Effect of brazing temperature on microstructure and tensile strength ofγ-TiAl joint vacuum brazed with micro-nano Ti−Cu−Ni−Nb−Al−Hf filler

A novel micro-nano Ti−10Cu−10Ni−8Al−8Nb−4Zr−1.5Hf filler was used to vacuum braze Ti−47Al−2Nb−2Cr−0.15B alloy at 1160−1220℃ for 30 min.The interfacial microstructure and formation mechanism of TiAl joints and the relationships among brazing temperature,interfacial microstructure and joint strength were emphatically investigated.Results show that the TiAl joints brazed at 1160 and 1180℃ possess three interfacial layers and mainly consist of α_(2)-Ti_(3)Al,τ_(3)-Al_(3)NiTi_(2) and Ti_(2)Ni,but the brazing seams are no longer layered and Ti_(2)Ni is completely replaced by the uniformly distributed τ_(3)-Al_(3)NiTi_(2) at 1200 and 1220℃ due to the destruction of α_(2)-Ti_(3)Al barrier layer.This transformation at 1200℃ obviously improves the tensile strength of the joint and obtains a maximum of 343 MPa.Notably,the outward diffusion of Al atoms from the dissolution of TiAl substrate dominates the microstructure evolution and tensile strength of the TiAl joint at different brazing temperatures.

Effect of cerium ion(Ⅲ) on corrosion resistance of organic-inorganic hybrid coating on surface of aluminum-tube used in refrigeration equipment

Organic?inorganic hybrid coating on the surface of aluminum-tube used in refrigeration equipment using cerium ion (III) as the additive was fabricated by sol?gel method, and the structure of the coating was confirmed by FT-IR. The results of the characterization show that the corrosion resistance of the coating with 1.5 mmol/L cerium ion (III) gains significant improvement, in which the colour retention time of CuSO4 extends to 500 s, the anti-acid and alkali corrosion rates reduce by 67% and 70% compared with the blank one, respectively, and the salt spray tests also show good corrosion resistance. The electrochemical tests demonstrate that the self-corrosion current density and potential of the sample with hybrid coating are about 2.877×10?7 A/cm2 and?0.550 V, respectively. The metallographic and SEM images show that the hybrid coating is uniform and dense, and the EDS analysis confirms that the coating is mainly composed of Al, Si and Ce elements.

Study on corrosion resistance of the BTESPT silane cooperating with rare earth cerium on the surface of aluminum-tube

Bis-3-(triethoxysilyl)propyltetrasulfide(BTESPT) silane-rare earth cerium composite coatings on aluminum-tube were prepared at 60 °C by immersion method.The performance of composite coatings to protect the aluminum-tube against corrosion was investigated with potentiodynamic polarization curves,electrochemical impedance spectroscopy(EIS),and salt spray test(SST).The results of potentiodynamic polarization curves and EIS indicated that the self-corrosion current decreased by two orders of magnitude and the i...

EFFECT OF BRAZING TIME ON TiC CERMET/IRON JOINT BRAZED WITH Ag-Cu-Zn FILLER METAL

The brazing of TiC cermet to iron was carried out at 1223K for 5-20min using Ag-Cu-Zn filler metal. The formation phase and interface structure of the joints were investigated by electron probe microanalysis (EPMA), scanning electron microscopy (SEM) and X-ray diffraction (XRD), and the joint strength was tested by shearing method. The results showed: there occurred three new formation phases, Cu(s.s), FeNi and Ag(s.s) in TiC cermet/iron joint. The interface structure was expressed as TiC cermet/Cu(s.s)+FeNi/Ag(s.s)+a little Cu(s.s)+a little FeNi/Cu(s.s)+FeNi/iron, With brazing time increasing, there appeared highest shear strength of the joints, the value of which was up to 252.2MPa when brazing time was 10min.

Research on the influence mechanism of brazing seam geometry on gas pores in brazed joints

Gas pore is a common defect in brazed joint. It lowers the brazing rate and affects the properties of joint. Experimental results show that the application of unequal-gap brazing seam effectively decreases the amount and volume of gas pores, and increases brazing rate.This paper establishes a force model of unequal-gap brazing seam, and proposes the constitutive relationship between expulsion force and curvature. The force condition of gas bubble in geometrically different brazing seams were calculated, and the results were verified with experiments. The results show that the expulsion force of gas bubble is positively correlated to the curvature of the seam geometry. The gas bubble tends to move towards the direction with large curvature and wider gap. The directional bubble movement is obtained through varying the configuration of gas-liquid interface to meet geometric conditions. Gas bubble accelerates to expulse with arc, hyperbola and cycloid brazing seams, in which the best drainage effects of gas bubble occur for cycloid seams.

Microstructure and properties of the joints of Cu/Cu and metallized Cu / kovar brazed with a low-silver vacuum brazing filler metal

In an attempt to develop low-silver brazing filler metals used for hermetic sealing materials in the vacuum interrupter industry,the ternary Ag-50Cu-5Ga low-silver vacuum brazing filler metal was investigated.The melting temperature was measured by differential scanning calorimetry(DSC),and the brazability of Ag-50Cu-5Ga alloy on copper and metallized copper/kovar were ascertained at 850℃under 1×10-4 Pa in this article.The microstructures of the filler metal and the joints have been analyzed by using scanning electron microscopy(SEM),equipped with an energy dispersive spectroscopy.The results show that vacuum brazing was success to join with copper or metallized copper/kovar using Ag-50Cu-5Ga filler and reliable joints were obtained.There were Ag-rich phase,Cu-rich phase and a fine eutectic structure of Ag-based solid solution and Cu-based solid solution in the copper joints and the width of brazing seam is about 60μm.The joints of kovar alloy to copper after surface nickel plating was composed of AgCu eutectic phase,Ag,Cu,Cu2Ga and CuNi2 phase.The tensile strength was 167 MPa and 150 MPa,respectively.The tensile results of joints show that the joint strengths were equivalent to the traditional brazing filler metals.

2D Finite Element Computer Analysis of Strength for Brazed Joint of Cemented Carbide and Silver Brazing Filler Metal

Brazing has a wide acceptance in industries and its simplicity in variety of application attracts more and more patronage. The strength of brazing joint determines the reliability of brazed engineering components. So the need to ascertain the reliability or to predict its failure （without some destructive testing） becomes high even with a computer aided analysis using the Finite Element Analysis. Here, we have employed the services of FEA software, Abaqus CAE, as a tool for the computer calculation to investigate a joint case of cemented carbide brazed with silver-based filler metal. In this paper, 2D analysis has been adopted because the thickness of the material （in 2D） does not influence the final calculation results. We have applied constant loading and constant boundary condition to explore data from the elastic and plastic strain analysis through which we were able to predict the maximum joint strength with respect to the joint thickness. The pattern of the meshing was also significant. And the result could be transferable to a real-life field situation. The final results showed that there is an optimum thickness of the filler metal with the maximum strength which matches that obtained from experiment.

Brazeability evaluation of Ti-Zr-Cu-Ni-Co-Mo filler for vacuum brazing TiAl-based alloy

Ti-47Al-2Nb-2Cr-0.15B(mole fraction,%)alloy was vacuum brazed with amorphous and crystalline Ti.25Zr-12.5Cu-12.5Ni-3.0Co-2.0Mo(mass fraction,%)filler alloys,and the melting,spreading and gap filling behaviors of the amorphous and crystalline filler alloys as well as the joints brazed with them were investigated in details.Results showed that the amorphous filler alloy possessed narrower melting temperature interval,lower liquidus temperature and melting active energy compared with the crystalline filler alloy,and it also exhibited better brazeability on the surface of the Ti.47Al.2Nb.2Cr.0.15B alloy.The TiAl joints brazed with crystalline and amorphous filler alloys were composed of two interfacial reaction layers and a central brazed layer.Under the same conditions,the tensile strength of the joint brazed with the amorphous filler alloy was always higher than that with the crystalline filler alloy.The maxmium tensile strength of the joint brazed at 1273 K with the amorphous filler alloy reached 254 MPa.

Microstructure and properties of induction brazing nickel base/WC composite coating

BNi-2/WC composite wear-resisting coating was prepared on carbon steel by the method of induction brazing.The microstructure and phase composition of the composite coating were analyzed,and the bonding strength and wear-resisting performance of the coating were tested.During the process of induction brazing,the tungsten carbide partially dissolves and reacts with the filler metal alloy to form NiW compound phase,which realizes the metallurgical combination of tungsten carbide and filler metal alloy.The matrix of the filler metal alloy consists of Ni solid solution and Ni_(3)B/Ni_(3)Si eutectic phase,and the metallurgical diffusion reaction occurs between the filler metal alloy and the steel matrix.The mechanical analysis results show that the self-strength of the composite coating reaches 140 MPa and the bonding strength of the filler metal alloy to the steel matrix reaches 360 MPa.The dry sand rubber wheel wear testing machine showed that the coating weight loss was only 0.2824 g,which was only 1/5 of the weight loss of 65 Mn matrix under the same conditions.

Simulation and Optimization of the Fluid Solidification Process in Brazed Plate Heat Exchangers

When a brazed plate heat exchanger is used as an evaporator,the working mass in the channel may undergo soli-dification,thereby hindering the refrigeration cycle.In this study the liquid solidification process and its optimi-zation in a brazed plate heat exchanger are investigated numerically for different inlet velocities;moreover,different levels of corrugation are considered.The results indicate that solidificationfirst occurs around the con-tacts,followed by the area behind the contacts.It is also shown that deadflow zones exist in the sharp areas and such areas are prone to liquid solidification.After optimization,the solidification area attains its smallest value when a corrugation spacingλ=4.2 mm is considered.

Research on the heat conduction mechanism of induction brazecoating

Induction brazecoating technology is an important means to improve the surface properties of materials.In this paper,copper plate and corundum are selected as substrates for induction brazecoating respectively.The temperature variation of powder and paste coating is systematically studied,and the heat conduction mode and path in the brazecoating process are analyzed.The results show that rise of the coating temperature mainly depends on the heat absorption from the substrate.The liquid-solid interface conducts heat violently and advances step by step,which promotes the melting spread of metal filler metal.The powdery brazecoating material is in a free state,and there is a gas insulation film between the powder particles and the diamond,making it difficult for substrate to conduct heat to the coating.The binder not only assists forming,shell making and oxygen isolation,but also plays an important role during melting.

大尺寸AlN活性金属焊接覆铜基板的界面结合机理

基于190 mm×139 mm×0.635 mm的大尺寸AlN表面活性金属钎焊(AMB)覆铜板工艺制程,开展其界面显微组织、物相组成等的研究,确定钎焊界面结合机理,为制备大尺寸、低气孔、高剥离强度AlN-AMB覆铜板提供支持。结果表明,在大尺寸AlN-AMB覆铜板钎焊过程中,Ag-Cu-Ti合金钎料中的Ag-Cu合金与Cu箔扩散溶合,形成强的冶金结合界面。同时,钎料中的活性Ti原子向AlN基板表面扩散,并与其反应,生成厚度为0.5~1μm的TiN反应层,形成强的反应结合界面。此外,钎料熔体难以填充基板的AlN晶界和凹坑,其中的Ti原子也不与Y-Al-O第二相颗粒反应,导致AlN基板表面TiN反应层不连续分布,形成气孔,降低大尺寸AlN-AMB覆铜板的界面结合强度及可靠性。

保温时间对钛合金板翅式换热器真空钎焊过程温度场及残余应力的影响

钛合金板翅式换热器成品率较低、残余应力较大,该文针对钛合金板翅结构真空钎焊过程开展热-固耦合建模与仿真研究,阐述了钎焊过程温度均匀性及残余应力分布特征,探明保温时间对钛合金板翅式换热器真空钎焊过程温度场及残余应力的影响机理.结果表明,板翅结构两侧温度较高,中部温度较低,延长保温时间可有效改善板翅结构的温度均匀性.残余应力均主要集中于翅片上表面与隔板背侧中部,在钎缝及夹持点处存在明显的应力集中现象,保温时间越长翅片钎缝的残余应力越小.模拟得到钛合金板翅式换热器真空钎焊中残余应力与试验结果相吻合,相对误差为5.3%,验证了该模型的准确性.

MONOBRAZE单层翅片箔与三层复合翅片箔耐腐蚀性能对比研究

采用金相显微镜、电位计、EPMA和SWAAT腐蚀试验等手段,研究了分别采用三层复合翅片箔和MONOBRAZE单层翅片箔钎焊后的两种冷凝器接头断面形貌、微观组织、元素扩散、电极电位和耐腐蚀性能。结果表明:与热轧三层复合翅片箔相比,MONOBRAZE单层翅片具有同样的钎焊连接效果,而且钎焊后强度更高、无明显熔蚀、翅片厚度无明显减薄,为MONOBRAZE翅片进一步减薄、大面积替代复合翅片、降低热交换器制造成本创造了有利条件。同时,采用MONOBRAZE单层翅片钎焊后的冷凝器有着更优良的耐腐蚀性能,MONOBRAZE翅片优先被腐蚀,可以对MPE管起到更好的牺牲阳极保护作用,大幅提高热交换器整体寿命。

石墨管与不锈钢管钎焊接头的组织和残余应力

为使石墨材料能够在空间核电散热装置中更充分地发挥其价值,本文采用BNi-2钎料真空钎焊连接等静压石墨管和304不锈钢管,研究了石墨/BNi-2/不锈钢接头在1010℃、保温90 min条件下的显微组织和不同冷却工艺对接头残余应力的影响。研究表明:在1010℃,保温90 min条件下,钎焊接头致密无裂纹,Cr元素在石墨侧与石墨基体反应形成Cr_(7)C_(3)反应层,在不锈钢侧形成了σ-FeCr扩散层,界面接头组成为石墨/Cr_(7)C_(3)/Ni(s,s)+Ni_(3)Si/σ-FeCr/不锈钢;经缓冷工艺处理的接头,常温剪切强度为28.38 MPa,比炉冷处理的接头剪切强度提高了22%;有限元数值分析结果表明,采用缓慢冷却的钎焊工艺可以有效缓解钎焊接头在冷却过程中产生的残余应力,符合剪切实验结果。

TC4低熔蚀钎料设计及对接头组织和性能的影响

薄壁钛合金的焊接是制造高性能板翅式钛合金换热器的关键步骤,针对薄壁钛合金钎焊时母材熔蚀严重的问题,设计并制备了Zr-16Ti-9Cu-11Ni低熔点非晶箔带钎料,对TC4钛合金在840~980℃,保温时间10~120 min范围内进行钎焊,结合扫描电子显微镜(SEM)和X射线衍射(XRD)以及透射电镜(TEM)分析了接头典型组织及其演变过程。结果表明,焊缝组织主要由(Ti,Zr)_(2)(Cu,Ni)化合物、α-Ti和β-Ti组成,随钎焊温度升高和保温时间延长,接头脆性相逐渐减少直至消失,母材熔蚀程度逐渐加重。通过接头抗剪强度对其性能进行评估,结果表明,当钎焊温度在940℃、保温时间10 min时,接头强度最优,为386 MPa,但此时母材熔蚀程度较大,不适合实际生产中的焊接;综合考虑母材熔蚀程度与接头抗剪强度,880~920℃为合适的生产温度区间;通过观察接头断裂路径及断口形貌,接头的断裂模式为脆性断裂。

基于钎焊工艺的环路热管耦合系统设计及验证

随着航天技术的发展,航天器的功能集成度提升,对系统散热要求越来越高。环路热管作为一种两相态高效传热部件,具备远距离、逆重力、布局灵活等特点,常应用于单一热源下的定向热量传输;对于多点热源的复杂环境,环路热管系统稳定性差,一般很难适应。针对复杂空间热流下多点分散热源的散热需求,设计了一种基于钎焊工艺的环路热管强耦合热管理系统,对关键耦合参数进行了敏感性分析,并开展了相关试验,验证了界面低热阻、强耦合等关键技术的可行性,提升平台散热能力达52%。环路热管实现了在陆地探测四号01星载荷舱上的应用,为国际首次在平台系统的大规模应用,载荷舱散热能力由4 kW提升到6 kW,为大功率固态放大器提供0~20℃在轨温度环境。环路热管突破了在平台应用的约束限制,为后续环路热管的热耦合系统设计提供借鉴。

热流道板真空钎焊有限元模拟与分析

采用BNi-2镍基钎料对热流道板进行真空钎焊,须根据钎焊件设定加热工艺曲线。加热工艺曲线的设定是钎焊过程最重要的环节之一,决定着钎焊的质量和效率。该文结合真空加热的特点及钎焊要求,运用Ansys有限元软件数值模拟的方法,对壁厚、体积较大的多层热流道板真空钎焊进行仿真分析,通过对比不同工艺方案及不同钎焊件的模拟结果,探究真空钎焊过程升温规律,从而调整各阶段的相关参数及制定合理的加热工艺曲线,避免了现场反复调试参数造成的资源浪费,节约了时间和成本,提高了效率。此外,通过在实际钎焊试验过程中布置热电偶对钎焊件测量温度,并与数值模拟结果对比,两者基本吻合,验证了有限元分析的准确性,能为之后其他零部件的真空钎焊提供参考。

混合钎料对镍基单晶高温合金大间隙钎焊接头组织和性能的影响

【目的】采用一种新型镍基钎料和母材成分一致的高熔点合金粉混合的方法制备出混合钎料,研究了添加的高熔点合金粉的粒径和配比对钎缝微观组织和力学性能的影响。【方法】采用扫描电子显微镜对钎焊接头的析出相、元素分布、微观组织进行了分析,并对钎焊接头的硬度及持久性能进行了测试。【结果】研究表明,接头主要由钎料合金区(FAZ)、界面连接区(IBZ)和扩散影响区(DAZ)三部分组成。钎料合金区主要由M3B2和M8B型硼化物及γ/γ′相组成。界面连接区由γ和γ′沉淀强化相组成。当合金粉粒径为44μm和75μm时,均可得到无缺陷的焊接接头;但当合金粉粒径尺寸达177μm时,钎缝内会形成孔洞缺陷。【结论】随着合金粉比例的提高,接头连接区的显微硬度有所上升。当合金配比由30%到50%,接头的持久寿命由15 h增加至34 h;但进一步提升比例至60%时,接头的持久寿命下降至0.6 h。该文的结果可为实现高温热端零部件的连接和修复工程应用提供理论依据和参考价值。

AlN基板表面状态对AlN-AMB覆铜板剥离强度影响机理的研究

为了探究AlN基板表面状态对AlN-AMB覆铜板剥离强度影响的机理,对研磨型和即烧型两类AlN基板表面的微观形貌及其制备的AlN-AMB覆铜板界面反应层、断面和断层微观显微结构进行分析。结果表明,即烧型AlN基板表面平整、致密,其制备的AlN-AMB覆铜板界面反应层平整、致密,铜与AlN基板剥离的断层位于基体内部,Cu发生明显塑性变形,剥离强度高达19.053 N/mm。而研磨型AlN基板表面存在微裂纹和碎晶粒,由其制备的AlN-AMB覆铜板界面反应层凹凸不平,且不连续,钎料渗入AlN基板亚表层的微裂纹中,易于诱发应力集中,铜与AlN基板剥离的断层位于AlN基体的亚表层,Cu塑性变形小,剥离强度只有5.789 N/mm。