Tungsten/steel diffusion bonding using Cu/W-Ni/Ni multi-interlayer

Diffusion bonding between tungsten and 0Cr13Al stainless steel using a Cu/90W-10Ni powder mixtures/Ni multi-interlayer was carried out in vacuum at 1150 °C with a pressure of 5 MPa for 60 min. The microstructures, composition distribution and fracture characteristics of the joint were studied by SEM and EDS. Joint properties were evaluated by shear experiments and thermal shock tests. The results showed that the joints comprised tungsten/Cu-Ni sub-layer/W-Ni composites sub-layer/Ni sub-layer/0Cr13Al stainless steel. The W-Ni composites sub-layer with a homogeneous and dense microstructure was formed by solid phase sintering of 90W-10Ni powder mixtures. Sound bonding between tungsten base material and W-Ni composites sub-layer was realized based on transient liquid phase (TLP) diffusion bonding mechanism. Joints fractured at bonding zone of W-Ni composites sub-layer and Ni sub-layer during shear testing, and the average strength was 256 MPa. Thermal shock tests showed that joints could withstood 60 thermal cycles quenching from 700 °C to room temperature.

Interfacial microstructure and chemical stability during diffusion bonding of single crystal Al_2O_3-fibres with Ni25.8Al9.6Ta8.3Cr matrix

BN coated A1203 fibre-reinforced NiAl-alloy composites were fabricated by hot pressing at 1 200-1 400 ℃, and the interracial microstructure and chemical stability of BN coated Al2O3 fibre-reinforced NiAl-alloy composites were investigated by scanning electron microscopy （SEM） and analytical transmission electron microscopy （TEM）. It was found that the complicated chemical reactions and diffusion processes happened in the interface area between BN-layer and Ni25.8A19.6Ta8.3 during the hot pressing at 1 200-1 400 ℃. A continuous AlN-layer was formed at the interface due to the reaction between NiAl and BN. At the same time, Cr diffused extensively into the BN-layer and reacted with boron to form Cr boride precipitates （CrsB3）. In addition, a few particles of Ta-rich phase were also precipitated in NiAl matrix near the interface.

Influences of diffusion bonding process parameters on bond characteristics of Mg-Cu dissimilar joints

In many circumstances,dissimilar metals have to be bonded together and the resulting joint interfaces must typically sustain mechanical and/or electrical forces without failure,which is not possible by fusion welding processes.The melting points of magnesium(Mg)and copper(Cu)have a significant difference(nearly 400℃)and this may lead to a large difference in the microstructure and joint performance of Mg-Cu joints.However,diffusion bonding can be used to join these alloys without much difficulty.This work analyses the effect of parameters on diffusion layer thickness,hardness and strength of magnesium-copper dissimilar joints.The experiments were conducted using three-factor,five-level,central composite rotatable design matrix.Empirical relationships were developed to predict diffusion layer thickness,hardness and strength using response surface methodology.It is found that bonding temperature has predominant effect on bond characteristics.Joints fabricated at a bonding temperature of 450℃, bonding pressure of 12 MPa and bonding time of 30 min exhibited maximum shear strength and bonding strength of 66 and 81 MPa, respectively.

Development of processing windows for diffusion bonding of Ti-6Al-4V titanium alloy and 304 stainless steel with silver as intermediate layer

As titanium alloy is chemically reactive,it is very difficult to join by conventional welding techniques.Titanium alloys can easily pick up nitrogen and oxygen from the atmosphere.In the fusion welding method,brittle intermetallic compounds are formed when joining titanium alloy and stainless steel,which decrease the mechanical behavior of the couples.Hence,for joining of titanium alloy,diffusion bonding is recommended.This work dealt with the measurement of feasible process parameters for diffusion bonding of Ti-6Al-4V and AISI 304 stainless steel with silver as an intermediate layer.The quality of the bonds was confirmed by the lap shear test and microstructural analysis.With the experimental results obtained,diffusion bonding windows were constructed and this will act as reference maps to identify the process parameters for obtaining defect free bond.Bonding was successful in the temperature range of 750-800 °C.Maximum lap shear strength was achieved under a bonding pressure of 5 MPa and holding time of 90 min.

Diffusion bonding of Al 7075 and Mg AZ31 alloys:Process parameters, microstructural analysis and mechanical properties

Al 7075 and Mg AZ31 alloys were joined by diffusion bonding method. Joining process was performed in pressure range of 10-35 MPa at temperatures of 430-450 ℃ for 60 min under a vacuum of 13.3 MPa. The microstructure evaluation, phase analysis and distribution of elements at the interface were done using scanning electron microscopy （SEM）, energy-dispersive X-ray spectroscopy （EDS） and X-ray diffraction （XRD）. The pressure of 25 MPa was determined as the optimum pressure in which the minimum amount of plastic deformation takes place at the joint. Different reaction layers containing intermetallic compounds, such as Al12Mg17, Al3Mg2 andα（Al） solid solution, were observed, in interfacial transition zone （ITZ）. Thickness of layers was increased with increasing the operating temperature. According to the results, diffusion of aluminum atoms into magnesium alloy was more and the interface movement towards the Al alloy was observed. The maximum bond strength of 38 MPa was achieved at the temperature of 440 ℃ and pressure of 25 MPa. Fractography studies indicated that the brittle fracture originated from Al3Mg2 phase.

SUPERPLASTICITY AND DIFFUSION BONDING OF IN718 SUPERALLOY

The superplasticity and diffusion bonding of IN718 superalloy were studied in this article. The strain rate sensitivity index m was obtained at different temperatures and various initial strain rates using the tensile speed mutation method; m reached its maximum value 0.53 at an initial strain rate of 1×10^-4s^-1 at 1253K. The diffusion bonding parameters, including the bonding temperature T, pressure p, and time t, affected the mechanism of joints. When the bonded specimen with 25μm thick nickel foil interlayer was tensile at room temperature, the shear fracture of the joints with nickel foil interlayer took place at the IN718 part. Microstructure study was carried out with the bonded samples. The microstructure shows an excellent bonding at the interfaces. The optimum parameters for the diffusion bonding are： T = 1273-1323K, p = 20-30MPa, t = 45-60min.

Vacuum diffusion bonding of Ti_(2)AlNb alloy and TC4 alloy

The Ti_(2)AlNb alloy was joined with TC4 alloy by vacuum diffusion bonding.The relationship between bonding parameters,and joint microstructure and shear strength was investigated.The results indicated that the diffusion of Al,Ti,Nb and V elements across bonding interface led to the formation of three reaction layers:B2/βlayer andα2 layer on the TC4 side,andα2+B2/βlayer on the Ti_(2)AlNb side.The bonding temperature determined the atomic activity,thus controlling the growth of reaction layers and influencing the shear strength of the joint.When the Ti_(2)AlNb alloy and TC4 alloy were bonded at 950℃for 30 min under 10 MPa,the shear strength of the joint reached the maximum of 467 MPa.The analysis on the fracture morphology showed that the fracture occurred within the B2/βlayer and the fracture model was ductile rupture.Meanwhile,the formation mechanism of the Ti_(2)AlNb/TC4 joint was discussed in depth.

Microstructure and mechanical properties of Ti−6Al−4V/Ti−22Al−25Nb joint formed by diffusion bonding

Ti-6Al-4V(wt.%) and Ti-22Al-25Nb(at.%) were joined by diffusion bonding at 950 ℃ and 15 MPa for 100 min, and the microstructure and mechanical properties of the resulting joints were investigated. The composition of the diffusion layer is B2/discontinuous α/α2 layer/necklace-shaped β+α’ layer, where the content of any element at a given point mainly depends on the distance of the point from the interface and the phase type at the point. The tensile strength of the joint is 894 MPa, which is almost the same as that of the Ti-22Al-25Nb base alloy. The fracture surfaces on both sides of the joint are composed of two main regions. One region displays a relatively flat surface and fractures along the bonding interface. The other is composed of a moderate number of irregularly-shaped cavities on the Ti-6Al-4V side and many irregularly-shaped bulges on the Ti-22Al-25Nb side. Both regions result from fracture along the boundaries between β+α’ layers and αp grains or from the transcrystalline fracture of αp grains.

Diffusion Bonding of Silicon Carbide Particulate Reinforced 2024 Al Composites

A study has been made on diffusion bonding of SiCp/2024Ai composites by means of pure Al interlayer. In the condition of TB=843 K, PB=16 MPa, tB= 60 min, the diffusion bonded joint, with a shear strength of 235 MPa, was obtained when a 15 μm thick interlayer was used. The results of the shear testing and SEM indicate that fracture of the joint presented characteristics of ductile rupture.

Diffusion Bonding of Ti_3Al Base Alloy

: The effects of diffusion bonding temperature and holding time on the joint strength of Ti3Al base alloy has been investigated in this paper. The shear strength of Ti-14Al-21Nb-3Mo-V alloy diffusion bonding joint under pressure of 12 MPa at 990℃ for 70 min was obtained to 797.6 MPa which approaches the base material strength. In addition, a short-time diffosion bonding process was studied in order to decrease the bonding cost. With the deformation of the specimens of 2.5% and the bonding temperature of 990℃ for 15 min, the bonding strength could reach 801 MPa.

Diffusion bonding of Ti-6Al-4V to ZQSn10-10 in vacuum

The experimental investigation of the direct diffusion bonding of Ti-6Al-4V to ZQSn10-10 was carried out in vacuum. The microstructure of bonded joint was studied by scanning electron microscopy （SEM）, energy dispersive spectroscopy （ EDS ） and the mechanical properties were detected by the tensile experiments. The microstructure and tensile strength of the joint mainly depend on the bonding temperature and bonding time. A satisfying diffusion bonded interface with a tensile strength of 73.9 MPa can be obtained under the condition of bonding temperature 850℃ for 30 rain. Three kinds of reaction products were observed in the bonded interface, namely β-Ti, CoaTi and CuSn3Ti5. And the brittle Cu3Ti and CuSn3 Ti5 are mainly responsible for lowering the strength of the bonded joint. The diffusion distances of Sn , Cu and Ti and square root of bonding time are approximately linear relationship. And diffusion velocity of Sn, Cu and Ti in the diffusion reaction layer are 0. 013 9,0. 069 7 and 0. 056 4 mm^2/s.

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.

A two-step transient liquid phase diffusion bonding process of T91 steels

In this study, a two-step heating process is introduced for transient liquid phase （ TLP） diffusion bonding fo r sound joints with T91 heat resistant steels. At first, a short-time higher temperature heating step is addressed to melt the interlayer, followed by the second step to complete isothermal solidification at a low temperature. The most critical feature of our new method is producing a non-planar interface at the T9／ heat resistant steels joint. We propose a transitional liquid phase bonding of T91 heat resistant steels by this approach. Since joint microstructures have been studied, we tested the tensile strength to assess joint mechanical property. The result indicates that the solidified bond may contain a primary solid-solution, similar composition to the parent metal and free from precipitates. Joint tensile strength of the joint is not lower than parent materials. Joint bend＇s strengths are enhanced due to the higher metal-to-metal junction producing a non-planar bond lines. Nevertheless, the traditional transient liquid phase diffusion bonding produces planar ones. Bonding parameters of new process are 1 260 °C for 0. 5 min and 1 230 °C fo r 4 min.

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.

Diffusion bonding of Ti−6Al−4V titanium alloy powder and solid by hot isostatic pressing

The Ti−6Al−4V(TC4)alloy powder and forged solid were diffusion bonded by hot isostatic pressing(HIP)to fabricate a powder−solid part.The microstructure of the powder−solid part was observed by scanning electron microscope(SEM).The microhardness and tensile tests were conducted to investigate the mechanical properties.The results showed that the powder compact was near-fully dense,and the powder/solid interface was tight and complete.The microhardness of the interface was higher than that of the powder compact and solid.The fractures of all powder−solid tensile specimens were on the solid side rather than at the interface,which indicated that a good interfacial strength was obtained.The tensile strength and elongation of the powder compact were higher than those of the solid.It is concluded that the HIP process can successfully fabricate high-quality Ti−6Al−4V powder−solid parts,which provides a novel near net shape technology for titanium alloys.

XRD and TEM Analysis in the Interface of Diffusion Bonding for Fe_3Al/Q235 Dissimilar Materials

Phase structure characteristics near the interface of Fe3Al/Q235 diffusion bonding are investigated by means of X raydiffraction (XRD), transmission electronic microscope (TEM) and electron diffraction, etc. The test results indicatedthat obviously a diffusion transition zone forms near the interface of Fe3Al/Q235 under the condition of heatingtemperature 1050~1100℃, holding time 60 min and pressure 9.8 MPa, which indicated that the diffusion interfaceof Fe3Al/Q235 was combined well. The diffusion transition zone consisted of Fe3Al and a-Fe(Al) solid solution.Microhardness near the diffusion transition zone was HM 480~540. There was not brittle phase of high hardness inthe interface transition zone. This is favorable to enhance toughness of Fe3Al/Q235 diffusion joint.

Transient liquid phase diffusion bonding of a single crystal superalloy DD6

DD6 alloy was bonded by transient liquid phase (TLP) diffusion bonding. The main compositions of the interlayer alloy employed were similar to those of the base metal, DD6, and a certain amount of element B was added as the melting point depressant. The results show that it is difficult to obtain the joints with the microstructures completely homogeneous. For the joint TLP diffusion bonded at 1290℃ for 12h, about half areas of the beam possessed a γ+γ′ microstructure, nearly identical with that of the base metal, and the other local areas consisted of γ-solution, borides, etc. Prolonging the bonding time to 24h, the inhomogeneous areas in the joint reduced, and the joint property improved. The joint stress-rupture strength at 980℃ and 1100℃ reached 90%-100% and 70%-80% of those of the base metal respectively.

DIFFUSION BONDING OF TiAl TO Ti AND TC4 ALLOY

TiAl was diffusion bonded to Ti and TC4 alloy in vacuum furnace. Results showed,at the TiAl-Ti interface,the reaction layer of stratification Ti3Al was formed closest to TiAl base,and the a phase and the α + βphase arised closest to Ti base at 1173K and 1573K respectively. The phase structure of TiAl/ and the phase structure of TiAlwere observed be- tween AiAl and TC4 under respetive bonding temperature.The fiacture at tensile testing occurred in the bond - line, producing very flat fracture surfaces with some pull-out of the TiAl materials.The ultimate tensile strengths of the joint were approximate to γ-TiAl base marterial.

Study of diffusion bonding of Ti-6Al-4V and ZQSn10-10 with metal interlayer

The diffusion bonding was carried out to join Ti alloy （Ti-6Al-4V） and tin-bronze （ ZQSn10-10 ） with Ni and Ni ＋ Cu interlayer. The microstructures of the diffusion bonded joints were analyzed by scanning electron microscope （SEM）, energy dispersive spectroscopy （ EDS ） and X-ray diffraction （ XRD ）. The results show that when the interlayer is Ni or Ni ＋ Cu transition metals both could effectively prevent the diffusion between Ti and Cu and avoid the formation of the Cu-Ti intermetallic compounds （Cu3Ti, CuTi etc. ）. But the Ni-Ti intermetallic compounds （NiTi, Ni3Ti） are formed on the Ti-6Al-4V/Ni interface. When the interlayer is Ni, the optimum bonding parameters are 830 ℃/10 MPa/30 min. And when the interlayer is Ni ＋ Cu, the optimum bonding parameters are 850 ℃/10 MPa/20 min. With the optimum bonding parameters, the tensile strength of the joints with Ni and Ni ＋ Cu interlayer both are 155.8 MPa, which is 65 percent of the strength of ZQSn10-10 base metal.

Evaluation of TiAl and 40Cr diffusion bonding quality using ultrasonic reflection spectrum

Combined with ultrasonic pulse-echo technique, reflection spectrum analysis was introduced to evaluate TiAl and 40Cr diffusion bonding quality. Frequency dependence of reflection coefficient was used to distinguish perfect bonding from imperfect bonding. It is found that the reflection coefficient from perfect bonding interface does not vary with frequency. When the size of imperfections is much smaller than the wavelength of ultrasound, the reflection coeffwient depends on frequency. When the size of imperfections is the same order of or even larger than the wavelength of ultrasound, the reflection coeffwient does not exhibit frequency dependence. However the amplitude of imperfect interface is higher than the amplitude of perfect bonding interface. A combination of reflection spectrum analysis and ultrasonic pulse-echo technique provides more accurate information about the bonding quality of dissimilar materials.