Large Area Active Brazing of Multi-Tile Ceramic-Metal Structures

Lightweight ceramic-metal combinations are one option for advanced structures.  These structures can require the fabrication of large area arrays of ceramic tiles on a metallic backing.  However, the process of fabricating a combination of lightweight ceramics and metals is complicated by the need to bond these very dissimilar materials together.  For severe applications, a strong bond between the ceramic and metal is required.  One option for achieving this strong bonding in ceramic-metal systems is active metal brazing.  The active brazing alloys wet most materials (including ceramics and corrosion-resistant metals such as titanium alloys and stainless steels) and forms strong, metallurgical bonds.  However, the high processing temperatures result in large strain (stress) build-up from the inherent differences in coefficient of thermal expansion (CTE) of the substrates.  There are some techniques available to alleviate the strains on the ceramic, such as using an interlayer, which either has an intermediate value (between the metal and ceramic) of CTE and/or is “soft” (plastically deforms).  However, it is still extremely challenging to actively braze large specimens when there is a considerable CTE gradient.  This study will introduce pyramidal core structures as one of many possible interlayers between ceramic and metal.  The processing techniques to successfully fabricate lightweight, large area ceramic-metal arrays will be discussed and the mechanical testing results of the various bonds will also be presented.