MAKING CERAMICS DUCTILE

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