Abstract:

The combination of yttria co-stabilization and spark plasma sintering (SPS) allowed full densification of CeO2-containing ZrO2 ceramics in a graphite environment, while avoiding spontaneous catastrophic material degradation due to ceria reduction. Tetragonal ZrO2 ceramics were obtained by spark plasma sintering (SPS) of 1 mol% Y2O3 + 6 mol% CeO2 (1Y6Ce) stabilizer-coated monoclinic ZrO2 powder with 2 wt% Al2O3 as sintering additive for 2 min at 1450º or 1550ºC under a maximum pressure of 60 MPa. In addition, a 2 mol% Y2O3 doped ZrO2 (2Y) ceramic was used as reference material to elucidate the effect of CeO2 reduction in the densified 1Y6Ce ceramics. The influence of the CeO2 reduction and sintering temperature on the microstructure and mechanical properties of the costabilized ZrO2 ceramics was investigated. A graded microstructure with a gradient in color and mechanical properties were observed in the 1Y6Ce ceramic sintered at 1450ºC, whereas the 1Y6Ce ZrO2 sintered at 1550ºC and the 2Y ceramic had a uniform color and mechanical properties. Additionally, the formation of an elongated CeAl11O18 (Ce2O3 . 11Al2O3) phase was observed in the 1Y6Ce ceramic sintered at 1550ºC. The formation of the graded color, the presence of the CeAl11O18 phase, as well as the graded fracture toughness profile were explained in terms of the gradual reduction of CeO2 to Ce2O3 in the 1Y6Ce ceramic.