The use of transient FGM interlayers for joining advanced ceramics

Functionally graded materials are designed to exhibit a desirable gradient in a property, due either to a gradient in composition, or microstructure, or both. In this paper, progress in the use of multilayer interlayers with microdesigned gradient structures for the purpose of joining is summarized. In contrast to conventional FGMs, the gradient structures of specific interest are not designed to be permanent, but are instead designed to facilitate processing by forming a thin layer of a transient liquid phase (TLP). This allows joining by a process that resembles brazing, but allows the formation of refractory joints al reduced processing temperatures, and provides access to joining chemistries that are not accessible by conventional joining methods. The method has been applied to the joining of Al2O3, Si3N4, and SiC, and is now being applied to the joining of SiC-SiC composites. Prior work is reviewed and recent progress in joining of these materials is described. (C) 1997 Elsevier Science Limited.