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.

Brazing of directionally solidified TiAl-based alloy with Ti-Zr-Ni-Cu filler metal

Brazing of directionally solidified TiAl-based alloy with Ti-Zr-Ni-Cu filler metal was investigated.For brazing,according to the experiments,the relationship between brazing parameters and the joints strength was analyzed and the optimum brazing parameters were obtained.The maximum shear strength is 248 MPa for the joint brazed at 1050 ℃ for 10 min,and the interface structure is TiAl/the diffusion layer of base metal and the filler metal+Ti3Al/the residual filler metal+Ti3Al/the diffusion layer of base metal and the filler metal+Ti3Al/TiAl.

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.

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。

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。

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。

WC含量对WC增强镍基复合涂层界面组织的影响

WC(碳化钨)增强镍基复合涂层具有高耐磨、耐腐蚀、高硬度特点,在盾构部件、旋耕刀具、石油钻探等领域广泛应用.为提高水力机械过流部件服役寿命,以WC颗粒和镍基粉状钎料为涂层材料,采用真空炉中热辐射钎涂方法在奥氏体不锈钢表面成功制备WC增强镍基复合钎涂层,借助扫描电镜、X射线衍射仪等对钎涂层显微组织和界面行为进行系统分析.结果表明,硬质相WC与镍基钎料界面结合存在机械咬合与冶金结合双重作用;钎涂层与钢基体之间存在一定程度的成分扩散,其较狭窄扩散区宽度约100μm;当WC含量低于25%时,复合钎涂层对不锈钢基体润湿性较好,可制备出最低孔隙率1.08%的复合钎涂层.

(TiZrHf)_(40)(NiCu)_(55)Al_(5)高熵非晶钎料真空钎焊Ti_(2)AlNb/GH4169合金

设计了一种高熵非晶钎料(TiZrHf)_(40)(NiCu)_(55)Al_(5)对Ti_(2)AlNb合金与GH4169镍基高温合金进行真空钎焊,分析了钎焊工艺对Ti_(2)AlNb合金/GH4169镍基高温合金接头界面组织形貌、力学性能及断裂行为的影响规律.结果表明,钎焊接头可划分为Ti_(2)AlNb/等温凝固区(Ⅰ区)/钎缝中心区(Ⅱ区)/扩散反应区(Ⅲ区)/GH4169;钎焊接头典型界面组织为Ti_(2)AlNb/B2+Ti_(2)Ni(Al,Nb)/(Ti,Zr,Hf)(Ni,Cu)/(Ni,Cr,Fe,Ti)ss+Cr-rich(Ni,Cr,Fe)ss+Ni-rich(Ni,Cr,Fe)ss+(Ni,Cr,Fe)ss/GH4169;随钎焊温度升高和保温时间延长,钎焊接头的抗剪强度均呈现出先增大后减小的趋势,当钎焊温度为1020℃、钎焊时间为15min时,接头的抗剪强度达到最大237 MPa.断口分析表明,接头主要断裂在Ti_(2)Ni(Al,Nb)+(Ti,Zr,Hf)(Ni,Cu)+(Ni,Cr,Fe,Ti)ss处,并逐渐向扩散反应区扩展,断口形貌呈现出典型的解理断裂特征.

银铜侧向复合材料界面结合机理分析

本文采用“包覆锭坯+扩散烧结+冷轧复合”联合工艺制备了银铜侧向复合带材,利用金相显微镜(OM)、扫描电镜(SEM)和能谱仪(EDS)观察分析银铜复合界面结构和元素分布,并分析其银铜复合界面的结合机理。结果表明,银铜复合界面形成过程为:1)银铜接触界面处凹凸不平的表面在轧制力的作用下相互咬合,形成机械结合界面;2)接触面在轧制力的作用下,银铜表面氧化膜破裂,新鲜表面质点间在轧制变形热的作用下产生原子结合;3)在扩散烧结过程中,银铜界面处的原子在高温作用下被激活,银铜原子相互扩散,在界面处发生银铜共晶反应形成液相金属层,随着烧结时间的延长,其共晶反应液相层厚度逐渐增加,随后冷凝结晶,使银铜实现侧向冶金结合。4)在后续中间退火过程中,共晶层与两侧的铜、银基体相互扩散,铜、银原子向更深的方向逐渐扩散,在靠近共晶层铜侧和银侧逐步形成固溶体层,使银与铜的结合强度进一步提高。银铜侧向复合界面结合机理包含机械咬合结合、接触共晶反应自钎焊结合和原子扩散结合3种,复合界面结合强度较好,剪切强度达220 MPa。