Tribological experience with hard coats on soft metallic substrates

TiN films were deposited on an aluminum alloy substrate by magnetron reactive sputtering. Tribological evaluations conducted show the feasibility of wear control with the deposition of hard films on soft substrates.     

A TEM study of the electron-beam interaction with small supported palladium particles and alumina and titania substrates

The interaction of 100 and 200 keV electron beams with amorphous alumina and titania substrates and nanometer-size palladium particulate deposits was investigated for the two extreme cases of (a) large-area electron-beam flash-heating and (b) small-area high-intensity electron-beam irradiation. The former simulates a short-term heating effect with minimum electron irradiation exposure; the latter simulates high-dosage irradiation with minimum heating effect. All alumina and titania samples responded to the flash-heating treatment with significant recrystallization. However, the size, crystal structure, shape, and orientation of the grains depended on the type and thickness of the films and the thickness of the Pd deposit. High-dosage electron irradiation also readily crystallized the alumina substrate films but did not affect the titania films. The alumina recrystallization products were usually either all micron-size grains in the alpha phase, or they were a mixture of much smaller grains in a number of low temperature forms including γ-, δ-, κ-, β-, and θ-aluminas. Palladium deposits reacted heavily with the alumina substrates during either treatment, but they were very little affected when supported on titania. The study suggests that under illumination conditions typical for very high resolution, very high magnification microscopy with modern high-performance electron microscopes, electron beam effects on oxide-supported metal particle specimens may be severe.     

Welding of tribologically optimized polyetheretherketone films with metallic substrates

A thermal impact welding process has been developed which allows the thermal joining of polyetheretherketone (PEEK) matrix materials with steel and aluminum substrates, respectively. The objective is to render manufacturing of innovative slide elements possible without the need for an up to now commonly used layer of sintered bronze in order to enhance the adhesion of the polymer. It is proven that excellent joining quality and wear resistance of the polymer layer can be achieved without sintered bronze.     

Note: Low temperature superconductor superconducting quantum interference device system with wide pickup coil for detecting small metallic particles

A one-channel low temperature superconductor superconducting quantum interference device system comprising a second-order axial gradiometer with a sensing area of 10 mm × 190 mm was developed. The gradiometer was mounted in a liquid-helium dewar (450-mm diameter; 975-mm length), with a gap of 12 mm between the pickup coil and the dewar-tail surface. The magnetic field sensitivity was measured to be 16 fT∕Hz(1∕2) in the white noise regime above 2 Hz. The system was used to measure stainless steel particles of different sizes passing through the sensing area. A 100-μm diameter SUS304 particle was readily detected passing at different positions underneath the large pickup coil by measuring its 1.3-pT magnetic field. Thus, the system was shown to be applicable to quality control of lamination sheet products such as lithium ion batteries.     

S型金属蜂窝载体成形的关键技术研究

针对目前我国汽车尾气净化器用金属蜂窝载体的生产现状进行了研究,提出了一种新型的S型金属蜂窝载体成形方法.通过分析其生产工艺和成形过程,进行了S型金属蜂窝载体的成形装置的结构设计,提高了生产效率和质量.对S型金属蜂窝载体的成形原理进行了理论分析及动态仿真.     

HREM image simulations for small particle catalysts on crystalline supports

The imaging conditions for electron microscope studies of supported ultrafine particle catalysts have been investigated by multislice simulations. Images of Pt and ReO₄ particles ranging from 0·4 to 2·3 nm in size were simulated in both plan view and profile view with a rutile (TiO₂) support. It was shown that particle visibility varied greatly with the objective lens defocus. Optimum defocus was not favourable for supported particles in plan view since the ultrafine supported particles were least visible at this defocus. Underfocusing, especially at defoci corresponding to half-spacing fringes in the TiO₂ support, led to improved visibility and resolution of the supported particles. Although the structure and shape of supported ultrafine particles should be resolved better with a 400-kV high-resolution electron microscope, their detectability is poorer than with a 200-kV instrument. An ReO₄ cluster should be detectable at 200 kV on TiO₂ supports up to 5 nm in thickness, whereas it is only likely to be detectable at 400 kV on supports up to 3 nm in thickness. The simulations confirmed that optimum defocus is most favourable for imaging supported particles in profile view. Atomic information for particles as small as a 13-atom Pt cuboctahedral cluster should be resolvable with a 400-kV instrument. The crystalline Ti monolayer observed on surfaces of Pt particles, which could explain the mechanism known as SMSI, was simulated as an example of profile imaging.     

On the size of small protein particles determined by electron microscopy of unidirectionally shadowed freeze-etched preparations

The influence exerted by the thickness of the deposited metal layer and the ionic strength of the solution on the apparent size of particles of bovine serum albumin in unidirectionally shadowed freeze-etch preparations of spray-frozen specimens was investigated. It appeared that the size increase due to shadowing is nearly twice the thickness of the deposited metal layer. Apparent particle size was shown to increase linearly with the inverse square root of the ionic strength of the solution. At ionic strength 0·001 the particles appeared about 30% larger than at infinite ionic strength.     

Phase identification of individual crystalline particles by electron backscatter diffraction

Recently, an electron backscatter diffraction (EBSD) system was developed that uses a 1024 × 1024 CCD camera coupled to a thin phosphor. This camera has been shown to produce excellent EBSD patterns. In this system, crystallographic information is determined from the EBSD pattern and coupled with the elemental information from energy or wavelength dispersive X-ray spectrometry. Identification of the crystalline phase of a sample is then made through a link to a commercial diffraction database. To date, this system has been applied almost exclusively to conventional, bulk samples that have been polished to a flat surface. In this investigation, we report on the application of the EBSD system to the phase identification analysis of individual micrometre and submicrometre particles rather than flat surfaces.     

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.     

Investigations of the structure of amorphous and partially crystalline metallic alloys by high resolution electron microscopy

A number of amorphous and partially crystalline palladium-silicon alloys have been examined by high resolution transmission electron microscopy at 500 kV. With the directly interpretable resolution extending beyond the first peak in the structure factor at 0?23 nm, details of the local microstructure at the atomic level are visible. Images of small metallic particles show a well-defined pattern of fringes over local regions. In some instances, especially in partially-ordered alloys, neighbouring or overlapping fringe patterns appear to be orientationally-related in a similar manner to fringe systems seen in symmetrically multiply-twinned particles. The significance of this type of structural examination for amorphous metals is discussed.     

Stability of disperse particles in a metallic matrix with slipping friction

A model is proposed for the interaction of a particle in a metal matrix with a counterbody, in slipping friction. Stability conditions are formulated for the disperse particles in the metallic matrix when using machine parts with composite electrochemical coatings.     

Quantification of small, convex particles by TEM

It is shown how size distributions of arbitrarily oriented, convex, non-overlapping particles extracted from conventional transmission electron microscopy (TEM) images may be determined by a variation of the Schwartz-Saltykov method. In TEM, particles cut at the surfaces have diminished projections, which alter the observed size distribution. We represent this distribution as a vector and multiply it with the inverse of a matrix comprising thickness-dependent Scheil or Schwartz-Saltykov terms. The result is a corrected size distribution of the projections of uncut particles. It is shown how the real (3D) distribution may be estimated when particle shape is considered. Computer code to generate the matrix is given. A log-normal distribution of spheres and a real distribution of pill-box-shaped dispersoids in an Al-Mg-Si alloy are given as examples. The errors are discussed in detail.     

An improved preparation method for cross‐sectional TEM specimens of films deposited on metallic substrates

Cross‐sectional TEM analysis is one of the most important techniques to characterize microstructures of films. However, the complex process, low efficiency, and low success rate of specimen preparation limit its application. This paper analyzed the main causes of low success rate and proposed an improved method for specimen preparation of films deposited on metallic substrates. This method consisting of twin‐jet electropolishing and one‐sided rocking ion milling is high in efficiency and success rate. Microsc. Res. Tech. 79:276–279, 2016. © 2016 Wiley Periodicals, Inc.     

A theoretical study on the acoustically driven oscillating flow around small spherical particles

In order to study the oscillating flow induced by a high intensity acoustic field, a computer code which employs the two-dimensional, unsteady mass and momentum conservation equations for laminar flow in spherical coordinates has been developed. The displacement amplitude of the incident sound wave is large compared to the characteristic length of particles, and the acoustic Reynolds number based on the particle diameter and the velocity amplitude of the oscillating flow is less than about 100. Numerical solutions of these equations give the velocity field, axial pressure gradient, shear stress and flow separation angle around the particle for acoustically oscillating flow as a function of acoustic Reynolds number and Strouhal number. The axial pressure gradient, shear stress and separation angle are proportional to the magnitude of oscillating flow at low frequency (～50Hz) and can be approximated by the quasi-steady analysis. The effects of flow oscillation increase with increasing frequency (～2000Hz) due to combined effects of curvature and flow acceleration, giving different values of axial pressure gradient, shear stress and separation angle for different frequencies of 500, 1000 and 2000 Hz.     

The STEM approach to the imaging of surfaces and small particles

The characteristics of scanning transmission electron microsopy, which make it a particularly powerful tool for the study of surfaces and small crystals, include the serial nature of the image signal which makes it amenable to recording and image processing procedures, the possibility of correlating the image data with microdiffraction patterns and microanalysis of chosen small regions and the possibilities for combining several different image signals obtained simultaneously. Images obtained from surfaces using reflected diffraction beams may be very sensitive to variations of surface structure but the resolution, depth of focus and contrast of the images are strongly dependent on the nature of the surface and the aperture sizes used in the microsope. Microdiffraction patterns may be obtained from small surface features. Electron energy loss analyses of the diffracted beams provides sensitive indications on surface electron excitations. Microdiffraction patterns obtained in transmission from regions of 1–5 nm diameter provide valuable information on the structure and defects of small crystals, such as those of platinum and gold which are of interest in relation to the study of catalysts.     

Evaluation of various methods to detect metallic wear particles in lube-oil filter debris

Studies were conducted to evaluate methods of detecting metallic wear particles in lube-oil filter debris. The methods studied were: low-temperature oxidation of the organic constituents in the debris, separation of ferromagnetic particles by passage through a magnetic field, and counting/sizing of metallic particles in a fluid stream using a commercially available detector. Laboratory-prepared simulations of wear debris and actual filter debris samples from operational military aircraft systems were used in the evaluation. The relative ability of each method to detect metallic wear particles is discussed, along with the effects of each method on subsequent debris examination.     

A turbulent friction and heat transfer study of dispersed fluids with ultra-micronized metallic particles

Turbulent friction and heat transfer behaviors of dispersed fluids with ultra-micronized metallic particles are experimentally investigated in a circular pipe. Viscosity measurements are also conducted by using a viscometer. Aqueous mixtures with γ-Al₂O₃ and TiO₂ particles of which the mean diameters are 13 and 27 nm, respectively, are used to represent the dispersed fluids. The ranges of Reynolds and Prandtl numbers tested are 10⁴～10⁵ and 5.6～10.7, respectively. The relative viscosity of the dispersed fluid with γ-Al₂O₃ particles is about two hundred at the 10% volume concentration, while that of the dispersed fluid with TiO₂ particles is about twenty at the same volume concentration. Both of the relative viscosities are the unexpected results compared with predictions from classical theory of suspension rheology. Darcy friction factors for the comparatively dilute dispersion fluids used in present study coincide well with Kays correlation for tubulent flow of a single phase fluid, which implies that additional pumping power is not required despite adding solid particles into water. The Nusselt number of both the dispersed fluids for fully developed turbulent flow increases with increasing the volume concentration as well as the Reynolds number as expected. At the maximum volume concentration of 3% approximately, the percentage heat transfer enhancement due to addition of particles for the γ-Al₂O₃ and TiO₂ dispersing fluid systems are 60% and 30%, respectively. Under the range of volume concentration in the present study, the new correlation for turbulent convective heat transfer for both of the dispersed fluids is given by the following equation: Nu=0.021Re^0.8Pr.^0.5     

基于GSM的高速公路能见度检测系统设计

GSM移动通信技术提供了强大可靠的短信息服务和数据传输服务,因此基于GSM数据传输平台的各种应用也不断被开发。文中着重介绍了高速公路能见度检测系统中采用TC35i型模块和AT89C52单片机构成通信单元的设计方案,以及该方案的硬件和软件设计方法,同时对GSM在高速公路系统设计过程中的主要注意事项做了简要说明。