MAKING CERAMICS DUCTILE

Distributed irreversible deformation in otherwise brittle ceramics (sp ecifically, in silicon carbide and micaceous glass-ceramic) has been o bserved in Hertzian contacts. The deformation takes the form of an exp anding microcrack damage zone below the contact circle, in place of th e usual single propagating macrocrack (the Hertzian ''cone fracture'') outside. An important manifestation of this deformation is an effecti ve ''ductility'' in the indentation stress-strain response. Control of the associated brittle-ductile transition is readily effected by appr opriate design of weak interfaces, large and elongate grains, and high internal stresses in the ceramic microstructure.