The vast majority of man-made structures, from skyscrapers to microelectronic devices, require joints between similar or dissimilar materials. Ideally, joining is fast, reliable, and inexpensive. Conventional joining technologies often fail to provide these characteristics for applications involving materials with fragile microstructures (e.g., nanostructures and metallic glasses) or materials intended for high-temperature applications (e.g., ultrahigh-temperature ceramics). Difficulties arise because joining temperatures are sufficiently high to degrade the microstructure, the joining time is excessive, or the use temperatures of the joined assemblies are constrained. Transient-liquid-phase (TLP) joining is an elegant means to reduce the joining temperature relative to conventional methods while retaining the potential for high-temperature use. However, TLP bonding is often time-intensive. The rapid development of strong, defect-free joints requires: (i) favorable wetting behavior to eliminate defects and (ii) rapid interdiffusion kinetics to reduce processing times. We show in this paper that Ni/Nb/Ni interlayers develop transient-liquid films that satisfy both criteria, enabling rapid, reliable, reducedtemperature TLP bonding of a model ceramic system. While the focus of this paper is on joining ultrahigh-strength Al 2 O 3 , recently we have successfully extended the method to joining Y 2 O 3 -stabilized ZrO 2 (YSZ) and ZrO 2 -toughened Al 2 O 3 (ZTA). By designing multilayer interlayers with similar wetting and interdiffusion characteristics, it should be possible to extend this novel approach to an even broader range of advanced materials combinations.
Joining methods based on welding, soldering, and brazing all involve heating to form a liquid that ideally flows to fill gaps between the pieces being joined, and subsequent cooling to induce solidification of the bonding media; the joint region differs chemically and microstructurally
[*] Prof.