Effect of Al 2 O3 film on weld appearance of stationary electron beam welded aluminum

Aluminum specimens with and without chemically cleaning were welded by electron beam to investigate the effect of、Al ₂ O₃ film on weld appearance. The removal mechanism of Al ₂ O₃ film during vacuum electron beam welding of aluminum was analyzed and the effect of Al ₂ O₃ film on molten pool flow behavior and weld appearance was investigated. The results showed that the weld width of the specimen was enlarged by chemically cleaning. The solid Al ₂ O₃ film transformed into gaseous Al ₂ O via the reaction with liquid aluminum at the temperature higher than 1 350 K was the main reason for the removal of the film. The weld width was narrowed down by the oxide film due to the inhibition of outward flow driven by the surface tension gradient and the drag force between the Al ₂ O₃ film and liquid Al. The weld penetration was reduced in the initial stage and then enhanced in the metastable stage.     

基于确定压缩采样的矢量水听器阵列舰船目标方位估计

使用较少的硬件电路和计算量实现高分辨率的目标方位估计一直是海域防御系统具有挑战性的研究工作。本文将压缩感知理论应用于矢量水听器阵列,利用确定测量矩阵建立了确定压缩采样的矢量水听器阵列（deterministic compressive sampling vector hydrophone array,DCV）结构,并将其与改进的多重信号分类算法（modified multiple signal classification,MMUSIC）相结合,提出了确定压缩采样的矢量水听器阵列的MMUSIC（DCV-MMUSIC）算法。将该算法用于相关或非相关模拟舰船目标的方位估计,通过对算法的可行性、高分辨能力和改变测量次数、信噪比和快拍数等多种仿真,得出该算法可以在低信噪比和小快拍下对舰船目标进行方向估计,并且具有使用硬件电路少、计算量低和估计偏差小等优点。又将其用于实际商船目标的方位估计,得到了较好的方位估计性能。     

电子束定点焊接304不锈钢熔池流动行为数值模拟

基于电子束焊接过程的传热与受力物理过程分析,建立相应模型,对电子束定点焊接304不锈钢的温度场与流场进行数值模拟,研究电子束焊接熔池流动行为及焊缝成形规律.结果表明,电子束加热阶段,熔池上表面温度梯度达到106 K/m,熔池表面峰值温度高,在沸点温度附近波动,强烈的金属蒸汽反作用力成为熔池流动的主要作用力,促使熔池中心下凹并不断波动,熔池冷却凝固阶段,金属蒸汽反作用力下降,熔池金属表面张力梯度引起的Marangoni对流成为熔池金属流动主要驱动力,促使焊缝表面熔宽增大,熔池凝固后焊缝上表面宽度为1.9 mm,中心处宽度为1.6 mm,下表面宽度为1.8 mm.     

Relief of the residual stresses in Si3N4/Invar joints by multi-layered braze structure – Experiments and simulation

An Ag–Cu–Ti+TiNp/Cu/Ag–Cu three-layered filler was designed to braze Si₃N₄ ceramic and Invar alloy. The effect of the Cu-foil thickness on the microstructure and the mechanical properties of the brazed joints was investigated. Compared with single-layer Ag–Cu–Ti+TiNp filler, the formation of Fe₂Ti and Ni₃Ti compounds is widely inhibited by using multi-layered filler. The shear strength of the brazed joint is 47.9% higher than that of joints brazed with single Ag–Cu–Ti+TiNp filler when a 200 μm thick Cu interlayer is used. A simplified unit cell model was designed to obtain the physical properties of the TiNp reinforced filler. The model provides the elastic modulus and yield stress that satisfy the Hashin–Shtrikman bounds and N. Ramakrishnan׳s equations, respectively. In the three-layered brazing, the finite element (FE) model shows that system residual stresses decrease significantly by increasing the thickness of Cu foil in the multi-layered system.     

Microstructural evolution during the brazing of Al2O3 ceramic to kovar alloy by sputtering Ti/Mo films on the ceramic surface

Alumina (Al₂O₃) ceramics were metallized by magnetron sputtering Ti/Mo bilayer films on the surface with a subsequent high temperature sintering and were brazed to Kovar alloy (Fe-Ni-Co) using Ag-Cu eutectic alloy. The Ti/Mo metallization film and the brazing seam microstructures were investigated and the correlation between the Al₂O₃/Kovar joining strength and the microstructures of the brazing seam was discussed. The results show that the joining strength is related to the thickness of the Ti/Mo adhension layer which depends on the holding time during brazing. The mutual diffusion of the elements at the interface firstly increases the thickness of the adhension layer as the holding time increases and the Mo film acts as a barrier layer to block the diffusion of Ti atoms into the seam. The optimal brazing joining strength of 72.6±5.0 MPa could be achieved at a brazing temperature of 810 °C for 14 min However, if the holding time is further prolonged, Mo atoms will diffuse into the (Ni, Cu) solid solution, resulting in the diffusion of Ti atoms and the adhension layer becoming indistinguishable. Therefore, the intermetallic Ni₃Ti forms in the seam and the titanium oxide changes from TiO to Ti₂O₃ or Ti₃O₅, which leads to the joint strength decreasing.     

TiZrNiCu/Ti60润湿性及与TiBw-TC4钎焊研究

本文采用座滴法在真空下系统研究了硼含量对TiZrNiCu/Ti60润湿性的影响,且在940°C保温10分钟条件下实现了与的钎焊。通过SEM、XRD以及剪切实验研究了界面显微组织及剪切力学性能。添加B元素可以与Ti原位合成TiBw,从而细化界面的显微组织。当B含量为0.3 wt %时,TiBw-TC4 /TiZrNiCu-B/Ti60接头的最大剪切强度为177 MPa,比无B含量的接头强度高65%。然而,过量的B含量使TiZrNiCu-B在Ti60合金基体上产生大量的TiBw,导致润湿性恶化,在钎焊接头形成微孔和未焊合区域,从而使剪切强度下降。     

振动加速度对等离子增材制造Fe314合金应力变形和组织性能的影响

在等离子堆焊Fe314自熔性合金粉末增材制造过程中施加振动,利用盲孔法、扫描电子显微镜、拉伸试验等表征方法,对比分析了施加振动后成形件应力变形和组织性能的变化情况。结果表明,施加振动后,虽然对薄壁件和精细结构的成形是不利的,但是成形试样的残余变形和残余应力都有一定程度的改善,其中4 m/s²的振动加速度对残余应力的降低效果最明显,6 m/s²的振动加速度对残余变形的降低效果最佳;施加振动后,成形试样的组织发生明显的细化,拉伸性能得到提升,其中4 m/s²的振动加速度对枝晶的细化效果最优且对材料的综合力学性能提升最佳。     

镀Cu层调控AZ31B/TC4激光熔钎焊接特性

采用钛表面电镀铜作为中间层,开展镁(AZ31B)/钛(TC4)对接激光填丝熔钎焊,对镁/钛非互溶不反应焊接体系进行调控. 主要研究了激光功率对镁/钛接头焊接质量的影响规律,进一步分析了不同工艺参数条件下镁/钛界面组织及接头力学性能. 结果表明,铜镀层提高了熔融焊丝在母材表面的润湿铺展并卷入到焊缝组织中,随着激光功率的增加,镁/钛界面形成Ti₃Al反应层的能力提高,界面结合强度随之提高. 在较高激光功率1 700 W时,接头拉伸载荷最高达到3 085 N,为镁母材的76.2%,而接头在较高激光功率下的断裂模式也由完全界面断裂转变为部分界面断裂.     

Q235钢搅拌摩擦焊接头微观组织与力学性能分析

在焊接速度为100 mm/min和搅拌头转速为450 r/min的工艺参数下,采用钨铼合金搅拌头对3 mm厚Q235钢进行了搅拌摩擦焊试验,并对接头的微观组织及力学性能进行了研究. 结果表明,在该工艺参数下可以获得表面无缺陷、成形良好的焊缝. 焊后搅拌头表现出一定程度的磨损及氧化. 接头截面各区域承受不同的热力联合作用,经历了不同的组织转变过程,但均保持铁素体和珠光体组织. 接头显微硬度最大值位于焊核区. 接头拉伸断裂位置处于热影响区,拉伸断口呈韧性断裂特征.     

圆柱形离子阱质谱仪关键技术研究及参数优化

采用EI电离源,研制了采用圆柱形离子阱为质量分析器的质谱仪,结合电子倍增管、小信号放大系统和数据采集卡,实现了离子的检测和数据采集,并通过LabVIEW控制整个系统。在真空系统中,优化了该质谱仪的灯丝电流、推斥极电压、背景气体压强及质量扫描速度等工作参数,并给出不同工作参数下谱峰的变化规律。使用优化后的参数对水杨酸甲酯进行检测,结果表明,该仪器性能良好,可以获得准确的有机物谱图信息,完成物质的质量分析。