Microstructure and strength of brazed joints of TiB2 cermet to TiAl-based alloys

In this study, TiB2 cermet and TiAl-based alloy are vacuum brazed successfully by using Ag-Cu-Ti filler metal.The microstructural analyses indicate that two reaction products, Ti ( Cu, Al ) 2 and Ag bused solid solution ( Ag ( s. s ) ) , are present in the brazing seam, and the iuterface structure of the brazed joint is TiB2/TiB2 Ag ( s. s ) /Ag ( s. s ) Ti ( Cu,Al)2/Ti( Cu, Al)2/TiAl. The experimental results show that the shear strength of the brazed TiB2/TiAl joints decreases us thebrazing time increases at a definite brazing temperature. When the joint is brazed at 1 223 K for 5 min, a joint strength up to 173 MPa is achieved.     

Microstructure and properties of the joints of ZrO_2 ceramic/stainless steel brazed in vacuum with AgCuTi active filler metal

The ZrO_2 ceramic was successfully jointed to stainless steel by vacuum brazing with active filler metal. The AgCuTi active filler metal was used and the joining was performed at a temperature of 850 ℃ for 10 min. The microstructures of the joints were characterized by metallographic microscopy,scanning electron microscopy( SEM),and energy dispersive spectroscopy( EDS).Metallographic microscopy analysis shows that the morphology of the cross section was a sandwich structure and the Ti O is observed in the surface of ZrO_2/stainless steel. The diffusion and enrichment of the elements are the key roles in the brazing of ZrO_2 ceramic and stainless steel. The formation of TiCu compounds inhibited the further diffusion of titanium into stainless steel or the ZrO_2 ceramic to form TiO compound. In the experimental conditions,the average tensile strength is 80 MPa for the joint of ZrO_2 ceramic/Ag Cu Ti/stainless steel systems. A complete joint is formed between the ZrO2 ceramic and stainless steel with the leakage rate at the degree of 10~(-12) Pa·m~3/s.     

Effect of parameters on interface of the brazed ZrO2 ceramic and Ti-6Al-4V joint using Ti-based amorphous filler

A commercially available Ti47 Zr28 Cu14 Ni11 (at. pct) amorphous filler foil was used to join ZrO2 ceramic and Ti-6Al-4V alloy. According to experimental observations, the interface microstructure accounts for the mechanical properties of the joints. The effects of brazing conditions and parameters on the joint properties were investigated. The joint shear strength showed the highest value of about 108 MPa and did not monotonously increase with the brazing time increasing. It was shown that decreasing of brazing cooling rate and appropriate filler foil thickness gave higher joint strength.     

Graphene-coated copper foam interlayer for brazing carbon/carbon composite and niobium

Problems such as poor structural integrity, inhomogeneous dispersion, and agglomeration of graphene in the brazing seam are typically encountered for graphene additives in a brazed joint interface. To resolve these problems, a plasma-enhanced chemical vapor deposition process was employed for in-situ preparation of a high-quality graphene-coated copper (Cu) foam composite interlayer prior to be applied for brazing carbon/carbon composite and niobium. The prepared graphene and the brazed joints were characterized via Raman spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The results revealed that graphene was evenly distributed in the brazing seam with the help of the Cu foam, which was characterized by interconnected porosity. Simultaneously, the excellent chemical inertia of graphene inhibited the collapse of the Cu foam, based on which the thermal residual stress in the joint was effectively mitigated due to the synergistic reinforcement effect of the Cu foam (with good plastic deformation capacity) and graphene (with extremely low coefficient of linear expansion). This effect led to significant improvement in the average shear strength of the joint.     

Electron beam braze-welding of vanadium alloy to stainless steel with electroplated Cu/Ag coatings

Cracks may easily occur in the fusion weld between vanadium alloys and stainless steel due to the brittle intermetallics and welding stress.The high vacuum electron beam braze-welding has been successfully used to join vanadium alloy(V-5Cr-5Ti) to stainless steel(HR-2) with electroplated Cu and Ag coating.To investigate the effects of electroplated coating on the weldability,the joint appearance,the microstructure and the mechanical properties of the joints have been thoroughly analyzed.The results show that the joint surface configuration was good and root reinforcement was full and smooth.A reaction zone(RZ) was gained on the interface between the VSCrSTi alloy and HR-2 stainless steel base metals.The width of reaction zone at the top of the joint was up to 0.65 mm,wider than that in the bottom of the joint(0.46 mm).The reaction zone consisted of considerably smaller dendritic structures with an average grain size of less than 10 μm.Element Ag and Cu almost enriched the interface between V-5Cr-5Ti alloy substrate and RZ,serving as a physical barrier which decreases or avoids the formation of intermetallics.The maximum tensile strength of vanadium alloy/stainless steel dissimilar alloy joint was more than 300 MPa.The joint was defects free.     

Characterization of diffusion-bonded joint between Al and Mg using a Ni interlayer

Aluminum and magnesium were joined through diffusion bonding using Ni interlayer. The microstructure and mechanical performance of the Al/Ni/Mg joints at different temperatures was investigated by means of scanning electron microscope(SEM), electro-probe microanalyzer(EPMA), X-ray diffraction(XRD), Vickers hardness testing, and shear testing. The results show that the addition of Ni interlayer eliminates the formation of Mg–Al intermetallic compounds and improves the bonding strength of the Al/Mg joints. The Al/Ni/Mg joints are formed by the diffusion of Al, Ni and Mg, Ni. The microstructure at the joint interface from Al side to Mg side is Al substrate/Al–Ni reaction layer/Ni interlayer/Mg–Ni reaction layer/Mg substrate multilayer structure. The microhardness of the Mg–Ni reaction layer has the largest value of HV 255.0 owing to the existence of Mg_2Ni phase.With the increase of bonding temperature, the shear strength of the joints increases firstly and then decreases.The Al/Ni/Mg joint bonds at 713 K for 90 min, exhibiting the maximum shear strength of 20.5 MPa, which is greater than that of bonding joint bonded directly or with Ag interlayer. The fracture of the joints takes place at the Mg–Ni interface rather than the Al–Ni interface, and the fracture way of the joints is brittle fracture.     

New approaches for brazing temperature sensitive materials

PVD deposited copper interlayers as filler materials were used in order to manufacture TLP brazed magnesium joints. The microstructure and interface characteristics of the overlap joints were investigated by optical microscopy, scanning electron microscope with energy dispersive spectrometer and tensile testing. Sound brazed joints could be achieved. The dwell time is the main factor to control the thickness of the reaction layer. It was shown that the deposited copper filler metal clearly reacted with the magnesium substrate , resulting in the formation of a magnesium solid solution （Mg） with different amount of copper, aluminum and zinc as well as Mg2Cu phases. With the progressing diffusion, the formation of intermetaUic compounds was suppressed and the hardness distribution in the brazing seam homogenized. The joints fractured at the interface, and the maximum average tensile shear strength of overlap joints reached 85 MPa.     

Study on interracial structure and strength of Si3N4/Ti/Cu/Ti/Si3S4 PTLP bonding

Partial transient liquid-phase bonding （PTLP bonding） of Si3N4 ceramic with Ti/Cu/Ti multi-interlayer is performed with changing the thickness of Ti foil. The influence of Ti foil thickness on interface structure and joint strength was discussed. The joint interface structures are investigated by scanning electron microscope （SEM） and energy dispersion spectroscopy（EDS）. The results show that the maximum joint strength of 210 MPa is obtained at room temperature in the experiments. When joining temperature and time are not changed and the process of isothermal solidification is sufficient , interface structure, reaction layer thickness and isothermal solidification thickness change with the thickness of Ti foil.     

Brazing of 5A01 aluminum alloy using Al-Cu-Si-Ni filler metal

The vacuum brazing of 5 A01 aluminum alloy using Al-Cu-Si-Ni filler metal was investigated at 550 ℃ and 560 ℃,respectively. Microstructure and properties of brazed 5 A01 alloy joints were investigated by tensile-shear tests and scanning electron microscopy analysis. The effects of brazing temperature and holding time on the shear strength and microstructure of the joints were studied. The results show that the different intermetallic compounds such as Al-Cu-Ni and Mg_2 Si formed in the bonding area. Shear strength increased with holding time and brazing temperature. The average shear strengths increased from 42. 3 MPa brazed at 550 ℃for 5 min to 68 MPa brazed at 560 ℃ for 15 min. Discontinuous cracks were found in the joint brazed at 550 ℃ for 5 min,and the joint showed poor shear strength. high shear strength were obtained in the joints brazed at 560 ℃ for 15 min.     

Microstructure and fracture morphology of Mo－Cu/Cr18－Ni8 brazed joint in vacuum*

Mo-Cu composite and Cr18-Ni8 stainless steel were brazed with Ni-Cr-P filler metal in a vacuum of 10-4 Pa and a Mo-Cu/Cr18-Ni8 joint was obtained. Microstructure in Mo-Cu/Cr18-Ni8 joint was investigated by field-emission scanning electron microscope( FE-SEM) with energy dispersive spectrometer( EDS). Shear strength of Mo-Cu/Cr18-Ni8 lap joint was measured by electromechanical universal testing machine. An excellent Mo-Cu/Cr18-Ni8 joint with a shear strength of 155 MPa was achieved at 980 ℃ for 20 min. Brazed joint was mainly comprised of eutectic structure in the center of brazing seam,matrix structure and lump structure. Ni-Cu( Mo) and Ni-Fe solid solution were at the interface beside Mo-Cu composite and Cr18-Ni8 stainless steel,respectively. Shear fracture exhibited mixed ductile-brittle fracture feature with trans-granular fracture,ductile dimples and tearing edges. Fracture originated from the interface between brazing seam and Mo-Cu composite.     

Interface structure and strength of brazed joints between TiC ceramic and iron

Abstract

The brazing of TiC ceramic to iron was carried out at 1123–1273 K for 5–20 min using Ag–Cu–Zn filler metal. Interface structure and shear strength of joints were investigated, the former via electron probe microanalysis, scanning electron microscopy, and X-ray diffraction, and the latter via the shearing method. The results show the formation of three phases in the TiC ceramic–iron joint, namely, copper base solid solution, FeNi, and silver base solid solution. The highest joint shear strength of 256.5 MPa is obtained for a brazing temperature of 1173 K and brazing time of 5 min.     

添加Zn对AgCu钎料在TiC金属陶瓷表面润湿性的影响

分别采用AgCu共晶钎料和AgCu共晶钎料中添加30%(质量分数)Zn的AgCuZn钎料在TiC金属陶瓷表面进行润湿试验.结果表明,Zn元素的添加显著改善了钎料在TiC金属陶瓷表面的润湿性;AgCu钎料润湿TiC金属陶瓷时,从近钎料外表面到钎料/陶瓷界面,组织依次为Ag(s.s)+Cu(s.s)/(Cu,Ni)+Ag(s.s)/TiC金属陶瓷+Ag(s.s)+Cu(s.s)/TiC金属陶瓷;而采用AgCuZn钎料润湿TiC金属陶瓷后,从近钎料外表面到钎料/陶瓷界面,组织依次为Ag(s.s)+Cu(s.s)+(Cu,Ni)/Ag(s.s)+Cu(s.s)/(Cu,Ni)/TiC金属陶瓷+Ag(s.s)+Cu(s.s)/TiC金属陶瓷.Zn元素在真空中挥发促进了界面处Ni原子的溶解和扩散,使钎料在陶瓷表面的润湿角由120.6°减小到33.9°.     

AgCuNiLi钎焊TiC金属陶瓷与GH3128界面结构及接头性能

采用AgCuNiLi钎料对TiC金属陶瓷与GH3128镍基高温合金进行钎焊。结果表明:当钎焊温度为840℃,保温10min时,接头典型界面结构可以表示为:TiC金属陶瓷/(Cu,Ni)/Ag(s.s)+Cu(s.s)/(Cu,Ni)/GH3128。随着钎焊温度的升高或保温时间的延长,TiC金属陶瓷附近的(Cu,Ni)固溶体层厚度增大,且向钎料内部呈树枝状长大,钎料内部的Ag-Cu共晶组织逐渐减少。界面机理分析表明:钎料中Li的加入能促进界面上(Cu,Ni)固溶体的形成;但(Cu,Ni)固溶体的继续长大则受钎料中Cu元素的扩散程度控制。当加热温度由810℃升高到960℃,接头抗剪强度呈现先增大,然后缓慢减小的变化趋势。当加热温度为880℃、保温时间为10min时,接头抗剪强度达到最大值204MPa。     

Ag-Cu-Ti钎料高频感应钎焊TiAl/40Cr

采用高频感应加热的方式 ,在Ar气保护条件下 ,用Ag -Cu -Ti钎料实现了TiAl基合金与 4 0Cr钢的钎焊连接 ;采用扫描电镜、电子探针、X射线衍射分析等手段对断口、界面、生成相进行了分析 ,并且测试了接头的抗拉强度。结果表明 ,在界面上有Ti(CuAl) 2 、Ag[s,s]、TiC等反应相生成 ,典型接头界面结构为TiAl/Ti(CuAl) 2 +Ag[s ,s]/Ag[s,s]/TiC/ 4 0Cr) ;断裂位置及接头的抗拉强度随保温时间而变化 ;当钎焊连接温度为 114 3K ,保温时间 0 .9ks时接头抗拉强度值最高 ,达到 2 98MPa,断裂主要发生在Ti(CuAl) 2 层内部     

SiC陶瓷真空钎焊接头界面结构及机理分析

采用Ti-Zr-Ni-Cu钎料对SiC陶瓷进行了真空钎焊,研究了SiC陶瓷真空钎焊接头的界面显微组织和界面形成机理.试验中采用扫描电子显微镜(SEM)对接头组织进行了观察,并进行了局部能谱分析.结果表明,接头界面产物主要有TiC,Ti₅Si₃,Zr₂Si,Zr(s,s),Ti(s,s)+Ti₂(Cu,Ni)和(Ti,Zr)(Ni,Cu)等.接头的界面结构可以表示为:SiC/TiC/Ti₅Si₃+Zr₂Si/Zr(s,s)/Ti(s,s)+Ti₂(Cu,Ni)/(Ti,Zr)(Ni,Cu).钎焊过程分为五个阶段:钎料与母材的物理接触;钎料熔化和陶瓷侧反应层开始形成;钎料液相向母材扩散、陶瓷侧反应层厚度增加,钎缝中液相成分均匀化;陶瓷侧反应层终止及过共晶组织形成;钎缝中心金属间化合物凝固.在钎焊温度960℃,保温时间10 min时,接头抗剪强度可达110 MPa.     

Zn元素含量对AgCuZn钎料在TiC金属陶瓷表面润湿性的影响

在AgCu共晶钎料中添加不同量的Zn元素熔炼成AgCuZn钎料,并在陶瓷表面进行润湿试验.结果表明,当Zn元素含量为25%(质量分数)时,钎料在陶瓷表面润湿角最小,为23.5°;从近钎料外表面到钎料/陶瓷界面,组织依次为(Cu,Ni)+Ag(s.s)+Cu(s.s)/Ag(s.s)+Cu(s.s)/(Cu,Ni)/Ag(s.s)+Cu(s.s)+TiC金属陶瓷/TiC金属陶瓷.随着钎料中Zn元素含量增加,钎料/TiC金属陶瓷界面处(Cu,Ni)固溶体形态由块状弥散分布变为层状分布;Zn元素在真空中挥发能促进界面元素的溶解和扩散,从而使固液界面张力减小、钎料表面张力增大,最终导致润湿角随着钎料中Zn元素含量增加而出现最小值.     

TiAl基合金与Ti合金的真空钎焊

采用Ag-Cu钎料与Ti-Zr-Ni-Cu钎料,对TiAl与Ti合金进行了真空钎焊试验,主要研究了采用两种钎料时的界面反应以及钎焊温度对界面组织及性能的影响.研究发现,采用Ag-Cu钎料时界面结构为:Ti/Ti(Cu,Al)2/TiCux Ag(s,s)/Ag(s,s)/Ti(Cu,Al)2/TiAl,当钎焊温度T=1 223 K,保温时间t=10 min时接头的剪切强度达到223.3 MPa;采用Ti-Zr-Ni-Cu钎料时在界面出现了Ti2Ni,Ti(Cu,Al)2等多种金属间化合物,当钎焊温度T=1 123 K,保温时间t=10 min时接头的剪切强度达到139.97 MPa.     

AgCu钎料钎焊TC4钛合金与QCr0.8铬青铜接头界面结构及性能

采用AgCu28钎料实现了TC4钛合金与QCr0.8铬青铜的真空钎焊,利用SEM, EDS以及XRD等分析方法确定TC4/AgCu/QCr0.8接头的典型界面结构为TC4钛合金/CuTi +Cu3Ti2 +CuTi2/Ag(s,s) +Cu4Ti/Ag(s,s)+Cu(s,s)/QCr0.8铬青铜. 研究了工艺参数对接头组织和性能的影响. 结果表明,随着钎焊温度和保温时间的增加,钎缝中银铜共晶组织减少,钛铜化合物增多. 接头抗剪强度随钎焊温度的升高先增加后降低,在钎焊工艺参数为890 ℃/0 min时,获得最大抗剪强度449 MPa.保温时间的延长使得接头脆性钛铜化合物增多,接头性能下降,因此随保温时间延长接头抗剪强度显著降低.     

Interface structure and mechanical property of the brazed joint of graphite and copper

A kind of self-made AgCuTiSn braze alloy powder was used to join graphite and copper. The whole brazing process was performed under vacuum circumstances at different temperatures (1033-1193 K) for several holding time (300-1800 s). According to scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and electron probe X-ray microanalysis (EPMA) results, the reaction products of the interface are TiC, Ti3Sn, Cu(s. s), Ag(s. s) and Cu-Sn compound. As the brazing parameters increase, the quantity of Ag(s. s) in the braze alloy and C fibers on graphite/AgCuTiSn interface reduce, while that of Cu (s. s) in the braze alloy improves. When the brazing temperature is 1093 K and holding time is 900 s, the joint can obtain the maximum room temperature shear strength 24 MPa.