热轧态镍基高温合金电子束焊接接头裂纹容限

对GH4169合金电子束焊接接头进行了裂纹尖端张开位移(CTOD)试验分析,试验温度为20℃和650℃,评价GH4169合金接头的抗断裂性能.在CTOD试验的基础上,开展GH4169合金电子束焊接接头裂纹容限评定.试验结果表明,不论是在常温下(20℃)还是在高温下(650℃),母材的CTOD值高于其焊缝值,即母材的抗断裂能力优于焊缝值,并且焊缝的CTOD值较低,易发生脆性断裂.裂纹容限的计算结果表明,在同一应力水平下,母材的裂纹容限比焊缝值高,但母材与焊缝的裂纹容限差值随着应力水平的升高而减小.     

Investigation of the formation of the secondary current signal in plasma in electron beam welding with oscillations of the electron beam

The results of investigation of the formation of the secondary current signal in plasma and electron beam welding with the oscillation of the beam along and across the joint are presented. The secondary signal is analysed by the synchronous storage method. The results show that the parameters of the function, which is the result of processing the secondary signal by the synchronous storage method, depend on the focusing conditions.     

电子束焊高压放电的工艺控制措施

文中从电子枪的结构和工作原理入手,针对电子束焊接时金属蒸汽的影响方式,分析了高压放电产生的初步原因,并在不对设备进行改造的前提下提出高压放电的工艺防止措施,通过采取这些措施,较好地控制了电子束焊易挥发材料时的高压放电现象。     

Microstructural characterization of electron beam welded joints of TiAl-based intermetallic compound

The feasibility to use election beam welding to join the nominal composition Ti-48Al-2Cr-2Nb (at.%) alloy was assessed. The microstructure characterization and cracking susceptibility of the joints were evaluated by means of OM, SEM, XRD, and microhardness.It was found that the welded microstructure exhibited columnar and     

电子束焊接技术研究及进展

简要介绍了电子束焊接技术的发展、基本原理以及应用范围。着重介绍了电子束钎焊、活性剂电子束焊接、电子束复合焊接、电子束填丝焊、局部真空电子束焊接、电子束扫描焊接等电子束焊接新技术在国内的研究现状,并对电子束焊接未来的发展做出了展望。     

电子束焊接过程束流品质的调控技术

研究到达工件前的束流品质,束流品质的量化表征是通过基于二次电子的间接测量方式和基于能量密度测试传感器的直接测量方式相结合来实现。通过自动束流对心和矫形程序实现对束流品质偏移距离和形貌因子两个表征参数的调控,并使其达到最优。研究电压、束流、聚焦电流等电子束焊接工艺参数与束流的三维能量分布指标的内在联系。通过建立的二次方模型,利用Design-Expert软件优化(Optimization)模块不仅可以预测不同电参数作用下的四个表征参数的具体数值,而且能根据设定的四个表征参数推算出三个电控参数的优化方案,选择期望度最大的一组电控参数值作为调控的基本参数。在此基础上利用电子束能量直接测试系统,进行电控参数的微调,并实时监测四个三维特征参量的变化,直至达到调控的预定值。     

Laser beam welding of wrought aluminium alloys

Abstract

Laser beam welding is now a common manufacturing method for a wide range of steel products from automobiles to razor blades. However, the process has only recently been approved for critical applications involving aluminium alloys, notably in the aerospace and automotive industries. The properties of aluminium alloys influence the interaction between the beam and the material to a far greater extent than for steels. The challenge of developing industrial welding procedures has therefore been considerable. The present review describes the effects of CO₂ and Nd–YAG laser beam processing parameters and the properties of the most common wrought aluminium alloys on the characteristics of welded joints. Porosity, solidification cracking, and poor weld bead geometry are shown to be the most frequently encountered imperfections. These can be eliminated through the use of appropriate filler materials, process gases, material preparation, and in some instances, adaptive control systems. Very little work has been reported on the corrosion properties of laser welded aluminium alloys. Experimental processing parameters are presented and compared using an analytical model, which can also be employed for predictive purposes. A number of industrial applications are described. These demonstrate that, for specific alloys, the process is now sufficiently well understood to be approved for high volume production, particularly in the transport industries.     

钛合金电子束焊熔宽PID控制系统建模与仿真

由于焊接过程的复杂性,因此很难得到熔池动态过程的解析数学模型,使得焊接过程建模成为焊接过程控制的一大难题．为了建立电子束焊熔池动态过程模型,采用阶跃响应法确定出了钛合金电子束焊电子束流与熔宽的数学模型的类型和结构,计算出了该模型的参数,建立了电子束流与熔宽的传递函数模型．利用获得的电子束流与熔宽的数学模型,采用Z-N经验公式法确定出了PID控制器参数,在此基础上利用MATLAB／SIMULINK建模与仿真平台建立了钛合金电子束焊熔宽PID控制系统模型,并对该模型进行了仿真试验．结果表明,所设计的控制系统动态性能和稳态性能良好．     

Investigation of the thermal electromotive force of steels and alloys of different structural grades in electron beam welding

The results of investigations of the thermoelectric properties of steels of different structural grades and also nickel- and cobalt-based alloys are presented. The temperature dependencies of the absolute thermal electromotive force and the thermal electromotive force coefficient of materials are determined.     

电子束焊接热效应对镁合金焊缝显微硬度的影响

研究了真空电子束焊接热效应对AZ91D和AZ31B镁合金焊缝显微硬度的影响机制,实验结果表明,真空电子束焊接热效应对AZ91D、AZ31B镁合金焊缝均有不同程度的强化作用。当焊接热输入较大时,影响AZ91D镁合金焊缝硬度的主要因素为因Mg元素烧损而产生的强化相变化,焊接热输入越大,焊缝中的Mg元素烧损增加,使Al元素含量(质量分数,下同)逐渐增加,从而在焊缝中生成了更多的强化β相,使焊缝硬度得到提高,产生的强化相越多,焊缝硬度相对越大;当焊接热输入较小时,影响AZ31B镁合金焊缝硬度的主要因素为焊后冷却速度,焊接热输入越小,焊后冷却速度越快,焊缝晶粒越细小,焊缝硬度相对越大。     

The model of formation of a non-self-sustained discharge in the plasma in electron beam welding

A model of formation of a non-self-sustained discharge in plasma in electron beam welding is proposed. The electron concentration and electron energy in the plasma above the zone of the effect of the electron beam are calculated by solving the convection–diffusion equations for the density and mean electron energy. Numerical calculations in the construction of the model are carried out using a package of applied software Comsol 4.3, the Plasma Module and the extension DC discharge. The model can be used to calculate the plasma parameters both above the welding zone and directly in the penetration channel.     

Characterization of microplasticity in TiAl-based alloys

Three different characteristic microstructures of Ti–44Al–8Nb–1B (at.%) have been studied by in situ loading, with acoustic emission and image correlation and ex situ by electron backscatter diffraction and transmission electron microscopy. Microyielding and pre-yield cracking occur at different applied stress levels; nearly fully lamellar material yielding at the lowest and duplex material at the highest stress. The early microyielding in the lamellar microstructures is explained by strain heterogeneity seen in the early stages during loading; the microyielding is higher in lamellae at 45° than in lamellae parallel or perpendicular to the loading direction. Duplex microstructures show no detectable strain heterogeneity until macroscopic yield occurs. The lower bound of the internal stress present in undeformed near lamellar and fully lamellar samples was estimated by observations of dislocation loops at alpha-2/gamma interfaces. The observations are discussed in terms of the influence of internal stress on the tensile and fatigue properties of the different microstructures.     

The fatigue resistance of TiAl-based alloys

TiAl-based alloys are a class of intermetallic alloys that show potential as a high-temperature structural material. Many applications considered for TiAl-based alloys require certain damage-tolerance characteristics. In this article, the fatigue resistance of two-phase TiAl alloys is reviewed to assess the current understanding of the fatiguedamage processes in this class of emerging materials. Salient features of fatigue-crack growth and stress-life curves are summarized to identify the challenges these fatigue characteristics present in the life assessment of TiAl components.     

Pre-yielding and pre-yield cracking in TiAl-based alloys

Samples of Ti44Al8Nb1B (at.%) and Ti46Al8Nb (700 wt ppm oxygen) and of the alloy K5 (Ti-46.5Al-2Cr-3Nb-0.2W-0.15B-0.4C (800 wt ppm oxygen) have been heat treated to produce duplex, near fully lamellar and fully lamellar microstructures. These samples have been tested in tension, using detectors to detect acoustic events during pre-yielding. Many acoustic emission events and corresponding cracking, occur well below the 0.2% proof stress in the near fully lamellar samples of Ti44Al8Nb1B, in fully lamellar Ti46Al8Nb and fully lamellar K5. In fully lamellar Ti44Al8Nb1B alloy some samples show no acoustic events before yield and others show only single acoustic emission events. Duplex samples generate no signals until the applied stress exceeds the macroscopic yield point. The stress–strain curves from Ti448Nb1B, Ti46Al8Nb and from K5 show that in near fully lamellar and fully lamellar samples significant pre-yielding occurs, but none is obvious in the duplex samples. These observations are discussed in terms of the factors contributing to pre-yield plasticity and to pre-yield cracking in these alloys and with reference to earlier acoustic emission work where the reported behaviour is very different. It is concluded that yield, within sufficiently long lamellae or within gamma grains, can give rise to pre-yield cracking and thus to acoustic emission in lamellar samples.     

Finite element simulation of magnesium alloys laser beam welding

In this paper, a three-dimensional finite element model is developed to simulate thermal history magnesium-based alloys during laser beam welding. Space–time temperature distributions in weldments are predicted from the beginning of welding to the final cooling. The finite element calculations were performed using Cast3M code with which the heat equation is solved considering a non-linear transient behaviour. The applied loading is a moving heat source that depends on process parameters such as power density, laser beam dimensions and welding speed, and it is associated to moving boundary conditions. Experiments were carried out to determine temperature evolution during welding and to measure the laser weld width. By comparing the thermal model answers with the measurements, it is found that numerical simulations results are in a good agreement with the experimental data.     

Prediction of penetration depths during electron beam welding

Abstract

An analytical penetration model for electron beam welding is presented, based on a combination of the moving line source solution and the solution for a cylindrical cavity moving through a plate of finite thickness. The input parameters are the net beam power, welding speed, keyhole wall temperature, and diameter of the electron beam from which the penetration depth can be calculated for a range of base materials, such as stainless steels, titanium grade 2, and aluminium alloy AA 5052. It is concluded that the penetration model is sufficiently comprehensive and relevant to be used as a predictive tool in ordinary production welding and some possible applications are briefly outlined.