Recent progress in large-grain REBCO melt texturing

Melt texturing large-grain yttriumbarium-copper-oxide materials has evolved in the last few years into a technology capable of producing large quantities of high-perfor-mance superconducting bulk materials. Such materials are used for developing novel engineering devices, such as energy-storage systems and motors. This article gives an overview of the principles of large-grain growth, various processing strategies for these materials, and the limitations of present processing techniques. On the basis of this overview, some directions for further improving superconducting properties and the processing techniques of these materials are discussed. For more information, contact W. Lo, University of Houston, Texas Center for Superconductivity and Department of Mechanical Engineering, Calhoun Road, Houston, Texas 77204; (713) 743-4530; fax (713) 743-4503.     

熔融镁合金定量输送技术进展

定量浇注是压铸生产中的重要环节,对近年来国外熔融镁合金定量输送技术的工作原理和优缺点进行了综述与分析,并提出了未来理想的熔融镁合金定量输送装置应达到的技术要求。     

铸态稀土铝锰黄铜的超塑性

研究了铸态大晶粒稀土铝锰黄铜ZHAlMn52-2-5-RE的超塑性与变形温度、应变速率之间的关系，测定了不同变形条件下的流变应力、最大延伸率。结果表明，该材料在铸态大晶粒条件下可获得超塑性。     

冷轧辊毛化技术的对比研究

系统分析了几种国内外正在使用或试验研究的冷轧辊毛化技术，并依据其加工特性，从毛化轧辊的表面粗糙度、峰值密度、形貌传递特性、环境污染及设备运行成本等方面进行了较为深入的比较研究。在分析比较的基础上，提出了冷轧辊毛化技术的研究方向及发展趋势。     

激光造型技术综述

对激光造型技术的优点、应用价值、加工机理等作了简单阐述,另外就该技术的发展历史和国外的研究状况作了具体介绍,之后对国内的研究情况作了归纳性介绍。根据目前激光造型技术的相关研究,提出激光造型技术今后的研究方向,并展望了未来的应用前景。     

The application of laser-induced multi-scale surface texturing

Recently, there has been interest in controlling microstructure and surface texture on smaller and smaller scales. However, in nature, materials are organized on length scales varying from the nano- to the micro- and larger. In order to realize hierarchical structuring for use in biomedical and mechanical systems, two methods for producing multi-scale surface microstructures and physical textures are explained. The first investigates the use of a marking laser to produce multi-scale texturing of zirconia coatings on Ti-6Al-4V substrates and the second method discusses the design and challenges associated with laser interference surface texturing along with process and material factors controlling surface structures. For more information, contact N.B. Dahotre, University of Tennessee, Department of Materials Science and Engineering, Knoxville, TN 37996; (865) 974-3609; fax (865) 974-4115; e-mail ndahotre@utk.edu     

Development of a maskless electrochemical texturing method

A simple method is demonstrated for texturing metallic surfaces by electrochemical machining, termed ‘maskless electrochemical texturing’ (MECT). The method allows a single cathode tool, in which the texture is incorporated through a pattern of perforations, to be used for many texturing operations and avoids the need for masks to be applied to individual workpieces. It therefore has significant advantages over conventional methods of texturing by electrochemical machining. The method has been applied to low-carbon steel workpieces and features up to 50 μm in depth have been produced. Current efficiencies of more than 90% have been achieved, and the texturing time is short enough for application in an industrial context. The process has been characterised in terms of the effects of current pulse history and electrolyte flushing conditions on current efficiency, material removal rate and feature definition.     

轧辊表面光纤激光毛化工艺研究

利用光纤激光柔性工作站对轧辊表面进行毛化,研究了激光射出头姿态、侧吹角对毛化点形貌、毛化后轧辊表面粗糙度的影响,分析了其影响规律,总结出最佳毛化工艺.结果表明,12点位置和3点位置在特定侧吹角度时,毛化点分布相对独立,凸台金属分布集中,无点与点搭接现象,毛化点形貌满足要求.12点位置和9点位置各侧吹角度下的毛化表面粗糙度均满足要求.综合对毛化点形貌和毛化后轧辊表面粗糙度要求,12点位置的毛化效果优于3点位置.研究结果已应用于实际生产.     

拉深模激光毛化区域的研究

针对拉深件容易产生的起皱和拉裂缺陷进行分析,为提高板料的抗破裂性,讨论了利用激光毛化技术控制金属的流动,提高板料拉深成形性能.通过不同毛化区域对板料抗破裂性和模具使用寿命的影响进行分析,结合激光毛化表面摩擦磨损性能的试验研究,提出了拉深模激光毛化区域;同时,拉深模应对凸模进行毛化,以提高板料的拉深成形性能;若对凹模进行毛化,虽可提高模具使用寿命,但会降低板料的拉深成形性能.试验结果表明,对凸模进行毛化可增加拉深件危险断面的厚度,提高板料的拉深成形性能.     

SiC的激光表面微造型工艺研究

采用灯泵浦YAG-T50系列激光打标机对SiC进行了端面螺旋槽激光微造型加工实验。采用PS50型非接触式三维表面形貌仪测量了槽深和槽内表面粗糙度。通过实验,研究了有效矢量步长、有效矢量步间延时、Q频率、激光电流等工艺参数对微造型加工质量的影响。实验结果表明,当有效矢量步间延时增大或激光电流增大时,螺旋槽深度随之增大;当有效矢量步长增大或Q频率增大时,螺旋槽深度不断减小;而表面粗糙度值则随着有效矢量步间延时、Q频率和激光电流的增大而减小,随着有效矢量步长的增大而增大。从而得出碳化硅的最佳微造型工艺参数为:有效矢量步长0.001mm、有效矢量步间延时60μs、Q频率20kHz、激光电流17A。     

An analysis of the surface generation mechanics of the elliptical vibration texturing process

The elliptical vibration texturing process is a vibration assisted machining method for the fast generation of micro structured surfaces. It adds a higher order motion component to the cutting tool that leads to periodic changes in the cutting depth during the machining process. This results in the creation of micro-dimples on the machined surface, whose shape is a function of the tool geometry and trajectory. This paper studies the surface generation mechanics of the elliptical vibration texturing process through experimentation and modeling. A surface generation algorithm is presented for this newly developed process. The model fully describes the motion and the 3D geometry of the cutting tool including its rake face, flank face, and the cutting edge, since all these tool features influence the topography of the generated surface. Since the process takes place in the micro/meso-scale cutting regime, the model includes the minimum chip thickness and elastic recovery effects. The experimental results are shown to validate the simulation model. The simulation model is used to characterize the influences of the process parameters on the texture patterns. The effects of the tool geometry on the process, including the cutting edge radius, are also analyzed.     

Recent advances in bismuth-based superconductors

Significant progress has been made in the development of high-critical-temperature (high-T_c) mono- and multifilament bismuth-based superconductors by the powder-in-tube (PIT) technique. High critical current density (J_c) has been achieved in both short- and long-length monofilament conductors. J_cs up to 1.2 × 10⁴ A/cm² were achieved in an 850 m long multifilament conductor. Pancake-shaped coils and test magnets, fabricated from long conductors, were characterized at various temperatures and applied magnetic fields. One such magnet containing 480 m of high-T_c tape generated a record-high field of 2.6 T at 4.2 K. Multifilament conductors appear to possess better mechanical properties and retain a higher percentage of their initial critical current under strain than monocore conductors, which is important for practical considerations. PIT processing of superconducting tapes with Ag-Al₂O₃ as the sheath material is perhaps another route to improve mechanical properties.