Effect of process parameters on semi-solid TLP bonding of Ti–6Al–4V to Mg–AZ31

The semi-solid transient liquid-phase bonding (Semi-solid TLP bonding) of titanium alloy Ti–6Al–4V to magnesium alloy Mg–AZ31 was performed using a eutectic forming nickel foil. The process parameters were optimized to achieve higher shear strength. The effect of temperature and pressure on microstructure evolution and mechanical characteristics were examined for bonding time between 5 and 60 min. Three reaction layers L1, L2 at Ni/Mg–AZ31 interface and L3 along the Ni/Ti–6Al–4V interface were determined within joint zone at a bonding temperature of 515 °C. The L1 and L2 reaction layers continued to be seen when the bonding temperature increased to 540 °C. When the bonding pressure increases from 0.2 to 0.7 MPa, a new reaction layer L4, at the Ni/Ti–6Al–4V interface was observed. The results showed that as the bonding time increased up to 60 min, the width of the joint decreased due to isothermal solidification. Maximum shear strength of 39 MPa was obtained for 540 °C and 0.2 MPa with a holding time of 20 min. However, further increase in bonding time to 60 min resulted in a decrease in shear strength to 8 MPa, and this decrease in strength was attributed to the increase in intermetallics forming within the joint zone.     

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 diffusion-bonded 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). Interfacial microstructure of TiNi+CuTis+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: y2=K0exp(-150000/RT)t, and K0=2.9×10~7 m2/s is figured out from the experiment data.     

Diffusion bonding between Ti -6Al -4V alloy and microduplex stainless steel with copper interlayer

Abstract

In the present study, diffusion bonding was used to join Ti -6Al- 4V alloy to a microduplex stainless steel using a pure copper interlayer. The effects of heating rate and holding time on microstructural developments across the joint region were investigated. After bonding, microstructural analysis including metallographic examination and energy dispersive spectroscopy (EDS), microhardness measurements, and shear strength tests were carried out. From the results, it was seen that heating rate and holding time directly affect microstructural development at the joint, especially with respect to the formation of TiFe intermetallic compounds, and this in turn affects the shear strength of the bonds. A sound bond was obtained with a heating rate of 100 K min ^-1 and holding time of 5 min, and this was related to the small amount of TiFe intermetallics formed close to the duplex stainless steel side at this bonding condition. Although Ti₂Cu and TiFe intermetallics were formed in all specimens, it was seen that the most deleterious intermetallic was TiFe. As the heating rate was decreased and holding time increased the amount of TiFe intermetallics increased, and consequently shear strength decreased. As a result, from the microstructural observations, EDS analysis, microhardness measurements, and shear strength tests, it was concluded that a high heating rate and a short holding time must be used in the diffusion bonding of Ti-6Al- 4V to a microduplex stainless steel when pure copper interlayers are used.     

Joining of Zirconia and Ti-6Al-4V Using a Ti-based Amorphous Filler

Polycrystalline ZrO2-3 mol.%Y2O3 was brazed to Ti-6Al-4V by using a Ti47Zr28Cu14Ni11(at.%) amorphous ribbon at 1123-1273 K in a high vacuum. The influences of brazing temperature on the microstructure and shear strength of the joints were investigated. The interfacial microstructures can be described as ZrO2/TiO+TiO2+Cu2Ti4O+Ni2Ti4O/α-Ti+(Ti,Zr)2(Cu,Ni) eutectic/acicular Widmanst¨aten structure/Ti-6Al-4V alloy. With the increase in the brazing temperature, the thickness of the TiO+TiO2+Cu2Ti4O+Ni2Ti4O layer reduced, the content of the α-Ti+(Ti,Zr)2(Cu,Ni) eutectic phase decreased, while that of the coarse α-Ti phase gradually increased. The shear strength of the joints did not show a close relationship with the thickness of the TiO+TiO2+Cu2Ti4O+Ni2Ti4O layer. However, when the coarse (Ti,Zr)2(Cu,Ni) phase was non-uniformly distributed in the α-Ti phase, or when α-Ti solely situated at the center of the joint, forming a coarse block or even connecting into a continuous strip, the shear strength greatly decreased.     

Transient liquid phase (TLP) bonding of Al7075 to Ti–6Al–4V alloy

TLP diffusion bonding of two dissimilar aerospace alloys, Ti–6Al–4V and Al7075, was carried out at 500 °C using 22 μm thick Cu interlayers for various bonding times. Joint formation was attributed to the solid-state diffusion of Cu into the Ti alloy and Al7075 alloy followed by eutectic formation and isothermal solidification along the Cu/Al7075 interface. Examination of the joint region using SEM, EDS and XPS showed the formation of eutectic phases such as, ?(Al₂Cu), T(Al₂Mg₃Zn₃) and Al₁₃Fe along grain boundaries within the Al7075 matrix. At the Cu/Ti alloy bond interface a solid-state bond formed resulting in a Cu₃Ti₂ phase formation along this interface. The joint region homogenized with increasing bonding time and gave the highest bond strength of 19.5 MPa after a bonding time of 30 min.     

Diffusion bonding of Ti-6Al-4V alloy at low temperature: metallurgical aspects

The diffusion bonding of the Ti-Al-4V alloy at low temperature (850°C) has been studied. The principal objective of this investigation was the development of a diffusion bonding procedure suitable for Ti-6Al-4V alloy and capable of being used as part of a superplastic forming/diffusion bonding process. It was found that high-quality joints can be obtained by bonding at 850°C, with pressures of 4 MPa and times in the range 90–120 min. Mechanical properties of the joints were determined using cylindrical and plane test pieces. Tensile, shear and peeling tests were used to determine the strength of the joints. On bonding with the above conditions, the parent alloy strength was reached. Little reduction in these values was measured because the heat treatment was applied during bonding. A metallographic study by scanning electron microscopy and energy dispersive spectroscopy was performed to determinate the influence of the previous parameters on the microstructural changes that occur in the joint. Grain growth kinetics and ratio of bonding area were also studied. The results shows that a new method of diffusion bonding for Ti-6Al-4V alloy has been developed. This method can be carried out using lower bonding temperatures than in conventional processes.     

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.     

Improvement of Joint Strength of SiCp/Al Metal Matrix Composite in Transient Liquid Phase Bonding Using Cu/Ni/Cu Film Interlayer

The compact oxide on the surface of SiCp/Al metal matrix composite （SiCp/Al MMC） greatly depends on the property of the joint. Inlaid sputtering target was applied to etch the oxide completely on the bonding surface of SiCp/Al MMC by plasma erosion. Cu/Ni/Cu film of 5μm in thickness was prepared by magnetron sputtering method on the clean bonding surface in the same vacuum chamber, which was acted as an interlayer in transient liquid phase （TLP） bonding process. Compared with the same thickness of single Cu foil and Ni foil interlayer, the shear strength of 200 MPa was obtained using Cu/Ni/Cu film interlayer during TLP bonding, which was 89.7% that of base metal. In addition, homogenization of the bonding region and no particle segregation in interfacial region were found by analysis of the joint microstructure. Scanning electron microscopy （SEM） was used to observe the micrograph of the joint interface. The result shows that a homogenous microstructure of joint was achieved, which is similar with that of based metal.     

The microstructural observation and wettability study of brazing Ti-6Al-4V and 304 stainless steel using three braze alloys

Both Ti-6Al-4V and 304 stainless steels (304SS) are good engineering alloys and widely used in industry due to their excellent mechanical properties as well as corrosion resistance. Well-developed joining process can not only promote the application of these alloys, but also can provide designers versatile choices of alloys. Brazing is one of the most popular methods in joining dissimilar alloys. In this study, three-selected silver base filler alloys, including Braze 580, BAg-8 and Ticusil®, are used in vacuum brazing of 304SS and Ti-6Al-4V. Based upon dynamic sessile drop test, Braze 580 has the lowest brazing temperature of 840°C, in contrast to 870°C for BAg-8 and 900°C for Ticusil® braze alloy. No phase separation is observed for all brazes on 304SS substrate. However, phase separation is observed for all specimens brazed above 860°C on Ti-6Al-4V substrate. The continuous reaction layer between Braze 580 and 304SS is mainly comprised of Ti, Fe and Cu. The thickness of reaction layer at Braze 580/Ti-6Al-4V interface is much larger than that at Braze 580/304SS interface. Meanwhile, a continuous Cu-Sn-Ti ternary intermetallic compound is found at the Braze 580/Ti-6Al-4V interface. Both Ticusil® and BAg-8 brazed joint have similar interfacial microstructures. Different from the Braze 580 specimen, there is a thick Cu-Ti-Fe reaction layer in both BAg-8/304SS and Ticusil®/304SS interfaces. The formation of Cu-Ti-Fe interfacial layer can prohibit wetting of BAg-8 and Ticusil® molten brazes on 304SS substrate. Meanwhile, continuous Ti₂Cu and TiCu layers are observed in Ti-6Al-4V/BAg-8 and Ti-6Al-4V/Ticusil® interfaces.     

Mechanical properties and microstructure of SiC-reinforced Mg-(2,4)Al-1Si nanocomposites fabricated by ultrasonic cavitation based solidification processing

Nano-sized SiC enhanced magnesium matrix nanocomposites, Mg-2Al-1SiC with 2% SiC and Mg-4Al-1Si with 2% SiC, were successfully fabricated by ultrasonic cavitation based dispersion of SiC nanoparticles in Mg-(2,4)Al-1Si magnesium alloy melts. As compared to the magnesium alloy matrixes, the mechanical properties including tensile strength and yield strength of the Mg-2Al-1Si/2% SiC and Mg-4Al-1Si/2% SiC nanocomposites were improved significantly, while the ductility of magnesium alloy matrix castings was retained. While there were some SiC micro-clusters in the microstructure of nanocomposites, the SiC nanoparticles were dispersed well outside the areas of micro-clusters. Most micro-clusters were located along the grain boundaries while most separate SiC nanoparticles were embedded inside the grains. TEM study of the interface between SiC nanoparticles and Mg-(2,4)Al-1Si metal matrixes suggested that SiC bonds well with the metal matrixes without forming an intermediate phase.     

Microstructural development of diffusion-brazed austenitic stainless steel to magnesium alloy using a nickel interlayer

The differences in physical and metallurgical properties of stainless steels and magnesium alloys make them difficult to join using conventional fusion welding processes. Therefore, the diffusion brazing of 316L steel to magnesium alloy (AZ31) was performed using a double stage bonding process. To join these dissimilar alloys, the solid-state diffusion bonding of 316L steel to a Ni interlayer was carried out at 900 °C followed by diffusion brazing to AZ31 at 510 °C. Metallographic and compositional analyses show that a metallurgical bond was achieved with a shear strength of 54 MPa. However, during the diffusion brazing stage B₂ intermetallic compounds form within the joint and these intermetallics are pushed ahead of the solid/liquid interface during isothermal solidification of the joint. These intermetallics had a detrimental effect on joint strengths when the joint was held at the diffusion brazing temperature for longer than 20 min.     

Comparative study on characteristics of hybrid laser-TIG welded AZ61/Q235 lap joints with and without interlayers

AZ61 Mg alloy to Q235 mild steel were lap joined using hybrid laser-TIG welding technique. At the joint interface and fusion zone (FZ), microstructure was revealed by scanning electron microscopy equipped with energy dispersive X-ray spectroscopy; element distribution was analyzed by electron probe micro-analyzer; intermediate phases were identified using X-ray diffraction test. Comparing with interlayer-free joints, the new intermediate phases Mg₂Ni and Mg₂Cu were generated in the FZ and at the Mg alloy/interlayer interface, and the solid solution of Ni or Cu in Fe was found along the edge of weld pool on steel side. It was found that direct joint without any interlayer was mechanical bonding, while Ni- and Cu-added joints were semi-metallurgical bonding. The joint shear strength was not only related to the penetration depth, but also related to the bonding mode. The strengthening effect on Cu-added joint was higher than that on Ni-added joint.     

Mg/Zn/Al瞬间液相过冷连接界面的组织与性能研究

采用瞬间液相过冷连接方法对AZ31镁合金/锌中间层/5083铝合金进行连接,利用SEM、XRD、拉伸实验机和微观硬度计对结合界面的微观组织、力学性能进行了表征。结果表明,以锌作中间层,采用瞬间液相过冷连接可以实现AZ31镁合金与5083铝合金的有效连接,接头的最高抗拉强度可以达到38.5MPa,随着低温扩散保温时间的延长,扩散层厚度随之增加,接头的抗拉强度也随之升高;接头的拉伸断口属于脆性断裂,结合界面形成了MgZn2和少量的Mg17Al12金属间化合物;结合界面的微观硬度最高达170。     

Effect of surface finish and sheet thickness on isostatic diffusion bonding of superplastic Ti-6Al-4V

Abstract

The aim of the present work was to determine the process conditions of pressure, temperature, and time required to produce high quality isostatic diffusion bonds in Ti-6Al-4Vfor two surface finishes. In addition, the conditions to produce a sound bond between two sheets or plates of Ti-6Al-4V having different thicknesses were investigated. An assessment of the quality of bonds produced was made on the basis of metallographic examination, lap shear strength measurements, and SEM examination of the shear fracture surfaces. Sound bonds were produced in the as received and pickled 1.6 mm thick sheet in under 1 h with an applied pressure of 2.1 MPa at both 940 and 920°C and for the P60 ground surface finish at 940°C, but the time increased to 1.5 h at 920°C for the coarser surface finish. Variations in sheet thickness from 1.6 to 10 mm were found to have no effect on the bonding time. These results were compared with the predictions of a model of isostatic diffusion bonding.     

Open-cell copper foam joining: joint strength and interfacial behaviour

A copper (Cu) foam was brazed with Cu-4.0Sn-9.9Ni-7.8P filler foil for joint strength and interface analysis. Brazed 50 pores per inch (PPI) Cu foam yielded a maximum compressive strength of 14.4?MPa with a 127% increment compared to nonbrazed Cu foam. 15 PPI Cu foam produced a maximum shear strength of 2.7?MPa. Scanning electron microscopy showed that the thickness of the brazed seam decreased with increasing the Cu foam’s PPI. The formation of the Cu, Cu₃P (P: phosphorus) and Ni₃P (Ni: nickel) at the Cu/Cu foam interface was validated using energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction. EDX line scanning analysis revealed the diffusion of P and Ni into Cu foam, which took place via capillary force action.     

Infrared brazing of high-strength titanium alloys by Ti–15Cu–15Ni and Ti–15Cu–25Ni filler foils

Microstructures and fracture behaviors of infrared heated, vacuum brazed Ti–6Al–4V and Ti-15-3 alloys using two Ti–Cu–Ni braze fillers have been characterized to establish the effects of brazing process parameter and chemical composition on the strength of brazed joints. The brazed joint initially contains two prominent phases; a Ti alloy matrix alloyed with V, Cr, Ni, Cu and Al and a Cu–Ni-rich Ti phase. Brazing temperature and soak time control the amount of Cu–Ni-rich Ti phase in the brazed joints. The fracture mode changes from brittle cleavage to quasi-cleavage to ductile dimple as the amount of Cu–Ni-rich Ti phase is reduced in the brazed joint. Both brazing temperature and soak time are critical to eliminate the Cu–Ni-rich Ti phase for optimal shear strength and ductile fracture of brazed joints. A post-brazing annealing at lower temperature is also shown to be an effective way to homogenize the microstructure of brazed joint for improved joint strength.     

GH3044镍基合金钎焊接头的界面组织和强度分析

采用Ni基箔片钎料对GH3044镍基合金进行钎焊连接,利用电子扫描显微镜(SEM)及能谱分析仪,对接头的界面组织进行观察和分析;采用电子万能试验机对GH3044镍基合金的钎焊接头进行抗剪试验,评价接头的室温抗剪强度.试验结果表明:当钎焊温度为1070℃,保温时间为10min时,界面处有(Cr,W)2+Ni固溶体析出,钎缝中有(Cu,Ni)固溶体组织+Ni-Mn金属间化合物层及η″+ξ′金属间化合物层生成,此钎焊工艺参数下获得的钎焊接头具有最高的室温抗剪强度319MPa.     

Interface contribution to the SiC-titanium and SiC-aluminium tensile strength prediction

Fragmentation tests of single SiC filaments embedded in an aluminium (1050 and 5083 alloys) or a titanium (Ti-6Al-4V) matrix have been analysed in an effort to obtain the interface contribution in terms that could be incorporated into a tensile fracture model for unidirectional composites. Depending on the matrix, two regimes of interfacial stress transfer can be distinguished within the whole range of tested temperatures. For the SCS2/5083 system, plastic deformation of the alloy limits the stress transfer, and the interface contribution thus finds its expression in the shear stress of the matrix. for the SCS6/Ti-6Al-4V system, friction is the leading process and the interface contribution strongly depends on the stress state around the fibre. Assuming a temperature dependent compressive radial stress up to 925C, an effective transfer shear stress may be easily calculated for unidirectional SCS6/Ti-6Al-4V composites.     

Notch effects on high-cycle fatigue properties of Ti-6Al-4V ELI alloy at cryogenic temperatures

Notch effects on the high-cycle fatigue properties of the forged Ti-6Al-4V ELI alloy at cryogenic temperatures were investigated. Also, the high-cycle fatigue data were compared with the rolled Ti-5Al-2.5Sn ELI alloy. The one million cycles fatigue strength (FS) of the smooth specimen for the forged Ti-6Al-4V ELI alloy increased with a decrease of test temperature. However, the FS of each notched specimen at 4 K were lower than those at 77 K. On the other hand, the FS of the smooth and the notched specimens for the forged Ti-6Al-4V ELI alloy at 4 K were lower than those for the rolled Ti-5Al-2.5Sn ELI alloy. This is considered to be the early initiation of the fatigue crack in the forged Ti-6Al-4V ELI alloy compares with the forged Ti-5Al-2.5Sn ELI.     

Effect of bonding time on microstructure and mechanical properties of transient liquid phase bonded magnesium AZ31 alloy

The transient liquid phase (TLP) bonding of a magnesium alloy AZ31 was undertaken using pure nickel interlayers. The formation of a eutectic between the magnesium and nickel was obtained by bonding at 515 °C and the microstructural developments across the joint region were examined as a function of hold time from 5 to 120 min. Reaction zones were identified within the joint and the changes of width of the reaction zones were examined with respect to changes in the joint shear strength and hardness. The results showed that as the bonding time was increased to 60 min, the width of the eutectic zone was completely removed and the joint solidified isothermally. Under these conditions a maximum hardness value of 179 VHN was recorded and the highest joint shear strength of 36 MPa was obtained. However, when the bonding time was increased to 120 min, the shear strength of the interface decreased and this was attributed to the formation and segregation of brittle Mg–Ni intermetallics within the joint.