In order to improve the strength, fracture toughness and thermal stability of 12Ce-ZrO
2 ceramics, Zirconia composites consisting of 12Ce-ZrO
2 and 3Y-ZrO
2 were fabricated by normal sintering at 1450°C and post HIP treatment at 1350°C. Some mechanical properties were evaluated for these composites. The bending strength and fracture toughness were measured by three-point bending test and indentation fracture (IF) method, respectively. The microstructures of the composites were characterized by SEM observations and TEM-EDS analysis. The phase stability in these composites were also evaluated by hydrothermal aging test at 150°C and 0.48 MPa. The addition of Y-ZrO
2 into Ce-ZrO
2 suppressed grain growth of 12Ce-ZrO
2 matrix and improve the mechanical properties of 12Ce-ZrO
2. Ce-ZrO
2/Y-ZrO
2 composites exhibited higher bending strength above 1000 MPa and higher fracture toughness above 8 MPa · m
1/2 in the composition region of 80∼90 wt% 12Ce-ZrO
2. The tetragonal→monoclinic phase transformation under hydrothermal conditions was inhibited in this composition region. It was found that the distribution of CeO
2/Y
2O
3 in the ZrO
2 matrix has a great influence on the mechanical properties and phase stability.
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