Controlled Surface Flaw-Initiated Fracture in Reaction-Densified Silicon Carbide

Controlled surface flaws were produced in commercial reaction-densified SiC by Knoop microhardness indentation. The flaws themselves could not be observed easily, thus an etching technique was used to delineate their semielliptical shape, thereby enabling calculation of the critical stress- intensity factor K _IC at room temperature. Room-temperature fracture was insensitive to annealing environment (air or vacuum), flaw "healing" being observed at ?1000°C. The variation in fracture stress of indented specimens with temperature showed 3 distinct regions of behavior which were interpreted in terms of residual stress relief, flaw healing, and Si-SiC bond weakening.