A Method for Evaluating the Thickness of Ultrathin Films

A method for determining the thickness of ultrathin (<10 nm) films using an atomic-force microscope is described. Films were deposited onto a porous glass substrate that has smooth surface areas between the pores when the flow of the evaporated material incident on the substrate is at an angle of 20°–30° with respect to the normal to its surface. In order to obtain pores with sharp edges, the substrate surface was preliminarily sputtered by an oxygen ion beam directed at an angle of 90° to this surface. Images of such films obtained using the atomic-force microscopy technique clearly resolve the position of the pore edge–film boundary, making it possible to evaluate the film thickness by the height of the step between the pore edge and the by surface in the cross section of the surface topography.     

A method of observing the area of contact and the mechanical breakdown of a surface film

A new method of observing the contact area was applied to the investigation of the effect of surface roughness on the mechanical breakdown of a surface film. This method uses the difference in secondary electron emission yields from the carbon surface film and from the base metal. Contact spots between the gold surfaces are visible as bright spots on the secondary electron image.

The contact resistance decreases with increasing surface roughness in the region of low surface roughness. However, the greater the tangential displacement and contact load, the less the surface roughness effect becomes. The results of contact resistance are supported by analyses of the area of film removal.     

高压涡轮动叶吸力面气膜冷却特性研究

为了研究某航空发动机高压涡轮动叶吸力面的气膜冷却特性,通过数值模拟的方法,采用SST κ-ω湍流模型,分析了高压涡轮动叶在静止和旋转条件下,吸力面气膜冷却效率的影响规律.结果表明:在静止条件下,相同主流湍流度时吹风比对吸力面气膜冷却效率影响显著,冷却效率随着吹风比的增大而减小;在小吹风比下,气膜冷却效率随着主流湍流度的...     

Development and application of a new spray impingement model considering film formation in a diesel engine

The present article presents an extension to the computational model for spray/ wall interaction and liquid film processes that has been dealt with in the earlier studies (Lee and Ryou, 2000a). The extensions incorporate film spread due to impingement forces and dynamic motion induced by film inertia to predict the dynamic characteristics of wall films effectively. The film model includes the impingement pressure of droplets, tangential momentum transfer due to the impinging droplets on the film surface and the gas shear force at the film surface. Validation of the spray/ wall interaction model and the film model was carried out for non-evaporative diesel sprays against several sources of experimental data. The computational model for spray/wall interactions was in good agreement with experimental data for both spray radius and height. The film model in the present work was better than the previous static film model, indicating that the dynamic effects of film motion should be considered for wall films. On the overall the present film model was acceptable for prediction of the film radius and thickness.     

Surface roughness of ultra‐thin silver films sputter depositedon a glass

Silver was sputter deposited on a glass with a thin film thickness ranging from 10 to 80 nm. Scanning tunnelling microscopy was used to study the morphology of the obtained Ag–glass surfaces and to estimate the surface roughness. An equation for the surface roughness of the thin film was evaluated using parameters related to the thin film features: the surface roughness of the substrate, the compressibility of the thin film and the film thickness. The experimental results were fitted using the evaluated equation, and the conditions favouring lower or higher surface roughness were analyzed.     

一个表面带单粗糙峰的线接触时变微弹流润滑数值分析

通过数值求解研究了一个固体表面的单粗糙峰对两固体形成的线接触时变弹流润滑区压力、膜厚分布曲线的影响。结果表明：粗糙峰的出现，使其对应位置上的压力、膜厚发生急剧变化；粗糙峰的移动，对压力和膜厚的变化、固体表面的凹陷现象以及Hertz接触区的出口颈缩均有不同的影响；另外，压力峰和油膜形状随着粗糙峰幅值和半波长的变化而变化。结果亦表明：准稳态解比时变解过高地估计粗糙峰对压力和膜厚的影响。     

Frequency dispersion of love waves in a piezoelectric nanofilm bonded on a semi-infinite elastic substrate

Research on the propagation of elastic waves in piezoelectric nanostructures is very limited. The frequency dispersion of Love waves in layered piezoelectric nanostructures has not yet been reported when surface effects are taken into account. Based on the surface elasticity theory, the propagation of Love waves with surface effects in a structure consisting of a nanosized piezoelectric film and a semi-infinite elastic substrate is investigated focusing on the frequency dispersion curves of different modes. The results show that under the electrically-open conditions, surface effects give rise to the dependence of Love wave dispersion on the film thickness when the thickness of the piezoelectric film reduces to nanometers. For a given wave frequency, phase velocity of Love waves in all dispersion modes exhibit obvious toward shift as the film thickness decreases or the surface parameters increase. Moreover, there may exist a cut-off frequency in the first mode dispersion below which Love waves will be evanescent in the structure due to surface effects. The cut-off frequency depends on the film thickness, the surface parameters and the bulk material properties.     

Substrate surface energy effects on a liquid lubricant film at nanometre scalesubstrate surface energy effects on a liquid lubricant film at nanometre scale

In this paper is discussed the effect of the physical characteristics of substrate surfaces on the lubrication properties of thin films at nanometre scale. Different coatings with different surface energies have been formed on the surface of a steel ball by means of plasma assisted sedimentation (PAS). The ball was put in a pure rolling system in point contact, where the lubricant film is measured by relative optical interference intensity (ROII). Experimental results show that the film thickness is closely related to the substrate surface energy when the film is in the nanometre scale, and that the combined surface roughness in the contact region is closely related to the liquid lubricant film thickness and the contact pressure. The thinner the film and the higher the contact pressure, the smaller will be the combined surface roughness. Lastly, the relationship between critical film thickness and its influencing factors is discussed.     

Mechanical analysis of the blistering of a thin film deposited on a glassy polymer

In most cases, scratching of the surface of a polymeric glass elicits brittle behavior. A common way to improve the scratch resistance of a sensitive surface is to coat it with a thin film. Further work is required to explain the improvement in scratch resistance due to coating technique and predict the cracking in anti-scratch coatings. Moreover, the substrate/thin film adhesion must be well controlled and measurable. The present study contributes to these aims. Using a single-asperity scratching device allowing in situ observation of the scratch, the fracturing of a thin nano-composite coating deposited on a polycarbonate substrate was investigated under different conditions of temperature and scratching speed. Four types of fracture mechanisms were observed, depending on these two variables. A global energy balance model of the blistering process which is obtained for some experimental conditions permits one to determine the adhesion of the system. The adhesion can be measured by following the delaminated area (quantified by image analysis) as a function of the scratching distance during blistering. The particular case of an experimental stable blistering process was studied and the corresponding substrate/thin film adhesion was derived using the global energy balance model.     

Changes in the mechanical properties of oil used in a gasoline engine

This study is concerned with the changes in and deterioration of the mechanical properties of oil used in a gasoline engine. The properties analysed were friction and antiwear performance, wear debris, load-carrying ability and the formation of surface films. It was found that the oil run in an engine deteriorated so as to increase the wear and friction and decrease the load-carrying ability as the running distance of oil was increased. The main cause of deterioration was related to the ability to form a protective film in the contact zone. When the film was produced by additives (sulphur), this could properly protect the surface in the contact zone undepleted from wear and friction. But as the oil deteriorated, it could not form such a film and so its protective ability on sliding surfaces diminished.     

Effect of surface roughness on the couple-stress squeeze film between a sphere and a flat plate

In this paper, a theoretical study of the effect of surface roughness on the hydrodynamic lubrication of couple-stress squeeze film between a sphere and a flat plate is presented on the basis of Christensen's stochastic theory for hydrodynamic lubrication of rough surfaces. The modified Reynolds equation accounting for the couple stresses and the surface roughness is mathematically derived. The modified Reynolds equation is solved for the fluid film pressure and the bearing characteristics, such as the load carrying capacity and the time–height relationship, are obtained. It is found that the surface roughness considerably influences the squeeze film characteristics. The load carrying capacity and squeeze film time are found to increase for an azimuthal roughness pattern as compared to the corresponding smooth case, whereas the reverse trend is observed for a radial roughness pattern.     

剪切应力影响下近壁微液膜测量技术及波动特性研究

基于尺度分离理论,近壁微液膜波动特性对临界热负荷的产生有至关重要的影响。针对水平管内分层流动近壁微液膜在气流剪切应力作用下的波动特性进行研究,分析声学法,射线法,电学法和光学法等不同检测方法在近壁薄液膜厚度测量上的应用,并比较各种方法的优缺点。最终采用光学法,即利用光谱共焦位移传感器,对不同气、液流速条件下近壁微液膜进行测量,分析剪切夹带对液膜厚度变化的影响规律,获得液膜撕裂的临界条件。研究结果表明：微液膜平均厚度在气流剪切夹带影响下随气速的增大而减小。由于液滴夹带现象影响程度的不同,在不同气、液流速条件下,试验段出口处液膜平均厚度液膜呈现线性或非线性的变化趋势。气流剪切应力增大时,液膜厚度超过临界厚度即发生撕裂现象,液膜撕裂存在随机性,当壁面条件一定时,临界液膜厚度不随气、液流速的变化而变化,但在高气、液流速条件下液膜波动加剧。     

A study of boundary lubrication thin films producedfrom a perfluoropolyalkylether fluid on M-50 surfaces. I. Filmspecies characterization and mapping studies

A surface thin film was observed in a wear scar area resultingfrom a boundary lubrication experiment performed on areciprocating cylinder on plate tribometer. The lubricant usedwas a perfluoroalkylether (PFPAE) fluid. The wear scar area hadblue and yellow colors observable under an optical microscope.The blue area was surrounded by an envelope of yellow scar area.The film thickness found in the blue area was approximately 15times thicker than that observed in the yellow area. The mostdramatic change in thickness occurred at the intermediate areabetween these two colors. The thin film species wascharacterized as a perfluorocarboxylate surface specieschemisorbed on the wear scar area of a M-50 flat specimen. Amonodentate configuration was determined to be the geometry forthis surface thin film species. Thickness mapping studies alongboth x- and y-axes were performed on the wear scar.The x-axis thickness variations can be attributed to thenormal stress distribution on the cylinder and the y-axisfilm thickness variation can be explained by the temperaturegradient originating from the cylinder velocity variation. A``hat' model is proposed to represent the physical picture ofthe surface thin film species chemisorbed on the M-50 wear scararea.     

Fluid flow and heat transfer on a falling liquid film with surfactant from a heated vertical surface

The addition of surface active agent to a falling liquid film affects the flow characteristics of the falling film. In this study, the flow and heat transfer characteristics for a falling liquid film have been investigated by addition of the surfactant. The falling liquid film was formed on a vertical flat plate. Contact angle of a liquid droplet above a plate surface can be substantially reduced with an increase in the surfactant concentration. The results obtained indicate that not only the wetted area of falling liquid film is increased but also the film thickness is decreased as the surfactant concentration is increased. It is also found that heat transfer rate is significantly increased while the heat transfer coefficient is almost constant value with an increase in the surfactant concentration at a given mass flow rate.     

Analysis of the piston ring lubrication with a new boundary condition

Research on the inlet and outlet lubricational characteristics of the piston ring have been intense and ongoing. Many researchers had considered that the entire surface of the ring was enveloped in an oil film, but much experimental research has discovered that not all the entire surface was soaked. To consider a partially lubricated ring, the following conditions are presupposed; oil starvation is applied to the inlet region and the open-end assumption to the outlet region. This algorithm confirms flow continuity and permits the nadir of the pressure to go down to the saturation pressure. Using these new boundary conditions, the actual effective width participating in ring lubrication is determined and the minimum film thickness and flow rate for the ring pack can be calculated. The effective width is expected to be about 20 to 30 percent of the whole width of the ring, and the minimum film thickness is less than the result obtained by using the Reynolds cavitation boundary condition.     

聚醚醚酮复合材料的转移膜研究

用物理共混-模压法制备了Ekonol／PEEK和Ekonol／石墨／MoS2／PEEK复合材料，通过摩擦磨损实验方法对材料的耐磨件能进行了研究，并用SFM对对偶件表面进行了观察和分析，以探讨对偶面上转移膜的特性对复合材料耐磨性能的影响，结果表明：PEEK能在对偶面上形成不连续、厚薄不均的转移膜；Ekonol的加入能促进转移膜的形成；Ekonol和固体润滑剂能协同改善PEEK所形成转移膜的质量，从而提高PEEK的耐磨性能；复合材料在其对偶面上形成的转移膜质量的好坏对其耐磨性能产生直接影响。     

Microscopic Cracking and Spalling Behavior of the Duplex Layer of a Gas-Nitrided Gun Bore Surface

In the present study, the initial wear behavior of the duplex layer consisting of an oxide film and a compound layer on gun bores was investigated. The duplex layer was produced by the gas-nitriding and the post-oxidization to the surface of the 5.56mm gun bores. The thickness of the duplex layer was measured from the specimen taken from a new gun barrel with an optical microscope. After real firing, the specimens were cut from the barrels. The microscopic wear behavior and phase identification of the duplex layer were observed by using a SEM and a XRD, respectively. A lot of surface cracks linked together to form the network of the cracks on the surface and the parallel cracks occurred in the interface between the oxide film and the compound layer. When the surface cracks and the parallel cracks join orthogonally, the spalling takes place.     

Effects of tool surface irregularities on machining rate of a hydrodynamic polishing process

The effect of tool surface irregularities on the machining rate of the hydrodynamic polishing process is examined in this study. It is proposed that the tool surface irregularities will affect the film thickness or shear stress distribution between the tool and the work surface. Accordingly, the machining rate of this process is affected. Based on the elastohydrodynamic lubrication theorem and the machining mechanism of this process, the relationship between machining rate and tool surface topography is derived by the statistical analysis. It is shown that the machining rate has a linear relationship with the average variance of tool surface irregularities. The sensitivity of this relationship depends on the average film thickness. A large film thickness will result in a reduction of surface irregularities on machining rate. However, the randomness of machining rate due to the variation of tool surface topography cannot be effectively improved by increasing the film thickness. The experimental study shows that the qualitative and quantitative trends of machining rate verse tool surface irregularities can be well predicted by analytical analysis.     

Cam and Tappet Lubrication III — Radioactive Study of Phosphorus in the EP Film

A radioactive tracer, phosphorus-32 synthesized into zinc dialkyl dithiophosphate molecules, was used to study the EP films formed by this motor oil additive on cast iron cams and tappets. The tightly bound films, which contain phosphorus and zinc, formed rapidly and then approached steady-state values in static and dynamic tests. The amount of film increased with oil temperature (200 to 300F) and with available surface area. Dynamic test conditions greatly increased the amount of film formed, indicating the marked effect of surface temperature, pressure or wear. The film is maintained on parts run in additive oil; moreover, the film was not easily worn off in non-additive oil. The chemical and physical properties of the films appeared to vary with the conditions of film formation. Radioactive counting was used to determine the film on tappets and the thermal stability of the compounded oil. Autoradiographs showed the concentration and distribution of the film on cams and tappets.     

Theory of Life Prediction of a Viscoelastic Lubricating Surface Film

A solid lubricating surface film is modeled as a general linear viscoelastic material. The appropriate governing equations are solved for the displacement of such a thin film under repeated loadings. The predicted transient motion of the surface is monitored. The gradual diminution of the lubricant film thickness under repeated loadings is considered film wear. The failure of solid lubricating film occurs when the existing thickness is to the same order of magnitude as the substrate surface roughness.