Microstructural Characterization and Fracture Toughness of Cordierite‐ZrO 2 Glass‐Ceramics

Crystallization of an MgO‐Al 2 O 3 ‐SiO 2 ‐ZrO 2 sintered glass frit was studied. Heat treatment at 850° or 900°C caused initial crystallization of μ‐cordierite and tetragonal ( t ) ZrO 2 . The t ‐ZrO 2 crystallized with an irregular dendritic morphology and could be transformed to monoclinic ( m ) symmetry under certain conditions; the cordierite underwent the μ→α a transformation with extended annealing. Heat treatments at 1000°C caused crystallization of t ‐ZrO 2 rods and spheroids in an α‐cordierite matrix; these ZrO 2 crystals, however, are resistant to transformation to m ‐ZrO 2 . The beneficial effects of ZrO 2 on the fracture toughness of cordierite‐based glass‐ceramics are described.