The effect of silica content on microstructure and mechanical properties of calcia-stabilized tetragonal zirconia polycrystalline ceramic

The present study was aimed at investigating the effect of silica impurities on structure and mechanical properties of zirconia ceramics, stabilized in tetragonal phase by addition of 6.5?mol% calcia. The effect of silica was studied in 0–5?mol% silica concentration range. It was shown that notable increase in fracture toughness (from 7.5?MPa?m^0.5 to 12.5?MPa?m^0.5) as well as limited rise in hardness (from 12?GPa to 13?GPa) can be achieved by addition of ~ 2.5?mol% of SiO2. It was shown that further increase in SiO₂ concentration above 3.75?mol% results in destabilization of tetragonal phase and degradation of mechanical properties. It is suggested that silica reacts with calcia resulting in formation of amorphous calcium silicate, decreasing calcia content in zirconia matrix, and facilitates sintering and grain growth, resulting in lower stability of tetragonal phase.