应用硅和非硅MEMS技术的微型直接甲醇燃料电池

分别以硅和不锈钢材料为极板研制了两种结构简单、体积小、比能量密度高的微型直接甲醇燃料电池,并介绍了该电池的工作原理和结构。利用光刻、溅射和腐蚀等MEMS技术完成了硅基微型直接甲醇燃料电池的制作,实验测试表明,在室温条件下,使用1.5 mol/L甲醇溶液供液时其开路输出电压为520 mV,最大输出功率密度达到5.9 mW/cm²;利用非硅微加工技术完成的不锈钢微型直接甲醇燃料电池,在室温下用2 mol/L甲醇溶液供液时开路输出电压为650 mV,最大输出功率密度达到15.8 mW/cm²。     

Oil-Lubricated Fretting Behaviors of 304 Stainless Steels under Different Fretting Strokes and Normal Loads

The influence of oil lubrication on the fretting wear behaviors of 304 stainless steel flat specimens under different fretting strokes and normal loads has been investigated. The results proved that fretting regimes and fretting wear behaviors of 304 stainless steels were closely related to the fretting conditions. In general, the increase in normal load could increase wear damage during sliding wear. However, according to the results, a significant reduction in wear volume and increase in friction coefficient was observed when the normal load was increased to critical values of 40 and 50 N at a fretting stroke of 50 μm due to the transformation of the fretting regime from a gross slip regime to partial slip regime. Only when the fretting stroke further increased to a higher value of 70 μm at 50 N, fretting could enter the gross slip regime. There was low wear volume and a high friction coefficient when fretting was in the partial slip regime, because oil penetration was poor. The wear mechanisms were fatigue damage and plastic deformation. There was high wear volume and low friction coefficient when fretting was in the gross slip regime, because the oil could penetrate into the contact surfaces. Unlike the wear mechanisms in the partial slip regime, fretting damage of 304 stainless steels was mainly caused by abrasive wear in the gross slip regime.     

Micro-Raman analysis of stress in machined silicon and germanium

Residual strain in single point diamond machined crystalline silicon and germanium has been measured with high spatial resolution (≈ 2 μm) using Raman microprobe spectroscopy. Raman spectroscopy is a direct, non-destructive technique which provides a spatial resolution down to the excitation wavelength and which may be applied to a wide range of non-conducting materials. Raman scattering was used to measure local strain at various points across single point plunge and feed cuts in crystalline silicon and germanium. Spectra were obtained using various excitation wavelengths (514.5 and 488.0 nm), which, due to their differing penetration lengths in the various materials, can provide depth profiles of the residual stress down to approximately 1 μm. In single point plunge cuts little evidence of surface damage was seen and the residual stresses are compressive. Using a 514.5 nm excitation wavelength, we measure a compressive stress of 250 MPa (2.5 kbar) near the outer edge of a single point plunge cut in silicon. At this wavelength, the penetration depth of the laser is 1.0 × 10⁻⁴ cm. This compressive stress was observed to increase to 600 MPa (6.0 kbar) at a depth of 0.6 × 10⁻⁴ cm which was measured using a 488.0 nm excitation wavelength. In single point feed cuts, regions of heavy fracturing were observed as well as regions of little visible damage. In damaged areas tensile stresses of 200–300 MPa (2.0–3.0 kbar) were measured in silicon while in germanium the tensile stress in such regions is 50–100 MPa (0.5–1.0 kbar). In undamaged areas the stresses are compressive with measured values of 50 and 30 MPa (0.5 and 0.3 kbar) for silicon and germanium respectively.     

Genetic algorithm based optimization of the process parameters for gas metal arc welding of AISI 904 L stainless steel

The present study is focused on welding of super austenitic stainless steel sheet using gas metal arc welding process with AISI 904 L super austenitic stainless steel with solid wire of 1.2 mm diameter. Based on the Box — Behnken design technique, the experiments are carried out. The input parameters (gas flow rate, voltage, travel speed and wire feed rate) ranges are selected based on the filler wire thickness and base material thickness and the corresponding output variables such as bead width (BW), bead height (BH) and depth of penetration (DP) are measured using optical microscopy. Based on the experimental data, the mathematical models are developed as per regression analysis using Design Expert 7.1 software. An attempt is made to minimize the bead width and bead height and maximize the depth of penetration using genetic algorithm.     

Study of solid particle erosion on AISI D2 using angular silicon carbide and steel round grit particles

Abstract

In this study, the performance of AISI D2 steel subjected to solid particle erosion tests was analysed. This material has applications for tools and dies for blanking, wood milling cutters, cold-extruding and other operations requiring high compressive strength and excellent wear resistance. The erosion tests performed by using a rig developed according to some parameters of the ASTM G76-95 standard. Two abrasive were used, angular silicon carbide (SiC) and steel round grit, both, with a particle size of 400–420 μm. This allowed comparing the erosion severity of each abrasive particle. The tests were conducted using four different incident angles 30, 45, 60 and 90° with a particle velocity of 24±2 m s^?1 and a flow rate of 21±2·5 g min^?1 for silicon carbide and 48·5±3·5 g min^?1 for the steel round grit. The exposure testing time was 10 min. Subsequently, the surface damage was analysed with a scanning electron microscope (SEM) to identify the wear mechanisms. Additionally, atomic force microscopy (AFM) was conducted in order to obtain roughness of the surface damage at 60°. The results indicated that higher amount of mass loss was obtained by angular silicon carbide particles.     

Transmission and scanning electron microscopy studies of deformation at erosion impact sites

Scanning and transmission electron microscopy methods have been employed to study topographic features and subsurface damage associated with erosive-particle impact craters in annealed 310 stainless steel surfaces. Angular Al₂O₃ and spherical glass particles approximately 50 μm in diameter were projected at a velocity of 59 m s^?1 to impact the surface at attack angles of 90° and 20°. Under these conditions, material was found to be displaced but not removed from the surface at isolated impact sites. A comparison was made with damage produced at diamond pyramid hardness indentations. Substantial differences were not observed. In general, a high dislocation density zone a few microns wide was found to surround both impact craters and hardness indentations. The width of this zone varied according to the size and shape of the crater and the direction of particle motion. Deformation twinning occurred at some impact sites. The plastic strain associated with impact craters in 310 stainless steel and copper was also determined by a method that is based on an analysis of selected-area electron channelling patterns.     

The effect of number of cycles on the critical transition boundary between fretting fatigue and fretting wear

The object of the present study was to investigate the influence of number of cycles on the critical amplitudes of tangential force and displacement, identifying the transition from a mixed stick-slip regime (fretting fatigue) to a gross slip regime (fretting wear) over a wide range of test conditions. Fretting experiments were conducted on three metal specimen combinations: copper/copper; stainless steel/stainless steel; copper/stainless steel. All experiments took place in air, at ambient temperature, using a crossed-cylinder geometry. Normal loads of 3.4 and 11.4 N were applied with frequencies ranging from 10 to 800 Hz. In most cases, n = 1.2×10⁴ and n = 6×10⁶ were adopted as the representative lower and higher number of cycles, respectively. At different numbers of cycles, critical amplitudes of tangential force and displacement were measured. The scars fretted under separately selected conditions were examined by scanning electron microscopy.

It was found that the critical amplitudes of both tangential force and displacement dropped with increasing number of cycles for all test combinations, but there was an upper limit above which the drop of critical transition values no longer occurred with further increases in the number of cycles. The micromorphology of fretting scars (in a mixed stick-slip regime) revealed that the stick zone has shrunk after a larger number of cycles under the conditions of constant amplitude of tangential force and displacement, and that the damage mechanisms vary for different combinations, although they are all characterized by a central stick zone surrounded by a slip annulus. It was suggested that the decrease of critical amplitudes after a larger number of cycles results from the shrinkage of the stick area, which may be a complex process related to plastic deformation, strain hardening, and the change of stress distribution on the contact surfaces.     

SEM electron channelling patterns as a technique for the characterization of ion-implantation damage

Electron channelling patterns (ECPs) formed in back-scattered images in the scanning electron microscope (SEM) have been used occasionally to confirm surface amorphization during ion implantation. In order to place such observations on a more quantitative basis, the study reported here has explored the variation of ECP appearance with both specimen damage levels (and thus subsurface structures) and SEM accelerating voltage (i.e. sampled depth). Polished and annealed (0001) single crystal sapphire discs were implanted to various damage levels up to both subsurface and full surface amorphization. Damage levels were measured independently by Rutherford back-scattering (RBS). Selected-area ECPs were obtained in a Jeol-840 electron microscope operating over the range 5–40 kV in 5-kV steps. Progressive ECP degradation—in terms of high-order line disappearance—was observed with increasing dose, culminating in total pattern loss when full surface amorphization occurred. However, ECP information could still be obtained from the damaged near-surface material even when a subsurface amorphous layer was present, thus demonstrating the shallow retrieval depth of information from the ECP technique. Indeed, because the spatial distribution of damage from ion implantation is both calculable and measurable, these experiments have also allowed us, for the first time, to explore and demonstrate the shallow sample depths from which the majority of ECP contrast originates (< 150 nm in sapphire at an accelerating voltage of 35 kV), even when the beam penetration is considerable by comparison (～ 5 μm). Furthermore, the way in which this sampled depth varies with SEM accelerating voltage is both demonstrated and shown to be a powerful diagnostic technique for studying the distribution of near-surface structural damage.     

Adhesive wear of stir cast hypereutectic Al–Si–Mg alloy under reciprocating sliding conditions

This paper describes an attempt to enhance the wear properties of hypereutectic cast aluminium–silicon alloys produced by semi-solid metal (SSM) processing technique. The rheological experiments on SSM slurries were performed under continuous cooling condition from liquidus temperature. Wear characteristics of alloy under investigation were studied using pin on flat wear system over a range of normal load (10–40 N) at constant average sliding speed (0.2 m/s) against cast iron and stainless steel counter surface. Stir cast alloy showed lesser weight loss compared to conventional cast alloy. Stir cast and conventional cast alloys showed higher weight loss against the stainless steel as compared to that against cast iron counter surface. Optical microscopy of the conventional cast and stir cast hypereutectic alloy has shown that stir casting causes refinement of primary silicon particles and modification of eutectic silicon compared to conventional cast alloy. The scanning electron microscopy of wear surfaces was carried out to investigate the mode of wear.     

Assessment of precipitates of isothermal aged austenitic stainless steel using measurement techniques of ultrasonic attenuation

AISI 316L stainless steel is widely used as a structural material of high temperature thermoelectric power plants, since austenitic stainless steel has excellent mechanical properties. However, creep damage is generated in these components, which are operated under a high temperature and high pressure environment. Several researches have been done on how microstructural changes of precipitates affect to the macroscopic mechanical properties. And they investigate the relation between ultrasonic parameters and metallurgical results. But, these studies are limited by experiment results only. In this paper, attenuations of ultrasonic with isothermal damaged AISI 316L stainless steel were measured. Also, simulation of ultrasonic attenuation with variation of area fraction and size of precipitates were performed. And, from the measured attenuations, metallographic data and simulation results, we investigate the relations between the ultrasonic attenuations and the material properties which is area fraction of precipitates for the isothermal damaged austenitic stainless steel specimens. And, we studied parametric study for investigation of the relation between ultrasonic parameters and metallurgical results of the isothermal damaged AISI 316L stainless steel specimens using numerical methods.     

Effect of Sintering Temperature and Atmosphere on Nonlubricated Sliding Wear of Nano-Yttria-Dispersed and Yttria-Free Duplex and Ferritic Stainless Steel Fabricated by Powder Metallurgy

The nonlubricated sliding wear behavior of nano-yttria-dispersed and yttria-free duplex and ferritic stainless steel against a diamond tip was studied. The stainless steel samples were fabricated by a conventional powder metallurgy route in which nano-yttria-dispersed and yttria-free duplex and ferritic stainless steel powders were cold compacted and then conventionally sintered at either 1000, 1200, or 1400°C in an argon atmosphere. For comparison, another set of samples was sintered at 1000°C in a nitrogen atmosphere. The wear behavior of sintered stainless steel samples against a diamond indenter was investigated using a pin-on-disc apparatus at 10 and 20 N loads and at a constant speed of 0.0041 m/s. It is proposed that yttria-dispersed stainless steels showed higher wear resistance compared to yttria-free stainless steel due to their improved hardness and density. Stainless steel sintered in a nitrogen atmosphere exhibited better wear resistance than those sintered in an argon atmosphere due to the formation of hard and brittle Cr₂N. The wear mechanisms of stainless steels against diamond were found to be mainly abrasive and oxidative. Semiquantitative analysis of the worn surfaces and wear debris confirmed the occurrence of oxidation processes during wear.     

A study on surface polishing of SiC with a tribochemical reaction mechanism

This work investigates the surface polishing of silicon carbide SiC using the tribochemical reaction mechanism. Different metal discs – cast iron, AISI 304 stainless steel, S45C medium carbon steel plated chromium, brass and copper – are used to polish SiC in water and kerosene, respectively. The experimental results show that ferrous metal discs can effectively polish SiC in water. Also, no surface damage or scratches on the polished surface of SiC are observed by this method. The polishing debris was analyzed by electron spectroscopy for chemical analysis. The analyzed results indicate that the polishing surface of SiC is removed tribochemically with the aid of catalytic effect of iron oxide. Moreover, in this process the maximum material removal rate is about 0.06 m/h.     

A Study of Surface Damage at Low-Amplitude Slip

The effect of extremely small slip amplitudes (0 to 5 μm) on transitions in the fretting process, such as initiation of surface damage, development of severe surface damage, microcrack initiation and the development of mild wear, was investigated. For SAE 52100 against SAE 52100 steel, the minimum slip amplitude associated with the onset of mild oxidation or surface staining was approximately 0.06 μm. Studies at higher amplitudes of motion indicated a transition from minimal surface damage to severe or significant damage at 2.8 μm. A further slight increase in amplitude to approximately 3.0 μm resulted in a transition into a regime characterized by fatigue crack formation. These transformations were found to be influenced to some extent by material composition and hardness. The onset of severe surface damage occurred at 1.1 μm for SAE 52100 against SAE 1018 and at 0.5 μm for a nickel chrome Hastelloy B alloy against SAE 1018 steel. In general, the amplitude of microslip characterizing the transition from extremely mild to severe surface damage was found to increase with increasing material hardness.     

新的多轴非比例加载低周疲劳寿命估算公式

利用对 3 16L不锈钢多轴非比例加载低周疲劳的试验结果 ,对现有的多轴低周疲劳寿命估算方法进行讨论 ;基于 3 16L不锈钢非比例加载低周疲劳的微观机理 ,选择最大剪应变以及应变路径的非比例度作为损伤参量 ,建立基于临界面方法的新的非比例加载低周疲劳寿命估算公式 ;利用新的非比例加载低周疲劳寿命估算公式对寿命的预测结果表明 ,新的寿命估算公式对剪切型破坏的 3 16L与 3 16LN不锈钢及拉伸型破坏的 3 0 4不锈钢非比例加载低周疲劳寿命预测精度比现有的临界面方法高     

Wear of metals at high sliding speeds

High speed sliding wear of AISI 1020 steel, AISI 304 stainless steel and commercially pure titanium (75A) was studied using a pin-on-ring geometry. All the tests were carried out in air without any lubricant. The sliding speed was 0.5–10.0 m s^?1 and the normal force was 49.0 N (5 kgf).The friction coefficient of all the materials tested decreased with the sliding speed; this appears to be a consequence of oxide formation. The wear rate of 304 stainless steel increased monotonically with speed, whereas the wear rate of 1020 steel and titanium first decreased and then increased and again decreased, with a maximum occurring at about 5 m s^?1. The complex variation of the wear rate as a function of speed is explained in terms of the dependence of the friction coefficient, hardness and toughness of the materials on temperature. Microscope examinations of the wear track, the sub-surface of worn specimens and the wear particles indicate that the wear mode was predominantly by subsurface deformation, crack nucleation and growth processes, i.e. the delamination process, similar to the low speed sliding wear of metals. Oxidative and adhesion theories proposed in the past to explain the high speed sliding wear of metals are found to be incompatible with the experimental observations.     

Friction and wear of titanium alloys sliding against metal, polymer, and ceramic counterfaces

Recent advances in lower-cost processing of titanium, coupled with its potential use as a light weight material in engines and brakes has renewed interest in the tribological behavior of titanium alloys. To help establish a baseline for further studies on the tribology of titanium against various classes of counterface materials, pin-on-disk sliding friction and wear experiments were conducted on two different titanium alloys (Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo). Disks of these alloys were slid against fixed bearing balls composed of 440C stainless steel, silicon nitride, alumina, and polytetrafluoroethylene (PTFE) at two speeds: 0.3 and 1.0 m/s. The friction coefficient and wear rate were lower at the higher sliding speed. Ceramic sliders suffered unexpectedly higher wear than the steel slider. The wear rates, ranked from the highest to the lowest, were alumina, silicon nitride, and steel, respectively. This trend is inversely related to their hardness, but corresponds to their relative fracture toughness. Comparative tests on a Type 304 stainless steel disk supported the fracture toughness dependency. Energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analyses confirmed the tendency of Ti alloys to transfer material to their counterfaces and suggested possible tribochemical reactions between the ceramic sliders and Ti alloy disks. These reaction products, which adhere to the ceramic sliders, may degrade the mechanical properties of the contact areas and result in high wear. The tribochemical reactions along with the fracture toughness dependency helped explain the high wear on the ceramic sliders.     

The study on the atomic force microscopy base nanoscale electrical discharge machining

This study proposes an innovative atomic force microscopy (AFM) based nanoscale electrical discharge machining (AFM-based nanoEDM) system which combines an AFM with a self-produced metallic probe and a high-voltage generator to create an atmospheric environment AFM-based nanoEDM system and a deionized water (DI water) environment AFM-based nanoEDM system. This study combines wire-cut processing and electrochemical tip sharpening techniques on a 40-μm thick stainless steel sheet to produce a high conductive AFM probes, the production can withstand high voltage and large current. The tip radius of these probes is approximately 40 nm. A probe test was executed on the AFM using probes to obtain nanoscales morphology of Si wafer surface. The silicon wafer was as a specimen to carry out AFM-base nanoEDM process in atmospheric and DI water environments by AFM-based nanoEDM system. After experiments, the results show that the atmospheric and DI water environment AFM-based nanoEDM systems operate smoothly. From experimental results, it can be found that the electric discharge depth of the silicon wafer at atmospheric environments is a mere 14.54 nm. In a DI water environment, the depth of electric discharge of the silicon wafer can reach 25.4 nm. This indicates that the EDM ability of DI water environment AFM-based nanoEDM system is higher than that of atmospheric environment AFM-based nanoEDM system. After multiple nanoEDM process, the tips become blunt. After applying electrochemical tip sharpening techniques, the tip radius can return to approximately 40 nm. Therefore, AFM probes produced in this study can be reused.     

Basic observations in the flat lapping of aluminum and steels using standard abrasives

This research studies the characteristics of aluminum 2024, 304 stainless steel, and 1018 steel during lapping with three different types of abrasives, namely, garnet, silicon carbide, and white aluminum oxide, through detailed experimental analysis. Specifically, the effects of different abrasives on material removal rate and surface finish were evaluated. It was found that silicon carbide and white aluminum oxide abrasives removed more material per minute than garnet. A higher mean frictional force and mean coefficient of friction were obtained in aluminum lapped with SiC and white Al₂O₃ abrasives, and a lower mean frictional force was obtained in 304 stainless steel lapped with SiC. From geometric and energy-dispersive spectroscopy analysis obtained using scanning electron microscopy, it was confirmed that some abrasives became embedded into the lapped metal substrates. No burn was observed on the lapped samples, and scratches and unfinished lapped parts were observed mainly in 304 stainless steel. In order to determine the quantitative influence of each variable, an analysis of variance was performed. It was found that the main effects of abrasive types, size of abrasives, and type of work material had statistically significant influence on material rate and surface finish. In addition, there was a highly significant two-way interaction between abrasives and workpiece.     

Use of vibratory polishing for the location of ion-bombardment induced voids in metal foils

The technique of vibratory polishing has been successfully applied to the controlled removal of surfaces for examination of ion-irradiation damage structure in nickel, a nickel-based alloy, and stainless steel. The application of this technique to the study of voids formed in localized layers in nickel and stainless steel during high dose 20 MeV carbon ion irradiation is described. Transmission electron microscopy observations of the vibratory polished surfaces reveal mechanical damage in the form of linear tracks (～ 100 nm wide) which are produced by the abrasive Al₂O₃ particles used for polishing. These tracks do not prevent observation of irradiation damage structure. An example is shown of a thin (～ 100 nm edge thickness) foil produced entirely by this mechanical polishing process. It is proposed that this technique will be equally applicable to the preparation of transmission electron microscope specimens from a wide range of metals, from alloys containing second-phase particles and from ceramics, glasses and oxides which are not amenable to preparation by chemical or electro-polishing.     

不锈钢焊条工艺稳定性分析与评价

焊条渣壁过渡形态的倾向大小是衡量不锈钢焊条工艺稳定性的主要标志。利用汉诺威弧焊分析仪对不锈钢焊条的焊接电参数进行测试分析,提取短路电压概率密度和、平均电弧电压、平均焊接电流和短路频率等与不锈钢焊条渣壁过渡倾向大小有关的4个特征信息,然后采用主成分分析法确定不锈钢焊条工艺稳定性评价指数。研究结果为定量判断不锈钢焊条熔滴过渡形态和科学评价不锈钢焊条工艺稳定性提供了新方法。