study on thin films of AgBr(001)

We performed scanning force microscopy (SFM) in ultrahigh vacuum (UHV) on AgBr thin films which were in situ deposited on NaCl(001) substrates. The morphology of the initial growth stage and the nanotribological properties of these thin films are characterized and discussed. The lateral (frictional) forces are measured as a function of normal load. The local friction coefficients are extracted by means of the two-dimensional histogram technique. In the low load regime, friction coefficients of 0.33 ± 0.07 and <0.03 are found between probing SiO _x tip and AgBr and NaCl, respectively. The two-dimensional histogram reveals the transition from the force regime of wearless friction to the initial stage of wear on this thin film system. High-resolution SFM images of AgBr(001) are presented which reveal the atomic-scale periodicity of an unreconstructed AgBr(001) surface. The stick-slip nature of the frictional force is demonstrated.     

薄膜疲劳失效预测方法与损伤机制的研究进展

薄膜材料的尺寸范围、结构以及其服役环境的特殊性,制约了薄膜失效行为、寿命预测及可靠性评估技术研究的开展。对薄膜疲劳寿命的预测方法进行综述,分析常用的单向循环加载法和悬臂梁弯曲法。详细介绍纳米级动态载荷法,包括连续刚度法和纳米冲击试验法,此法能够对实际服役环境更好地模拟,可以实现分相测试以及多种功能模块的原位定点检测,以及定量分析薄膜的疲劳性能。对薄膜疲劳损伤失效机制与寿命预测模型的研究进行探讨与展望,发现薄膜材料失效过程的研究与定量分析是今后研究的重点。     

基于LuGre模型的转子压缩机滑片-滑槽运动副摩擦力测试

为研究转子压缩机滑片-滑槽运动副的摩擦特性,根据LuGre摩擦模型的建模方法和该运动副的运行特点及工况特点,设计并搭建了滑片-滑槽等效摩擦力测试系统,分析了该系统的摩擦力跃动现象、数据采集区域和摩擦力测量的重复性问题,并进行了摩擦力测试实验。结果表明：该摩擦力测试系统可以根据压缩机的实际工况,对滑片均匀加载相应的正压力FH,并能实现不同匀速直线运动下的摩擦力测量;可以有效消除低速润滑不均匀导致的摩擦力跃动现象;通过润滑初始化可以较准确地获得基于滑片速度变化的摩擦力表达曲线。实验结果与数值计算结果吻合,从而为正确辨识LuGre摩擦模型的参数提供了实验依据。     

Evaporation during preparation of unsupported thin vitrified aqueous layers for cryo-electron microscopy

Evaporation of water cannot be fully avoided when an unsupported thin vitrified film of an aqueous suspension is prepared for cryo-electron microscopy. This results in increasing concentration of solute which could affect the observed material. We have quantitatively studied this effect by measuring the contrast of polystyrene spheres in a metrizamide solution. The drying effect is generally negligible when specimens are prepared on a hydrophilic perforated support but it is frequently important when hydrophobic films are used instead. A flow of humid air, double blotting with minimal exposure of the thin liquid film to the atmosphere, or an automatic plunger optimizing the blotting conditions are simple methods for reducing drying effects. With this third device acting on a hydrophilic supporting film, the increase of solute concentration is limited to less than 20%.     

Low-Temperature Friction in the XPS Analytical Ultrahigh Vacuum Tribotester

In this work, we present the capability of ultrahigh vacuum analytical tribometry for studying mechanisms of friction at low temperatures. We investigated the low-temperature frictional behavior of two different materials: ice and polyethylene (PE). We successfully formed a thin layer of ice on a steel surface, at temperature as low as 123 K in an ultrahigh vacuum. The surface characterization technique used for this study was X-ray photoelectron spectroscopy (XPS). We investigated the frictional behavior of such a thin ice layer. The changing friction as a function of temperature indicates that the ice might undergo pre-melting even at temperatures below 123 K. A polyethylene (PE) film previously deposited on a metal surface also showed changing friction as a function of temperature in the range 123 to 400 K. As there is no change in the nature of the surface chemistry of the polymer, as indicated by XPS, the results are therefore interpreted in terms of change in ductile-to-brittle transition of the polymer film over the temperature range. This work enables the fundamental investigation of friction at low temperatures with the help of surface analysis.     

杆式抽油泵间隙漏失行为分析及优化研究

抽油泵是有杆抽油系统中的重要装置,由于泵筒两端存在压力差,泵筒和柱塞之间为往复运动的间隙配合,其在工作时就会有漏失产生.由于所选用理论基础不同,现有抽油泵漏失理论并不完善,无法保证漏失计算的准确性.针对这一问题,本文结合间隙漏失特性和抽油泵的漏失试验结果,研究了间隙漏失理论.并建立抽油泵间隙流体的三维模型,运用FLUE...