Electrochemical micromachining of microstructures of micro hole and dimple array

This paper proposes a method of electrochemical micromachining of micro hole or dimple array, in which a patterned insulation plate coated with metal film as cathode is closely attached to workpiece plate. When voltage is applied across the workpiece and cathode film over which the electrolyte flows at high speed, hole or dimple array will be produced. The proposed technology offers unique advantages such as short lead time and low cost. The effect of process parameters on the microstructure shape was demonstrated numerically and experimentally. Arrays of holes or dimples of several hundred micrometers diameter have been produced.     

Micro electroforming of high-aspect-ratio metallic microstructures by using a movable mask

A novel micro electroforming process, which targets the cost efficient fabrication of high-aspect-ratio metallic microstructures, is presented in this paper. An insulating mask with patterned features for localizing the deposition region moves periodically along the metal growth direction during electrodeposition instead of the traditional patterned photoresist mask coated on a substrate. The proposed technology offers some unique advantages such as re-using of mask and avoiding removal of photoresist. The current density distribution and metal deposition in the proposed process were studied. Typical high-aspect-ratio metallic microparts in the scale of several hundred microns have been produced.     

光刻胶掩膜微细电化学加工参数的试验研究

对光刻胶掩膜微细电化学加工参数进行了试验分析研究，发现光刻胶厚度、开口角度、咏冲电源频率、脉宽及电解液配方对加工质量都有影响，在此基础上提出改善加工质量的可行性方案。     

Grain growth phenomena in tungsten wire

This paper describes a three-dimensional lattice model for the study of the recrystallization and grain growth of tungsten wires in comparison to additional experiments. Microstructures similar to experimental ones were obtained. The experimentally obtained grain size data was used to determine the grain growth exponent and the activation energy for grain boundary migration at temperatures ranging from 1500 to 1900 °C. The evolution with time and temperature of the average grain size has been calculated by the Monte-Carlo method. For this, a relation between length and time scale in simulation and experiment, based on intrinsic material parameters, was developed. In general, the results agree very well with the experimental observations.     

Gas tungsten arc welding of titanium using flux cored wire with magnesium fluoride

Abstract

Grade 2 Ti–CP was gas tungsten arc welded using flux cored (FC) wires and flux pastes that contained various MgF₂ contents. The effects of MgF₂ on bead morphology, chemical composition and hardness of weld bead were investigated and interpreted. With an increase of MgF₂ content in the flux paste, depth/width ratio of weld bead increased gradually with little variation in interstitial element contents and hardness. Weld bead made with cold FC wire feed showed even deeper and narrower bead, indicating the greater effectiveness of wire feed than flux paste on weld penetration. While the 50% MgF₂ FC wire produced complete slag coverage and smooth weld bead surface, 85% MgF₂ wire resulted in incomplete slag coverage and rough weld surface. Arc spectroscopy revealed that the 50% MgF₂ FC wire produced plasma spectrum with atomic and ionised titanium peaks, which is an indication of a high temperature arc and a larger amount of flux vapours in the arc. Therefore, it is believed that deep weld penetration associated with high MgF₂ fluxes in this experiment is caused by arc constriction, resulting from the greater amount of flux vapours owing to high arc temperature.     

100 years of doped tungsten wire

From a historical point of view, the development of the PM processing steps and tools “for making tungsten ductile” by William D. Coolidge in 1909 marks the breakthrough for the usage of tungsten filaments in the lighting industry and the beginning of the industrial era of modern Powder Metallurgy.     

A novel molten wire tungsten inert gas welding process

ABSTRACT

A novel molten wire tungsten inert gas welding process was presented. In this process, a welding arc is used to melt the workpiece, and a melting arc is used to melt the feeding wire. Metal transfer is separated from the melting of the wire and the workpiece, and the arcs are stable no matter the droplet transfer mode is spraying or globular. The spatter rate in the process is close to zero. Mechanical properties of low carbon steel joint bonded with this process are superior to those bonded with the metal inert gas welding process.     

空心钨极同轴填丝焊接丝弧交互作用机制

空心钨极同轴填丝焊接焊丝与电弧(丝-弧)交互过程是决定焊接质量的关键.首先利用高速摄像观察分析了空心钨极电弧与实心钨极电弧形态,及其对焊缝成形特征的影响规律,然后构建了熔丝过程受力模型,系统分析了同轴填丝焊接过程中熔滴形成及过渡过程动力学特征.结果表明,空心钨极电弧表面辐照区域大于实心钨极,在大电流工艺条件下焊缝成形稳定;熔滴形成阶段,焊丝末端熔滴处于静力平衡状态,在较大表面张力作用下,无法自发从焊丝末端直接过渡进入熔池;熔滴过渡阶段,部分电流从焊丝流过,产生电磁收缩力,引起焊丝与熔池之间的熔滴摆动.     

Electrochemical investigation on hydride electrode with tungsten carbide additive

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Laser micromachining for biomedical applications

Laser micromachining is becoming a common method for fabrication of microstructured medical devices. Developments in pulsed laser technology have made it possible to achieve precision machining of sub-micrometer features with minimal damage to the surrounding material. Several aspects of laser micromachining, including machining methods, types of lasers used in micromachining, and laser-material interaction, are discussed in this article. Biomedical applications of laser micromachining are also reviewed. The ablation behavior of silicon was examined as a function of laser energy, aperture, and repetition rate. In vitro studies showed that microscale grooves on silicon substrates may be used to orient human aortic vascular smooth muscle cells. We anticipate that the use of laser micromachining for modifying medical and dental devices will become more significant over the coming years.     

硅对SAl5356铝合金焊丝显微组织和性能的影响

研究了硅对SAl5356焊丝及其焊接的5083铝合金焊缝显微组织及力学性能的影响. 结果表明,Si元素含量在0~0.12%时,随着Si元素含量的增加,SAl5356焊丝及其焊接接头强度稍有升高,塑性稍有下降;当Si元素含量高于0.12%时,随着Si元素含量的增加,SAl5356焊丝及其焊缝组织中含硅粗大相增多,焊丝拉伸性能下降,硬度不均匀性加剧,焊接接头强度及弯曲性能变差. 特别是当Si元素含量超过0.2%后,合金中含硅粗大相在晶界处富集,与α(Al)基体构成鱼骨状共晶组织,焊丝及其焊接接头力学性能下降更加明显,铝线材的强度比峰值下降了约12%,断后伸长率下降了约45%. 因此从提高SAl5356焊丝及其焊缝性能角度考虑,Si元素含量不宜超过0.2%,以控制在0.12%以内最佳.     

Analyzing superplastic microstructures using interactive EBSP methods

Microtexture and boundary characteristics have been analyzed in a comparative study of post-deformation tensile specimens of a superplastically processed Al-10Mg-0.1Zr alloy using electron backscatter pattern methods in the scanning electron microscope. Interactive methods were employed to capture nearest-neighbor (sub)grain diffraction patterns and the data were subsequently computer analyzed to produce information on the character of the interfacial boundary represented by the misorientation between neighboring crystals. The data from this study are used to determine whether grain boundary character is a microstructural feature responsible for the distinctly different tensile behavior observed in material processed according to two different thermomechanical processing schedules.     

A multiprocess machine tool for compound micromachining

Compound micromachining is the most promising technology for the production of miniaturized parts and this technology is becoming increasingly more important and popular because of a growing demand for industrial products, with an increased number not only of functions but also of reduced dimensions, higher dimensional accuracy and better surface finish. Compound micromachining processes that combine multiple conventional and non-conventional micromachining processes have the capability to fabricate high aspect ratio microstructures with paramount dimensional accuracy. Such machining should be carried out on the same machine with minimum change of setups. At the same time, on-machine tool fabrication along with on-machine tool and workpiece measurement facilities should also be available for further enhancement of the functionality of the machine and higher productivity. In order to achieve effective implementation of compound micromachining techniques, this research seeks to address four important areas, namely (a) development of a machine tool capable of both conventional micromachining including microturning, micromilling, etc., and non-conventional micromachining including microelectrical discharge machining (micro-EDM), wire-cut electrical discharge machining (WEDM), etc.; (b) process control; (c) process development to achieve the necessary accuracy and quality and (d) on-machine measurement and inspection. An integrated effort into these areas has resulted in successful fabrication of microstructures that are able to meet the miniaturization demands of the industry. This paper presents a few tool-based approaches that integrate micro-EDM, micro-EDG, microturning and microgrinding to produce miniature components on the same machine tool platform in order to demonstrate the capabilities of compound micromachining.     

不同焊丝对6082铝合金焊接接头组织性能的影响

采用ER5356和ER5087铝合金焊丝对6082-T6铝合金板材进行焊接,研究了不同焊丝对6082-T6铝合金力学性能和显微组织影响。结果表明,ER5087焊丝焊接的焊缝硬度高于ER5356焊丝的焊缝硬度,这是由于ER5087焊丝中的Zr细化焊缝晶粒的结果。拉伸试验时焊接接头均断裂于热影响区,ER5087焊丝焊接的接头比ER5356焊丝焊接的接头平均屈服强度和抗拉强度高,断后伸长率稍好。     

Influence of filler wire composition on weld microstructures of a 444 ferritic stainless steel grade

Seven compositions of metal cored filler wires for gas metal arc welding (GMAW), containing the same weight percent of chromium (Cr) and molybdenum (Mo) as 444 steel, but with different titanium (Ti) and niobium (Nb) contents were investigated. Experimental results pointed out that the filler wire Ti content required to be twice time more than the amount expected in the deposited metal. This was due to the low Ti transfer ratio during arc welding. Moreover, Ti increased the wetting angle and promoted penetration. It was supposed that Ti affected the weld pool surface tension what led to inward Marangoni convection.Columnar to equiaxed grain transition (CET) was also promoted thanks to the precipitation in the weld pool of Ti rich refractory compounds which act as heterogeneous nucleation sites for equiaxed grains. A minimum 0.3% Ti was required in the filler wire to form a completely equiaxed grain structure in the fusion zone. Niobium in the filler wire did not seem to have any effect on penetration, wetting and grain structure of the fusion zone.     

Microstructure,mechanical behaviour and fracture of pure tungsten wire after different heat treatments

Plastic deformation of tungsten wire is an effective source of toughening tungsten fibre-reinforced tungsten composites (W_f/W) and other tungsten fibre-reinforced composites. To provide a reference for optimization of those composites, unconstrained pure tungsten wire is studied after various heat treatments in terms of microstructure, mechanical behaviour and fracture mode. Recrystallization is already observed at a relatively low temperature of 1273 K due to the large driving force caused by a high dislocation density. Annealing for 30 min at 1900 K also leads to recrystallization, but causes a rather different microstructure. As-fabricated wire and wire recrystallized at 1273 K for 3 h show fine grains with a high aspect ratio and a substantial plastic deformability: a clearly defined tensile strength, high plastic work, similar necking shape, and the characteristic knife-edge-necking of individual grains on the fracture surface. While the wire recrystallized at 1900 K displays large, almost equiaxed grains with low aspect ratios as well as distinct brittle properties. Therefore, it is suggested that a high aspect ratio of the grains is important for the ductile behaviour of tungsten wire and that embrittlement is caused by the loss of the preferable elongated grain structure rather than by recrystallization. In addition, a detailed evaluation of the plastic deformation behaviour during tensile test gives guidance to the design and optimization of tungsten fibre-reinforced composites.     

空心钨极同轴填丝焊空间热场分布特征

利用理论建模与试验相结合的方法,系统研究了空心钨极同轴送丝焊接过程中焊丝熔化热量的来源. 结果表明,基于磁流体力学的理论模型分析结果和实际情况高度吻合;在高温电弧热辐射及钨极热传导共同作用下,钨极内孔形成的梯度式高温区会对焊丝起到一定的预热作用;环状空心钨极电弧中轴线上近几何中心区域的温度最高,焊接电流400 A时温度高达13 700 K;熔滴与液态熔池接触后电势相等,在最小电压原理作用下,部分高温电弧的阳极作用区会由液态熔池转变至焊丝表面,同时部分焊接电流会从焊丝流过,形成的电阻热也是高效熔丝的主要原因之一;熔滴过渡分析结果表明空心钨极同轴填丝焊接具有较高的工艺稳定性,是一种极具发展前景的焊接新方法.     

电磁场法原位合成WC_p/W丝增强铁基复合材料

通过对钨丝和灰口铸铁熔体组成的体系施加电磁场,在1573 K时,熔体中的碳原子与钨原子能够原位反应合成碳化钨颗粒。结果表明:当电磁场频率小于4 kHz,得到碳化钨颗粒与钨丝混杂增强灰口铸铁基复合材料;当电磁场频率达到4 kHz时,得到碳化钨颗粒增强灰口铸铁基复合材料。电磁场除了加速熔体中的质量传递外,还有助于在钨丝周围形成一系列的Fe-W-C三元微区,该微区中钨的浓度较高,利于改善原位合成WC颗粒的动力学条件。但是,WC颗粒的间隙类似于一个过滤器,降低了元素的扩散速度。复合材料较好的耐磨性归因于WC颗粒的较高硬度以及颗粒的弥散分布。     

GH2132合金材料平板堆焊层的组织性能

针对GH2132高温合金熔敷金属热裂纹敏感性问题,通过采用试制焊丝、熔敷金属焊接试验、组织及断口分析、凝固计算等手段对熔敷金属组织、凝固行为、开裂机制等进行了研究. 结果表明,试验熔敷金属金相组织主要由柱状树枝晶γ相(NiCrFe固溶体)、枝晶间富Ti的Laves相(Cr,Fe,Ni)₂ (Ti,Mo)、MC碳化物与共晶组织组成,凝固路径为L→L + γ→L + γ + MC→L + γ + MC + Laves→γ + MC + Laves,裂纹断口呈典型的鹅卵石共晶花样,整个断口形貌被呈自由表面的液膜所覆盖,属于发生在高温段的结晶裂纹. 结晶裂纹开裂机理为在凝固过程的终了阶段,发生了L→γ + Laves的低熔点共晶反应,在凝固收缩应力作用下,残余液相未及时补充而形成. Laves相的形成主要与凝固过程中Ti元素的偏析有关,理论计算结果表明,GH2132结晶裂纹指数(solidification cracking index, SCI)值为1944 ℃,(solidification temperature range, STR)为258 ℃,在结晶裂纹敏感性评价方面,相比STR,SCI指标能相对更为合理地实现结晶裂纹敏感性的量化评价,但仍存在考虑因素不全等问题.