Numerical Simulation of Superplastic Forming and Diffusion Bonding of Ti Alloys

The research on numerical simulation for combinative process of SPF/DB is carried out in this paper. The contacting problem of sheets is analyzed by using the penalty method. In order to solve the contact problem of different parts of the sheet, a new algorithm for contacting judgment is proposed. According to the relation of the distance vector and the vector of contacting element area, and the condition of contact, it can be judged whether or not a node on the slave surface and the corresponding master surface are in the state of SPF/DB. The Mindlin shell element is employed to simulate SPF/DB process of an asymmetry double-cell cup of Ti-6Al-4V to examine the efficiency of the new algorithm using ARVIP-3D. The results of the numerical simulation are in good agreement with experimental results.

Superplastic Forming and Diffusion Bonding for Sandwich Structure of Ti-6Al-4V Alloy

Superplastic forming and diffusion bonding (SPF/DB) is a well-established process for the manufacture of components almost exclusively from Ti-6AI-4V sheet material. The sandwich structure of Ti-6AI-4V alloy is investigated. The effects of the microstructure on the SPF/DB process were discussed. The microstructure at the interfaces and the distribution of thickness were researched.

SUPERPLASTICITY AND DIFFUSION BONDING OF IN718 SUPERALLOY

The superplasticity and diffusion bonding of IN718 superalloy were studied in this article. The strain rate sensitivity index m was obtained at different temperatures and various initial strain rates using the tensile speed mutation method; m reached its maximum value 0.53 at an initial strain rate of 1×10^-4s^-1 at 1253K. The diffusion bonding parameters, including the bonding temperature T, pressure p, and time t, affected the mechanism of joints. When the bonded specimen with 25μm thick nickel foil interlayer was tensile at room temperature, the shear fracture of the joints with nickel foil interlayer took place at the IN718 part. Microstructure study was carried out with the bonded samples. The microstructure shows an excellent bonding at the interfaces. The optimum parameters for the diffusion bonding are： T = 1273-1323K, p = 20-30MPa, t = 45-60min.

Study on process and mechanism of superplastic diffusion bonding of dissimilar steels

The probability, main effect factors and diffusion theory of structural superplastic diffusion bonding of W6Mo5Cr4V2/45 steel have been observed and analyzed by means of tensile test at the room temperature, scanning electron microscope and microhardness test. Results show that after fine graining treatment and short time superplastic pressing formation under the conditions of superplastic temperature and strain rate, W6Mo5Cr4V2/45 specimens can achieve solid state diffusion bonding and the property of welded area is the same as the other parts in the specimen. The diffusion path of carbon element is intergranular and of dislocation.

Research on the diffusion bonding of superplastic magnesium alloy

The elevated temperature tensile experiments have been carried out on the magnesium alloy and results indicate that the magnesium alloy has excellent superplastic property. Gleebe 1500 testing machine was used in the diffusion bonding experiment on the superplastic magnesium alloy. Then, the shear strength of the joints under different conditions is obtained through shear testing and the optimum processing parameters for the diffusion bonding are achieved. By metallurgical microscope and scanning electron microscope (SEM), it is revealed that the micromechanism of diffusion bonding is the slide of grain boundaries caused by the growth of grains and atom diffusion of the superplastic magnesium alloy.

Superplasticity and Diffusion Bonding of Ti_3AI Intermetallic Compounds

The superplasticity of Ti_3Al intermetallic compounds has been investigated in this paper.The Ti-14Al-21Nb ternary alloy showed 477% elongation at the strain rate of 1.49×10^(-5) s^(-1) and 950℃.The elongation of Ti-14Al-21 Nb-3Mo-1V quinary alloy approached to 573% at the strain rate of 4.52×10^(-5) s^(-1) and the same temperature,and it was found that the elongation value in- creased to 1096.4%as temperature was raised up to 980℃ at the same strain rate.Ti_3Al base al- loys were bonded by diffusion bonding technology and good joints were created,the simulated specimens were performed by SPF/DB process.

THE DIFFUSION BONDING OF Ti－6AI－4V TITANIUM ALLOY UNDER SUPERPLASTIC CONDITION

The effect of main technological parameters of diffusion bonding for titanium alloy, such as temperature,pressure and time,on joint strength was studied. A threedimensional curved surface among'joint strength and temperature,pressure,time was drawn. It can be used for selecting reasonable technological parameters.In order to have an overall understanding of the effeCt of technological parameters on the quality of bonded interfaces,the observation of fracture appearance by SEM was also carried out.

DIFFUSION BONDING OF SUPERPLASTIC AI ALLOY LC4

Diffusion bonding of supcrplastic Al alloy LC4,with prior surface treatment of organic solution protecting coating after electroplishing and stainless steel wool brushing,was performed by Gleeble test machine under conditions ranged 490—530 ℃,1.0—3.0 MPa. 30—180 min and vacuum of 1.0×10^(-3) Pa.The joints were examined to have similar strength and microstructure to the base metal Discussion was made on the effect of superplastic treatment on bonding.The micromechanism for diffusion bonding of super- plastic metal was suggested as the migration of original bond interfaces caused by atomic diffusion and grain growth. Experimental results for the alloy as quench-aged state were presented to compare with the superplastic one.

Effect of superplastic deformation on the bonding property of 00Cr25Ni7Mo3N duplex stainless steel

The superplastic deformation diffusion bonding of 00Cr25Ni7Mo3N duplex stainless steel was performed on a hot simulator. The microstructure of the bonding interface was characterized by scanning electron microscopy （SEM） and electron backscatter diffraction （EBSD）. The mechanical properties of the specimen were investigated by a shear strength test. The results indicated that the shear strength was improved with the increase of superplastic deformation reduction. When the deformation reduction was up to 50%, the shear strength of the specimen achieved 417 Mpa, approaching to that of the base metal. In addtion, the superplastic diffusion bonding technique was not very sensitive to surface roughness levels. When the surface roughness of the bonding specimen surpassed 0.416 pan （level G2）, the shear strength achieved at least 381 MPa.

Theoretical Model of Transformation Superlastic Diffusion Bonding for Eutectoid Steel

Based on current theories of diffusion and creep cavity closure at high temperature, a theoretical analysis of phase transformation diffusion bonding for T8/T8 eutectoid steel is carried out. The diffusion bonding is mainly described as two-stage process: Ⅰ The interfacial cavity with shape change from diamond to cylinder.Ⅱ The radius of the cylindrical cavity are reduced and eliminated gradually. A new theoretical model is established for the process of transformation superplastic diffusion bonding (TSDB) on the basis of a theoretical model for isothermal superplastic diffusion. The model can predict the bonding quality which is affected by technological parameters, such as limit cycling temperature, the compressive stress, the numbers of thermal cycles and temperature cycling through the phase transformation in the thermal cycling and so on. Results show that the maximum temperature, the compressive stress, the numbers of thermal cycles and the rate of temperature changing speed in the thermal cycling have an important influence on TSDB process. Meanwhile, reasonable technological parameters chosen from theoretical analysis is in good agreement with those obtained from experimental results.

Superplastic Tension Behavior of Dissimilar TC4/SP700 Laminate through Diffusion Bonding

Superplastic forming is a practical method to manufacture complex-shaped parts of titanium alloys with large deformation.Laminated parts of dissimilar titanium alloys fabricated by superplastic forming can achieve excellent performance by combining the advantages of components.This work displays the superplastic tension behavior and microstructural evolution of dissimilar TC4/SP700 laminate prepared by the diffusion bonding process.Two titanium alloys can achieve metallurgical bonding at parameters of 800℃/1 h/5 MPa.Except for dynamic recrystallization and grain growth behaviors upon superplastic tension,stress-induced phase transformation plays an important role inαtoβphase transformation apart from the elevated temperature.The superplastic deformation can be attributed to the grain boundary sliding accommodated multiplex motion of dislocations.In addition,the retained strengths of all dissimilar TC4/SP700 laminates after superplastic deformation with different strain rates and temperatures range from 807 to 890 MPa.

SP-700钛合金超塑性能及双层结构SPF/DB工艺研究

在720~820℃,5×10^(-2)~1×10^(-3) s^(-1)应变率范围内对SP-700钛合金超塑性能进行测试和研究。结果表明:在780~800℃,1×10^(-3) s^(-1)应变率下,材料展现出良好超塑性,伸长率超过762%。为验证SP-700钛合金低温超塑成形工程化应用的工艺性,实现高效率研制,选定工艺参数为780~800℃,应变率为5×10^(-3) s^(-1),采用SPF/DB技术进行典型双层结构件试制,采用三维扫描测量技术分析构件成形精度,进行力学性能测试、金相组织分析和氢氧含量测试,并与Ti-6Al-4V合金相应性能进行对比。结果表明:在选定的工艺参数下,SP-700钛合金可成形符合标准的多层结构SPF/DB零件,成形精度<0.5 mm;与Ti-6Al-4V相比,该材料具有良好低温超塑性,可替代Ti-6Al-4V工程化应用。

超塑成形工艺及设备浅析

超塑成形/扩散焊接(SPF/DB)技术是利用材料在超塑性状态下良好的固态粘合性能而发展起来的一种组合工艺技术。本文对超塑成形/扩散焊接(SPF/DB)成形工艺、热成形机和真空氩气成形系统进行了详细介绍分析。

Ti_(2)AlNb合金蜂窝结构电流辅助成形-扩散连接工艺研究

Ti_(2)AlNb合金蜂窝结构采用辊弯-热校形-点焊复合工艺制备,存在工艺周期长、能耗高、构件精度低、可靠性差等缺陷。本文提出Ti_(2)AlNb合金蜂窝瓦楞板电流辅助辊压成形工艺,利用局部成形位置的高电流密度抑制构件回弹。同时,采用扩散连接工艺制备蜂窝结构,实现蜂窝结构的可靠连接。当电流密度高于阈值(20 A/mm^(2))时,电流密度对于V形弯曲回弹的抑制作用显著。当电流密度达到60 A/mm^(2)时,V形弯曲回弹已基本消除。在瓦楞板电流辅助辊压成形过程中,当最大电流密度增大至66 A/mm^(2)时,瓦楞板的成形角度由125.5°降低为121.3°。设计了Ti_(2)AlNb蜂窝结构扩散连接工装,在970℃/15 MPa/2 h热压工艺参数下,制备了蜂窝结构样件,六边形元胞的尺寸一致、精度高。

超塑成形/扩散连接设备的设计与开发

开发了一种超塑成形设备,确定并详细叙述了超塑成形设备的设计方案。设备主体框架采用液压预紧组合拉杆框架式结构,采用6个活塞缸和4导向杆结构,确保了加压的均匀性和导向精度。液压系统采用伺服电机驱动油泵形式,降低了能源消耗,气压控制精度保证了超塑成形/扩散连接零件的准确度。设备具有结构紧凑、耐用性强、工件成品率高等特点。

超塑成形设备技术现状与发展

超塑成形技术是一种利用材料的超塑性大变形能力制造薄壁复杂构件的先进成形技术。超塑成形及超塑成形/扩散连接过程中的工艺参数变量多,参数同步性控制要求高,一般在专用超塑成形设备上进行,可更方便实现坯料温度、工模具温度、变形区、变形速度、变形应力等关键参数控制。传统超塑成形设备压制单向性、功能集成度不够、自动化程度低等,远不能满足科研生产的需要。因此,本文重点阐述了近年来出现的多向加载、“气–液”耦合控制、自动上下料3种超塑成形设备新功能。随着先进制造技术、信息技术等的集成和深度融合,超塑成形设备将朝着大型化、清洁化、自动化、多能场复合化及专用化等方向进一步发展,并将进一步改善超塑成形技术的生产效率及应用范围。

钛合金空心点阵超塑成形/扩散连接成形工艺和性能研究

钛合金空心点阵是典型的承载–功能一体化结构,采用单轴拉伸方法,在不同温度、应变速率条件下测定TA15、TA32钛合金的超塑拉伸延伸率,最大延伸率分别达到1450%和950%,后在不同温度、压力条件下进行扩散连接试验。根据超塑拉伸和扩散连接试验,确定了超塑成形和扩散连接(Superplastic forming/diffusion bonding,SPF/DB)的最佳工艺参数为:920℃/1.5~2.0 MPa/2 h,制备了不同构型和几何参数的TA15、TA32钛合金空心点阵结构件。采用平压方法和三点弯曲方法测定了钛合金空心点阵的力学性能,压缩和弯曲强度最大值分别达到23.83 MPa、596MPa,通过有限元和试验分析的方法,研究了几何参数对钛合金空心点阵平压和弯曲性能的影响规律。采用单面加热方法,研究了钛合金空心点阵结构的隔热性能,在400℃/1 h条件下,隔热温差达到276.3~310℃。

电流辅助成形技术研究进展及展望

超塑成形/扩散连接(SPF/DB)工艺是指在一个热循环内材料同时完成成形和扩散连接的加工过程。随着航空航天领域对轻质高强难变形金属材料需求增加,迫切需要探索这类材料的成形新方法。电流辅助成形能够降低材料流动应力,提高其成形精度,与SPF/DB工艺相结合能够高效制备复杂结构件,这对高强难变形金属材料成形具有重要意义。介绍了电致塑性原理,梳理了电流辅助成形、扩散连接和SPF/DB的特点与优势,阐述了目前电流辅助成形工艺面临的挑战与展望。

TA15钛合金局部减重中空双层结构超塑成形/扩散连接工艺

在应变速率为0.001 s^(-1)、0.005 s^(-1)、0.01 s^(-1),温度为880℃、900℃、920℃、940℃的条件下对TA15钛合金进行了高温拉伸试验,材料在920℃以上、0.005 s^(-1)以下的延伸率可超过500%,具有优异的超塑性能。计算了TA15钛合金的本构方程及在应变速率为0.005 s^(-1)时,不同温度下的应变敏感性指数m值和材料常数K值。通过超塑成形/扩散连接(SPF/DB)工艺,采用有限元模拟对双层结构件的壁厚分布进行分析,并获得了气压加载压力–时间曲线。在温度为920℃时,采用预镂空面板制得了局部减重的中空双层结构件,最小壁厚为0.31 mm,采用超声波C扫描对零件的扩散面积进行分析,结果表明,焊合率高于95%。

TA15钛合金超薄中空四层结构超塑成形/扩散连接一体化成形及精度控制

本文采用TA15钛合金热轧薄板作为原材料,探究超薄中空四层结构的超塑成形/扩散连接工艺。首先通过高温拉伸试验对TA15钛合金的超塑变形行为进行研究,获得了超塑成形过程的应力–应变曲线。然后通过有限元软件对薄壁横向局部贯通四层纵筋结构的超塑成形过程进行模拟,对成形过程中壁厚减薄、应力分布等行为进行研究,为后续超塑成形/扩散连接试验提供有效指导。最终成功制备了芯板直立筋良好、三角区宽度仅0.9 mm的超薄中空四层结构,其中面板最大减薄率为18.6%,芯板最大减薄率为55.1%,芯板与面板之间扩散连接区域的焊合率为92.1%~98.5%。TA15钛合金板材的原始显微组织晶粒细小破碎且呈等轴状,平均晶粒尺寸小于5μm,经长时间的超塑变形与热暴露后晶粒显著长大。