TWI Industrial Member Report Summary 584/1996
W B Hanson
Few techniques are available for joining ceramics to metals, particularly for high temperature applications (>l000°C). This study has looked at the family of materials based on glass-ceramics which may be appropriate as high temperature joining media.
The main problems encountered when bonding ceramics to metals include the relative chemical inertness and low thermal expansion coefficient of the ceramic material. When combined with the brittle nature of ceramics, these problems present significant difficulties, particularly when the bond must withstand high, or sudden changes, in temperature and mechanical loading.
Procedures which are being investigated include graded interlayers (metal/ceramic mixes), produced via HIPing, and brazing with mechanically compliant interlayers which are able to accommodate interfacial strains. A further solution is to take advantage of a class of materials known as glass-ceramics. These materials can be developed to provide a wide range of thermal expansion coefficients, dependent on composition, and thus can provide ideal interlayer materials.
Glass-ceramics are crystalline inorganic materials formed from controlled crystallisation of a parent glass. They are usually based on silicate materials, typically MO-SiO 2-Al 2O 3, where MO is a metal oxide. In the glass phase, these materials are easy to process, either as a melt or in powder form. As such, they offer significant scope as interlayer materials. Few data currently exist on appropriate compositions for ceramic/ceramic or ceramic/metal joining, and on processing requirements for achieving high temperature applications (up to 1200°C).
- To establish the key factors influencing the properties and applications of glasses and glass-ceramics which makes them suitable as joining media.
- To determine the manufacturing route and existing applications of high temperature ceramic/ceramic and ceramic/metal joints using glass-ceramic bonding media.