恒定动能作用下薄壁管的冲击微动磨损行为研究

在新型冲击微动磨损试验机上对四种常见材料的薄壁管(不锈钢、铜合金、纯钛和铝合金)进行了冲击磨损试验,考察了材料属性、冲击能量对薄壁管损伤行为的影响。对其冲击动力学行为、磨损行为进行了分析。研究结果表明,不同材料金属管的能量吸收率、冲击接触力和冲击管变形有显著差异;同一种材料,随着初始冲击动能的增大,冲击过程中接触力、冲击管变形和冲击吸收能也在增大。通过分析磨痕微观形貌和磨痕轮廓,发现薄壁管的冲击磨损抵抗性能与材料属性密切相关;随着初始冲击动能的增加,材料损伤加剧,其损伤机制为疲劳磨损。     

Erosion of metals by flyash particles

The erosion of metal targets by flyash from power station electrostatic precipitators was investigated using a novel test rig. Targets of BG303 stainless steel and HE30 aluminium were used. The effects of target temperature and angle of impingement were studied. The size of particles used was less than 66 μm. The rig utilizes a tube with a fine bore to accelerate particles borne by an air flow; the air flow is then separated from the particle stream with a simple Coanda effect attachment on the end of the tube. The targets are heated indirectly with a high resistance heater element. Target temperatures up to 750 °C were attained. The observed erosion characteristics are consistent with previous work. For stainless steel, the erosion rate increases with increasing temperature above 400 °C. For aluminium the erosion rate reaches a maximum value at approximately 300 °C.     

Mutual transfer of materials for dry sliding of brass against stainless steel

A comparison of dry sliding friction and wear in vacuum (6.67 × 10⁻³ Pa) and air has been made for brass against stainless steel. The results show that the mean sliding friction coefficients in vacuum are a factor of 1–2 larger than in air. The mutual transfer of surface materials during sliding wear has been studied. The surface atom diffusion increases and the adhesion action increases in this process.     

Scanning electron microscopy observations of worn surfaces of metals in tribological contact with loose solid particles

Surfaces of a 40–60 brass worn by three-body abrasion with SiC grits were observed under the scanning electron microscope. Similar observations were carried out on targets of steel and commercially pure aluminium which had been impacted with hardened steel balls. The brass develops alternating bands of hills and valleys when undergoing three-body abrasion. The hills wear by direct rubbing against the steel counterface. The valleys, however, are embedded with grits which are later removed and probably carry an amount of brass during their departure. The impact process creates craters which show severe deformation. Radial plastic flow of metal also occurs in the target around a crater. It appears that under repeated attack these deformed areas produce wear debris by microspalling. Metal may also be removed by nucleation and propagation of cracks.     

Mirrorlike pulsed laser deposited tungsten thin film

Mirrorlike tungsten thin films on stainless steel substrate deposited via pulsed laser deposition technique in vacuum (10(-5) Torr) is reported, which may find direct application as first mirror in fusion devices. The crystal structure of tungsten film is analyzed using x-ray diffraction pattern, surface morphology of the tungsten films is studied with scanning electron microscope and atomic force microscope. The film composition is identified using energy dispersive x-ray. The specular and diffuse reflectivities with respect to stainless steel substrate of the tungsten films are recorded with FTIR spectra. The thickness and the optical quality of pulsed laser deposition deposited films are tested via interferometric technique. The reflectivity is approaching about that of the bulk for the tungsten film of thickness ～782 nm.     

Tribological behaviour of DLC coatings compared to different materials used in hip joint prostheses

The goal of the study carried out in the laboratory was to quantify the wear and the friction of two materials used for the manufacturing of hip prostheses. Tests used had to obtain in a short time the tribological behaviour laws of the materials. Tests on a hip simulator have been excluded because their cost and their duration were too high for a program of preliminary development of new materials.

To amplify wear phenomena, dry friction tests were carried out for two configurations: ball-on-disc and pin-on-disc. The influence of the contact pressure at constant sliding velocity on the wear of materials has been clearly shown.

Results obtained with several different tested materials (stainless steel/UHMWPE, stainless steel+DLC coating/UHMWPE, stainless steel+DLC coating/stainless steel+DLC coating, titanium alloy+DLC coating/UHMWPE, titanium alloy+DLC coating/titanium alloy+DLC coating, zirconium dioxide/UHMWPE, alumina/UHMWPE, alumina/alumina) have shown the superiority of DLC coatings. Promising results obtained during this study are in the validation stage on a hip simulator.     

摩擦偶件对PDDA/PSS分子沉积膜摩擦磨损行为的影响

利用分子沉积技术在单晶硅基底上制备了PDDA/PSS分子沉积膜。采用UV-vis吸收光谱对沉积过程进行了跟踪检测,用原子力显微镜观察了分子沉积膜的表面形貌,考察了摩擦偶件材料对PDDA/PSS分子沉积膜摩擦学行为的影响,并探讨了其磨损机制。实验结果表明,薄膜与较硬的偶件材料对摩时,剪切应力较大,薄膜很容易被磨穿,抗磨寿命极短;在相同实验条件下,薄膜与Cu球对摩时,薄膜的耐磨寿命最长,不锈钢球次之,与Si3N4球和WC球对摩时,薄膜的耐磨寿命较短。     

Determination of flow stress of thin-walled tube based on digital speckle correlation method for hydroforming applications

The flow stress, used to describe the plastic deformation behavior of thin-walled tube, is one of the most important parameters to ensure reliable finite element simulation in the tube hydroforming process. In this study, a novel approach of on-line measurement based on digital speckle correlation method is put forward to determine flow stress of thin-walled tube. A simple experimental tooling is developed and free-bulged tests are performed for 304 stainless steel and H62 brass alloy tubes. An analytical approach is proposed according to the membrane theory and the force equilibrium equation. The developed method is validated by means of FE simulations. The results indicate that the present method is acceptable to define the flow stress in the tube hydroforming process.     

沉积温度对脉冲真空弧源沉积类金刚石薄膜性能的影响

利用脉冲真空弧源沉积技术在Cr17Ni14Cu4不锈钢和Si(100)基体上制备了类金刚石(DLC)薄膜,研究了基体沉积温度对DLC薄膜的性能和结构的影响。研究表明,随着沉积温度由100 ℃提高到400 ℃,DLC薄膜中sp3 键质量分数减少,sp2键质量分数增多,薄膜复合硬度逐渐降低。当DLC薄膜沉积温度达到400 ℃时,薄膜中C原子主要以sp2键形式存在,与沉积温度为100 ℃时制备的DLC薄膜相比,薄膜复合硬度降低50%。DLC薄膜具有优异的耐磨性,摩擦因数低,随着沉积温度由100 ℃提高到400 ℃,Cr17Ni14Cu4不锈钢表面沉积的DLC薄膜耐磨性降低。沉积温度为100 ℃时,Cr17Ni14Cu4不锈钢表面沉积的DLC薄膜后,耐磨性大幅度提高。DLC薄膜与不锈钢基体结合牢固。     

外加电场对3种陶瓷/金属摩擦副摩擦行为的影响

使用自制面接触往复式滑动摩擦磨损实验机,采用质量百分比浓度为１％的硬脂酸锌水基乳化液作为润滑剂,研究了边界润滑状态下外加直流电场的几处施加方式对３种摩擦副在低速滑动时摩擦行为的影响。实验结果显示,外加电压的存在显示地改变了３种摩擦副的摩擦系数以及摩擦系数曲线的平稳程度,摩擦系数是最大相对增加量和最大相对减少量分别达到２００％和４０％。摩擦系数的改变与外加直流电压的通断是对应的,不同摩擦副对电压接通     

Wear of metal stirring rods in molten aluminium and suspensions of alumina particles in molten aluminium

The wear of stainless steel and titanium stirring rods in molten aluminium and a suspension of alumina particles in molten aluminium was studied. The known characteristic of more rapid wear by stainless steel than titanium was confirmed and the suspension of alumina particles was found to accelerate wear of both metals. Examination of worn specimens revealed that the stainless steel rods were separated from the liquid aluminium by a layer of iron, chromium and aluminium. Wear proceeded by the shedding of projections that formed on the layer into the liquid aluminium. Alumina particles accelerated wear by abrasion of the projections. The titanium was surrounded by a much thinner layer of titanium and aluminium mixture with no projections into the molten aluminium. The distribution of wear around the blades was controlled by the flow of liquid metal and of the alumina particles around each blade.     

Cutting performance of an indexable insert drill for difficult-to-cut materials under supplied oil mist

In this study, the cutting performance of an indexable insert drill with an asymmetric geometry for cutting difficult-to-cut materials was investigated. A solid twist drill with a symmetric geometry was used to compare the cutting characteristics. The cutting characteristics were evaluated using the thrust force, inner-surface roughness of the drilled hole, wear behavior, and tool temperature. Workpieces made of stainless steel, titanium alloy, and nickel-based alloy were selected as difficult-to-cut materials, and carbon steel was also selected. The tool temperature was higher in the order of carbon steel, stainless steel, titanium alloy, and nickel-based alloy for every drill under minimum quantity lubrication cutting. The influence of the workpiece material on the thrust force was different from that of the tool temperature for the indexable insert drill, whereas that of the solid twist drill was similar to the tool temperature tendency. When cutting the titanium alloy and nickel-based alloy, the tool temperature and thrust force of the indexable insert drill were lower than those of the solid-type twist drill. The inner-surface roughness of a hole drilled with the indexable insert drill had almost the same quality as that of a hole drilled with the solid-type twist drill when cutting the difficult-to-cut materials. The wear behavior of the indexable insert drill was remarkably different from that of the solid-type twist drill, and the flaking of the coating and the abrasion wear at the rake face were notable in the indexable insert drill.     

Evaluation of fan-pattern spray nozzle wear using scanning electron microscopy

Worn nozzles on spray equipment severely affect the efficiency of crop management systems while causing unnecessary pesticide contamination of non target areas. Scanning electron microscopy (SEM) that has been applied for direct measurement of pesticide deposition, was used to observe worn and unused brass and stainless steel fan-pattern spray nozzles. Wear and other changes were observed in both nozzle materials. Scanning electron microscopy can provide nozzle manufacturers with greater insight and needed information on nozzle mechanics to improve performance. More reliable delivery of pesticide spray should enhance integrated pest and disease management and crop protection for growers.     

钢衬铜管在空调产品上的使用工艺性研究

空调行业竞争日益激烈,各空调企业一直在寻求价格低廉、质量可靠的铜管替代品,钢衬铜管具有较好的焊接性能和不错的抗氧化能力得到关注.通过对钢衬铜管和铜管理化性能以及机械性能进行对比试验,对钢衬铜管与铜管的焊接工艺性和加工工艺性进行研究,以期确认钢衬铜管使用在空调产品上可行性.     

Nondestructive test of brazed cooling tubes of prototype bolometer camera housing using active infrared thermography

The active infrared thermography technique is used for assessing the brazing quality of an actively cooled bolometer camera housing developed for steady state superconducting tokamak. The housing is a circular pipe, which has circular tubes vacuum brazed on the periphery. A unique method was adopted to monitor the temperature distribution on the internal surface of the pipe. A stainless steel mirror was placed inside the pipe and the reflected IR radiations were viewed using an IR camera. The heat stimulus was given by passing hot water through the tubes and the temperature distribution was monitored during the transient phase. The thermographs showed a significant nonuniformity in the brazing with a contact area of around 51%. The thermography results were compared with the x-ray radiographs and a good match between the two was observed. Benefits of thermography over x-ray radiography testing are emphasized.     

Microstructure grooves with a width of less than 50 μm cut with ground hard metal micro end mills

Mechanical microengineering is an easy and cheap way to fabricate microstructures; for example, molds for injection molding or hot embossing. Restrictions remain in the selection of materials and in the minimum structure size. Especially for cutting microstructures in steel, these limitations included the lack of available small tools and the poor surface quality. We discovered that microstructures can be cut in both brass and stainless steel workpieces by using ground hard metal micro end mills. The minimum groove width achieved is less than 50 μm for cutting brass and about 100 μm for cutting stainless steel. Burrs are removed by a subsequent diamond-cutting step or electrochemical polishing, respectively. Our results represent the first step toward a microstructured, resistant, and cheap mold made of steel, which is then used for mass production of plastic microstructures.     

Workpiece and electrode influence on micro-EDM drilling performance

In recent years, the need for products containing micro-features has shown a pronounced and steady growth in several fields of application. For the development of micro-holed devices, one of the most important technologies is micro-EDM (Electro Discharge Machining). Micro-EDM can be considered as an ideal process to obtain burr-free micron-size features with high aspect ratios. In particular, micro-EDM is a non-contact material removal process in which rapid electric spark discharges remove the material composing the workpiece by means of melting and vaporizing phenomena. The present work deals with the fabrication of micro holes using micro-EDM technology. The investigation focuses on the influence of different electrodes and workpiece materials on the process performance, expressed in terms of tool wear ratio. In particular, the influence of four different workpiece materials (stainless steel, titanium, magnesium and brass), three electrode materials (copper, brass and tungsten carbide) and two different electrode shapes (cylindrical and tubular) was investigated. Moreover, an analysis of the geometrical characteristics of the micro holes in terms of conicity and diametrical overcut was carried out. An influence of electrode geometries, electrode material and workpiece material on the final output was found.     

High-energy x-ray backlighter spectrum measurements using calibrated image plates

The x-ray spectrum between 18 and 88 keV generated by a petawatt laser driven x-ray backlighter target was measured using a 12-channel differential filter pair spectrometer. The spectrometer consists of a series of filter pairs on a Ta mask coupled with an x-ray sensitive image plate. A calibration of Fuji? MS and SR image plates was conducted using a tungsten anode x-ray source and the resulting calibration applied to the design of the Ross pair spectrometer. Additionally, the fade rate and resolution of the image plate system were measured for quantitative radiographic applications. The conversion efficiency of laser energy into silver Kα x rays from a petawatt laser target was measured using the differential filter pair spectrometer and compared to measurements using a single photon counting charge coupled device.     

温度对不锈钢/铝/不锈钢层状材料轧制复合行为的影响

研究了热轧复合不锈钢／铝／不锈钢层状材料的粘结行为，采用剥离试验、OM、SEM及EDAX等研究了坯料加热温度对界面粘结强度及特征的影响规律。结果表明：在523～773K范围内，粘结强度随着温度的升高而明显增加；温度低于523K时，铝／钢界面为机械结合状态，粘结强度低于7．8Nmm^-1，剥离断口位于其初始界面；温度高于673K后，界面达到近冶金结合状态，粘结强度超过20．3Nmm^-1,剥离断口几乎位于铝基体而非初始界面。钢层变形远小于铝层变形，界面两侧金属剪切流动导致的新表面接触及扩散行为是促使界面粘结的主要机制。     

Development of novel sustainable neat-oil metal working fluids for stainless steel and titanium alloy machining. Part 1. Formulation development

This paper introduces and describes the development and application of methodologies for the formulation of novel sustainable neat-oil metal removal fluids. A further paper will describe the methodologies being employed and the results of the performance benchmarking of the final fluid formulations for stainless steel and aerospace-grade titanium alloy materials. In this paper, a stepwise approach to the development of novel sustainable neat-oil metal removal formulations is described with a detailed discussion and analysis of the approach taken and the methodologies developed and applied. Two target applications were identified for cutting stainless steel and aerospace-grade titanium alloys. The key required properties of the fluids for these applications were combined with targets identified for cost, low temperature properties, kinetic viscosity (KV) and oxidative stability. Samples of base oils were obtained and characterised. The oils ranged from commodity commercial and specialist natural vegetable oils to chemically modified vegetable-oil-derived fatty acid esters and polyols. The selected oils were used to create blends which were screened for their key properties. From this work, four blends of base oils were identified for being taken forwards to the formulation screening stage. These blends represented a range of natural and modified oils blended in such a way as to achieve all of the required key properties of cost, KV, melt/pour points and oxidative stability. To determine if the oils were likely to also perform well as metal cutting fluids, they were subjected to a range of tests with and without the addition of certain additives, and their performances were benchmarked against a range of mineral oil and polyol-ester-based commercial fluids currently supplied to the target applications areas. The tests employed were: SRV, microtap and oxidation stability. The issues involved in the extrapolation of results from tribological testing to the prediction of fluid cutting performance are highlighted and discussed. From this work, one base oil blend for each of the two target applications was identified and the best performing mineral and polyol ester benchmark fluids were selected. Full-scale drilling and rigid torque tapping tests were used to refine formulations and to screen other additives identified in parallel microtap tests. The durability, oxidation stability, machine tool compatibility and misting potentials of the final formulations were also benchmarked using a range of standard and novel methodologies—this work will be described in a later paper.