In‐Situ Plate‐Like Calcium Hexaluminate (CA 6 ) Reinforcement in Al 2 O 3 Composites From Particle‐Stabilized Foam

ABSTRACT High‐performance Al 2 O 3 /CA 6 composite ceramics with tailored microstructure were successfully fabricated via foam‐structured, precursor‐derived ceramic technology combined with hot pressing. Different from conventional sintering routes, this foam‐derived strategy enables effective impurity purification and uniform dispersion of CaCO 3 precursors, which significantly regulates the phase composition and grain microstructure of composites. During pre‐sintering, the in‐situ decomposition of CaCO 3 promotes the growth of plate‐like CA 6 grains, and numerous high‐density dislocations and stacking faults generated within CA 6 grains further optimize the local microstructure. The doping of trace Ca (1.00 at.%) effectively restrains abnormal grain growth and brittle phase formation, achieving a ∼30% enhancement in flexural strength compared with pure Al 2 O 3 and conventional, sintered Al 2 O 3 /CA 6 composites. Benefiting from multiple toughening mechanisms of crack deflection and crack bridging originating from the high‐aspect‐ratio CA 6 platelets with weak (001) plane bonding, the 2.00 at.% Ca‐doped composite obtains an optimal fracture toughness of 7.25 MPa·m 1/2 . Calculated thermal shock resistance indices reveal an improved R value, while R '''' evolves non‐monotonically with increasing Ca content. This work demonstrates that the foam precursor strategy combined with trace Ca doping is a feasible and efficient route to fabricate high‐strength and high‐toughness alumina‐based structural ceramics.