Microstructural Refinement in Oxide Eutectic Ceramics by Post‐Flash Annealing

ABSTRACT Microstructural refinement is a powerful approach to improve the mechanical properties of materials and has been widely used in metals. However, there is currently no method that can refine the microstructure of bulk ceramics because of their inherent brittleness. Here, we show that the microstructure of a dense Al 2 O 3 –Y 3 Al 5 O 12 (YAG) eutectic ceramic can be rapidly refined by post‐flash annealing. The responsible mechanism is a recrystallization process due to the generation and accumulation of dislocations caused by electrical energy input. The highest hardness of the refined ceramic reaches 21.2 GPa, which is much higher than that of similar materials prepared by other techniques. We show that the hardness of the ceramic increases as the lamellar thickness decreases, and the ultrahigh hardness results from the combination of the Hall–Petch effect and the Bragg effect. We anticipate that these results will have implications in the development of process technology for refining microstructures of oxide eutectic ceramics to improve their mechanical properties.