Effect of intermetallic compounds on heat resistance of hot roll bonded titanium alloy-stainless steel transition joint

The effect of intermetallic compounds on the heat resistance of transition joint was investigated. The experiment of post-weld heat treatment for the hot roll bonded titanium alloy-stainless steel joint using nickels interlayer was carried out, and the interface microstructure evolution due to heat treatment was presented. There was not found significant interdiffusion at stainless steel/nickel interface, when the specimens were heat treated in the temperature range of 600-800 °C for 10 and 30 min, while micro-cracks occurred at the stainless steel/nickel interface heat treated at 700 °C for 30 min. The thickness of intermetallic layers at nickel/titanium alloy interface increased at 600 °C, and micro-cracks occurred at 700 and 800 °C. The micro-cracks occurred between intermetallic layers or between intermetallic layer and nickel interlayer as well. The tensile strength of the transition joint decreased with the increase of heat treatment temperature or holding time.

Effects of electron beam welding parameters on the microstructure of titanium to aluminum alloy joints

Electron beam welding of titanium alloy to aluminum alloy was carried out by melting and melt-brazing to investigate the effects of welding parameters on microstructure of the joint. The results indicated that the joint of the specimen welded by melting was well-formed but contained a large amount of intermetallic compounds. These intermetallic compounds were mainly composed of brittle phases such as TiAl and TiAl3 that decreased the ductility of the joints and resulted in a tensile strength 50 % lower than that of the base metal. In the melt-brazing experiment, direct heat was applied to the aluminum alloy to melt the aluminum rather than the titanium alloy, creating a well-formed joint. The weld was mainly composed of Al element and only a 3 ~m thickness of intermetallic compounds formed near the fusion line at the Ti side. The ductility and the performauce of the joint were significantly improved compared with those of the melting-only joint. In addition, the tensile strength of the joint reached 80 % of that of the aluminum base metal.

Research on microstructure and property of electron beam welding joints of titanium alloy sheets

This paper reports research into the microstructures and properties of electron beam welding （EBW） joints of a Ti alloy sheet. To control the TC4 sheet joint formation during electron beam welding is not an easy task. However, the electron beam current has a significant influence on joint formation and a good appearance of a T-joint can be obtained by increasing the heat input and using the electron beam scan method. It was found that all acicular martensite in the fusion zone （FZ） consisted primarily of α＇ phase titanium, with some β phase present. Grain coarsening occurred in the heat-affected zone （HAZ） due to transformation of the β phase. Butt joints possessed high strength, hardness of the fusion zone, and the heataffected zone of these joints performed better than that of the parent metal. The highest shear strength of T-joint was 615 MPa and the fracture mechanism was a gliding fracture.

Fatigue Crack Growth Behavior of Different Zones in an Annealed Automatic Gas Tungsten Arc Weld Joint of TA16 and TC4 Titanium Alloys

Based on the investigated microstructure of different zones in the annealed automatic gas tungsten arc weld joint of TA16 and TC4 titanium alloys,the mechanical property of them was assessed under fatigue crack growth rate tests.For evaluation of fatigue crack growth rate,three points bending specimens were used.The correlation between the range of stress intensity factor and crack growth rate was determined in different zones of the annealed weld joint.Fatigue crack growth rates were obviously different in different zones of weld joint of dissimilar titanium alloys,due to their different microstructures.Scanning electron microscope examinations were conducted on the fracture surface in order to determine the relevant fracture mechanisms and crack growth mechanisms with respect to the details of microstructure.

New filler metal systems for the brazing of titanium alloys

It＇ s well known welding takes the leading role in development of titanium structures. However, in number of cases technological processes of brazing are more appropriate and, sometimes, being the single possible, in particular, during production of multilayer thin-wall structures. It should be noted that brazing filler metals of Ti-Cu-Ni, Ti-Zr-Cu-Ni, Zr-Ti-Ni and Cu-Zr-Ti systems in a form of plastic foils, as well as in powder form are mainly used in world practice for brazing of titanium alloys. Present work provides the results of complex investigations of brazing filler metals of Ti-Zr-Fe, Ti-Zr-Mn and Ti-Zr-Co systems using differential thermal analysis, light and scanning microscopy, X-ray microspectrum analysis. Data on melting ranges of pilot alloys were obtained, and liquidas su^Caces of given systems using simplex-lattice method were build. Brazing filler metals covering brazing temperature range of current structural titanium materials based on solid solutions as well as intermetallics were proposed. Structure, chemical inhomogeniety and strength characteristics of brazed joints were studied. It is determined that brazing of solid solution based alloys （OT4, VT6 ） using indicated brazing fiUer metals ensures strength characteristics of joints, which are not inferior to that obtained with application of known brazing filler metals even if they are received at lower brazing temperature.

Microstructures and microhardness for sheets and TIG welded joints of TA15 alloy using friction stir spot processing

Effects of friction stir spot processing(FSSP)on the microstructures and microhardness of tungsten inert gas(TIG)welded TA15titanium alloy joints were investigated.The macro/micro structural observation and microhardness evaluation of the TA15alloy sheets and TA15TIG welded joints were carried out using optical microscope and microhardness tests.The results show that FSSP effectively improves the microstructure and increases the microhardness of the TA15sheets.As for the TIG welded joints,FSSP also effectively improves the microstructure of joints.And the average microhardness value in weld nugget zone is improved significantly,while a small increase of this value in heat affected zone is observed.The hardness in stirring zone is significantly higher than that in the base metal.Two peak values of hardness appear along the width direction in stirring zone.After FSSP,the average hardness of the weld zone of TA15TIG welded joint is significantly higher than that before FSSP.Under the present process parameters,both the surface oxidation in TA15sheets and in TIG welded joints after FSSP are not evident,while the surface forms the bright white layer,which is composed of a great multitude of fine grains.

Microstructure and mechanical properties of laser beam welded TC4/TA15 dissimilar joints

The microstructure and mechanical properties of laser beam welded dissimilar joints in TC4 and TA15 titanium alloyswere investigated. The results showed that the coarse columnar grains containing a large amount of acicular α and martensite α′ werepresent in the fusion zone (FZ), some residual α phases and martensite structure were formed in the heat-affected zone (HAZ) onTC4 side, and bulk equiaxed α phase of the HAZ was on TA15 side. An asymmetrical microhardness profile across the dissimilarjoint was observed with the highest microhardness in the FZ and the lowest microhardness in TA15 BM. The orders of yield strengthand ultimate tensile strength were as follows: TC4 BM > TC4/TC4 similar joint > TA15 BM > TA15/TA15 similar joint > TC4/TA15dissimilar joint, and increased while hardening capacity and strain hardening exponent decreased with increasing strain rate from1×10?4 s?1 to 1×10?2 s?1. The TC4/TA15 dissimilar joints failed in the TA15 BM, and had characteristics of ductile fracture atdifferent strain rates.

Stress-strain characteristics of linear friction welding of TC11 and TC17 alloys

Abstract Transient stress and strain fields of dissimilar titanium alloys （TCll and TC17 ） joint during linear friction welding （ LFW） were investigated by a two-dimensional model with ABAQUS/Explicit. The results showed that in the X-axis, the maximum compressive stress of 850 MPa occurred in the center zone of friction interface , and the maximum tensile stress of 190 MPa distributed at the flash; in the Y-axis, the maximum compressive stress of 1 261 MPa located at the junction region between the welding fixture and edge of the specimen, and the maximum tensile stress of 320 MPa distributed in the connecting portion between the flash and edge of the specimen. In addition, areas of plastic strain increased gradually during welding process. In the X-axis, tensile strain mainly existed at the heads of the specimens; in the Y-axis, compressive strain mainly occurred at the heads of the specimens.

基于缺口应力方法的钛合金薄板焊接接头疲劳性能研究

文中对TA23薄板钛合金设计了对接接头和十字接头两种接头尺寸,开展了系列疲劳试验,得到了两种焊接接头的疲劳等级曲线.参考现有规范及学者建议的三种不同虚拟半径值0.05、0.3、1 mm,基于缺口应力评估方法对两种接头在焊趾处构建了三种不同的虚拟半径圆弧,建立有限元模型.计算对应的缺口应力,结合试验数据,拟合两种焊接接头在三种不同虚拟半径下统一的S-N曲线,分析分散带指数.结果表明:1 mm的虚拟半径更适用于TA 23薄板钛合金.

3D打印膝关节曲面磨粒流抛光数值模拟及实验研究

目的解决磨粒流加工3D打印制造的TC4钛合金膝关节时存在配合端面抛光效率低以及表面质量不均匀的问题。方法运用FLUENT软件并结合非牛顿流体的Carreau-Yasuda方程对有、无仿形工装的磨粒流加工3D打印膝关节进行对比分析,研究仿形工装对磨粒流加工的影响规律,并通过单因素实验确定颗粒直径倍数与流道间隙大小的关系,从而完成最佳仿形工装设计。结果仿真对比分析结果表明,仿形工装有助于减小压力损失,并且膝关节表面的切削量显著提升,最大提升了182.92%。同时,在双向磨粒流工艺下,膝关节表面切削量的不均匀程度平均降低73%,提升了表面质量的均匀性,证实了仿形工装的有效性。加工结果表明,当仿形流道间隙大小为5倍Si C颗粒直径、工作压力为2 MPa、加工时间为45 min、使用双向磨粒流工艺时,3D打印膝关节的整体表面粗糙度显著降低,平均表面粗糙度为0.67μm。主要配合曲面呈现镜面效果,表面粗糙度达0.38μm与0.46μm。结论当仿形工装的流道间隙为5倍SiC颗粒直径时,磨粒流抛光效果最优。采用双向磨粒流工艺,获得了优于单向磨粒流工艺的均匀表面压力,从而有效提升了表面质量的均匀性,为3D打印钛合金人工骨复杂曲端面的光整加工提供了理论参考和实验依据。

置氢TA10合金焊接接头组织和高温压缩性能

航改燃气轮机焊接修复的钛合金叶片服役于含氢环境中常发生氢脆损伤.试验重点研究了不同置氢量的钛合金氩弧焊接头的微观组织、维氏硬度及氢作用机理、高温压缩性能.结果表明,置氢0.12%(质量分数)焊接接头组织中析出大层片δ氢化物,其尺寸随H元素含量增加而增大,母材、热影响区及焊缝微观组织发生明显改变;置氢0.21%的硬度明显高于其它置氢量,高氢提升焊接接头硬度;低氢时氢固溶强化使α晶粒硬度略提升,高氢时氢化物析出伴随晶格体积膨胀使金属局部塑性变形产生大量位错,位错运动需绕或切过氢化物,导致α晶粒硬度明显提升.压下量对高温压缩流变应力影响有限,再结晶软化作用主要受变形温度控制,随压下量增大,焊缝组织中层片α晶粒连同氢化物沿垂直压下方向被拉长或与压下方向呈一定角度被弯折,氢化物沿层片α晶界生长,热压缩过程中组织再结晶现象不明显.

Ti55钛合金双激光焊接T型接头组织与力学性能研究

对1.5⊥1.5 mm的Ti55钛合金T型接头进行了双激光焊接试验,观察了接头的宏观形貌,分析了接头不同区域的组织结构,以及接头的高温拉伸性能和常温剪切性能。结果表明:Ti55钛合金T型接头焊缝表面成形较好,横截面没有焊接缺陷。从接头母材区域到熔合区,接头的晶粒尺寸逐渐增大,β相含量逐渐减少,α与α'相含量逐渐增多。随着拉伸温度的升高,T型接头的抗拉强度逐渐降低,而伸长率逐渐升高。接头去除立筋后的剪切性能比母材高3.3%。

海水环境中Ti6321焊接接头点蚀萌生与生长模型

针对钛合金焊接接头在海水中长期服役可能面临的点蚀风险,通过电化学测试、预制点蚀凹坑试样的弯曲加载浸泡试验,结合累积概率、分布函数等统计学分析方法研究了Ti6321焊接接头在海水环境中的点蚀萌生和生长行为,利用极值统计法建立了点蚀生长动力学模型。结果表明:点蚀萌生时间包括点蚀萌生的驱动电位达到阈值的时间和亚稳态点蚀产生并向稳态点蚀转变的诱导时间,根据点蚀萌生时间的试验和理论推算结果保守估计,在静态海水自然腐蚀条件下,Ti6321焊接接头难以自发产生稳态点蚀;90%R_(e)弯曲加载条件下Ti6321焊接接头在海水中的最大点蚀深度符合Gumbel分布。本研究为钛合金在海水环境中点蚀萌生和生长提供了一种基于电化学、统计分析的快速试验和预测方法。

工况外载条件下钛合金/钢钻杆接头有限元分析对比研究

由于我国的优质天然气资源主要集中在深层及超深层,超深井的钻探对钻柱提出了更高的性能要求。钛合金钻杆由于具有高强、低密、耐蚀、抗疲劳、耐热和无磁性等优点,是超深层天然气钻柱的研究热点。本文使用三维有限元分析方法,对比研究不同外载条件下钛合金材料和钢钻杆材料对高承载钻杆接头承载性能和密封性能的影响,并分析高承载钻杆接头在工况下的失效方式和力学特性。结论表明:钛合金材料可以使钻杆接头的整体应力水平降低20%,抗扭能力提高约60%,但在同样扭矩上扣后螺纹接头的主台肩密封压力比钢制钻杆接头低15%~20%;当加载内压+拉伸+弯矩的复合载荷后,螺纹的最大危险点由外螺纹主台肩圆弧凹槽处转移到了在外螺纹主台肩侧第一圈齿根处,螺纹整体的应力水平增高,密封性能下降。因此为了满足超深井天然气井钻采需求,使用钛合金/钢钻杆复合钻柱时,可适当提高钛合金钻杆的上扣扭矩,提高螺纹接头的密封性能。

TC4钛合金T形接头双光束激光焊接组织与力学性能研究

开展了1.5 mm⊥2 mm组合的TC4钛合金T形接头双光束激光焊接工艺试验,旨在研究该T形接头的微观组织与力学性能。结果显示,T形接头焊缝区主要为网篮状组织,在上部热影响区的交叉区为少量的针状α'相以及初生α相,下部热影响区交叉区为α相等轴组织。接头力学性能显示,抗拉强度与母材相当,平均弯曲角度为33.1°。完成了典型件的焊接,接头内部没有裂纹与气孔等缺陷,为轻量化构件制造提供了有效的焊接工艺。

Ti6321钛合金焊接接头高温-中应变率力学性能及微观组织

采用Gleeble热模拟试验机对焊接接头不同区域进行了高温-中应变率压缩试验,研究了焊接接头不同区域组织对其力学性能的影响,分析了温度和应变率对其变形过程的影响。结果表明,在高温-中应变率压缩时,热影响区强度最高,母材区较差,焊缝区强度最差。高温下(350℃和550℃),随应变率增加(1s^(-1)和10s^(-1)),变形主导因素由应变硬化效应转变为热软化效应。母材绝热剪切敏感性较低,在高温-中应变率压缩变形时沿剪应力最大方向发生大范围晶粒协调变形。由于热影响区组织均匀,应变率的增加相对于温度的增加,更能促进热影响区绝热剪切带的生成。焊缝区压缩时,应力易于在晶界处集中,此时温度对其压缩变形时绝热剪切带的生成更为有利。

Enhancing adhesive bond strength of CFRP/titanium joints through NaOH anodising and resin pre-coating treatments with optimised anodising conditions

Adhesively Bonded Carbon Fibre Reinforced Plastic(CFRP)and titanium alloy have been extensively used as a hybrid structure in modern aircrafts due to their excellent combination of mechanical properties and chemical stabilities.This study utilised NaOH anodising method to create micro-rough titanium surfaces for enhancing adhesive bonding between titanium alloy and CFRP laminates.A special and simple technique named Resin Pre-Coating(RPC)was also employed to improve the surface wetting of anodised titanium and grinded CFRP substrates.The influences of anodising temperature and duration on the surface morphology,wettability and adhesive bond strength were investigated.The single lap shear test results showed that the bond strength of specimens anodised at 20℃for 15 min improved by 135.9%and 95.4%,respectively,in comparison with that of acid pickled and grinded specimens(without RPC treatment).Although increasing the anodising temperature and duration produced rougher titanium surfaces,the adhesively bonded joints were not strong enough due to relatively friable titanium oxide layers.

Interfacial microstructure and mechanical properties of diffusion-bonded joints of titanium TC4 (Ti-6Al-4V) and Kovar (Fe-29Ni-17Co) alloys

Diffusion bonding is a near net shape forming process that can join dissimilar materials through atomic diffusion under a high pressure at a high temperature.Titanium alloy TC4（Ti-6 Al-4 V）and 4 J29 Kovar alloy（Fe-29 Ni-17 Co）were diffusely bonded by a vacuum hot-press sintering process in the temperature range of 700-850°C and bonding time of 120 min,under a pressure of 34.66 MPa.Interfacial microstructures and intermetallic compounds of the diffusion-bonded joints were characterized by optical microscopy,scanning electron microscopy,X-ray diffraction（XRD）and energy dispersive spectroscopy（EDS）.The elemental diffusion across the interface was revealed by electron probe microanalysis.Mechanical properties of joints were investigated by micro Vickers hardness and tensile strength.Results of EDS and XRD indicated that（Fe,Co,Ni）-Ti,TiNi,Ti_2Ni,TiNi_2,Fe_2 Ti,Ti_（17） Mn_3 and Al_6 Ti_（19） were formed at the interface.When the bonding temperature was raised from 700 to 850°C,the voids of interface were reduced and intermetallic layers were widened.Maximum tensile strength of joints at 53.5 MPa was recorded by the sintering process at 850°C for 120 min.Fracture surface of the joint indicated brittle nature,and failure took place through interface of intermetallic compounds.Based on the mechanical properties and microstructure of the diffusion-bonded joints,diffusion mechanisms between Ti-6 Al-4 Vtitanium and Fe-29 Ni-17 Co Kovar alloys were analyzed in terms of elemental diffusion,nucleation and growth of grains,plastic deformation and formation of intermetallic compounds near the interface.

钛合金薄壁T形接头激光焊接力学性能研究

开展了厚度为1.5mm立筋与厚度为2mm底板的TC4钛合金T形接头的激光焊接工艺试验,对接头的力学性能进行了测试,观察了接头的组织形貌。结果显示:带立筋接头的抗拉强度、屈服强度及伸长率均与母材相当,而去除立筋后的正常区的抗拉强度与屈服强度最高,起弧区的抗拉强度与屈服强度最低,但去除立筋后收弧区的断后伸长率最高、起弧区最低,接头的剪切性能比母材提高了3.4%,持久测试试样没有发生断裂。接头焊缝区组织由大的柱状晶组成,主要由α相、α’相与β相组成,随着距焊缝中心距离的增加,接头组织晶粒尺寸降低,且α’相的尺寸也降低。

钛合金焊接接头表面超疏水涂层的构建及性能研究

为提高钛合金焊接接头的耐蚀性能,以TA2焊接接头为基体,采用微弧氧化和低能修饰相结合的方法,分别在母材区、焊缝区和热影响区制备超疏水涂层。使用金相显微镜、扫描电子显微镜(SEM)、X射线衍射仪(XRD)、傅立叶变换红外光谱仪(FTIR)表征了试样的显微组织、微观形貌和化学成分,通过电化学阻抗谱(EIS)测试了试样在3.5%(质量分数)NaCl溶液中的耐蚀性能。结果表明:微弧氧化处理获得了大脑状微米级沟槽结构,其物相组成为锐钛矿型TiO_(2),经过低能修饰后,3个区域的水接触角分别为154.5°、152.3°和153.6°,滚动角分别为2.9°、4.4°和3.2°,表现出良好的超疏水性。在EIS测试中,超疏水涂层的容抗弧半径最大、微弧氧化涂层的次之,二者均提高了基体的耐蚀性能,其中,热影响区超疏水试样的电荷转移电阻相较于基体的提高了近7倍,具有最佳的耐腐蚀性能。