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.

Effect of superplastic deformation on the bonding property of 00Cr25Ni7Mo3N duplex stainless steel

The superplastic deformation diffusion bonding of 00Cr25Ni7Mo3N duplex stainless steel was performed on a hot simulator. The microstructure of the bonding interface was characterized by scanning electron microscopy （SEM） and electron backscatter diffraction （EBSD）. The mechanical properties of the specimen were investigated by a shear strength test. The results indicated that the shear strength was improved with the increase of superplastic deformation reduction. When the deformation reduction was up to 50%, the shear strength of the specimen achieved 417 Mpa, approaching to that of the base metal. In addtion, the superplastic diffusion bonding technique was not very sensitive to surface roughness levels. When the surface roughness of the bonding specimen surpassed 0.416 pan （level G2）, the shear strength achieved at least 381 MPa.

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.

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.

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.

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.

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.

Study on process and mechanism of superplastic diffusion bonding of dissimilar steels

The probability, main effect factors and diffusion theory of structural superplastic diffusion bonding of W6Mo5Cr4V2/45 steel have been observed and analyzed by means of tensile test at the room temperature, scanning electron microscope and microhardness test. Results show that after fine graining treatment and short time superplastic pressing formation under the conditions of superplastic temperature and strain rate, W6Mo5Cr4V2/45 specimens can achieve solid state diffusion bonding and the property of welded area is the same as the other parts in the specimen. The diffusion path of carbon element is intergranular and of dislocation.

A New Model of Interfacial Physical Contact in Diffusion Bonding

Through eliminating voids not affecting the primary bonding process, and incorporating interlayer and flexible base material, the interface geometry character and brief mathematics process were put forth. Through analyzing contact process of diffusion bonding, contact area model was settled. It can interpret the phenomenon of different interface areas taking on different strengths. In the course of physical contact, shear stresses serve an important function for the plastic deformation and the cohesion of interface voids.

Diffusion bonding between nickel－base superalloy K24 and heat－resisting steel 1Cr11Ni2W2MoV

The Vacuum diffusion bonding between nickel-base superalloy K24 and heatresisting steel 1Cr11Ni2W2MoV was studied and the effects of welding parameters,including bonding temperature T,pressure P,time t,vacuum V and interlayer thickness h ,on the microstructure and properties of the joint were investigated.The optimum parameters for the diffusion bonding were found to be:T=1100￣1200℃,t=5￣30 MPa,V≥1×10-2 Pa.When the welded specimens are tensioned at room temperature,ductile fracture takes place at the nickel-base superalloy part or at the joint and the tensile strength reaches 850 MPa,When the tensile tests are carried out at 500℃ ,all the bonded specimens fractured at heat-resisting steel part,and tensile strength is 750 MPa.The interlayer thickness greatly affects the joint properties,and the interlayer thickness depends on the size of the bonded specimen.The impeller of nickel-base superalloy K24 and shaft of heat-resisting steel 1Cr11Ni2MoV,which are used in aerospace engine,has been successfully jointed jointed by means of high frequency induction diffusion bonding.

FEM simulation on residual stress distribution during diffusion bonding between Ti （ C, N） metallic ceramic/interlayer/40Cr steel

Based on ANSYS FEM software, the distribution of residual stress in the diffusion bonding joints between Ti（ C,N） metallic ceramic/interlayer/4OCr steel was calculated and experimentally ver^ed. The results showed that the trend on the distribution of residual stress field in the joints was not changed with the use of interlayer. The maximum residual stress was always located in metallic ceramic with area ranging from 1 mm to 4 mm to the interlayer. The maximum residual stress in the joints was also affected by diffusion temperature. The satellite pulse current during the initial stage on diffusion bonding can promote the formation of liquid film at the interface, by which diffusion temperature and loading pressure can be greatly decreased. The crack initiation was easily produced at the corner of Ti （ C, N） metallic ceramic close to the interlayer. If a higher residual stress produced in the joints, the crack was propagated into the whole ceramic.

Research on the diffusion bonding of superplastic magnesium alloy

The elevated temperature tensile experiments have been carried out on the magnesium alloy and results indicate that the magnesium alloy has excellent superplastic property. Gleebe 1500 testing machine was used in the diffusion bonding experiment on the superplastic magnesium alloy. Then, the shear strength of the joints under different conditions is obtained through shear testing and the optimum processing parameters for the diffusion bonding are achieved. By metallurgical microscope and scanning electron microscope (SEM), it is revealed that the micromechanism of diffusion bonding is the slide of grain boundaries caused by the growth of grains and atom diffusion of the superplastic magnesium alloy.

Diffusion Bonding of Ti-6Al-4V to QAl 10-3-1.5 with Ni/Cu Interlayers

Ti-6Al-4V and QAl 10-3-1.5 diffusion bonding has been carried out with Ni/Cu interlayers. The diffusionbonded joints are evaluated by scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS） and microhardness test. Intermetallic compounds at the interface zone are detected by X-ray diffraction （XRD）. Interracial microstructure of TiNi＋CuTi3＋α-Ti forms at the Ni/Ti-6Al-4V transition zone and Cu （ss. Ni） solid solution forms between Ni/Cu interlayers. The thickness of reaction layer （TiNi） increases with bonding time by a parabolic law： y^2=Koexp（-150000/RT）t, and K0=2.g×10^-7 m^2/s is figured out from the experiment data.

DIFFUSION BONDING OF SUPERPLASTIC AI ALLOY LC4

Diffusion bonding of supcrplastic Al alloy LC4,with prior surface treatment of organic solution protecting coating after electroplishing and stainless steel wool brushing,was performed by Gleeble test machine under conditions ranged 490—530 ℃,1.0—3.0 MPa. 30—180 min and vacuum of 1.0×10^(-3) Pa.The joints were examined to have similar strength and microstructure to the base metal Discussion was made on the effect of superplastic treatment on bonding.The micromechanism for diffusion bonding of super- plastic metal was suggested as the migration of original bond interfaces caused by atomic diffusion and grain growth. Experimental results for the alloy as quench-aged state were presented to compare with the superplastic one.