A unique role of TiO 2 on the superplastic flow in tetragonal zirconia polycrystals

Abstract

Superplasticity in fine-grained ceramics was first reported in 1986 by Wakai et al. Yttria-stabilized tetragonal zirconia polycrystals (TZP) exhibit huge tensile elongations at high temperatures, e.g. an elongation of 800% is obtained in TZP at 1,550 C and a strain rate of 8.3 {times} 10{sup {minus}5}s{sup {minus}1}, and 1,038% in SiO{sub 2}-doped TZP at 1,400 C and a strain rate of 1.3 {times} 10{sup {minus}4}s{sup {minus}1}. The extensive ductility in TZP must be related to the grain size stability during high temperature plastic flow. The grain size of about 0.3 {mu}m in TZP is very stable at high temperatures in comparison with other ceramics. However, the superplastic flow in TZP cannot always be explained just on the basis of grain size stability. The present paper reports that TiO{sub 2}-doping into TZP results in a grain size increase, but decreases the flow stress, and enhances the tensile ductility at high temperatures.