ELASTIC-MODULUS AND FRACTURE-TOUGHNESS OF CEO2-CONTAINING TETRAGONAL ZIRCONIA POLYCRYSTALS

The lattice constants, elastic modulus and fracture toughness of 12 mol% CeO2-containing tetragonal zirconia polycrystals with grain sizes of 2.8 mum (sintered at 1500-degrees-C, Z12C-I) and 6.1 mum (sintered at 1600-degrees-C, Z12C-PI) were measured. Lattice constants (a(t) and c(t) axes) of tetragonal zirconia for Z12C-PI were larger than those for Z12C-I. On the other hand, the axial ratio ct/square-root 2 a(t) for Z12C-PI was smaller than that for Z12C-I. Therefore, it was estimated that tetragonal zirconia in Z12C-PI was more stable than that in Z12C-I. Young's modulus at room temperature was 194-195 GPa 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 179-180 GPa at 400-degrees-C. Fracture toughnesses at room temperature were 6.4 MPa.m1/2 for Z12C-I and 6.7 MPa.m1/2 for Z12C-PI. 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 4.0 MPa.m1/2 for Z12C-I and 4.2 MPa.m1/2 for Z12C-PI at 300-degrees-C. The monoclinic zirconia content on the fracture surface for Z12C-PI 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-PI, by transgranular mode. It is concluded that the fracture toughness for Z12C-PI was larger than that for Z12C-I because of the difference in fracture modes.