Development of high-strain-rate superplastic oxide ceramics

Examinations of factors limiting the strain rate available to superplastic deformation lead to the following guide: simultaneously controlling the initial grain size, diffusivity, dynamic grain growth, homogeneity of microstructure and the number of residual defects is essential to heighten the strain rate available to superplastic deformation in oxide ceramics. Along this guide, high-strain-rate superplasticity (HSRS) is attained in materials consisting of tetragonal zirconia, alpha-alumina and a spinel phase: tensile ductility reached 300-2500 % at a strain rate of 0.01-1.0 s(-1). Post-deformation microstructure indicates that some secondary phases may suppress cavitation damage and thereby enhance HSRS. The guide is also effective in lowering the limit of deformation temperature for a given strain rate. In monolithic tetragonal zirconia, grain-size refinement combined with doping of aliovalnt cations such as Mg2+, Ti4+ and Al3+ led to HSRS at 1350 degrees C.