Mechanisms for low temperature densification and enhanced mechanical properties of (Ti, Zr, Hf, Nb, Ta)(C, N) using CrSi2 as an additive: formation of (Ti, Zr, Nb)2Cr4Si5 and grain boundary strengthening

• • CrSi2 addition lowers the densification temperature of (Ti, Zr, Hf, Nb, Ta)(C, N) by 200 °C, enabling sintering at reduced thermal budgets and mitigating grain coarsening. • • The dual-phase ceramic achieves a hardness of 24.65 ± 0.23 GPa and fracture toughness of 6.03 ± 0.48 MPa m1/2, outperforming most reported HECN-UHTCs. • • Formation of (Ti, Zr, Nb)2Cr4Si5 via interdiffusion/cation exchange introduces lattice strain and grain boundary segregation, enhancing mechanical properties. • • The liquid-phase sintering strategy is broadly applicable to other UHTCs, offering a scalable route to improve sinterability and performance.