MECHANICAL-PROPERTIES AND MICROSTRUCTURE OF CA2SIO4-CAZRO3 COMPOSITES

Three types of dicalcium silicate (Ca2SiO4)-calcium zirconate (CaZrO3) composites were fabricated and their microstructures correlated with their mechanical properties. In the first type, Ca2SiO4 was added as a minor phase. The second type consisted of a 50 vol% Ca2SiO4-50 vol% C aZrO3 mixture, while in the third type, CaZrO3 constituted the minor p hase. Pure CaZrO3 was also studied as a control and found to have a to ughness which depended on its grain size. In composites with Ca2SiO4 a s the minor phase, a toughness increase was observed and found to be a function of matrix grain size. The composite with the second type of microstructure had the highest toughness of about 4.0 MPa-m1/2, which was about double that of the monolithic CaZrO3. No evidence was found for transformation toughening by the orthorhombic (beta) to monoclinic (gamma) transformation in Ca2SiO4. The main toughening mechanisms ide ntified were crack deflection and crack branching. Microstructural obs ervations indicated the existence of weak grain boundaries in CaZrO3 a gglomerates as well as weak interfaces between the two phases.