The enhancement of superplastic flow in tetragonal zirconia polycrystals with SiO 2-doping

Abstract

Superplasticity in SiO 2-doped tetragonal zirconia polycrystal (2.5Y-TZP) is investigated by means of tensile testing in a temperature range 1200–1500°C. The grain boundary SiO 2 phase reduces the flow stress and greatly enhances the tensile ductility in TZP. The stress and grain size exponents take a value close to 2 and 3, respectively, in this temperature range, but there is an abrupt change in activation energy at 1380°C in SiO 2-doped TZP. The activation energy for superplastic flow above and below this temperature is estimated to be 182 kJ/mol and 635 kJ/mol. The enhancement of superplasticity due to SiO 2-doping is explained in terms of the accelerated plastic flow in the grain boundary SiO 2 phase to accommodate the stress concentration generated by grain boundary sliding. The elongation to failure in the SiO 2doped TZP is phenomenologically described as a function of the Zener-Hollomon parameter. At high temperatures and low strain rates, the cavities tend to align and interlink parallel to the tensile axis, and the huge elongation in excess of several hundred percent is obtained.