Unveiling the dynamic instability mechanism of microstructure transformation in faceted oxide eutectic composite ceramics

•The microstructure transformation of faceted Al2O3/Er3Al5O12 thermal emission eutectic ceramic composites fabricated under high temperature gradient was studied in a comprehensive and in-depth approach, taking into account the solidification rates as well as compositions (13.5 mol%–22.5 mol% Er2O3), finally the regularization tendency and morphological transition mechanisms were determined.•A successful prediction of lamellar to rod-like eutectics is achieved associated with dynamic instability of lamellar eutectic. We creatively mapped the enlarged coexistence region of lamellar and rod-like eutectic based on the interface undercooling.•The flexural strength and selective optical absorption of as-designed Al2O3/Er3Al5O12 composites with microstructural tailoring have been enhanced significantly.