Elastic Modulus and Fracture Toughness of CeO<sub>2</sub>-Containing Tetragonal Zirconia Polycrystals

Abstract

The lattice constants, elastic modulus and fracture toughness of 12mol% CeO2-containing tetragonal zirconia polycrystals with grain sizes of 2.8μm (sintered at 1500°C, Z12C-I) and 6.1μm (sintered at 1600°C, Z12C-II) were measured. Lattice constants (at and ct axes) of tetragonal zirconia for Z12C-II were larger than those for Z12C-I. On the other hand, the axial ratio ct/√2at for Z12C-II was smaller than that for Z12C-I. Therefore, it was estimated that tetragonal zirconia in Z12C-II was more stable than that in Z12C-I. Young's modulus at room temperature was 194-195GPa for both specimens. The effect of grain size on Young's modulus was not observed. The Young's modulus decreased with increasing temperature and was 179-180GPa at 400°C. Fracture toughnesses at room temperature were 6.4MPa⋅m1/2 for Z12C-I and 6.7MPa⋅m1/2 for Z12C-II. That is, fracture toughness with a large grain size was larger than that with a small grain size. The fracture toughness decreased gradually with increasing temperature and was 4.0MPa⋅m1/2 for Z12C-I and 4.2MPa⋅m1/2 for Z12C-II at 300°C. The monoclinic zirconia content on the fracture surface for Z12C-II with large grain size was comparable to that for Z12C-I with small grain size at room temperature. Fracture modes in Z12C-I was characterized by intergranular mode and that in Z12C-II, by transgranular mode. It is concluded that the fracture toughness for Z12C-II was larger than that for Z12C-I because of the difference in fracture modes.