Core–shell SiC <sub>w</sub>@TiC composite whisker-reinforced Al <sub>2</sub>O <sub>3</sub> ceramics: Preparation, properties, and toughening mechanisms
Weixing Li, J.H.L. Pang, Zhixiao Zhang, Liyuan Cheng, Yafeng Wang, Xiaoliang Zhang, Jingbo Mu, Yu Dong, Yanming Wang, Xiaorong Zhang
Abstract
In this study, we propose a novel approach to enhance the fracture toughness of Al<sub>2</sub>O<sub>3</sub> ceramics by incorporating core-shell structural composite whiskers as secondary phases. In particular, Al<sub>2</sub>O<sub>3</sub> composite ceramics reinforced with TiC-coated SiC whiskers (SiC<sub>w</sub>@TiC) were successfully fabricated through a combination of molten salt synthesis and spark plasma sintering. The SiC<sub>w</sub>@TiC whiskers feature a SiC<sub>w</sub> core and a TiC shell layer (~85 nm thick) composed of nano-sized TiC grains. Remarkably, the core-shell structure is preserved within the Al<sub>2</sub>O<sub>3</sub> 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 (Al<sub>2</sub>O<sub>3</sub>/SiC/TiC), grain size (micron/nano nanoscale), and thermal expansion coefficients (3.8-7.4×10<sup>-6</sup>/K), which collectively generate a sophisticated stress field. This intricate microstructure enables the SiC<sub>w</sub>@TiC whiskers to dissipate crack propagation energy through multiple mechanisms, significantly improving the fracture toughness of the Al<sub>2</sub>O<sub>3</sub> matrix. The resulting Al<sub>2</sub>O<sub>3</sub>-SiC<sub>w</sub>@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<sup>1/2</sup>. This work establishes a paradigm for structural ceramic toughening through engineered core-shell architectures.