Core–shell SiC_w@TiC composite whisker-reinforced Al₂O₃ ceramics: Preparation, properties, and toughening mechanisms

In this study, we propose a novel approach to increase 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 (SPS). 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-scale), and thermal expansion coefficient (3.8×10⁻⁶–7.4×10⁻⁶/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.