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 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.

Effect of Zr on microstructure and mechanical properties of 304 stainless steel joints brazed by Ag-Cu-Sn-In filler metal

The effect of Zr on the microstructure and mechanical properties of 304 stainless steel joints brazed with Ag-Cu fillers was studied.The incorporation of Zr had little effect on the solid-liquid phase line of the fillers,and the melting temperature range of the fillers was narrowed,which enhanced their fluidity and wettability.The presence of Zr in the form of heterogeneous particles augmented the nucleation rate during solidification,transforming the intermittently distributed gray-black coarse dendrites into cellular crystals.This structural transformation led to fragmentation and refinement of the microstructure.The dissolution of Zr into Ag and Cu promoted the transformation of low-angle grain boundaries to high-angle grain boundaries(HAGBs),hindering crack propagation.Zr element in the brazing seam led to grain refinement and increased density of grain boundaries.The grain refinement could disperse the stress,and HAGBs could resist the dislocation movement,improving the joint strength.The results display that when Zr content was 0.75 wt.%,the maximum strength was 221.1 MPa.The fracture occurred primarily at the brazing seam,exhibiting a ductile fracture.

Evolution of interfacial microstructure and mechanical properties of Nb521/GH99 brazed joints using Ti-35Ni filler alloy

The dissimilar brazing of Nb521 niobium alloy to GH99 superalloy was achieved successfully using Ti–35Ni brazing filler under vacuum.The effects of brazing temperature and holding time were systematically analyzed on the interfacial microstructure evolution and mechanical properties of joints.The joints brazed at 1120℃ for 10 min exhibited a typical interfacial structure composed of Nb521/β-(Nb,Ti)+TiNi/TiNi+Ti_(2)Ni/TiNi+TiNi_(3)/Cr-rich TiNi/Ti-rich(Ni,Cr)_(ss)/(Ni,Cr)_(ss)/GH99.The findings indicated that as the brazing temperature or holding time increased,the presence of brittle Ti_(2)Ni compounds decreased while the formation of TiNi_(3) gradually increased and tended to coarsen.The shear strength of joints exhibited variations corresponding to changes in interfacial brittle compound,and reached the highest value of 121 MPa at 1120℃ for 10 min.In the context of shear testing,all joints displayed clear brittle fracture patterns,with fractures predominantly occurring at the brittle compounds,namely,Ti_(2)Ni and TiNi_(3) phases.

Contact-reactive brazing mechanism of Al_(0.3)CoCrFeNi high-entropy alloys using a niobium interlayer

The contact-reactive brazing of Al_(0.3)CoCrFeNi high-entropy alloys with a Nb interlayer was researched.The effects of Nb thickness and brazing temperature on the interfacial microstructure and mechanical properties of Al_(0.3)CoCrFeNi joints were investigated.The results show that with Nb thickness increasing from 10 to 100μm,the average width of Al_(0.3)CoCrFeNi joints is increased from 127 to 492μm and the erosion volume of Al_(0.3)CoCrFeNi base metals(BMs)by face-centered cubic-Nb eutectic liquid is enlarged accordingly.With increasing brazing temperature from 1280 to 1360℃,the intergranular penetration of eutectic liquid into Al_(0.3)CoCrFeNi BMs becomes more severe and lamellar Laves phase is broken-up and spherized.The shear strength of joint is increased gradually from 374 to 486 MPa and then decreased to 475 MPa.The maximum shear strength value of 486 MPa is obtained when brazing at 1340℃ for 10 min,reaching about 78% of the shear strength of Al_(0.3)CoCrFeNi BMs.Besides,the brazing mechanism was analyzed in details.

Microstructure and mechanical properties of SiC/Inconel 718 joints brazed with CoFeCu3.5Mn3.5Cr high-entropy alloy filler

Achieving high-quality joining of silicon carbide(SiC)ceramics and Inconel 718 alloy has become a significant challenge for the brazing process,which is strongly dependent on the filler material.A novel composite interlayer consisting of high-entropy alloys(HEAs),HEA/Ni/HEA,was proposed to reduce the formation of intermetallic compounds in the brazed joints of SiC ceramics and Inconel 718 alloy.A reliable SiC/Inconel 718 brazed joint was produced at 1120℃ for 60 min.The results showed a significant reduction in the number of NiSi compounds in the brazed joint.The brazing seam structure near SiC side was filled with face-centered cubic phases with good plasticity and soft Cu-rich phases due to the high-entropy effect,which effectively suppressed the formation of intermetallic compounds.The maximum shear strength of the brazed joint reached 88 MPa,showing excellent tensile strength.The results provide a valuable basis for improving the joint quality of SiC ceramics and metals by adding high-entropy alloy fillers.

Research status of crack problem in laser brazing diamond

Diamond tools have been widely used in national defense military,automobile manufacturing,resource exploitation and other fields.Laser brazing diamond technology is often applied to the preparation of diamond tools.However,the formation and expansion of cracks in the process of laser brazing diamond seriously affect the mechanical properties of diamond tools.In order to solve the crack problem of laser brazing diamond,many scholars are committed to the research on improving the solder,optimizing the laser process parameters,improving the laser brazing equipment,optimizing the design of joint form,and developing ultrasonic-assisted laser brazing technology,etc.These studies have achieved certain results.Aiming at the research status of laser brazing diamond crack problem,the crack characteristics of brazing diamond are firstly introduced,and the formation reasons of laser brazing diamond crack are elaborated.Then,the elemental characteristics of brazing filler metals used in brazing diamond are introduced.The influences of Ni-Cr and Ag-Cu-Ti alloy solder and laser process parameters on the crack problem are viewed.Finally,the solutions to the crack problem by scholars at home and abroad in recent years are summarized,and the future research directions to solve crack problem are prospected.

Application of energy,electronic and interface bonding properties in highly reliable brazing joints between dissimilar materials

Brazing,an important welding and joining technology,can achieve precision joining of materials in advanced manufacturing.And the first principle calculation is a new material simulation method in high-throughput computing.It can calculate the interfacial structure,band structure,electronic structure,and other properties between dissimilar materials,predicting various properties.It plays an important role in assisting practical research and guiding experimental designs by predicting material properties.It can largely improve the quality of welded components and joining efficiency.The relevant theoretical foundation is reviewed,including the first principle and density functional theory.Exchange-correlation functional and pseudopotential plane wave approach was also introduced.Then,the latest research progress of the first principle in brazing was also summarized.The application of first principle calculation mainly includes formation energy,adsorption energy,surface energy,adhesion work,interfacial energy,interfacial contact angle,charge density differences,density of states,and mulliken population.The energy,mechanical,and electronic properties were discussed.Finally,the limitations and shortcomings of the research in the first principle calculation of brazed interface were pointed out.Future developmental directions were presented to provide reference and theoretical basis for realizing high-throughput calculations of brazed joint interfaces.

PERFORMANCE OF BRAZED DIAMOND CUP-TYPE WHEELS WITH DEFINED GRAIN PATTERN IN GRINDING CEMENTED CARBIDE

A new cup-type grinding wheel of the brazed monolayer diamond is developed with a defined grain pattern on the wheel surface. Grinding performance of the brazed wheel in the surface grinding of cemented carbide is studied. Experimental results show that when continuous dry grinding is employed, grits of the brazed diamond grinding wheel fail mainly in attritious wear and fracture modes and no pull-out ones are found in conventional electroplated and sintered diamond wheels. It indicates the strong retention of brazing alloy to diamond grits and the longer service life of the wheel. In addition, the ground surface has good roughness. The theoretical surface roughness agrees well with experimental results.

Microstructure and shear strength of reactive brazing joints of TiAl/Ni-based alloy

Reactive brazing of TiAl-based intermetallics and Ni-based alloy with Ti foil as interlayer was investigated. The interfacial microstructure and shear strength of the joints were studied. According to the experimental observations, the molten interlayer reacts vigorously with base metals, forming several continuous reaction layers. The typical interfacial microstructure of the joint can be expressed as GH99/（Ni,Cr）ss（γ）/TiNi（β2）＋TiNi2Al（τ4）＋Ti2Ni（δ）/δ＋Ti3Al（α2）＋Al3NiTi2（τ3）/α2＋τ3/TiAl. The maximum shear strength is 258 MPa for the specimen brazed at 1000°C for 10 min. Higher brazing temperature or longer brazing time causes coarsening of the phases in the brazing seam and formation of brittle intermetallic layer, which greatly depresses the shear strength of the joints.

Contact reactive brazing of Al alloy/Cu/stainless steel joints and dissolution behaviors of interlayer

Contact reactive brazing of 6063 Al alloy and 1Cr18Ni9Ti stainless steel was researched by using Cu as interlayer. Effect of brazing time on microstructure of the joints, as well as the dissolution behaviors of Cu interlayer was analyzed. The results show that the product of reaction zone near 1Cr18Ni9Ti is composed of Fe2Al5, FeAl3 intermetallic compound （IMC）, and Cu-Al IMC; the near by area is composed of Al-Cu eutectic structure with Al （Cu） solid solution. With increasing the brazing time, the thickness of IMC layer at the interface increases, while the width of Al-Cu eutectic structure with Al（Cu） solution decreases. Calculation shows the dissolution rate of Cu interlayer is very fast. The complete dissolution time is about 0.47 s for Cu interlayer with 10 μm in thickness used in this study.

BONDING INTERFACE AND WEAR BEHAVIOR OF CBN GRAINS BRAZED USING NANO-TiC POWDER MODIFIED FILLER

A new kind of composite fillers,composed of Ag-Cu-Ti alloy and nano-TiC powders,is utilized to braze cubic boron nitride （CBN） grains and tool substrate. The bonding system,including the interfacial microstructure and reactive products between CBN grains and filler layer,is observed by optical microscope and scanning electron microscope （SEM）. Resistant-to-wear experiments of the brazed grains are performed. Results show that the nano-TiC powders evenly distribute in the filler layer so that the resultants grow compactly and uniformly on the surface of CBN grain. This indicates that the chemical bond is established between CBN grains and nano-TiC modified filler. Accordingly,the bonding strength of the grains is ensured. The CBN grains are worn smoothly without grain pull-out.

Microstructural characteristics of joint region during diffusion-brazing of magnesium alloy and stainless steel using pure copper interlayer

A novel joining method,double-stage diffusion-brazing of an AZ31 magnesium alloy and a 304L austenitic stainless steel,was carried out using a pure copper interlayer.The solid-state diffusion bonding of 304L to copper was conducted at 850 ℃ for 20 min followed by brazing to AZ31 at 520 ℃ and 495 ℃ for various time.Microstructural characteristics of the diffusion-brazed joints were investigated in detail.A defect free interface of Fe-Cu diffusion area appeared between the Cu alloy and the 304L steel.Cu-Mg reaction products were formed between AZ31 and Cu alloys.A layered structure including AZ31/Cu-Mg compounds/Cu/Fe-Cu diffusion layer/304L was present in the joint.With time prolonging,the reduction in the width of Cu layer was balanced by the increase in the width of Cu-Mg compounds zone.Microhardness peaks in the zone between AZ31 and Cu layer were attributed to the formation of Mg-Cu compounds in this zone.

EFFECTS OF BRAZING ATMOSPHERES ON INTERFACIAL MICROSTRUCTURE BETWEEN DIAMOND GRITS AND BRAZING ALLOY

The samples of brazed diamond grits with NiCr brazing alloy are prepared in vacuum and argon gas. The microstructures are analyzed with scanning electron microscope （SEM）, energy dispersive X-ray spectroscopy （EDS） and X-ray diffraction（XRD）. The effects of brazing atmospheres on the as-brazed NiCr brazing alloy composite structures and interracial microstructure are studied between diamond grits and brazing alloy. Results show that： （1） There are different composite structures of as-brazed NiCr brazing alloy under different oxygen partial pressures in vacuum and argon gas. B203 exists on the surface of the brazed samples under argon gas furnace brazing. It indicates that oxygen plays an important role in the resultants of as-brazed NiCr brazing alloy during the brazing process. （2） There are different interfacial microstructures in different brazing atmospheres, but the main reaction product is chromium carbides. The chromium carbides in argon gas furnace brazing grow in a disordered form, but those in vacuum furnace brazing grow radiated. And the scale of grains in argon gas is smaller than those in vacuum.

Microstructure and properties of Cu/Al joints brazed with Zn-Al filler metals

The mechanical properties and microstructural distribution of the Cu/A1 brazing joints formed by torch-brazing with different Zn-A1 filler metals were investigated. The microstructure of the Zn-A1 alloys was studied by optical microscopy and scanning electron microscopy, and the phase constitution of the Cu/A1 joints was analyzed by energy dispersion spectrometry. The results show that the spreading area of the Zn-A1 filler metals on the Cu and A1 substrates increases as the A1 content increases. The mechanical results indicate that the shear strength reaches a peak value of 88 MPa when A1 and Cu are brazed with Zn-15AI filler metal. Microhardness levels from HV122 to HV515 were produced in the three brazing seam regions corresponding to various microstructure features. The Zn- and Al-rich phases exist in the middle brazing seam regions. However, two interface layers, CuZn3 and A12Cu are formed on the Cu side when the A1 content in the filler metals is 2% and more than 15%, respectively. The relationship between intermetallic compounds on Cu side and Zn-xA1 filler metals was investigated.

Effects of germanium additions on microstructures and properties of Al-Si filler metals for brazing aluminum

A series of Al?Si?Ge filler metals were studied for brazing aluminum. The microstructures and properties of the filler metals were investigated systematically. The results show that the liquidus temperature of Al?Si?Ge filler metals drops from 592 to 519 °C as the content of Ge increases from 0 to 30% (mass fraction). As the content of Ge increases, bright eutectic Ge forms. However, as the Ge content exceeds 20%, the aggregation growth of the eutectic structure tends to happen and coarsened primary Si?Ge particle forms, which is detrimental to the properties of alloys. The Al?10.8Si?10Ge filler metal has good processability and wettability with the base metal Al. When this filler metal is used to braze 1060 aluminum, the complete joint can be achieved. Furthermore, the shear strength test results show that the fracture of brazed joint with Al?10.8Si?10Ge filler metal occurs in the base metal.