锂离子蓄电池在DFH-4平台上的应用研究

在东方红四号(DFH-4)平台上应用锂离子电池,将大大减少供配电分系统的重量和体积,提高卫星的承载能力,增加经济效益。文章通过分析锂离子电池在空间应用的特点,结合DFH-4平台能力提升的迫切需求,提出了锂离子电池替代氢镍蓄电池的可行性方案,并对应用锂离子电池带来的接口变化以及适应性进行了深入的剖析,其分析结果可为卫星型号研制提供参考。     

助烧剂对无压烧结Si3N4力学性能的影响

研究了三种助烧剂MgO、Al2O3+AlN和Y2O3+AlN对1800℃×3h工艺下无压烧结Si3N4力学性能的影响情况。发现材料力学性能主要决定于助烧剂的种类,其次取决于含量。其Y2O3+AlN虽使最终生成的β-Si3N4长径比较小,线度尺寸最短,但最利于致密化,因而使材料力学性能最佳,添加量(质量分数)为12%Y2O3+6%AlN时,陶瓷的抗弯强度、断裂韧性和维氏硬度分别达到431.6MPa、5.10MPa*m1/2和14.52GPa。     

基于GPS信号的电离层S4指数计算方法研究

电波穿越电离层时,由于受到电离层不均匀结构的影响,电波的幅度、相位、时延等有时会发生快速抖动,这就是所谓的电磁波电离层闪烁现象.电离层闪烁会影响卫星通信系统的质量和导航系统的精度.本文分析了GPS信号研究电离层闪烁的基本原理,讨论了电离层闪烁监测中S4指数的计算方法及其修正方法.通过数据模拟,评估了原始S4指数计算方法及其修正方法的性能特点.针对原始S4指数计算方法及修正方法的不足,提出了一种新的修正方法,并采用实测GPS数据对上述方法进行了检验.结果表明,上述方法是有效的和可靠的.      

固溶时效对热等静压制备的TC4钛合金性能的影响

采用热等静压工艺对Ti一6A1—4V(简称TC4)雾化预合金粉的粉末冶金技术进行了研究,采用不同的固溶温度、时效温度以及时效时间,研究了热处理工艺对TC4钛合金组织和性能的影响。结果表明,采用预合金粉工艺制备的Ti一6A1—4V粉末钛合金材料力学性能良好,于965℃固溶并采用水冷,然后在470℃时效,试样具有优良的力学性能,适宜冷加工生产。     

基于Mn3+浓度和形貌控制的高性能LiNi0.5Mn1.5O4正极材料

为了改善高电压镍锰酸锂(LiNi_(0.5)Mn_(1.5)O_4)材料的电化学性能,提出利用退火热处理过程调控Mn~(3+)含量和材料形貌来制备LiNi_(0.5)Mn_(1.5)O_4正极材料。LiNi_(0.5)Mn_(1.5)O_4材料的电性能是材料结构、形貌等多因素影响的结果。退火热处理有助于Mn~(3+)氧化成Mn~(4+),实现Mn~(3+)含量调控。退火后材料的空间结构由Fd3m向P4_332转变,且具有微米级多面体形貌,有效提高了循环稳定性和放电平台。研究表明:700℃退火保温15 h合成的材料在20 C下具有118 mAh·g~(-1)放电比容量,循环100次容量保持率提高到92.8%。因此,通过优化Mn~(3+)含量、控制材料形貌可以实现高性能LiNi_(0.5)Mn_(1.5)O_4材料制备。     

基于数字图像相关的预腐蚀2024-T4铝合金疲劳开裂实验研究

通过三维数字图像相关(3D-DIC)方法研究预腐蚀2024-T4铝合金在三种不同最大应力水平和应力比下的疲劳开裂行为。通过应变场演化直观地显示裂纹萌生和扩展的时空特征,并通过扫描电镜观测关键损伤区域的断裂微观形貌。结果表明:试样边缘的局部腐蚀促进了疲劳裂纹萌生,影响了裂纹的形核位置,并引起材料氢脆现象;疲劳裂纹扩展方向与加载方向呈60°~68°角,表明疲劳裂纹扩展可以用KⅠ/KⅡ混合模式来描述;预腐蚀铝合金疲劳失效存在单裂纹断裂、多裂纹联合、多裂纹竞争和多裂纹平行扩展4种典型的失效模式。     

Joining of SiO2 ceramic and TC4 alloy by nanoparticles modified brazing filler metal

Nano-Al₂O₃ particles modified AgCuNi filler was adopted to braze the SiO₂ ceramic and TC4. The effects of filler size as well as the brazing temperature on the interfacial microstructure and mechanical property of the joints were investigated. Nanoscale filler reduced the phases dimension and promoted the homogeneous distribution of microstructure, obtaining a higher joint strength when compared to microscale filler. The increase of brazing temperature made the accelerating dissolution and diffusion of Ti, which promoted the increase of thickness of Ti₄O₇ + TiSi₂ layer adjacent to SiO₂ ceramic and diffusion layer zone nearby TC4 alloy. The hypoeutectic structure was produced in the brazing seam due to the high Ti content. The maximum shear strength of ∼40 MPa was obtained at 950 °C for 10 min.     

Investigation on surface integrity of electron beam melted Ti-6Al-4 V by precision grinding and electropolishing

Electron beam melting (EBM), as an excellent Additive Manufacturing (AM) technology, enables the printing of Ti-6Al-4 V alloy for a wide range of applications such as aerospace and biomechanical industries. It improves functionality and integrity of components and negates complexities in assembly processes. However, due to the poor surface and sub-surface integrity represented by the rough surface finish and low dimensional accuracy, achieving a favorable surface condition is quite challenging. Therefore, post processing becomes essential for these electron beam melted (EBM-ed) Ti-6Al-4 V alloys. Being the most common technique to improve such parts, milling of Ti-6Al-4 V alloy is very challenging and resulting tool wear issues, due to its unique material properties. Thus, this paper presents a comprehensive study on the surface integrity of EBM-ed Ti-6Al-4 V parts processed by precision grinding and electropolishing, aiming to qualitatively and quantitatively clarify the interrelation between process parameters and processed surface quality. The surface and subsurface characteristics such as profile accuracy, surface roughness, microstructure, defective layer and residual stress before and after post processing were compared and evaluated. The results show that by precision grinding, the profile accuracy was improved from over 300 µm PV to 7 µm PV, while surface roughness (R_a) was reduced from 30 µm to about 2 µm. The layer with partially melt particles was removed, but introduced a deformed subsurface layer with more residual stress. Then by applying electropolishing, the residual stress was released and the deformed layer was removed. In addition, R_a was further reduced to 0.65 µm. The research can serve as a reference for the integration of post machining processes with AM.     

一种基于自动相关信息四维运算的飞行间隔算法设计与实现

本文介绍了无人机（UAV：UnmannedAerialVehicle）航路规划的分层模式，提出了实时航路规划中四维接近算法，对UAV与静态和动态目标的接近距离进行了分析计算，为航路规划及时提供飞行过程中的危险接近信息，并进行了数字仿真。数字仿真表明：该算法具有较高的运算速度和较好预测精度，可快速提供UAV与周围静态和动...     

不同热处理工艺下激光增材制造TC4钛合金组织与性能研究进展

由于激光增材制造(Laser Additive Manufacturing,LAM)TC4钛合金加工成形过程的特殊性,导致该合金在力学性能上存在明显的各向异性,同时韧性、疲劳性能不能很好地满足使用要求。从材料组织与力学性能之间的关系出发,介绍了不同热处理工艺对激光增材制造TC4钛合金组织与力学性能的影响,指出了当前激光增材制造TC4钛合金热处理研究中存在的问题,并为后续激光增材制造TC4钛合金的热处理研究提供思路与方向。