Investigation on process and microstructure of Ti/Ni/Cu joints by electron beam welding

In this article, the electron beam welding of the Cu alloy （ QCrO. 8） with Ti alloy （TC4） sheet was processed and the joint microstructure as well as the welding process were studied. The results show that brittle reaction layer which was mainly composed of TiCu, Ti2Cu, Ti2Cu3 and TiCu2formed at the weld fusion line, regardless of welding on the middle or on the Cu side. The mechanical properties of the joint were severely deteriorated by the layer that tensile strength was only 89. 4 MPa for welding on the Cu side. The microstructure of the joint was improved with pure nickel as filler metal for the electron beam welding. The weld was mainly composed of solid solution. Intermetallic compound phase decreased signifwantly in fusion line compared with the joint without filler metal. The mechanical properties of the joint were obviously improved that the average tensile strength was 205.2 MPa and the bending strength was 413.3 MPa with O. 5 mm offset of electron beam on the Cu side.     

Numerical analysis on flow field of weld pool during deep penetration electron beam welding of titanium alloy

Flow field of weld pool during deep penetration electron beam welding of TA 15 titanium alloy was numerically and experimentally studied using a hybrid heat source of Gaussian surface heat source and rotational paraboloidal body heat source. And the formation mechanism of the weld pool flow field was analyzed. The results showed that the movement of the liquid metal in the top weld pool was the fiercest and weakened gradually in the middle and bottom of the weld pool. The maximum flow velocity of the liquid metal was about 0. 295 m/s in the top surface of weld pool. The primary driving forces of the movement of liquid metal in the weld pool were the recoil pressure of metal vapor and the surface tension.     

Analysis of metal transfer during electron beam welding with filler wire

The metal transfer mode of electron beam welding （EBW） with filler wire was studied experimentally. The spatial position between the electron beam and the filler wire was defined. Basing on the charge coupled device （CCD） visual sensing system, the metal transfer mode of filler wire was investigated. The results showed that there were five transfer modes during EBW process due to different wire feed rates and spatial positions between beam and filler wire, such as short-circuiting mode, molten metal bridge mode, small droplet mode, big droplet mode and mixed mode. By comparing the weld appearance of different transfer modes, the molten metal bridge transfer was proved to be the best transfer mode.     

Improvement of thermal and mechanical properties of graphite/copper composites through interfacial modification

Unidirectionally reinforced graphite/copper composites have been fabricated using a pressure infiltration casting procedure. T300 and T650 graphite fibers have been used to reinforce copper and copperchromium alloys. The effects of the chromium level in the copper matrix on the tensile strength, stiffness, and thermal expansion behavior of the composites have been evaluated through tensile and three-point bend testing, and thermal cycling. At the 0.5 wt% alloying level, chromium increases the stiffness and optimizes the thermal expansion behavior of graphite/copper composites. The longitudinal tensile strengths of these composites are above 1606 MPa, whereas the transverse tensile strengths are lower than 40 MPa due to incomplete infiltration during processing. Scanning electron microscopy analyses reveal that the unalloyed copper matrix composites experienced extensive fiber/matrix debonding under tensile loading. The addition of chromium to the copper increases the level of matrix bonding to the graphite fibers, as evidenced by observations of fractured tensile specimens. Auger electron spectroscopy analyses indicate that a chromium carbide phase present at the interface is responsible for the improved bonding.     

Investigations of microstructures and properties in electron beam welded joints of TiAl to TC4

The normally centered electron beam and non-centered electron beam welding of TiAl to TC4 was investigated in order to analyze the electron beam weldability between TiAl/TC4 dissimilar materials. Macroscopic cold crack easily occurred near TiAl substrate in the joints. The optimal tensile strength was related to the welding heat input. The weld structures were composed of bulky columnar grains and equiaxed grains. The isolated phases consisted of large quantities of α2 -Ti3Al phase, small quantity of B2 phase, γ-TiAl phase and YAl2 phase. Insufficient melting of the base metal occurred in the weld when the beam position leaned to the TC4 side. The tensile strength could be improved when the deflection was limited in the optimum range. Otherwise, non-fusion zone was easily generated in the weld, which led to the low tensile strength.     

Microstructure and corrosion behaviour of alloy 690–SUS 304L butt joints formed by electron beam welding

Abstract

This study investigates the microstructure and corrosion behaviour of alloy 690–SUS 304L stainless steel dissimilar weldments formed by electron beam welding (EBW). Slow strain rate tensile tests (SSRTs) are performed in air and in a 0·01M Na₂S₂O₃ + 1 wt-%NaCl corrosive environment. The microstructure, mechanical properties and corrosion behaviour of the weldments are analysed. Experimental results of this study reveal that the precipitation of chromium carbide is suppressed owing to the effect of rapid solidification of EBW in fusion zone (FZ). In addition, there is no chromium depletion found at the grain boundary at all. The interdendritic region of the FZ contains fine precipitates, which are a mixture of Ti rich phases with a rectangular shape and Cr rich phases with an oval shape. Fewer interdendritic phases are formed in the root than in the cap owing to the higher cooling rate in the root region of the weldment. Fracture tests indicate that all the specimens ruptured in the FZ by SSRTs preformed either in air and or in a corrosive environment. The tensile strength and total tensile elongation of the specimen deformed in the 0·01M Na₂S₂O₃ + 1 wt-%NaCl corrosive environment are lower than those of the specimen deformed in air. Fractographic investigations revealed that the fracture mode, in good accordance with mechanical behaviour and performance, transits from a ductile dimple rupture in the specimens tested in air to a mixed rupture of dimples and corrosion formation on fractured surface which obviously assisted the cracking in the specimens tested in the corrosive environment.     

电子束表面合金化合成(Cr,Fe)7C3复合层耐磨性

以Fe/Cr/C粉末为添加原料,采用可控电子束旋转线扫描方式对低碳钢表面进行表面改性.通过电子束加热工艺和粉末配比的优化,在表面复合层中原位合成了(Cr,Fe)7C3.对表面复合层的显微组织及室温干滑动磨损性能进行了分析.结果表明,表面复合层中主要包含两种相,即少量的初生硬化相(Cr,Fe)7C3以及奥氏体与(Cr,Fe)7C3组成的共晶相,共晶碳化物弥散分布于奥氏体基体中,呈不连续网状组织.表面复合层与基体之间为完全冶金结合.复合层与GCr15钢球的磨损机理为磨料磨损,在室温干滑动磨损下具有优异的耐磨损性能.     

Effect of welding parameters on Al/Ti joint property in electron beam welding-brazing

The electron beam welding-brazing being used to join 5A06 Al alloy to TC4 Ti alloy decreases the formation of brittle intermetallic compound. Experiments were carried out to study the influence of electron beam welding parameters on the tensile strength of welds, based on an orthogonal test and analysis method. The welding parameters include beam current, welding speed, scanning figure, scanning frequency, figure size, beam offset and focus current. The optimum parameters for 3 mm 5A06 Al alloy and 2 mm TC4 alloy were as follows: acceleration voltage was 60 kV, beam current was 11 mA, welding speed was 600 mm/min, focus current was 0 mA, scan figure was ○, scanning frequency was 1 000 Hz and beam offset was 0.5 mm. The results show that the joints were with good appearance and quality welded by the optimum parameters. The successful joints could be gained and the maximum tensile strength of Al/Ti dissimilar alloy joints could be up to 222.61 MPa using electron beam welding-brazing.     

离心铸造高铬合金铸铁气门座圈的组织及耐磨性能研究

采用离心铸造制备两种高铬合金铸铁气门座圈。利用X射线衍射仪(XRD)、金相显微镜、洛氏硬度计和扫描电镜(SEM),对气门座圈铸态及热处理态后的试样物相组成、金相组织、力学性能及拉伸断口形貌进行了观察和分析,同时在销盘式摩擦磨损试验机上对高铬合金铸铁气门座圈的耐磨性能进行了磨损试验。结果表明,热处理前高铬合金铸铁主要为由初生奥氏体、共晶奥氏体和碳化物组成的铸态组织,经淬火及回火处理后转变为马氏体和碳化物组成的组织,明显提高了气门座圈的硬度和强度,由于基体组织和碳化物的形貌及分布改善,高铬铸铁的耐磨性能在热处理后明显提升。     

不锈钢管板接头电子束钎焊

应用自主开发的基于虚拟仪器的电子束钎焊系统，成功实现了不锈钢毛细管板接头的电子束钎焊。研究了电子束束流、加热时间、聚焦电流和扫描幅值等电子束钎焊工艺参数对钎焊接头质量的影响规律。试验结果表明，随着电子束输入功率密度的增加，钎角高度和BNi-2钎料向毛细管壁的扩散深度都逐渐增大。在优化的电子束钎焊规范下，不锈钢管板接头钎透率100％，毛细管无溶蚀产生。通过电子探针显微分析仪研究了电子束钎焊接头中各相的化学组成，钎焊接头主要由硼化镍相、硼化镍和硅化镍相、硼化铬相以及镍的固溶体组成。     

铬膜制备及其膜内残余应力研究

对六价镀铬的工艺进行研究,在45℃、电流密度为15 A·dm-2时电沉积出光亮平整、无缺陷的铬膜.在此基础上在纯铁基体上电沉积制备出一系列不同厚度的铬薄膜,并对其残余应力进行测量和研究.结果表明:Cr膜的平均残余应力和分布残余应力均为拉应力,由于Cr膜在较薄时残余应力的骤降,可判断出其残余应力主要来自于Cr膜的界面应力,与基于Thomas-Fermi-Dirac-Cheng(TFDC)电子理论的判断结果相一致.     

离子束混合对铁的水溶液腐蚀行为的影响

本文应用电化学及俄歇电子能谱等技术,研究了离子束混合对铁的水溶液腐蚀行为的影响,旨在探讨离子束混合作为一种材料表面改性的新途径,用于提高纯铁腐蚀性能的可能性。电化学动电位扫描的结果表明,纯铁表面真空沉积铬薄层(～400),经氩离子束轰击混合后,其阳极致钝电流密度(I_i)和维钝电流密度(I_m)较混合前均有数量级的降低,此种腐蚀性能改进的效果随轰击剂量的增加而增加。钝化膜的俄歇电子能谱分析结果表明,腐蚀性能的改进可归因于表面形成了一层富铬的以氧化膜为主的钝化膜,也与混合界面上形成的亚稳相有关。同时,发现经氩离子轰击后,在混合层及其附近的铁衬底中产生了“氩泡”为主的物理损伤.     

Study on cracking in electron beam welding of A6061 (Al‐Si‐Mg alloy)

Electron beam surfacing in an electron accelerator using powder mixtures of chromium carbides with boron carbide in different weight ratios and with different radiation parameters was used to produce wear- and corrosion-resisting coatings. It is shown that there are compositions of the surfacing mixtures and conditions of electron beam effect ensuring maximum values of wear and corrosion resistance.     

铝锂合金的真空电子束焊接工艺及其接头组织与性能

采用真空电子束焊工艺焊接2090铝锂合金,并对获得接头进行拉伸强度、显微硬度等力学性能测试,时接头的金相组织、拉伸断口进行观察分析.结果表明,在电子柬流为8 mA,采用圆形扫描方式.焊接速度为1 000 mm/min的工艺条件下,获得的接头的力学性能最佳.接头微观分析显示,焊缝金属为细小等轴晶组织,在晶内均匀分布有数量...     

铬青铜与双相不锈钢异种材料电子束熔钎焊

对QCr0．8与1Cr21Ni5Ti偏铜电子束焊接接头的组织和力学性能进行了研究。研究结果表明，随电子束距对接中线铜侧偏移值的增加，QCr0．8／1Cr21Ni5Ti对接接头焊缝组织及成分逐渐均匀化，接头熔接状态得到改善；铜侧偏移值达0．8．1．0mm时。形成焊缝组织成分均匀化的熔钎接头，其抗拉强度可达330MPa左右，已可满足实际使用要求。     

Effect of chemical composition on anode area formation in TIG arc welding. Effect of chemical composition on weldability in fabrication in high alloyed steel (1st Report)

Summary

This paper describes a fundamental investigation of the weldability of A5052 wrought alloy and AC7A castings in electron beam welding and gas tungsten arc welding. Microscopic observations, hardness, tensile, and impact tests were used. In electron beam welding, the tensile and impact properties of the wrought alloy weld metal and heat affected zone are satisfactory. Micro-solidification cracks are found in the weld metal, whereas micro-liquation cracks are found in the AC7A HAZ. The tensile properties of the welds produced by GTAW (or TIG) are virtually equivalent or slightly inferior to those of the electron beam welded joints.     

离子束轰击对多层膜摩擦学性能的影响

用Ｎｅ离子束混合法制务了Ｎｉ／Ｃｒ多层膜，用Ａｕｇｅｒ光电子能谱（ＡＥＳ），Ｘ射线衍射（ＸＲＤ）分析离子束混合多层膜的元素组成，分布和相结构，将其结果与简单蒸发沉积的Ｎｉ／Ｃｒ多层膜结构进行比较，同时，对多层膜（轰击与未轰击）的硬度及摩擦学性能进行测定分析比较，结果表明，离子束混合多层膜的硬度和抗磨性能与简单蒸发沉积多层膜相比都相有提高，这主要是因为Ｎｅ离子的轰击使用使多层膜更加致密及膜内的碳化铬     

电子束选区熔化成形Nb521合金微观组织与性能分析

采用电子束选区熔化技术制备Nb521合金，研究其致密化成形工艺。通过对成形试样的组织、物相、显微硬度、室温拉伸性能的检测与分析，探讨了电子束选区熔化成形Nb521合金的机理。结果表明，电子束选区熔化成形过程中，电子束熔化电流及速度的合理匹配，是得到表面质量及内部质量优异的成形样品的基础；电子束能量密度为340 J/mm3时，样品的密度达到8.78~8.79 g/cm3；Nb521合金显微组织沿沉积方向呈柱状晶，晶粒沿（200）晶面有较强的择优生长取向；成形样品中除Nb基体相外，还存在少量的Nb2C与ZrC碳化物析出；样品室温抗拉强度达到384 MPa，屈服强度为307 MPa，断后延伸率为16.5%；显微硬度处于1 500~1 700 MPa之间，无各向异性。     

The Effect of Si Impurity at the Al ∑5 Grain Boundary： a First Principle Computational Tensile Test Study

First principle computational tensile tests （FPCTT） are performed to the Al ∑5 grain boundaries （GBs） with and without substitution or interstitial Si impurity. The obtained stress-strain relationships and atomic configurations demonstrate that the Al ∑5 GBs with and without substitutional or interstitial Si impurity show different fracture modes. The mechanisms of the different fracture modes are analyzed based on the charge density and the density of states. The results show that the charge redistributions of the atoms in the vicinity of GBs and the covalent interactions between Si and its neighboring Al atoms determine the fracture modes.     

Zr-4合金中氢化物析出长大的透射电镜原位研究

用透射电子显微镜拉伸试样台原位研究了应力、电子束辐照以及第二相对Zr-4合金中氢化物析出和长大的影响。结果表明,在拉应力作用下,裂纹易于沿氢化物扩展,并在裂尖垂直于拉应力方向析出新的氢化物。氢化物在拉应力诱发下的析出、开裂、再析出·····过程,导致了氢致延迟开裂。在较强的会聚电子束辐照下,Zr-4合金中的氢化物会分解,新的氢化物会围绕着附近的Zr(Fe,Cr)2第二相粒子析出,新析出的氢化物为面心立方结构的δ相。