In situ fabrication of high-toughness (Ti,W)C-based multiphase ceramics via ZrSi₂-assisted reactive hot pressing: Microstructural evolution and toughening mechanisms

Binderless (Ti,W)C-based multiphase ceramics with high density and toughness were fabricated via reactive hot pressing at a relatively low temperature of 1700 °C, using 10–30 mol% ZrSi₂ as a reactive sintering aid. Thermodynamic analysis and microstructural characterization indicate that ZrSi₂ serves a dual role: it acts as a transient liquid phase to facilitate near-full densification (relative density > 99.9%) and undergoes complete in situ reaction with the matrix.This reaction yields a complex multiscale architecture consisting of a (Ti,W,Zr)C solid solution, (W,Ti)Si₂, and acicular/nanoscale SiC and ZrC. The in situ formed nanoscale SiC effectively restricts matrix grain growth through Zener pinning and forms robust semi-coherent interfaces with the (Ti,W)C matrix. Consequently, the intrinsic brittleness typical of binderless carbides is substantially mitigated.The composite with 30 mol% ZrSi₂ achieves a fracture toughness of 6.4 MPa·m1/2 and a flexural strength of 430 MPa. The enhanced mechanical performance originates from a multiscale synergistic toughening mechanism, which includes atomic-level solid solution strengthening, nanoscale interfacial strengthening, and microscale crack deflection, bridging, and grain pull-out promoted by interlocking SiC/(W,Ti)Si₂ agglomerates. These findings offer a viable multiscale structural design strategy for developing advanced binderless ultra-high-temperature ceramics.