Enhancement of fracture toughness of Al2O3 ceramics using spherical-shell-structured TiCxOyNz as a novel toughening agent

In this study, a novel closed spherical-shell-shaped toughening phase morphology is purposely constructed within Al 2 O 3 ceramics. The continuous Al 2 O 3 matrix is segregated by the TiC x O y N z spherical shells, with both the interior and exterior of each shell maintaining the Al 2 O 3 phase. Such spherical shells with the thickness of approximately 150 nm are comprised of submicron-sized TiC x O y N z grains in stack. Accordingly, such hierarchical microstructure gives rise to a multidimensional crack propagation mode in which cracks repeatedly expand along the external and internal interfaces of TiC x O y N z spherical shell and Al 2 O 3 ceramic matrix on a microscaled level, as well as across TiC x O y N z grain interfaces within the shell layer on a submicron scale. This synergistic action significantly increases crack propagation resistance through continuous energy dissipation at multiple length scales. Consequently, the Al 2 O 3 -TiC x O y N z composite ceramic achieves a remarkable fracture toughness of 6.47 ± 0.21 MPa m 1/2 . This work provides a novel strategy for designing high-performance Al 2 O 3 ceramics through engineered toughening phase morphology.