Effect of partition coefficient on microsegregation during solidification of aluminium alloys

In the modeling of microsegregation, the partition coefficient is usually calculated using data from the equilibrium phase diagrams. The aim of this study was to experimentally and theoretically analyze the partition coefficient in binary aluminum-copper alloys. The samples were analyzed by differential thermal analysis (DTA), which were melted and quenched from different temperatures during solidification. The mass fraction and composition of phases were measured by image processing and scanning electron microscopy (SEM) equipped with an energy-dispersive X-ray spectroscopy (EDS) unit. These data were used to calculate as the experimental partition coefficients with four different methods. The experimental and equilibrium partition coefficients were used to model the concentration profile in the primary phase. The modeling results show that the profiles calculated by the experimental partition coefficients are more consistent with the experimental profiles, compared to those calculated using the equilibrium partition coefficients.     

Improvements in the microstructure and fatigue behavior of pure copper using equal channel angular extrusion

In this study, annealed pure copper was extruded using equal channel angular extrusion (ECAE) for a maximum of eight passes. The fatigue resistance of extruded specimens was evaluated for different passes and applied stresses using fatigue tests, fractography, and metallography. The mechanical properties of the extruded material were obtained at a tensile test velocity of 0.5 mm/min. It was found that the maximum increase in strength occurred after the 2nd pass. The total increase in ultimate strength after eight passes was 94%. The results of fatigue tests indicated that a significant improvement in fatigue life occurred after the 2nd pass. In subsequent passes, the fatigue life continued to improve but at a considerably lower rate. The improved fatigue life was dependent on the number of passes and applied stresses. For low stresses (or high-cycle fatigue), a maximum increase in fatigue resistance of approximately 500% was observed for the extruded material after eight passes, whereas a maximum fatigue resistance of 5000% was obtained for high-applied stresses (or low-cycle fatigue). Optical microscopic examinations revealed grain refinements in the range of 32 to 4 μm. A maximum increase in impact energy absorption of 100% was achieved after eight passes. Consistent results were obtained from fractography and metallography examinations of the extruded material during fatigue tests.     

Effective Palladium（Ⅱ） Catalyst for Oxypalladation of Alkene

A variety of Pd（ Ⅱ ）-catalyzed oxidative transformations ot allcenes with oxygen nucleophiles are catalyzed by PdXa（X=OAc, Cl, etc） with CuX.（ n = 1 or 2） under O2. In the so-called Wacker catalyst of such,Pd（OAe）2 is less reactive compared to PdCl2. In an attempt to increase the reactivity of Pd（OAe）2, we have now found that tuning of Cu site with catechol gives an intriguing reactivity to Pd（OAc）2, which is unprecedented in the chemistry of palladium.     

Microstructural characterization of Cu/Al composites and effect of cooling rate at the Cu/Al interfacial region

Cu/Al composites are of vital importance in industrial applications because of their numerous advantages. The influence of bonding temperature and cooling rate on the microstructure and morphology of Cu/Al composites was investigated in this paper. The interfacial morphology and constituent phases at the Cu/Al interface were analyzed by optical microscopy and field-emission scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy. The results indicate that effective Cu-Al bonding requires a higher bonding temperature to facilitate interdiffusion between the two metals. The microstructural characteristics are associated with various bonding temperatures, which impact the driving force of interdiffusion. It is observed that cooling rate exerts a significant influence on the morphology and amount of the intermetallic compounds at the interfacial region. Meanwhile, microhardness measurements show that hardness varies with the bonding temperature and rate of cooling.     

排针-辊式放电电流分布特性

为提高高压静电分选效率,须对排针型电极放电特性进行探究。采用自制排针-辊式高压放电装置,通过改变电晕电压、排针与辊面间距、排针与辊面夹角及排针数,测试了各因素对放电电流的影响,分析了1/4辊面电流的分布特性。在MATLAB平台上,利用电磁场理论,实现了对排针型电极的空间电场分布仿真模拟。实验结果表明:1其他条件一定,单排针与辊面间距越小,放电电流越大。排针-辊间距为80、100、120 mm时,辊面分电流极大值分别为6.78、5.3、3.34μA。2采用双排针结构,有效放电区域增大,辊面分电流有两个极大值,电晕电压23 k V时,双排针和单排针总电流相等,24~33 k V时,双排针总电流大于单排针。3采用三排针结构,辊面分电流有三个极大值。两侧两排针对中间一排针有排斥作用,三排针与水平方向夹角分别为30°、45°、60°和15°、45°、75°时,两侧电流极大值约为中间电流极大值的3倍和4倍。实验结果与仿真模拟一致,印证了辊面电流分布特性,为排针-辊式高压静电分选机优化设计提供了依据。     

层压板小质量物体冲击下接触力测量与损伤响应

为了发展复合材料层压板在小质量物体冲击下损伤性能的测试技术,研发了小质量冲击试验机,可模拟自由状态小质量物体产生的冲击,冲击能量可调节,冲击点挠度可测量。通过冲击头加速度和冲击点挠度测量接触力,结果显示,加速度传感器谐振会明显干扰测量信号。采用滤波技术后,冲击头的加速度响应可以有效地测量冲击接触力。用冲击点挠度计算接触力,结果也与试验结果吻合。对层压板进行多个能量下的冲击试验,发现产生明显分层损伤时,由加速度传感器测得的接触力在特定值处明显下降,随后可能继续升高;由冲击点挠度得到的接触力斜率发生变化,这可作为小质量冲击分层阈值力的识别方法。     

基于三维应变渐进损伤准则的复合材料层合板大开孔压缩损伤研究

针对复合材料层合板大开孔压缩,将二维应变渐进损伤准则修正为三维应变渐进准则,使其能够模拟层合板的分层损伤,建立了复合材料层合板大开孔压缩损伤分析模型。利用UMAT子程序将基于三维应变渐进损伤准则引入到分析模型中预测纤维、基体及分层等失效演化过程;并对大开孔复合材料层合板进行试验研究。试验结果表明所建立的基于三维应变渐进损伤准则的层合板大开孔分析模型能很好地模拟大开口复合材料层合板压缩过程中的损伤起始、损伤扩展及破坏模式;并最终预测复合材料层合板大开孔的破坏强度。     

贵州赫章可乐铜矿化带物质成分特征研究

通过对赫章可乐铜矿化带进行野外地质调查、赋矿围岩及铜矿石采样、化学成分分析、矿物成分分析、X衍射分析等,开展了铜矿石的物质组成研究。矿石含铜品位为1.67%-3.88%.综合分析常量元素和XRD测试结果,得出赋矿围岩-飞仙关组砂岩为海相碎屑沉积形成。蚀变岩型铜矿石中黏土矿物含量高,是导致蚀变岩型矿石中铜含量及稀土元素富集增高的原因。     

铜粉粒径对烧结式热管传热性能的影响

为了进一步优化烧结式吸液芯的结构,提高热管的热传导性能与效率,研究了外径分别为5、6、8mm和吸液芯厚度为0.5～0.6 mm的热管的传热特性,结果发现:铜粉粒径分布比较集中时,如果其平均粒径增大,吸液芯的孔隙率和热管的极限传输功率(MHTP)均会增大,热管的冷凝端温差及总热阻则略微减小;不同粒径范围的铜粉混合时,热管的冷凝端温差及总热阻在不同外径的热管内的变化规律不同;含70%小粒径铜粉的烧结式热管的MHTP最小,且粒径越小MHTP越低;含70%大粒径铜粉的烧结式热管的MHTP仅次于全部为大粒径铜粉的烧结式热管的MHTP;铜粉粒径的范围越小,热管的性能越优,平均粒径为(165±15)μm的铜粉适合于制作薄壁烧结式热管.     

Copper nanoclusters: Synthesis,characterization and properties

Metal nanoclusters with a core size smaller than 2 nm have attracted much attention because of their unique physical and chemical properties.Among the studied metal nanoclusters,gold and silver have been studied extensively by size-controlled synthesis, structural characterization and properties investigations.Recently,considerable research effort has been devoted to the investiga- tion of copper nanoclusters.In this review,we highlight recent progress in the study of copper nanoclusters in terms of synthesis methods,characterization techniques and their novel optical and catalytic properties.