Spherulitic Growth from a Phase‐Separated Vitreous Matrix in a Cordierite–Y‐Stabilized Zirconia Glass‐Ceramic

Crystallization behavior, especially spherulitic growth of a cordierite–3 mol% Y₂O₃–ZrO₂ glass composition annealed at 950° to 1370°C was studied by optical and electron microscopy. Microstructural analysis revealed that glass‐inglass phase separation occurred prior to the crystallization of β‐quartz solid solution (ss). ZrO₂ was involved in promoting the nucleation of β‐quartz ss; the crystallization evolved from a cellular to a spherulitic morphology, and β‐quartz transformed to α‐cordierite as the temperature was raised. ZrO₂ was eventually expelled intergranularly and intragranularly to form slightly misoriented domains upon annealing, and the dendritic or clustered tetragonal t‐ZrO₂ crystals transformed to monoclinic (m) in symmetry. A possible dragging force exerted between α‐cordierite and a glassy droplet phase is proposed to explain the corrugated cordierite/glass interface.