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

Surface tension of liquid metals and alloys — Recent developments

Using a reactive force field (ReaxFF), we investigated the structural, energetic, and adhesion properties, of both solid and liquid Al/alpha-Al2O3 interfaces. The ReaxFF was developed solely with ab initio calculations on various phases of Al and Al2O3 and Al-O-H clusters. Our computed lattice constants, elastic constants, surface energies, and calculated work of separation for the solid-solid interface agree well with earlier first-principles calculations and experiments. For the liquid-solid system, we also investigated the nonwetting-wetting transition of liquid Al on alpha-Al2O3(0001). Our results revealed that the evaporation of Al atoms and diffusion of O atoms in alpha-Al2O3 lead to the wetting of liquid Al on the oxide surface. The driving force for this process is a decrease in interfacial energy. The nonwetting-wetting transition was found to lie in the 1000–1100 K range, which is in good agreement with sessile drop experiments.

Adhesion and nonwetting-wetting transition in the Al/α-Al 2 O 3 interface

Interfacial phenomena in thermally sprayed multiwalled carbon nanotube reinforced aluminum nanocomposite

Twinning-Mediated Growth of Al2O3 Nanobelts and Their Enhanced Dielectric Responses

Experimental results are presented on the investigation of the correlation between wetting and bonding properties in Al/Al 2 O 3 couples. Applying the sessile drop method the wettability of alumina substrates by molten Al was investigated at temperatures from 953–1373 K under a dynamic vacuum of 0.2 mPa. A special procedure to study shear strength of metal–ceramic joints using the sessile drop samples has been elaborated. The results clearly indicate that the shear strength of Al/Al 2 O 3 joints strongly depends on wetting properties in Al/Al 2 O 3 system, i.e. the lower the contact angle Θ , the higher the value of interfacial shear strength.

Wetting and bonding strength in Al/Al2O3 system

The paper presents the description of an experimental complex that has been designed for investigations of high temperature capillarity phenomena by various testing methods (classical sessile drop, pendant drop, dispensed drop, sandwiched drop, transferred drop, drop sucking, drop pushing, drop smearing or rubbing) at a temperature of up to 2100 °C under vacuum of up to 10−7 hPa or in protective atmosphere (static or flowing gas with controlled rate at required level of pressure). Several examples of high temperature wettability tests are discussed in order to demonstrate the wide testing possibilities of the new experimental complex.

Experimental complex for investigations of high temperature capillarity phenomena

The paper discusses the scientific understanding of the role of interfacial phenom- ena in joining of dissimilar materials using liquid-phase-assisted processes. From the exam- ple of the Sn-alloy/Cu system, it is demonstrated that interaction in the liquid solder/substrate couples is accompanied by a number of complex interfacial reactions leading to significant changes in the structure and chemistry of interfaces (solder/substrate, solder/environment, substrate/environment) and remaining solder layer that finally influence the mechanical prop- erties of solder joints. The experimental data on wetting behavior, interface characterization, and mechanical properties of different solder/metal substrate couples are analyzed in order to display the role of such factors as time and temperature of interaction, environment (protective atmosphere, flux), presence of oxide films on interfaces, alloying additions to a solder, formation of inter- facial phases, and porosity.

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Factors affecting wettability and bond strength of solder joint couples

A fresh approach has been advanced to examine in the Al/Al2O3 system the effects of temperature, alloying of Al with Ti or Sn, and Ti and Sn coatings on the substrate, on contact angles measured using a sessile-drop test, and on interface strength measured using a modified push-off test that allows shearing of solidified droplets with less than 90 deg contact angle. In the modified test, the solidified sessile-drop samples are bisected perpendicular to the drop/Al2O3 interface at the midplane of the contact circle to obtain samples that permit bond strength measurement by stress application to the flat surface of the bisected couple. The test results show that interface strength is strongly influenced by the wetting properties; low contact angles correspond to high interface strength, which also exhibits a strong temperature dependence. An increase in the wettability test temperature led to an increase in the interface strength in the low-temperature range where contact angles were large and wettability was poor. The room-temperature shear tests conducted on thermally cycled sessile-drop test specimens revealed the effect of chemically formed interfacial oxides; a weakening of the thermally cycled Al/Al2O3 interface was caused under the following conditions: (1) slow contact heating and short contact times in the wettability test, and (2) fast contact heating and longer contact times. The addition of 6 wt pct Ti or 7 wt pct Sn to Al only marginally influenced the contact angle and interfacial shear strength. However, Al2O3 substrates having thin (<1 µm) Ti coatings yielded relatively low contact angles and high bond strength, which appears to be related to the dissolution of the coating in Al and formation of a favorable interface structure.

W. Radziwill

Papers

Wetting and bonding strength in Al/Al2O3 system

Experimental complex for investigations of high temperature capillarity phenomena

Factors affecting wettability and bond strength of solder joint couples

The effect of temperature, matrix alloying and substrate coatings on wettability and shear strength of Al/Al2O3 couples

The role of aluminium oxidation in the wetting-bonding relationship of Al/oxide couples