Controlling Al/Cu composite diffusion layer during hydrostatic extrusion by using colloidal Ag

In this study, intermetallic compound formation at the interface between aluminum and copper during hydrostatic extrusion was simulated by performing a solid state diffusion bonding experiment with various processing parameters, including bonding temperature and pressure and holding time, and by inserting an Ag colloid layer between the aluminum and copper. Regression equations were developed to predict thickness of diffusion layer and interface hardness.An intermetallic compound formed at the interface between the Al and Cu during diffusion bonding at 420 °C and 240 MPa for 60 min, and it was effectively controlled by inserting an Ag colloid. These experimental data will be useful for setting up processing parameters to prepare Al/Cu matrix composite materials by using hydrostatic extrusion.     

Phase constitution near the interface zone of diffusion bonding for Fe3Al/Q235 dissimilar materials

The characteristics of phase constitution near the interface of Fe₃Al/Q235 diffusion bonding are researched by means of scanning electron microscope, X-ray diffraction and transmission electron microscope, etc. The test results indicated that an obvious diffusion transition zone forms near the Fe₃Al/Q235 interface as a result of vacuum diffusion bonding (heating temperature 1050–1080 °C, holding time 60 min and pressure 9.8 MPa). The maximum value of the Al content in the transition zone was 16.6 wt.% (about 28.5 at.%). The micro-hardness in the diffusion transition zone was HM 200–400. The transition zone consists of Fe₃Al and α-Fe(Al) solid solution. There was no brittle phase of high hardness near the diffusion interface. This is favorable to the enhancing of the toughness of Fe₃Al/Q235 diffusion joint.     

Study of structure/property relationships of diffusion bonded Ti6Al4V + 10 wt-%TiC particulate composite

Abstract

Ti–C particulate reinforced Ti6Al4V metal matrix composites (Ti6Al4V + 10 wt-%TiC) have demonstrated a high strength-to-weight ratio as well as good high temperature properties. A poor fusion welding performance is commonly observed in these materials making solid-state diffusion bonding a potential process to produce complex structural components. This work aims to characterise the microstructure and the mechanical properties of Ti6Al4V + 10 wt-%TiC diffusion bonded joints. Microstructural evaluation has been performed using both optical and scanning electron microscopy. Mechanical characterisation consisted of room temperature microflat tensile tests for the different bonding conditions and microhardness along the joint. The best results were associated with a bonding temperature of 1000°C and pressure 5 MPa together with bonding times ranging from 35 to 60 min.     

Fe3Al合金与Q235钢扩散焊界面元素的扩散

对Fe3Al／Q235扩散焊界面附近元素的分布进行计算并通过电子探针进行测定。结果表明，界面附近Al、Fe元素分布计算值和实测值的扩散趋势一致。随着加热温度和保温时间的增加，Fe3Al／Q235扩散焊界面附近元素的扩散距离增大。Fe3Al／Q235扩散焊界面过渡区宽度与保温时间的关系符合抛物线生长规律，保温时间超过60min后界面过渡区宽度不再明显增加。     

Temperature gradient transient liquid phase diffusion bonding: a new method for joining advanced materials

Abstract

A novel method for transient liquid phase (TLP) diffusion bonding of aluminium based materials has been developed which is capable of reliably providing excellent bonds with parent material shear strengths. This new method relies on imposing a temperature gradient across the bond line during TLP diffusion bonding and this leads to the formation of sinusoidal or cellular interfaces. Consequently, bond strengths are increased, possibly as a result of the higher metal–metal contact along the non-planar interfaces compared with the planar interfaces associated with either conventional TLP or solid state diffusion bonding processes. This paper describes the results achieved, implementing the new method and using copper interlayers, when joining Al–Mg–Si, Al–Li alloys, and an aluminium metal matrix composite with SiC particles. Patent protection has been filed in the UK under UK Patent No. 9709167.2.     

Bonding characteristics and diffusion barrier effect of the TiC phase formed at the bonding interface in an explosively welded titanium/high- carbon steel clad

Microstructural aspects and bonding characteristics of the explosively welded titanium/high-carbon steel clad of the as-welded and postannealed states were investigated. Amorphous and βTi phases were observed at the interface in the as-welded clad. These were considered to be the trace of melting and subsequently rapid solidification of thin layers along the contact surface of both the parent materials. The melting layer was considered to be responsible for the substantial bonding. The TiC layer was formed at the bonding interface by postannealing, which served as a barrier for diffusion of species across the interface and suppressed the formation of Fe-Ti intermetallic compounds. As a result, high bonding strength was preserved even after prolonged annealing at elevated temperatures.     

Bonding characteristics and diffusion barrier effect of the TiC phase formed at the bonding interface in an explosively welded titanium/high- carbon steel clad

Microstructural aspects and bonding characteristics of the explosively welded titanium/high-carbon steel clad of the as-welded and postannealed states were investigated. Amorphous and βTi phases were observed at the interface in the as-welded clad. These were considered to be the trace of melting and subsequently rapid solidification of thin layers along the contact surface of both the parent materials. The melting layer was considered to be responsible for the substantial bonding. The TiC layer was formed at the bonding interface by postannealing, which served as a barrier for diffusion of species across the interface and suppressed the formation of Fe-Ti intermetallic compounds. As a result, high bonding strength was preserved even after prolonged annealing at elevated temperatures.     

Interaction mechanism between void and interface grain boundary in diffusion bonding

Abstract

The interaction process between void and migrating interface grain boundary (IGB) in the bonding interface of 1Cr11Ni2W2MoV steel joints produced by diffusion bonding has been examined, and the corresponding interaction mechanism was analysed. The results showed that there were two cases occurring in void–IGB interaction by comparing the IGB velocity with void velocity: if the IGB velocity exceeded the void velocity, the void would separate from the IGB and be trapped inside the grain; otherwise, the void would attach to and migrate with the IGB. It was also found that the void–IGB interaction was related to the radius of void. The bigger voids easily separated from the migrating IGB, while the smaller voids tended to attach to it. The approximate theoretical values of critical radius of voids for separation/attachment were derived, and they agreed well with the experimental values obtained.     

Investigation of the weldability by resistance welding of rails strengthened by heat treatment

Summary

In the work presented a study was carried out on microstructural and chemical changes taking place in the bond interface during diffusion bonding of two superplastic Al‐Li alloy plates. Changes were characterised using various microscopy and micro‐analysis techniques including: scanning and transmission electron microscopy, energy‐dispersive X‐ray spectroscopy, atomic force microscopy and secondary ion mass spec‐trometry. The use of Al‐Cu alloy interlayers in the welding process was also evaluated.     

Probing into diffusion bonding of laser surface treated γ-Ti–Al alloy/Ti–6Al–4V alloy

Abstract

In this work, a novel diffusion bonding technique combining the laser surface treatment (LST) with the diffusion bonding is used to join a γ-Ti–Al alloy with a Ti–6Al–4V alloy. By using the LST and subsequent heat treatment, a layer with a fine grain structure can be obtained on their surface of the two alloys. The diffusion bonding behaviour between γ-Ti–Al alloy and Ti–6Al–4V alloy with or without LST under the different bonding conditions is investigated. The result reveals that LST can improve the diffusion bonding behaviour of the two alloys, and the three point bending strength of the joints can be promoted. The sound bonding between the two alloys with the LST is achieved at 1173 K under 80 MPa in 2 h.     

A study on diffusion couples of Ti and polysynthetically twinned (PST) Ti–Al: I. Microstructure characterization

The microstructural evolution in multi-phase diffusion couples of polycrystalline Ti and polysynthetically twinned (PST) Ti–49.3 at.% Al is studied, with the diffusion direction parallel to the lamellar planes. A reaction layer or reaction zone (RZ) of polycrystalline α₂-Ti₃Al phase, having a wavy interface with the PST Ti–Al crystal, forms along the PST/Ti bonding interface and exhibits a deeper penetration in the α₂ lamellae, consisting of fine α₂ and secondary γ laths, than in the primary γ lamellae. Furthermore, high-resolution transmission electron microscopy observations reveal that the RZ/PST interface at the fine α₂ and secondary γ lathes is microscopically flat. The lamellar thickness and the mass balance across the RZ/PST interface are believed to be the major factors that lead to these different behaviors in the penetration depth of the RZ.     

A prediction for fatigue crack growth rate in diffusion bonded Al/Ti interface

A melt diffusion bonding technique was developed to make a joint of Ti and Al, which had been regarded as almost impossible because of high activity. Fatigue crack growth rates, da/dN of the Al/Ti interfaces were measured experimentally at various stress ratios and compared with pure Ti and Al. The interface showed a resistance to fatigue crack propagation as good as that of aluminum alloy. The proposed universal equations on the basis of the crack closure concept made it possible to predict da/dN for various ΔK and R. Fatigue crack was observed to grow in the Al side adjacent to the interface along the direction parallel to the interface. It was observed to form the intermetallic compounds in the interface region.     

Evaluation of intermediate phases formed on the bonding interface of hot pressed Cu/Al clad materials

The aim of the present study is to identify the properties of intermediate phases formed on the bonding interface of hot pressed Cu/Al clad materials by transmission electron microscopy and nano-indentation analyses. Cu/Al clad materials were fabricated by hot pressing under 200 MPa at 250 °C for 1 h and then heat treated at 400 °C for 1 h. Nano-indentation measurement was conducted to evaluate the nanohardness and modulus of the intermediate phases formed between the Cu/Al interfaces. A 3-tier diffusion layer was observed at the Cu/Al interfaces. Knoop microhardness values at the bonding interface were 7 to 11 times that of the Cu and Al matrix metals. The intermediate phases formed at the bonding interface were Al4Cu9, AlCu, and Al₂Cu. A mapping analysis confirmed that the Al and Cu particles moved via mutual diffusion toward the intermediate phases formed at the bonding interface. The nanohardness values of η₂-AlCu and γ1-Al₄Cu₉ were 4 to 7 times that of the Cu and Al matrix metals. Nanohardness and Knoop microhardness measurement curves exhibited similar tendencies. The rigidity values of the respective intermediate phases can be arranged in descending order as follows: γ₁-Al₄Cu₉ > η₂-AlCu > θ-Al₂Cu.     

Atomic diffusion properties in wire bonding

1 Introduction Ultrasonic bonding was applied primarily to wire bonding in microelectronic packaging industry, while the mechanism of ultrasonic bonding has not been understood very well. HARMAN[1] observed that the peeling underdeveloped bonds simulate a…     

Vacuum diffusion bonding of Ti2AlNb alloy and TC4 alloy

The Ti₂AlNb 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/β layer and α₂ layer on the TC4 side, and α₂+B2/β layer on the Ti₂AlNb 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 Ti₂AlNb alloy and TC4 alloy were bonded at 950 °C 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/β layer and the fracture model was ductile rupture. Meanwhile, the formation mechanism of the Ti₂AlNb/TC4 joint was discussed in depth.     

Numerical modelling and experimental investigation of diffusion brazing SS304/BNi-2/SS304 joint

Abstract

The kinetics of dissolution and isothermal solidification at the bonding temperature during diffusion brazing SS304/BNi-2/SS304 has been studied through a combination of analytical modelling and experimental investigations. The modelling is based on the diffusion theory and the consideration of transient motion of liquid/solid interface. A set of coupled finite differential equations has been programmed to track the motion of liquid/solid interface during the isothermal solidification of liquid filler. Four parameters can be mathematically determined from the analytical modelling including the evolution of solute concentration profile, the maximum diffusion distance, and the maximum liquid thickness as well as the time to complete the isothermal solidification. These analyses are helpful to understanding the joining mechanism during diffusion brazing. The temperature dependent diffusion coefficient used in the modelling is derived together with the experimental data from brazing the wedge shaped joint specimen of SS304/BNi-2/SS304. The effects of bonding temperature and initial joint thickness on the joining process have also been investigated.     

Grain morphology,texture, and microhardness gradients in aluminum diffusion-bonded to aluminum oxide

The evolution of grain morphology, crystallographic texture, and microhardness in Al bonded to Al₂O₃ is dealt with. Specimens of a bilayer Al–Al₂O₃ and symmetric trilayer Al₂O₃–Al–Al₂O₃ were produced by solid-state diffusion bonding. Metallographic examination revealed the size and shape of grains in the Al layer, and the X-ray diffraction technique was used to measure the crystallographic texture at various through-thickness and in-plane locations. The results showed the existence of gradients in grain size, grain shape, texture, and microhardness through the thickness of the Al. Away from the interface, the aluminum grains were equiaxed, with a sharp cube recrystallization texture. Near the interface elongated and slanted grains, with a rotated cube texture, were observed. The microhardness was seen to correlate with the distribution of grain size. Finite element analyses employing crystal plasticity models were carried out to simulate the polygranular flow of Al during diffusion bonding. The interface constraint imposed by the Al₂O₃ layer was found responsible for the evolution of the observed gradients in microstructure in the Al layer. The predicted grain morphology trend was also in agreement with experimental observations.     

Ultrasonic evaluation of TiAl and 40Cr diffusion bonding quality based on time-scale characteristics extraction

To solve the problem of ultrasonic pulse-echo method in the evaluation of kissing bond and unbond in TiAl and ⁴⁰Cr diffusion bonding, a characteristics extraction algorithm was proposed. The algorithm was based on continuous wavelet transform to convert ultrasonic TiAl and ⁴⁰Cr diffusion bonding interface signals into time-scale domain. The ultrasonic tests were performed by an ultrasonic C-scan imaging system using a 10 MHz focused transducer. The time-scale amplitude and phase of the interface signals were calculated and analyzed to distinguish the kissing bond and the unbond from the perfectly bonded interface. The kissing bond can be detected by the scale-dependent amplitude combined with phase variation and the unbond can be measured by the opposite phase. The amplitude and phase characteristics were extracted to reconstruct the amplitude and phase characteristics images for TiAl and ⁴⁰Cr diffusion bonding specimens evaluation. The amplitude and phase characteristics images are effective in the evaluation of bonding quality.     

High strength Mo/Ti6Al4V diffusion bonding joints: Interfacial microstructure and mechanical properties

Joining Mo to Ti6Al4V is of great interest for applications in the weaponry and aerospace fields. In this work, a diffusion bonding technique is developed to bond a MoZr alloy and Ti6Al4V using a Cr-Ni-Ti-Si composite interlayer. The formation of the interlayer ensured that crack-free bonds were obtained. The mechanical properties and microstructure of the interface were examined. The results show that as the temperature was raised, the thickness of the diffusion layer increased and Kirkendall voids formed on the Mo alloy side. At the Mo/Cr-Ni-Ti-Si interface, a diffusion layer formed as Cr, Ni, Si and Mo dissolved into Ti to form a substitutional solid solution. As a result, the lattice constant of Ti reduced. For diffusion bonding between Mo and Ti6Al4V, a maximum tensile strength of 369 MPa was attained while a processing temperature of 950 °C was used. Ductile fractures were observed at the Mo/Ti6Al4V joints, primarily in Mo adjacent to the Mo/Cr-Ni-Ti-Si interface. The findings in this study open up new possibilities for the use of Cr-Ni-Ti-Si composite interlayer to bind Mo alloys to Titanium alloys.     

Effect of heating time on bonding interface,atom diffusion and mechanical properties of dissimilar titanium joints produced by thermal self-compressing bonding

Solid-state bonding between pure titanium and Ti6Al4V (TC4) alloy was conducted by a new bonding method named as rigid restraint thermal self-compressing bonding. Effects of heating time on bonding interface, atom diffusion and mechanical properties of the joints were studied. Results show that atom diffusion between pure titanium and TC4 alloy significantly takes place during bonding. The diffusion depths of Al and V in pure titanium side are increased with increasing heating time. Due to the enhancement of atom diffusion, bond quality of the bonding interface is improved along with the increase of heating time. The heating time seems to have little effect on microhardness distribution across the joint. However, the tensile strength and ductility of the joint have close relation to heating time. Prolonging heating time can improve the tensile strength and ductility of the joint, especially the latter. When the heating time increases to 450 s, solid-state joint with good combination of strength and ductility is attained.