The 1980s was a boom time for engineering ceramics. Emerging materials such as silicon nitride and SiAlONs were seen as the shape of things to come in several industries, replacing metallic components on a grand scale. For more than a decade, intensive effort went into these new materials. One goal was to produce an all ceramic car engine. However, such an all ceramic future never materialised as reality failed to match up to expectations. Today, ceramics have an important part to play in conjunction with other materials. They can add particular functionality or provide added benefit to a component, eg as hard wearing surfaces, ultra-hard materials in cutting tools, for corrosion resistance or high temperature protection. As ceramics are not being used in isolation, joining is an increasingly vital technology for the integration of the materials.
Joining of Ceramics

Despite its obvious importance, joining is often neglected during the design process. Many engineers incorporate ceramics into a component as though they were high performance metals, giving little thought to service conditions or joining operations. This can lead to two outcomes, either the part fails and its designers conclude that the ceramic was unsuitable and that metals should be used as before, or an expensive redesign may be required if a ceramic must be used.
Joining Considerations

There are many important issues to be considered alongside joining such as materials selection, best practice and joint design, but this article concentrates on ceramic joining technologies and, in particular, some of the novel ways of producing ceramic/ceramic and ceramic/metal bonds.
Ceramic Joining Technologies

The ceramic joining technologies used today (few of which have been developed specifically for this class of materials) range from simple mechanical attachment such as the compression fit used in spark plugs, figure 1a, through to liquid phase processes such as adhesive bonding and brazing. The thermal protection system for the space shuttle uses adhesives, and the ceramic turbocharger rotor uses brazing, figure 1b. There are problems associated with these processes including processing considerations (such as component size and joining atmosphere), time constraints and costs, which is why the new ceramic joining technologies described in this article are being developed.