Porous Interfaces as Crack Deflecting Interlayers in Ceramic Laminates

A simple, general method for producing ceramic laminates with porous, crack deflecting interlayers is demonstrated. Both the strong laminae and the porous interlayers were made by tape casting suitable slurries using the same ceramic powders. The influence of the resulting porosity on the ability of an interlayer to deflect a growing crack was investigated. The ability of the interlayers to deflect cracks was found to depend only on the volume fraction of the pores, with crack deflection being observed for pore volume fractions of 0.29 and greater. A simple theoretical criterion was derived for the minimum volume fraction of pores required for crack deflection. This assumes that if useful crack deflection is to occur then the interfacial defects must not be able to kink into the laminae and predicts that deflection is influenced only by the volume fraction of pores in the path of the growing interfacial crack. For the equiaxed pores studied, this is equal to the overall volume fraction of pores in the laminate. Such a criterion gives very good agreement with the experimental observations and is consistent with other experimental and theoretical work. 12 refs.