Fabrication and crack deflection in ceramic laminates with porous interlayers

A simple and general method for making ceramic laminates with porous crack- deflecting interlayers is demonstrated. Both the strong laminae and the por ous interlayers are made by tape casting suitable slurries using the same c eramic powders. Porosity is introduced into the interlayer by adding starch particles to the slurry. The effects of the starch on the burn-out and sin tering behavior of the laminates has been fully described. The influence of resulting porosity on the ability of an interlayer to deflect a growing cr ack and to remain stable on prolonged heating has also been investigated. F or the pore morphologies studied here, it is the volume fraction of pores t hat controls whether crack deflection takes place. Using existing mechanics solutions, a simple theoretical criterion for this volume fraction of poro sity is given and is consistent with all the experimental observations.