Achieving superior strength-toughness synergy in TiC@(Ti,Ta)C multiphase ceramics via coherent core-shell architecture and multi-scale phase design

TiC@(Ti,Ta)C-SiC-Ti₃SiC₂ multiphase ceramics with a distinctive core-shell architecture were fabricated via low-temperature (1500 °C) in-situ reaction hot pressing of TiC, TaC, and Si powder mixtures. The interdiffusion of Ti and Ta induces a compositional gradient from a Ti-rich core to a Ta-rich shell, establishing a highly coherent core-shell interface. The in-situ generated nanoscale β-SiC particles exhibit a dual distribution: intergranular SiC pins the grain boundaries to suppress the coarsening of core-shell grains, while intragranular SiC co-precipitates within the Ti₃SiC₂ grains to constrain their aspect ratio. This combined effect leads to substantial microstructural refinement. The synergistic strengthening and toughening mechanisms derived from the coherent core-shell structure, nanoscale SiC, and lamellar Ti₃SiC₂ significantly elevate the mechanical performance of the composites. Optimally, the composite with 10 mol% TaC addition achieves an excellent combination of properties, yielding a flexural strength of 676 MPa and a fracture toughness of 6.4 MPa m^1/2. These values substantially surpass those of most conventional TiC- and TaC-based materials. This study provides a robust microstructural design strategy for developing high-performance core-shell ceramics.