The effect of thermal cycle on joint of Ti/stainless steel phase transformation diffusion bonding

The effects of thermal cycle parameters on the tensile strength and fracture characteristics of phase transformation diffusion bonding(PTDB) joint of titanium and stainless steel (Ti/SS) were studied in this paper. With the maximum cyclic temperature of 1 173～1 223 K , the minimum cyclic temperature of 1 073～1 093 K , the heating velocity of 30～50 K/s , the cooling velocity of 15～20 K/s , the cycle numbers of 15～20 and bonding pressure is 13 MPa , the tensile strength of joint is more than 380 MPa , exceeding 80% of that of Ti.

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.

HIP diffusion bonding of P/M titanium alloy Ti-6Al-4V and stainless steel 1Cr18Ni9Ti

The HIP diffusion bonding of P/M titanium alloy Ti-6Al-4V and stainless steel 1Cr18Ni9Ti using pure Ni as intermediate layer was studied. Bonding joint with complex bonding interface was obtained by HIPing pre-alloyed Ti-6Al-4V powders and stainless steel 1Cr18Ni9Ti in a vacuum canning. The joint strengths were examined and the characteristics of bonding joint were observed. The result shows that the maximized strength of HIP diffusion bonding between P/M titanium alloy Ti-6Al-4V and stainless steel 1Cr18Ni9Ti can be up to 388 MPa and the microstructure of bonding joint is acceptable.

Impact pressuring diffusion bonding of TA17 to 0Cr18Ni9Ti

Impact pressuring diffusion bonding tests were carried out to produce joint between TA17 titanium alloy and 0Cr18Ni9Ti stainless steel. The reaction products and microstructure near the bonding interface were analyzed. The diffusion of Fe, Cr, Ni and Ti in the bond was revealed by energy dispersive spectroscopy. A number of phases, such as β-Ti, Fe2Ti and σ phases were identified by X-ray diffraction. It was concluded that the bonded joint broke in the region somewhere between Fe-Ti intermetallics and β-Ti during tensile loading. The relationship between bonding parameters and tensile strength of the joint was also determined experimentally, and the optimum time of bonding was only 220 s with 293 MPa joint strength.

Impulse pressuring diffusion bonding of titanium to 304 stainless steel using pure Ni interlayer

In the present study, impulse pressuring diffu- sion bonding technology （IPDB） was utilized between commercially pure titanium and 304 stainless steel （SS） using pure nickel （Ni） as interlayer metal. The interfacial microstructures of the bonded joints were investigated by scanning electron microscopy （SEM） and energy dispersive spectroscope （EDS） analyses. It is found that with the aid of the Ni interlayer, the interdiffusion and reaction between Ti and SS can be effectively restricted and robust joints can be obtained. Intermetallic compounds （IMCs） including Ti2Ni, TiNi, and TiNi3 are detected at the Ti/Ni interface; however, only Ni-Fe solid solution is found at the Ni/SS interface. The maximum tensile strength of 358 MPa is obtained by IPDB for 90 s and the fracture takes place along the Ti2Ni and TiNi phase upon tensile loading. The existence of cleavage pattern on the fracture surface indi- cates the brittle nature of the joints.

Effect of Chromium-enhanced Diffusivity on Reverted Transformation in Metastable Austenitic Stainless Steels:Theoretical Calculation and Experiment

Effects of nucleation sites and diffusivity enhancement of chromium on reverted transformation of AISI 304 stainless steel during annealing process were investigated.Dynamics calculation revealed that the reverted transformation of strain-inducedα’-martensite→γaustenite could were closely associated with active nucleation sites and diffusivity enhancement of chromium in nanocrystallineα’-martensite.The experimental data and the results were in accordance with 2-grain austenite/α’-martensite junctions calculated theoretically,which could result from high chromium diffusion rate in nanocrystallineα’-martensite.In addition,low temperature is not conducive to reversed transformation,while high temperature and long annealing time will lead to inhomogeneous grain size distribution.

A method to study interface diffusion of arsenic into a Nb-Ti microalloyed low carbon steel

A novel diffusion couple method was used to investigate the interface diffusion of arsenic into a Nb-Ti microalloyed low carbon steel and its effects on phase transformation at the interface. It is discovered that the content of arsenic has great effect on grain growth and phase transformation at high temperature. When the arsenic content is no more than lwt%, there is no obvious grain growth and no obvious ferrite transitional region formed at the diffusion interface. However, when the arsenic content is no less than 5wt%, the grain grows very rapidly. In addition, the arsenic-enriched ferrite transitional layer forms at the diffusion interface in the hot-rolling process, which results from a slower diffusion rate of arsenic atoms than that of carbon in ferrite.

添加中间层的TC2钛合金/321不锈钢真空扩散焊研究

目的以Cu箔、Ni箔为中间层,使用真空扩散焊工艺实现TC2钛合金与321不锈钢的焊接。方法采用扫描电子显微镜、EDS能谱仪、X射线衍射仪、冲击韧性实验机、显微硬度计等仪器研究了焊接温度、典型中间层材料等工艺参数对TC2钛合金/321不锈钢焊接界面微观结构、界面元素扩散、接头力学性能的影响规律。结果在添加中间层的扩散焊接头中,是否会形成界面区和扩散区以及界面区和扩散区的宽度,受焊接温度的影响,也受中间层和母材成分及性能的影响。在以Ni为中间层的TC2钛合金与321不锈钢真空扩散焊接头中,扩散区会产生AlNi_(3)、NiTi等新物相,当以Cu为中间层时,扩散区中会产生Cu_(0.81)Ni_(0.19)等新物相。在实验条件下,使用铜箔作为中间层的TC2钛合金与321不锈钢真空扩散焊接头的力学性能优于使用镍箔作为中间层的真空扩散焊接头的力学性能。结论在实验条件下,添加中间层的TC2钛合金/321不锈钢真空扩散焊的最佳工艺参数如下:真空度为10^(-4)Pa,焊接温度为820℃,焊接压力为15MPa,焊接时间(即保温时间)为90min,保压时间为240min,以Cu作为中间层。

Electrochemical Study of Diffusion Bonded Joints between Micro-duplex Stainless Steel and Ti6A14V Alloy

In the present study, corrosion behavior of diffusion bonded joints formed between micro-duplex stainless steel （MDSS） and Ti6AI4V alloy （TiA） （at 900 ~C for 60 min under 4 MPa uniaxial pressure in vacuum） was investigated in 1 mol/L HCI and 1 mol/L NaOH solutions using various electrochemical measurements such as open circuit potential （OCP）, electrochemical impedance spectroscopy （EIS） and potentiodynamic polarization （PD）. For comparison, corrosion behavior of base metals （MDSS and TiA） was also evaluated. Bonded joint was characterized by light optical microscopy and scanning electron microscopy using backscattered electron mode. The layer wise σ phase and λ ＋ FeTi phase mixture has been observed at the bond interface and the bond tensile strength and shear strength were - 556.4 MPa and -420.2 MPa, respectively.

焊接温度对钛/钢复合管瞬时液相扩散焊接头组织与性能的影响

以内衬为TA2工业纯钛、外套为20钢的复合管为研究对象,采用BNi_(2)非晶合金箔为中间层,在氩气保护下,在1130~1200℃焊接温度下对钛/钢复合管进行瞬时液相扩散焊接,研究了焊接温度对钛/钢复合管接头组织和性能的影响。结果表明:不同焊接温度下的接头均成形良好,无孔洞、裂纹等宏观缺陷。随着焊接温度的升高,钛侧焊缝等轴晶组织长大,发生α→α'+β相变,焊缝边界逐渐模糊;钢侧焊缝针状铁素体和珠光体变粗大,黑色脆性相逐渐消失,中间层元素和母材元素的扩散距离增加。不同焊接温度下接头在拉伸时均先在钛侧焊缝处断裂,随着焊接温度的升高,接头抗拉强度先升高后降低,在1180℃时接头抗拉强度最高,为460 MPa,断裂方式为脆韧混合断裂。

Improved properties and thermal stability of a titanium-stainless steel solid-state weld with a niobium interlayer

Stainless steel(SS)and titanium alloys can be welded in the solid-state by high speed oblique impact.Here,the effect of a niobium(Nb)interlayer on weld strength and thermal stability is evaluated.Both Ti/SS and Ti/Nb/SS welds were subjected to thermal exposure ranging from 300℃ to 950℃ for 1.5 h.Thermal exposure monotonically decreases the strength and toughness of the Ti/SS pair with a dramatic falloff in strength and change in failure mode from partial pullout failure to full interfacial fracture at 600℃.With the interlayer,toughness was increased versus baseline up to 700℃ thermal exposure and then intermetallic formation again caused falloff in properties.Guidelines for the production,properties and applications of these classes of welds are provided.

钛合金与不锈钢的相变超塑性扩散焊工艺

用相变超塑性扩散焊法实现了钛合金TA17与不锈钢0Cr18N i9Ti之间的连接。研究了工艺参数对接头强度的影响,得到试验条件下钛合金与不锈钢焊接的优化工艺参数为循环上限温度890℃,循环下限温度800℃,循环次数10,焊接压力5 MPa,循环加热速度30℃/s。在优化的工艺条件下,接头强度达到307 MPa,而焊接时间仅为160 s。对拉伸断口进行了扫描电镜观察、能谱分析和X射线衍射分析,发现断裂沿FeTi和β-Ti层之间的某一个位置发生,FeTi金属间化合物层是接头的最薄弱环节。对接头进行了能谱分析,结合Fe-Cr-Ti三元相图发现,钛合金与不锈钢之间的反应区内依次形成了σ、Fe2Ti、FeTi和β-Ti层。

添加Ni＋Nb中间层的钛合金与不锈钢扩散焊工艺研究

分别采用常规工艺和阶梯状工艺的方法,对添加Ni+Nb复合中间层的TC4钛合金与1Cr18Ni9Ti不锈钢真空扩散焊进行了研究。利用光学显微镜(OM)、扫描电镜(SEM)以及能谱分析(EDS)对接头的组织结构、元素分布进行了分析,测试了接头的力学性能并分析了断口形貌和元素分布。结果表明,通过添加Ni+Nb中间层成功阻止了Fe-Ti金属间化合物生成,接头界面过渡区组织自不锈钢侧依次为Fe-Cr-Ni固溶体、Ni-Nb反应层、剩余Nb及Nb-Ti固溶体。阶梯状工艺下接头的结合质量明显优于常规工艺下的接头,在阶梯状工艺上限温度900℃条件下接头抗拉强度达到了396MPa,断口分析表明,接头断裂于Ni-Nb形成的反应层,该反应层是由Ni3Nb和少量Ni6Nb7金属间化合物组成的混合层,为接头过渡区关键环节。

钛合金和不锈钢的扩散焊接

对TA17钛合金与1Cr18Ni9Ti不锈钢的焊接接头强度进行了实验研究。采用恒温恒压扩散焊、相变超塑性扩散焊和脉冲加压扩散焊实现了钛合金和不锈钢的焊接,测试了焊接接头的强度,并对接头进行了金相观察。结果发现:3种接头的强度都达到了264MPa,且接头为多层次的多相组织。物相分析发现钛合金不锈钢接头中存在Fe2Ti和σ (FeCr)两种脆性金属间化合物。脉冲加压扩散焊能促进扩散过程,减少金属间化合物的形成,改善其分布,是一种较有前景的扩散焊方法。

镍作中间层脉冲加压扩散连接钛合金与不锈钢

采用纳米Ni粉、纳米Ni镀层、Ni箔作中间过渡层,对TA17近α型钛合金与0Cr18Ni9Ti不锈钢进行了脉冲加压扩散连接,接头抗拉强度分别达到了175,212,334 MPa。在金相显微镜下,对拉伸断口形貌进行了观察和分析;利用扫描电镜(SEM)、能谱仪(EDS)、X射线衍射分析(XRD)测定了连接接头各区域内的微区成分和物相。结果表明,纳米Ni粉致密度不够高,纳米Ni镀层质量不够高,在很大程度上限制了接头强度的提高;Ni箔中间层的存在成功地阻止了Fe与Ti之间的互扩散,避免了形成脆而硬的Fe-Ti系金属间化合物。

相变扩散连接工艺参数对钛与不锈钢接头强度的影响

分析了钛与不锈钢相变扩散连接的工艺参数 ,利用万能拉伸试验机测试了接头拉伸强度 ,利用扫描电镜 (SEM )及X射线衍射 (XRD)分析了接头断口形貌及组成相。结果表明 :当连接压力为 13MPa、上限温度为1183～ 12 0 3K、下限温度为 10 73～ 10 93K、加热速度为 30～ 5 0K/s、冷却速度为 15～ 2 0K/s、循环次数为 15～2 0次时 ,钛与不锈钢相变扩散连接接头界面无反应相生成 ,拉伸强度为 380MPa以上 ,实现了钛与不锈钢的高效高强度连接。

中间过渡金属对钛合金与不锈钢扩散焊接头强度的影响

采用加中间过渡金属的工艺方法，对钛合金ＴＣ４与不锈钢１Ｃｒ１８Ｎｉ９Ｔｉ扩散焊接头的结合强度进行了试验研究，利用扫描电镜、电子探针仪等对接头进行了微观分析。结果表明，采用纯镍作中间过渡金属虽然有效地防止了钛与铁、碳间的相互扩散和迁移，但在镍与钛之间却形成了金属间化合物薄层，致使接头的最高强度在３８０ＭＰａ左右；采用钒＋铜复合过渡金属彻底地消除了钛合金—不锈钢接头中的金属间化合物和碳化物，接头强度与软质中间层铜的厚度有关，最高强度达５４０ＭＰａ左右．

钛合金/不锈钢网的扩散连接

探讨了钛合金／不锈钢网扩散连接的可行性，确定了直接扩散连接条件下的最佳工艺参数，分析了影响扩散连接的主要因素及接头微观形态。针对实际构件，深入分析了加压方式和变形率的关系，并提出了控制变形量得到无变形接头的方法。

表面自纳米化对钛合金与不锈钢的扩散焊接的影响

用恒温恒压扩散焊接法实现了表面纳米化后的TA17近α型钛合金与0Cr18Ni9Ti不锈钢的连接。焊接材料用气动喷丸方式进行表面自纳米化。利用液压万能试验机测试了接头拉伸强度,并对焊接接头及断口形貌和组织进行了扫描电镜观察及能谱分析。结果表明:接头界面附近出现了不同的层,在不同温度下的焊接接头组织及分布大致相同;与未对材料进行表面自纳米化处理相比,材料经表面自纳米化处理后,加快了被焊偶件的接触进程,提高了原子的扩散速率和焊接接头的强度,并缩短了焊接时间。

纳米镍粉在钛合金-不锈钢扩散焊接中的应用

采用恒温恒压扩散焊、相变超塑性扩散焊、冲击加压扩散焊对直接对焊和加纳米镍粉中间层的钛合金-不锈钢焊接接头进行了研究。测试了接头强度,并进行了断口形貌观察和组织分析,结果表明:3种试验方法中,恒温恒压扩散焊所得接头强度较小,而冲击加压扩散焊所得接头强度较高;直接扩散焊时,接头上两种基体材料之间的互扩散程度很大程度上影响了钛合金-不锈钢接头的强度;采用纳米镍粉作中间层能形成强度较高的接头,达到了213MPa,但纳米镍粉的致密度不够高,接头的强度在很大程度上受到了限制。