Microstructural design for high-strain-rate superplastic oxide ceramics

Factors limiting the strain rate available to superplastic deformation in oxide ceramics are discussed from existing knowledge about high-temperature plastic deformation and cavitation mechanisms. Simultaneously controlling these factors is essential for attaining high-strain-rate superplasticity (HSRS). This is shown in monolithic tetragonal zirconia and composite materials consisting of zirconia, α-alumina and a spinel phase: at strain rates higher than 10^-2 s^-1, tensile ductility reached 300-600% in the monolithic material and 600-2500% in the composite materials. Post-deformation microstructure indicates that certain secondary phases should be effective in suppressing cavitation damage and thereby enhancing HSRS.