SIC-WHISKER-REINFORCED CERAMICS WITH MODULATED MICROSTRUCTURES

Randomly oriented extruded thread, produced from Si3N4 or Al2O3 cerami c slips containing 26 vol.% SiC whiskers (M. Farkash and D. G. Brandon , Mater. Sci. Eng. A, ?? (1994) ???), was filter pressed and then drie d and hot pressed to form a dense ceramic body. The resultant microstr ucture was modulated, with the reinforcing whiskers locally aligned on the scale of the original extruded thread. The fracture toughness of the SiC(w)-whisker-reinforced Si3N4 composites was significantly impro ved by the modulated microstructure but the bend strength was almost u naffected. In the alumina whisker-reinforced composites, the improveme nt in fracture toughness was marginal, but the composites with the mod ulated microstructure were found to be less sensitive to the deleterio us effects of residual porosity than the composites with random SiC(w) whisker reinforcement.