Core–shell SiC _w@TiC composite whisker-reinforced Al ₂O ₃ ceramics: Preparation, properties, and toughening mechanisms

In this study, we propose a novel approach to enhance the fracture toughness of Al₂O₃ ceramics by incorporating core-shell structural composite whiskers as secondary phases. In particular, Al₂O₃ composite ceramics reinforced with TiC-coated SiC whiskers (SiC_w@TiC) were successfully fabricated through a combination of molten salt synthesis and spark plasma sintering. The SiC_w@TiC whiskers feature a SiC_w core and a TiC shell layer (~85 nm thick) composed of nano-sized TiC grains. Remarkably, the core-shell structure is preserved within the Al₂O₃ matrix after sintering, forming a unique composite toughening phase. The interfacial regions surrounding the whiskers exhibit a complex geometric configuration and multi-dimensional heterogeneities, including variations in phase composition (Al₂O₃/SiC/TiC), grain size (micron/nano nanoscale), and thermal expansion coefficients (3.8-7.4×10^-6/K), which collectively generate a sophisticated stress field. This intricate microstructure enables the SiC_w@TiC whiskers to dissipate crack propagation energy through multiple mechanisms, significantly improving the fracture toughness of the Al₂O₃ matrix. The resulting Al₂O₃-SiC_w@TiC composite ceramics demonstrate exceptional mechanical properties, with a relative density of 99.16 ± 0.48 %, Vickers hardness of 21.38 ± 0.93 GPa, flexural strength of 693 ± 49 MPa, and fracture toughness of 7.15 ± 0.47 MPa·m^1/2. This work establishes a paradigm for structural ceramic toughening through engineered core-shell architectures.