Transient liquid phase (TLP) bonding is a relatively new bonding process that joins materials using an interlayer. On heating, the interlayer melts and the interlayer element (or a constituent of an alloy interlayer) diffuses into the substrate materials, causing isothermal solidification. The result of this process is a bond that has a higher melting point than the bonding temperature. This bonding process has found many applications, most notably the joining and repair of Ni-based superalloy components. This article reviews important aspects of TLP bonding, such as kinetics of the process, experimental details (bonding time, interlayer thickness and format, and optimal bonding temperature), and advantages and disadvantages of the process. A wide range of materials that TLP bonding has been applied to is also presented. Partial transient liquid phase (PTLP) bonding is a variant of TLP bonding that is typically used to join ceramics. PTLP bonding requires an interlayer composed of multiple layers; the most common bond setup consists of a thick refractory core sandwiched by thin, lower-melting layers on each side. This article explains how the experimental details and bonding kinetics of PTLP bonding differ from TLP bonding. Also, a range of materials that have been joined by PTLP bonding is presented.

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Overview of transient liquid phase and partial transient liquid phase bonding

Diffusion bonding was carried out between commercially pure titanium (cpTi) and 304 stainless steel (304ss) using copper as interlayer in the temperature range of 850–950 ◦ C for 1.5 h under 3 MPa load in vacuum. The microstructures of the transition joints were revealed in optical and scanning electron microscopy (SEM). The study exhibits the presence of different reaction layers in the diffusion zone and their chemical compositions were determined by energy dispersive spectroscopy. The occurrence of different intermetallic compounds such as CuTi2, CuTi, Cu3Ti2 ,C u 4Ti3, FeTi, Fe2Ti, Cr2Ti, T2 (Ti40Cu60−xFex ;5 <x < 17), T3 (Ti43Cu57−xFex ;2 1 <x < 24) and T5 (Ti45Cu55−xFex; 4< x < 5) has been predicted from the ternary phase diagrams of Fe–Cu–Ti and Fe–Cr–Ti. These reaction products were confirmed by X-ray diffraction technique. The maximum bond strength of ∼318 MPa (∼99.7% of Ti) was obtained for the couple bonded at 900 ◦ C due to better coalescence of mating surface. With the rise in joining temperature to 950 ◦ C, decrease in bond strength occurs due to formation of brittle Fe–Ti bases intermetallics. At a lower joining temperature of 850 ◦ C, bond strength is also lower due to incomplete coalescence of the mating

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Diffusion bonding of commercially pure titanium to 304 stainless steel using copper interlayer

Welding and Joining of NiTi Shape Memory Alloys: A Review

The Mg/Al laminated composite was fabricated by the accumulative roll bonding (ARB) using the pure magnesium and Al5052 alloy at 400 °C. Tensile properties along rolling direction and the transverse direction and the microhardness were evaluated at the ambient temperature. The tensile strength of the laminated Mg/Al composite along both directions increased gradually till two ARB cycles, but then decreased after the third ARB cycles. Optical microscopy and scanning electron microscopy (SEM) were utilized to reveal the microstructure evolution and the failure mechanism. Grain refinement of Mg layers was not obvious during the ARB process due to the high temperature and interval reheating. The obvious crack at the coarse intermetallic compounds and rupture of the Al layer after the third cycle led to the premature failure of the sample along the rolling direction during the tensile test.

Microstructure and mechanical properties of the Mg/Al laminated composite fabricated by accumulative roll bonding (ARB)

Solid state diffusion bonding of titanium to steel using a copper base alloy as interlayer

Diffusion Bonding of a Microduplex Stainless Steel to Ti-6Al-4V

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 see

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

Diffusion bonding is an advanced bonding process in which two materials, similar or dissimilar, can be bonded in solid state. This provides to bond materials in a wide range from low carbon steels to ceramics and composites which cannot be bonded with conventional welding methods. One of the major advantages of this method is to produce new bimetal or dissimilar material couples. The process is diffusion-based and occurs in solid state and because of its increasing use as a commercial process. The estimation of final bonding time is very important but difficult without experiments for many materials. In this study, therefore, a new mathematical model is presented to predict the final bonding time for a sound bonding interface prior to bonding practice. Being different from the previous models, this model assumes a new surface morphology as a sine wave and a new creep mechanism for duplex alloys. The mechanisms operating during diffusion bonding are based on those in pressure sintering studies but here mass transfer by evaporation has been ignored. The driving forces and rate terms for those mechanisms have been altered to reflect the difference of the geometries of the two processes. Also the effect of grain size has been included in the model in case of joining fine-grained materials. In determining diffusion coefficients for duplex alloys, Darken’s equation for binary alloys has been used. Depending on this new approach, it was shown that a more realistic final bonding time could be predicted for duplex alloys by comparing the results from this new model with those from the previous ones. As a result, it was determined that the new model could be used in order to estimate the final bonding time of the duplex alloys for a sound bond interface and the relationships between its parameters safely. The predictions from this new model show a very good agreement between practice and theory.

A new model for diffusion bonding and its application to duplex alloys

In this study, the effects of coarse initial grain size with varying heat inputs on microstructure and mechanical properties of weld metal and heat-affected zone (HAZ) were investigated. In the welding experiments, SAE 1020 steel specimens in hot-rolled and in grain-coarsened conditions were used. The specimens taken from the hot-rolled steel (original) plate were heat treated at 1100°C for 45 min and then cooled in a furnace in order to obtain a coarse initial grain size. The original and grain-coarsened specimens were welded using a submerged arc welding machine with heat inputs of 0.5, 1 and 2 kJ/mm. Following the welding, microstructure, hardness and toughness of weld metals and HAZs were investigated. From the results, we tried to establish a relationship between initial grain size, microstructure, hardness and toughness of weld metals and HAZs. From the results of the toughness tests, it was seen that the weld metals of coarse initial grain sized specimens and original specimens exhibited nearly the same toughness values with the same heat input, whereas different HAZ toughness values were obtained with the same heat input. Maximum toughness of HAZ of the coarse initial grain sized specimen was achieved with a high input, while maximum toughness of original specimen was obtained with a medium heat input. As a result, considering the heat input, it was observed that the coarse initial grain size had a great influence on the microstructure, hardness and toughness of HAZ of a low carbon steel. Thus, taking into consideration the plate thickness, a higher heat input should be used with respect to the maximum toughness of the HAZ in the welding of grain-coarsened low carbon steels.

Effect of coarse initial grain size on microstructure and mechanical properties of weld metal and HAZ of a low carbon steel

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 tha...

M. Eroglu

Papers

Diffusion Bonding of a Microduplex Stainless Steel to Ti-6Al-4V

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

A new model for diffusion bonding and its application to duplex alloys

Effect of coarse initial grain size on microstructure and mechanical properties of weld metal and HAZ of a low carbon steel

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