Preparation and toughening mechanism of Al ₂O ₃ composite ceramics toughened by B ₄C@TiB ₂ core–shell units

Abstract

In this paper, the concept of incorporating core-shell structured units as secondary phases to toughen Al 2 O 3 ceramics is proposed. Al 2 O 3 composite ceramics toughened by B 4 C@TiB 2 core-shell units are successfully synthesized using a combination of molten salt methodology and spark plasma sintering. The synthesis of B 4 C@TiB 2 core-shell toughening units stems from the prior production of core-shell structural B 4 C@TiB 2 powders, and this core-shell structure is effectively preserved within the Al 2 O 3 matrix after sintering. The B 4 C@TiB 2 core-shell toughening unit consists of a micron-sized B 4 C core enclosed by a shell approximately 500 nm in thickness, composed of numerous nanosized TiB 2 grains. The regions surrounding these core-shell units exhibit distinct geometric structures and encompass multidimensional variations in phase composition, grain dimensions, and thermal expansion coefficients. Consequently, intricate stress distributions emerge, fostering the propagation of cracks in multiple dimensions. This behavior consumes a considerable amount of crack propagation energy, thereby enhancing the fracture toughness of the Al 2 O 3 matrix. The resulting Al 2 O 3 composite ceramics display relative density of 99.7%±0.2%, Vickers hardness of 21.5±0.8 GPa, and fracture toughness 6.92±0.22 MPa•m 1/2 .

A reverse particle grading strategy for design and fabrication of porous SiC ceramic supports with improved strength

“…4 (g), with the increasing content of coarse particles, the route of crack deflection became longer, which could increase the resistance of crack propagation. This process requires higher fracture energy, which is conducive to the increase of bending strength [43]. However, when the content of W16 increased to 30 wt%, the resistance of crack declined because the number of neck connections in the route of crack decreased, which can be to some degree attributed to the less oxidation degree of coarse SiC particles [36].…”