Effect of minor SiO_2 addition on the creep behavior of superplastic tetragonal ZrO_2

摘要

A sigmoidal stress-creep rate relationship appearing in tetragonal ZrO_2 drastically changes with SiO_2 addition, where silicon segregates along the grain boundaries and dissolves into the ZrO_2 grains. This change is completed with the precipitation of glass pockets though the creep rate gradually increases with increasing the volume fraction. The glass pockets merely increase the creep rate by accelerating grain boundary sliding (GBS) by the viscous flow of the glass phase. Although the silicon segregated along the grain boundaries may enhance GBS, the solute silicon seems to control the rate of creep. The solute silicon increases the rate of Nabarro-Herring creep by accelerating the lattice diffusivity of cations at low stresses but decreases the rate of GBS by inhibiting the accommodation process at high stresses.