Phase Transition Behavior and Mechanical Properties of 9 Mol% CaO-PSZ with MnO2 Doping Under Thermal Stress

Abstract

MnO2-doped 9 mol% CaO-stabilized zirconia (CSZ) was investigated in terms of phase stability, microstructure, and mechanical properties before and after thermal cycling. As the MnO2 content increased from 2 to 4 mol%, the monoclinic phase fraction decreased significantly (from 32.6% to 2.5%), while the tetragonal phase fraction increased (from 58.2% to 90.3%), indicating an enhanced phase stability comparable to fully stabilized ZrO2. The cubic phase fraction decreased from 9.2% to 3.4% with 2-3 mol% MnO2, but increased to 7.2% at 4 mol%. The 9 mol% CSZ showed a mixture of grains around 2 mu m and 10 mu m, while the MnO2-doped CSZ exhibited only grains larger than 30 mu m, suggesting that MnO2 acted as a sintering aid. After thermal cycling, increasing the MnO2 content from 2 to 4 mol% led to an increase in the monoclinic phase fraction (from 7.8% to 17.2%) and a decrease in the tetragonal phase fraction (from 53.6% to 21.8%). The Vickers hardness and wear resistance of MnO2-doped CSZ were superior to those of undoped 9-CSZ, and improved as the MnO2 doping level increased. These mechanical properties were maximized in the CSZ doped with 3 mol% MnO2, and this trend persisted after thermal cycling. These results demonstrate that MnO2 doping effectively enhances the phase stability and mechanical performance of CaO-partially stabilized zirconia under thermal stress cycling conditions.