MB15超塑性镁合金扩散连接试验

根据原子扩散理论对MBl5超塑性镁合金进行了扩散连接工艺研究。扩散连接试验前采用三种不同方法去除MBl5镁合金表面的氧化膜，从中选出最佳方法。在Gleeble-1500型热／力模拟试验机上，对超塑性MBl5镁合金进行了在不同连接工艺条件下的扩散连接，在电子万能试验机上对扩散连接接头进行了剪切强度试验，从而获得了MBl5超塑性镁合金的最佳扩散连接工艺参数。利用金相显微镜、扫描电镜(SEM)，对扩散连接接头微观组织进行分析，得出了MBl5超塑性镁合金主要是通过原子扩散和晶粒长大造成的原始焊接表面晶界的移动，促使接头表面原子充分扩散，形成牢固的连接。     

摆动辗压成形件高度尺寸精度分析

扼要介绍了摆动辗压成形过程的工作原理及摆头运动轨迹；详细分析了摆头运动倾有（即摆角）的大小与摆头锥角不匹配和摆辗中心的偏移对摆动辗压成形件高度尺寸精度的影响，探讨了国内个摆辗机的合理应用范围，指出只有摆角较小的摆辗机才宜于净形与近似净形加工摆动辗压成形件。     

粉末冶金法制备SiC晶须增强MB15镁基复合材料

采用粉末冶金法制备了SiC晶须增强镁基复合材料(SiCW／MB15)试样。通过检测基体显微硬度探讨了SiCW对镁合金时效规律的影响，并借助扫描电镜(SEM)、透射电镜(TEM)和拉伸试验，研究了混粉方式对复合材料室温力学性能、SiCW分布及显微结构的影响。结果表明，MB15及其复合材料的时效硬化曲线上均存在双峰现象；SiCW的加入既提高了MB5的硬度，又加快了其时效速度：混粉方式对晶须分布及SiCW／MB15复合材料的室温力学性能影响很大。     

板坯连铸结晶器振动框架的改造

为确保某板坯连铸机的蒸汽管路改造项目顺利进行,技术人员决定对该铸机结晶器的振动框架进行局部改造,振动框架内设置有大量管路与支撑筋,且结构本身是由板材与管材进行焊接拼装后的一个复杂结构承受振动框架以及足辊载荷。针对预定的改造方案,通过理论分析、现场调研以及技术交流,对改造方案进行三维有限元综合应力分析,为振动框架结构改造提供充分的理论判据,以确保连铸机安全生产。     

微波水热法合成花状纳米ZnO及其光催化活性(英文)

使用氯化锌和精氨酸作为反应物,通过简单的微波水热技术制备花状纳米氧化锌。利用X射线衍射(XRD)和扫描电镜(SEM)对所合成的纳米氧化锌进行晶体结构和形貌的表征。通过拉曼光谱和光致发光(PL)光谱对纳米氧化锌的光学性能进行研究,证实了合成物为高结晶度的纳米氧化锌。在紫外光辐射下,合成的ZnO光催化降解亚甲基蓝(MB)有较好的效果,紫外光催化2h后亚甲基蓝的降解率达到95.60%。ZnO光催化降解亚甲基蓝可以描叙为一级动力学反应,降解速率常数在1.0675～1.6275h-1的范围中,这与所合成的ZnO形貌有关。     

Electroless cobalt deposition from a glycinate solution using morpholine borane as a reducing agent

Electroless cobalt films were deposited from a neutral pH glycinate solution without additives using morpholine borane (MB) as a reducing agent. The rate of deposition rises with increase in concentration of solution components (Co ions, MB and glycine), and pH. The efficiency of cobalt discharge increases when the deposition is performed from the Co(II) complex with glycine. XPS data indicate that boron and oxygen are incorporated into the cobalt films. Two forms of boron (elemental and its oxide) were detected in the electrolessly deposited cobalt films.     

磁致伸缩微机械悬臂梁的振动特性研究

研究了磁致伸缩薄膜和非磁衬底构成的微纳悬臂梁的振动问题,根据经典弹性理论构造出其弯曲振动方程并将其与Landau-Lifshitz方程联立得到体系的动力学方程组,并得到方程组的普遍解。在此基础上考虑具体磁性薄膜结构研究了体系的铁磁共振性、弯曲振动模式的激发和在铁磁共振背景下产生的机械共振等问题,为新型微机-电器件的设计提供一些可行的途径。     

结晶器非正弦振动参数的构建及取值限度

提出了一种用偏斜率表示的非正弦振动波形,并且构建了非正弦振动的振幅、振频、波形偏斜率以及拉坯速度所必需满足的工艺参数计算公式,给出了工艺参数取值限度,为结晶器非正弦振动先进技术的应用提供了必需的理论基础.     

Isothermal coarsening of primary particles during rheocasting

The isothermal coarsening behavior of primary solid particles in A356 aluminum alloy semi-solid slurry produced by angular oscillation (AO) technique was investigated. The comparison between the calculation and experimental results shows good quantitative agreement with Lifshitz-Slyozov-Wagner theory. The results show that the variation in shape factor and solid fraction is not significant, the average particle size increases with increasing holding time at the expense of the particle density. Ostwald repining is most likely the predominant growth mechanism in the AO-treated semi-solid slurry during rheocasting. The differences of coarsening occurred in rheocasting and partial re-melting process were also discussed.     

Visible light-induced photocatalytic activity of Ag-containing TiO2/carbon nanofibers composites

TiO₂/carbon nanofiber (CNF) composites containing Ag nanoparticles (Ag–TiO₂/CNF) were prepared and their photocatalytic degradation ability upon visible light irradiation assessed. The reduction of methylene blue (MB) adsorption in an aqueous solution by the photocatalysts occurred due to the combined effects of MB adsorption in the pores of CNFs and decomposition by the photocatalysts throughout the process. The Ag–TiO₂/CNF photocatalyst degraded MB 17 times faster than the TiO₂/CNF composites with no Ag nanoparticles after 3 h under visible light illuminations.     

等离子弧-MIG焊丝振荡式复合焊接工艺

针对现有的等离子弧-MIG复合焊接过程中的双弧排斥问题,基于MIG焊丝位移规律性改变提出了一种新型的MIG焊丝振荡与等离子弧共熔池的复合焊接工艺.通过调节MIG焊丝电机转速(振荡频率)和振荡振幅进行了焊接工艺试验.结果表明,随着电机转速(振荡频率0～41 Hz)的增加,等离子弧与MIG电弧排斥减弱,耦合趋势增大.尤其是电机转速为2 000 r/min(振荡频率33 Hz)时,共熔池复合焊接效果较好;MIG焊炬振荡振幅为1 mm时,电弧形状最为稳定,但振荡频率和振荡振幅过大均不利于焊接过程稳定性;MIG焊炬振荡提高了熔滴过渡频率,使焊丝尖部呈现小熔滴过渡,减小了焊接飞溅.对接试验力学性能测试表明,抗拉强度、抗弯强度均随振荡频率的提高呈现先增大后减小趋势,分析认为MIG焊炬振荡具有一定搅拌熔池的作用,有效提高了焊接接头的力学性能.     

Pd-AgNbO3光催化剂的合成及其光催化活性研究

研究了温度为150℃,电流密度为5.0×103A/cm2的条件下电迁移对Ni/Sn/Ni-P(Au)线性接头中界面反应的影响.结果表明电流方向对Ni-P层的消耗起着决定作用.当Ni-P层为阴极时,电迁移加速了Ni-P层的消耗,即随着电迁移时间的延长,Ni-P层的消耗显著增加;电迁移100 h后Ni-P层消耗了5.88 μm,电迁移200 h后Ni-P层消耗了13.46μm.在Sn/Ni-P的界面上形成了一层Ni2SnP化合物而没有观察到Ni3Sn4化合物的存在,多孔状的Ni3P层位于Ni2SnP化合物与Ni-P层之间.当Ni-P层为阳极时,在电迁移过程中并没有发现Ni-P层的明显消耗,在Sn/Ni-P的界面处生成层状的Ni3Sn4化合物,其厚度随着电迁移时间的延长而缓慢增加,电迁移200 h后Ni3Sn4层的厚度达到1.81 μm.     

人工心脏泵用磁轴承系统的起浮特性研究

基于新一代磁悬浮人工心脏泵,探讨不同流体、不同起浮方式下磁轴承受力与运动情况,并研究了起浮时电磁执行器的响应特性。在权衡考虑电压物理限制及起浮性能的基础上,确定了各介质下较佳的控制参数改善功耗与起浮性能,并通过实验验证其合理性。     

Fundamental study of narrow-gap welding with oscillation laser beam

Laser welding with oscillation laser beams enables control of the heat input distribution. In this study, we attempted to develop a narrow-gap welding process with oscillation laser welding. This process is expected to prevent a lack of fusion because the entire bottom to the groove can be melted by the oscillation laser. As the first step of the study, bead-on-plate welding experiments with an oscillation laser beam were performed to investigate the relationship between the welding conditions and welding results. The experiments revealed that the oscillation conditions strongly affect the welding penetration shape. It was clarified that the wire melting phenomena in oscillation laser welding differed from those of straight (non-oscillation) laser welding. Additionally, narrow-gap laser welding experiments were performed to investigate the relationship between the oscillation conditions and gap width. The results confirmed the effectiveness of oscillation laser welding for narrow-gap welding.     

Sorption of Methylene Blue on Polystyrene/Bentonite Film Composites

The method of mechanochemical dispersion of bentonite in a polystyrene solution was used to modify the polymer and obtain film materials with improved sorption characteristics with respect to the methylene blue (MB) thiazine dye. It is found that the kinetics of the dye sorption are described by the pseudo-first-order equation. The sorption equilibrium is described by the Langmuir isotherm. The values of the limiting sorption capacity and specific surface area of the composite are determined. It is shown that the sorption efficiency of the dye on the PS/bentonite composite increases tenfold as compared with the non-modified sorbent; the extraction rate increases from 10 to 90%. The method of IR spectroscopy is used to show that MB sorption on polystyrene and the PS/bentonite composite is accompanied by electrostatic and donor–acceptor interactions of the reaction sites of MB with the hydroxyl–containing groups of the composite.     

搅拌摩擦加工MB8镁合金的组织与力学性能分析

研究了MB8(Mg-1.5Mn-0.3Ce)合金在FSP不同工艺参数条件下的组织和力学性能。试验在加工速度恒定为60mm/min,旋转速度分别为800、1200和1800r/min的条件下进行。结果表明,经FSP加工,原始轧制态MB8镁合金的粗大不均匀组织受到搅拌头的剧烈搅拌作用而破碎、分散,并发生动态再结晶,获得细小、均匀的等轴晶粒。在转速为800r/min时,搅拌区的平均晶粒尺寸由原始轧制态的16.5μm细化至6μm。常温拉伸试验结果表明,MB8镁合金经FSP加工后抗拉强度大幅下降,但伸长率显著增大,在1200r/min时伸长率达57%,是原始材料伸长率的160%。此外,采用SEM观察拉伸试样断口,分析了MB8镁合金的断裂机制。     

VQ2(Q=H, D, T)热力学氢同位素效应的理论研究

基于量子力学第一性原理,采用赝势平面波函数与密度泛函结合的方法,计算并研究V、VH2、VD2、VT2体系的晶格动力学特征及热力学函数,采用热力学方法分析钒吸氢生成VQ2(Q=H,D,T)的热力学同位素效应。晶格动力学性质研究表明,VQ2的热力学同位素效应主要是氢同位素在钒晶格中的振动频率不同导致的。VQ2生成反应在10～1000K的温度范围内标准吉布斯自由能变由-50kJ·mol-1近似线性上升至140kJ·mol-1。平衡压力与温度关系表明,在高于常温的条件下,平衡压力随温度急剧升高;钒吸附氢同位素生成二氢化钒在整个温度范围内均表现为负同位素效应。     

Pendant droplet oscillation during GMAW

Abstract

This paper deals with pendant droplet oscillation in pulsed current gas metal arc welding (GMAW). Using a constant current power source, bead on plate welds were made on mild steel plates. The frequency of the pendant droplet oscillation was monitored visually (using a high speed video camera) and electronically (by analysis of the voltage signals). The results obtained are compared with the results predicted by a model based on a mass spring system. It was found that the oscillation frequency of small droplets revealed by both monitoring techniques matches that predicted by the model. For larger droplets, the oscillation frequency measured by voltage signal analysis tends to be higher than that revealed by video analysis and that predicted by the model. This implies that during droplet oscillation in (GMAW) the arc behaviour may change and as a result the arc voltage is not any more proportionally related to the arc length.     

超声冲击改善MB8镁合金焊接接头超高周疲劳性能机理探究

通过超声疲劳试验探究超声冲击对MB8镁合金焊接接头超高周疲劳性能的影响。同时,从应力集中、残余应力、晶粒细化等三个因素来探究超声冲击改善MB8镁合金焊接接头超高周疲劳性能的机理。结果表明：在1.0×108寿命下,焊态试样疲劳强度为31.62MPa,冲击态试样疲劳强度为39.81MPa,冲击态试样疲劳强度相较于焊态提高了26%。这说明超声冲击可以明显提高MB8镁合金焊接接头超高周疲劳性能。焊态试样焊趾处应力集中系数Kt1=1.95,冲击态试样焊趾处应力集中系数Kt2=1.67,应力集中系数降低了14.4%,所以超声冲击可以降低焊趾处的应力集中程度。超声冲击后试样焊趾处的应力由残余拉应力转变成残余压应力。超声冲击细化焊趾表面晶粒改善MB8镁合金焊接接头的超高周疲劳性能。     

基于非共振固有振荡的微细电火花加工脉冲电源的研究

实现微细电火花电源微能放电并提高脉冲电源的频率一直是理想之选,但由于受到电源电阻、电容、电感自带杂散电容和杂散电感的影响,使提高脉冲电源频率遇到了瓶颈。通过对电火花放电电路和联接线路的分析,提出了依靠电火花机床和连接线路的固有振荡制作微细电火花脉冲电源。通过理论计算和电路仿真,放电电路的振荡周期可控制在1.176 ns,脉宽低于650 ps,这为皮秒级电火花脉冲电源的制作和微细电火花纳米级加工提供了理论支持。