Transient Liquid Phase Diffusion Research Articles

Microstructural Evaluation and Ultrasonic Characterization of TLPD bonded 6061-SiCp Composite

Microstructural evaluation during transient liquid phase diffusion (TLPD) bonding of extruded aluminium based metal matrix composite (6061-15 wt% SiCP) using 50 μm thick copper interlayer was investigated by optical microscopy, scanning electron microscopy (SEM) together with SEM-based energy dispersive X-ray spectroscopy (EDS) and pulse echo ultrasonic test. Microstructural changes in the joint region were examined at five different holding time (20 min, 1 h, 2 h, 3 h and 6 h) for a bonding temperature of 560°C under two different applied pressures (0.1 MPa and 0.2 MPa). Kinetics of the bonding process was significantly accelerated in presence of reinforcement (SiC). This acceleration is attributed to the increased solute diffusivity through defect-rich SiC particle/matrix interface and porosity. The segregated particle at bond interface caused significant attenuation of ultrasonic wave, especially at lower bonding time. The attenuation effect decreased with increasing bonding time as width of particle segregation decreased.

TLP bonding of SiCp/2618Al composites using mixed Al–Ag–Cu system powders as interlayers

Mixed Al–Ag–Cu and Al–Ag–Cu–Ti powders were used as interlayers for transient liquid phase diffusion bonding (TLP bonding) of SiC particulate reinforced 2618 aluminum alloy matrix composite (SiCp/2618Al MMC). The results show that by using mixed Al–Ag–Cu powder with the eutectic composition as an interlayer, SiCp/2618Al MMC can be TLP bonded at 540 °C, however, the joining layer is porous. Adding a certain amount of titanium into the Al–Ag–Cu interlayer, the TLP bonding quality can be improved. The titanium added into the Al–Ag–Cu interlayer has an effect of shortening the solidification time of the joining layer, thus decreasing SiC particles from the parent materials entering into the joining layer. The joints bonded using Al–Ag–Cu–Ti interlayers have a maximum shear strength of 101 MPa when 2.1% titanium is added.

Transient liquid-phase diffusion bonding of two-dimensional carbon–carbon composites to niobium alloy

Two-dimensional carbon–carbon composites (C/C) were successfully bonded to Nb alloy with a Ti/Cu interlayer by transient liquid-phase diffusion bonding (TLP-DB) in vacuum condition. The joining process consisted of two stages: solid diffusion bonding at 780 °C under joining pressure of 4 MPa for 30 min, and TLP-DB at 1050 °C for 30 min under 0 or 0.03 MPa. The results show that the eutectic Ti–Cu liquid, produced during the second stage, presented good wettability on the C/C surface and further infiltrated into the C/C matrix to take “nail effect”, hence the bonding mechanisms were deduced; however, the residual Cu layer that was intentionally preserved as a stress relief buffer effectively relaxed the thermal stress of the joint, both of which made contributions to promote the shear strength of the joint that reached as high as 28.6 MPa.

Half-transient liquid phase diffusion welding: An approach for diffusion welding of SiCp/A356 with Cu interlayer

Aluminum matrix composite SiCp/A356 was welded by half-transient liquid Phase diffusion welding (HTLPDW) with a Cu interlayer. The effects of welding parameters and interlayer thickness on the properties of the welded joint were investigated, and the optimal welding parameters were subsequently put forward. The relationship between the tensile strength of the joint and the microstructure was studied by analyzing the microstructure of joint using a scanning electron microscope (SEM) and an electron probe micro-analysis (EPMA). Results confirmed the success of welding aluminum matrix composite SiCp/A356 utilizing HTLPDW method with a Cu interlayer. Shorter welding time was a prominent characteristic of HTLPDW as compared with conventional transient liquid phase (TLP) diffusion welding. Furthermore, its welded joints had a tensile strength almost 72% of its parent matrix composites, evidently signifying the suitable application of half-transient liquid phase diffusion welding in welding composite engineering structures.

Effect of Ti on TLP bonding of SiCp/2618Al composites using interlayers of mixed Al–Ag–Cu system powders

Transient liquid phase diffusion bonding of SiC particulate reinforced 2618 aluminium alloy matrix composite (SiCp/2618Al MMC) was carried out by using interlayers of mixed Al–Ag–Cu and Al–Ag–Cu–Ti powders. The effects of Ti on formation, microstructure and properties of the joints were investigated. The results show that adding a certain amount of Ti can obviously improve the TLP bonding quality of SiCp/2618Al MMC by using an Al–Ag–Cu interlayer with the eutectic composition. Besides improving the wettability of Al–Ag–Cu eutectic liquid to surfaces of the parent materials during bonding, the Ti added into interlayers has an effect of shortening the solidification time of the joining layer, thus decreasing SiC particles from the parent materials entering into the joining layer. The joints bonded using Al–Ag–Cu–Ti interlayers have a maximum shear strength of 101 MPa when 2·1%Ti is added.

Effect of transient liquid phase diffusion bonding on microstructure and properties of a nickel base superalloy Rene 80

A nickel base superalloy Rene 80 was bonded in the as received cast condition using transient liquid phase diffusion bonding with a Ni-base interlayer. The bonding process was carried out at 1100 °C under argon and vacuum atmospheres for various hold times. The bonds then homogenized at 1206 °C for 1 and 2 h. Microstructures of bonds were studied with optical and scanning electron microscopy. Microstructure studies showed intermetallic compounds within the joint region. However, these intermetallic compounds were removed by a post-bond heat treatment at 1206 °C for 2 h. Shear and hardness tests were undertaken to determine the mechanical properties of bonded samples. Results showed that the shear strength of bonds made under vacuum were higher than those of bonds made under argon atmosphere. The poor shear strength of bonds made under argon atmosphere was related to the formation of voids and porosities within the bond region and bond interface during bonding cycle. The variations of hardness within the joint region with bonding hold time and post-bond heat treatment time were discussed by considering the changes of alloying elements within the joint region.

Change of Microstructures of Directionally Solidified Ni Base Superalloy GTD-111 at High Temperature

In the case of transient liquid phase diffusion bonding with Ni base superalloy GTD-111, the bonding temperature was sustained at 1403K ~ 1453K. Thus, the microstructure of specimens heated at 1403K ~ 1453K was examined. In the raw material, γ-γ' eutectic phases, platelet η phases, MC carbide and PFZ were clearly observed in interdendritic regions or near the grain boundary and the size of primary γ' precipitates near the interdendritic regions were larger than the core. The primary γ' precipitated in the dendrite core dissolved early in the bonding process. γ' precipitated near the interdendritic regions were partially solubilized and their shape was changed. The dissolution rate increased with increasing temperature. Phases in the interdendritic regions or near the grain boundary changed continuously with time at the bonding temperature. At a bonding temperature of 1403K, the eutectic phases remained, but η phases were transformed from a platelet shape to a needle morphology and the PFZ region widened with time. The interdendritic region and near the grain boundary became partially liquid at 1423K and fully at 1453K by the reaction of η phases and PFZ. The interdendritic region and near grain the boundary became liquid and new phases which were mixed with η phases, PFZ and MC carbide crystallized during cooling at 1453K. Crystalline η phases were transformed from a rod shape to a platelet shape with increasing holding time.

The Effect of the Process Temperature on the Bondability in Transient Liquid Phase (tlp) Diffusion Bonding of AISI 430 Ferritic Stainless Steel with Nodular (Spheroid) Cast Iron Using a Copper Interlayer

Abstract The effect of the process temperature on the bondability in the transient liquid phase (tlp) was studied. The diffusion bonding of AISI 430 with nodular cast iron using a copper interlayer was investigated experimentally under a protective atmosphere at various temperatures and at a defined constant blow pressure which would cause macro deformation. Microstructure examinations were carried out with the help of optical microscopy, SEM and EDS. Hardness values were measured by HV scale under a load of 150 g. At the bond interface, decarburized and dechromised regions were observed on the ductile cast iron side and stainless steel side respectively. Best mechanical and metallurgical properties were observed for the specimen bonded at 1100°C for 20 min. As a function of an elevation of the process temperature, an increase in the amount of graphite atoms that migrated toward the interface and a reduction at the nodular graphite diameters was noticed.

TLP Bonding of DS Ni Base Superalloy, GTD-111 Using Mixed Powder of Base Metal and Filler Metal

The effect of a mixed powder on the wide gap transient liquid phase diffusion bonding of a directionally solidified Ni base superalloy, GTD-111 was investigated. The mixed powder consisted of a mixture of a powdered Ni base filler (GNi-3) and powdered base metal (GTD-111). The range of the base metal powder was 40 to 70wt%. Bonding was performed at a temperature of 1463K, using various holding time. In the case of a lower 50wt%, the base metal powders completely melted and base metal mating at the interface dissolved at an early time, and extent of dissolution of base metal decreased with increasing mixing ratio. Liquid was eliminated by isothermal solidification, which was controlled by the diffusion of B into the base metal. The solids in the bonded interlayer grew epitaxially from the mating base metal inward from the insert metal and the number of grain boundaries formed at the bonded interlayer corresponded with those of the base metal. The finishing time for isothermal solidification was about 74ks. In the case 60wt% and higher, the base metal powders partially melted and remained in the vicinity of bonded interlayer. The solid was formed from the remaining powder and base metal mating at the interface. Finally, the bonded interlayer underwent the poly-crystallization when isothermal solidification was complete. The contents of Al and Ti in the bonded interlayer with a holding of 74ks were equal to that of the base metal.

非線形超音波法を用いたγＴｉＡｌ合金／鋼拡散接合部の品質保証

These days, lightweight materials has been applied in automobile industries so as to make fuel consumption improvement. A turbine rotor for turbo-charger of automobiles made of γ-TiAl alloy is an example of such a component. The rotor blade made of gamma titanium aluminum alloy is bonded by the transient liquid phase diffusion bonding method to the rotor shaft made of chromium molybdenum steel. Conventional pulse-echo inspection has been applied to inspect the bond. Ability of the inspection is satisfied with requirements to keep the quality of the rotor, but it is restricted by the big mismatch in the acoustic impedance of the bonded materials. More than one thirds of the incident ultrasound is reflected at the interface; therefore indications from minute imperfections at the interface are indistinguishable. A nonlinear ultrasonic method has been applied actively to detect a closed gap. Applying high power ultrasound, with amplitude ten times greater than the conventional method, results in a generation and detection of second harmonic signals. A new nonlinear C-scan acoustic microscope has been developed and applied to the inspection of the bonds. As the result, no indication is observed on a C-scan image of fundamental frequency component of the bond whereas clear indications are observed on the C-scan image of the second harmonic components. The existence of closed cracks or gaps were confirmed at the indicated area by micrographic analysis followed the inspection. This paper describes the application of the conventional pulse echo inspection for the bond and a results of the application of nonlinear ultrasonic method for the bond with artificially made minute imperfections.

Joining of Aluminium Metal Matrix Composites

ABSTRACT Aluminium metal matrix composites (AlMMCs) offer several advantages relative to monolithic aluminium alloys such as high stiffness, strength, wear resistance, low thermal expansion coefficient, etc. However, despite considerable improvements in developing AlMMCs, the lack of reliable joining methods restrict their greater application. Fusion welding of AlMMCs has not proved successful because high temperature nature of the process normally causes unfavorable reactions between the reinforcement and the matrix, leading to the formation of a variety of defects. On the other hand, solid-state welding and diffusion bonding may not be suitable due to the presence of chemically stable surface layer of aluminium oxide, which, being insoluble in aluminium, inhibits metal-to-metal contact during diffusion bonding. Furthermore, diffusion bonding requires a very smooth and clean contact surface, which is difficult to obtain in industrial applications. As an alternative, transient liquid phase (TLP) diffusion bonding, which operates at a lower temperature, can be used to circumvent the problems associated with the oxide layer. The formation of liquid phase (eutectic) can assist the disruption of the oxide layer and promote metallic contact. The composite material used in the present study consisted of 6061 alloy containing 15 volume % of SiC particulates of 23 μm diameter. TLP bonding was carried out at 560 ˚C in argon atmosphere using copper as an interlayer with different pressures and holding times. TLP-bonded AlMMCs were characterized by optical and scanning electron microscopy, microhardness survey, and shear tests. The results indicated that adequate bond strength could be achieved with suitable bonding parameters such as holding time and initial pressure.

Phase Transition during Slow Heating in the Mixture Insert Metal Using TLP Bonded Interlayer

This study was carried out to investigate the effect of heating rate on the phase transition between additive base metal powder and liquid insert metal during transient liquid phase (TLP) diffusion bonding of Ni-based superalloy GTD-111. Heating rates studied were 10, 1, 0.5 and 0.1°Cs-1 in high vacuum conditions (3×10-5 torr) by means of a high frequency induction furnace. When heated at lower than 0.5°Cs-1, the transition of dissolution to solidification occurred during heating. In the case of very slow heating, the dissolution quickly finished at a lower temperature, and solidification soon started. The separated grains of additive base metal powders supplied the lager interface area for the diffusion of boron. Solidification transition temperatures of liquid phase were affected by the increase of diffusion interface and of duration time during slow heating. A minimum heating rate required to heat insert materials to a normal TLP isothermal bonding temperature of GTD-111 (≈1150°C) without a dissolution-solidification transition during heating should be higher than 1°Cs-1.

Microstructures and Properties of Transient Liquid Phase Diffusion Bonded Joints of DZ22 Superalloy

An investigation of transient liquid phase (TLP) diffusion bonding of a nickel-base directionally solidified superalloy, DZ22, was presented. Two interlayer alloys developed for DZ22 were employed. They were: Z2P, a powder alloy and Z2F, an amorphous foil. The results show that the microstructures and compositions of the joints bonded with Z2F amorphous foil were obvious more homogenous than the joints bonded with Z2P powder alloy. And the joints bonded with Z2F possessed a better stress-rupture property. The final obtained joint stress-rupture properties reached 90% of that of the base metal.

Effect of Heating Rate on Transient Liquid Phase Diffusion Bonding of Ni-Based Superalloy GTD-111

This study was carried out to investigate the effect of heating rate on dissolution and solidification behavior during transient liquid phase diffusion bonding of Ni-based superalloy GTD-111. The heating rate was varied by 0.1K/sec, 1K/sec, 10K/sec to the bonding temperatures 1373K and 1423K in vacuum. When the heating rate was slower and the bonding temperature was higher, the completion time of dissolution after reaching bonding temperature decreased. When the heating rate was very slow, the solidification proceeded before reaching bonding temperature and the time required for the completion of isothermal solidification was shorter. However, when the total time required for completion of solidification from the beginning of heating was considered, heating at 0.1K/sec was nearly the same as heating at 10K/sec.

Effect of transient liquid phase diffusion bonding on properties of ODS nickel alloy MA758

An oxide dispersion strengthened (ODS) MA758 nickel alloy was bonded in the fine grain and recrystallised conditions using transient liquid phase diffusion bonding at 1100°C for various hold times. A microstructural study was undertaken to investigate the effect of post-bond heat treatments at 1360°C for 1 hand changes in parent metal grain size on developments of bond microstructure. Shear and fatigue tests were carried out to determine the mechanical integrity of the bonded samples. Results showed that shear and fatigue strengths of diffusion bonds made in the recrystallised condition were higher than those of bonds made in the fine grain condition. The results from oxidation tests performed at 1000°C show that the oxidation rate for samples bonded in the fine grain condition is higher than for those bonded in the recrystallised condition. However, localised oxidation of the joint region was not observed and this indicated that compositional homogeneity across the diffusion bonds had been attained.

Transient liquid phase bonding of a microduplex stainless steel using amorphous interlayers

Microduplex stainless steels are two phase alloys which show excellent corrosion resistance and toughness. In order to join these special steels, fusion welding processes are normally used and a second post-weld heat treatment is necessary to regain the original ferrite to austenite ratio. In this study, transient liquid phase diffusion bonding was used to join a 2205 duplex stainless steel with the aid of amorphous interlayers. The research compares a Ni–B–Si ternary system with that of an Fe–B–Si interlayer, and compositional, microstructural and mechanical assessment was used to determine the quality of the bonds produced. These preliminary results show that the nickel based interlayer stabilises the austenitic phase along the bond length, which hinders grain growth across the joint region. In contrast, the iron based interlayer produces diffusion bonds, which show microstructural and compositional homogeneity across the joint region. Furthermore, mechanical and pitting corrosion tests show that transient liquid phase diffusion bonds can achieve properties similar to those of the parent alloy.

A Parametric Study of Solute Redistribution DuringTransient Liquid Phase Diffusion Bonding Process

A parametric study is performed to investigate the solute redistribution during the transient liquid phase (TLP) diffusion bonding process. The macroscopic solute diffusion in the liquid and the solid phase, as well as the solid transformation to the liquid due to solute macrosegregation, are considered in this study. The effects of the following parameters are considered: ratio of solute diffusivity in liquid and solid state alloy (ξ = Dl/Ds), holding temperatures (θ), a combined parameter related to solidus and liquidus slopes in the phase diagram (ϕ), and the re‐melting and re‐solidification time (τ). The thickness of the pure liquid zone and the mushy zone of the TLP diffusion bonding process are demonstrated with respect to the above‐mentioned parameters. It is shown numerically that the holding time, the holding temperature, and solute diffusivity ratio influence the solute distribution strongly, which in turn influences the liquid zone and mushy zone thickness significantly. It is concluded that for the TLP diffusion bonding process, the optimal technique parameters are high holding temperature, long holding time, and a large liquidus and solidus temperature slope ratio (ml/ms) of the interlayer material.

Transient liquid phase diffusion bonding under a temperature gradient: modelling of the interface morphology

Imposing a temperature gradient when transient liquid phase (TLP) diffusion bonding results in reliable joints with shear strengths as high as those of the parent material (e.g. aluminium-based alloys and composites). The key feature of this new method relies on the formation of non-planar interfaces as a consequence of morphological instability at the solid/liquid interface during solidification of the liquid layer (normally with a eutectic composition) at the bonding temperature. A model is proposed in this paper which is capable of predicting interface morphology and the bonding conditions which result in the formation of non-planar bond lines when using this new bonding method. The results of model provide an insight to the nature of the solidification process. The proposed model was verified experimentally when bonding pure aluminium and also an aluminium alloy (6082) using copper interlayers.

Analytical Modelling of Solidification during Temperature Gradient TLP Diffusion Bonding

Imposing a temperature gradient when transient liquid phase (TLP) diffusion bonding is the basis of a new bonding method which has recently been developed in the Department of Materials Science and Metallurgy, University of Cambridge (UK Patent 9709167.2). The use of temperature gradient TLP diffusion bonding results in joints with excellent reliability and also shear strengths as high as those of the parent material (e.g. aluminium-based alloys and composites). Another feature of this new method is that diffusion of solute in the solid phase is not necessary for solidification to take place and therefore bonding times are significantly shorter than those in conventional TLP diffusion bonding (when there is no imposed temperature gradient across the liquid phase). A mathematical model is proposed in this paper which is capable of predicting bonding times and bond line displacements when TLP diffusion bonding under a temperature gradient. The bond line displacement and bonding time predicted by the model for an ideal Al-Cu binary system are compared with experimental results obtained using pure aluminium and copper. The theoretical values predicted by the model are in agreement with the experimental results.

Analytical modelling of transient liquid phase (TLP) diffusion bonding when a temperature gradient is imposed

Transient liquid phase (TLP) diffusion bonding with a temperature gradient across the bond region is the basis of a new bonding method which results in joints with excellent reliability and also shear strengths as high as those of the parent material (e.g. aluminium-based alloys and composites). In contrast to conventional TLP diffusion bonding where diffusion of solute in the solid phase is traditionally assumed to be necessary for solidification to take place, this new method relies on the diffusion of solute in the liquid phase. A precise analytical solution is proposed which is capable of predicting bonding times and bond line displacements when TLP diffusion bonding under a temperature gradient. Based on a mass balance approach, a simpler solution for predicting the bond line displacements and the bonding times is also suggested. The proposed model was verified experimentally for the bonding of pure aluminium using a copper interlayer. The approach described also has the potential to model conventional TLP diffusion bonding.