Ceramic matrix composites – joining to metals

Ceramic matrix composites, such as SiC/SiC and C/SiC, are lightweight, hard, wear resistant and stable in oxidising environments to temperatures as high as 1600°C. However, because of the fibre reinforcement, they have improved mechanical properties, failing in a gradual rather than catastrophic mode. They are particularly suitable for applications in high temperature burner environments where they can outperform more conventional superalloys.

In many high temperature applications using ceramic matrix composites, there is a requirement to join them to other materials including metals. Brazing is a highly effective joining technique for many ceramic-ceramic and ceramic-metal joint systems. However, differences in coefficients of thermal expansion require specialised approaches to accommodate the mechanical stresses introduced by joining. This can be achieved, for example by flexible or ductile interlayers, or by careful selection of interlayers expansion matched to the ceramic. Additionally, non-melting materials, such as ceramic particles, can be dispersed in the braze to adjust its thermal expansion coefficient or ductility. Design of such joints, using techniques such as finite element modelling, is also of critical importance to minimise stresses.

For information about TWI’s capabilities please email contactus@twi.co.uk.

Cross-section of a ceramic-reinforced brazed joint in silicon carbide; brazed with Cu-Ag-Ti-10%SiC

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Ceramic matrix composites – joining to metals

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