激光立体成形Rene88DT镍基高温合金沉积态组织研究

目的基于激光立体成形(Laser Solid Forming, LSF)过程中所存在的近快速凝固特性,以Rene88DT合金为研究对象,考察激光立体成形Rene88DT沉积态微观组织特征和相形成规律。方法通过LSF技术制备Rene88DT镍基高温合金单道沉积试样,采用光学显微镜(OM)和扫描电子显微镜(SEM)对组织进行观察,并用能谱仪(EDS)对试样中的析出相及微区成分进行分析。结果激光立体成形Rene88DT合金沉积态组织主要由沿趋于平行沉积方向生长的γ柱状晶组成,由于枝晶偏析的存在,以富Nb为主的块状MC碳化物以及板条状η(Ni_3Ti)相于枝晶间区域析出。随着沉积高度的增加,一次枝晶臂间距有所增大,二次枝晶臂逐渐发达,同时,γ'相体积分数和尺寸逐渐减小,沉积层的硬度相应降低。结论尽管激光立体成形熔池凝固已属于近快速凝固范围,熔池凝固过程中,溶质原子同样易于在晶界处形成偏聚,导致晶界弱化,在成形热应力作用下易形成沿晶裂纹。     

A2017合金半固态压缩的变形机制和成形性能

利用Gleeble-1500热学-力学模拟机,对A2017半固态合金进行半固态压缩变形实验,分析了应力-应变曲线和组织变化,研究了压缩变形机制及成形性能结果表明,用单辊搅拌冷却(SCR)技术制备的A2017半固态合金的组织为细小均匀的非枝晶等轴晶,二次加热后可转化为均匀的球形晶和共晶液相组成的半固态组织;A2017合金半固态压缩变形的塑性好、变形抗力低;随着变形温度的升高或者变形速率的降低,变形的抗力降低.在稳定的流动变形阶段,A2017合金的半固态变形机制主要由液相流动和固相颗粒的转动与滑动组成,触变性能稳定,最大半固态加工变形范围为60%左右.     

Continuous synthesis of carbon nanotubes using a metal-free catalyst by CVD

This study demonstrates the first example of the use of a metal-free catalyst for the continuous synthesis of carbon nanotubes (CNTs) by chemical vapor deposition (CVD). In this paper silica nanoparticles produced from the thermal decomposition of PSS-(2-(trans-3,4-Cyclohexanediol)ethyl)-Heptaisobutyl substituted (POSS) were used as catalyst and ethanol was served as both the solvent and the carbon source for nanotube growth. The POSS/ethanol solution was nebulized by an ultrasonic beam. The tiny mists were continuously introduced into the CVD reactor for the growth of CNTs. The morphology and structure of the CNTs have been investigated by scanning electron microscopy, high-resolution transmission electron microscopy, and Raman spectroscopy. The obtained CNTs have a multi-walled structure with diameters mainly in the size range from 13 to 16 nm. Detailed investigations on the growth conditions indicate that the growth temperature and POSS concentration are important for achieving high-quality nanotubes, and that the existing of small amount of water in ethanol is effective to remove amorphous carbon species during the formation of CNTs. The mass production of CNTs without any metal contaminant will provide a chance for investing and understanding the intrinsic properties of CNTs and applications particularly in nanoelectronics and biomedicines.     

High capacity and good cycling stability of multi-walled carbon nanotube/SnO2 core-shell structures as anode materials of lithium-ion batteries

The multi-walled carbon nanotube/SnO₂ core-shell structures were fabricated by a wet chemical route. The electrochemical performance of the core-shell structures as anode materials of lithium-ion batteries was investigated. The initial discharge capacity and reversible capacity are up to 1472.7 and 1020.5 mAh g⁻¹, respectively. Moreover, the reversible capacity still remains above 720 mAh g⁻¹ over 35 cycles, and the capacity fading is only 0.8% per cycle. Such high capacities and good cyclability are attributed to SnO₂ network structures, excellent mechanical property and good electrical conductivity of the multi-walled carbon nanotubes.     

锌黄环氧酯底漆的电化学阻抗谱特性

利用电化学阻抗（EIS）技术对铝合金结构件上的锌黄环氧酯底漆进行了研究，提出了相关有效电路。结果表明，浸泡中期，随着浸泡时间的延长，涂膜电阻有一定程度的增加。     

Transformation of c-oriented nanowall network to a flat morphology in GaN films on c-plane sapphire

The work significantly optimizes growth parameters for nanostructured and flat GaN film in the 480–830 °C temperature range. The growth of ordered, high quality GaN nanowall hexagonal honeycomb like network on c-plane sapphire under nitrogen rich (N/Ga ratio of 100) conditions at temperatures below 700 °C is demonstrated. The walls are c-oriented wurtzite structures 200 nm wide at base and taper to 10 nm at apex, manifesting electron confinement effects to tune optoelectronic properties. For substrate temperatures above 700 °C the nanowalls thicken to a flat morphology with a dislocation density of 10¹⁰/cm². The role of misfit dislocations in the GaN overlayer evolution is discussed in terms of growth kinetics being influenced by adatom diffusion, interactions and bonding at different temperatures. The GaN films are characterized by reflection high energy electron diffraction (RHEED), field emission scanning electron (FESEM), high resolution X-ray diffraction (HRXRD) and cathodoluminescence (CL).     

铝熔体除氢

对铝熔体除氢的基础理论和各种除氢技术的发展现状进行了相应的综述,在综述过程中对我们近来的一些工作也给予了相应的总结.并指出了现有技术的不足继而提出了铝熔体除氢的发展趋势.     

铝合金熔剂的研究

本文介绍了熔剂在铝合金熔炼过程中的作用,熔剂的分类和要求,常用熔剂的组成,适用范围及使用方法等。     

球磨La2Mg17与Ni复合合金的电化学贮氢性能研究

利用机械合金化法制备了La2Mg17+200%(质量分数)Ni复合储氢合金,并对不同球磨时间时合金的微观结构和电化学性能进行研究。结果发现,在球磨过程中Ni粉诱导了La-Mg-Ni非晶/纳米晶结构的形成。XRD和HRTEM结果共同表征了球磨80h时,合金中有Ni金属的存在,且XRD衍射峰强度较低,宽化严重,SAD为宽化的多环,表明形成非晶结构。电化学及其反应动力学测试结果发现,不同球磨时间的电化学反应的动力学控制机理是不同的。球磨60和80h后合金中不仅存在La-Mg-Ni非晶相,同时也有催化剂金属Ni,使合金的表面电荷转移反应电阻较小,氢在合金体相内的扩散系数D和极限电流密度I L均最大,最终导致80h的放电容量为最大值948.3mAh/g。然而,当合金的球磨时间为100和120h时,合金粉化到纳米级,100h的电荷转移反应电阻R ct最大,合金表面电化学反应缓慢,且合金体相内的极限电流密度和氢扩散系数均最小,属于合金电解液表面间的电荷转移和氢向体相内扩散联合控制的过程,必然导致其放电比容量较小。     

锌锡锑三元合金纳米微粒的制备及贮锂性能

用化学还原-共沉淀法合成了锂离子电池纳米锌锡锑三元合金负极材料ZnSnSb2。通过XRD、TEM和电化学测试对材料进行了表征。所制备的材料粒径大小分布在5-15nm之间。在充放电电压为1.5V到0V范围内,初始可逆充电容量为708mAh/g,经过20周的循环后,充电容量保持为82.1%。充放电电压范围为0.9V到0V时,初始可逆充电容量为329mAh/g,经过20次充放电循环后,可逆充电容量仍然保持在95.7%。由于材料中非活性物质Li3Sb的作用以及材料所具有的纳米结构,使其循环性能大大提高。