Relationship between strength and failure mode of ceramic multilayers

The mechanical strength of ceramic multilayers for use in solid oxide fuel cell stacks was examined. The multilayers consist of a substrate, made of y ttria stabilised zirconia (YSZ), with a NiO/YSZ composite coating on both f aces. Under some processing conditions the mechanical strength of the multi layers was similar to that of pure YSZ, while a much lower strength was fou nd for other processing conditions, inspections of the fracture surfaces re vealed markedly different appearances, suggesting that a transition in fail ure mode had occurred. Fracture mechanics models for thin films on substrat es were used to interpret the observed fracture modes, providing insight to the underlying failure mechanisms. (C) 1998 Kluwer Academic Publishers.