Integrated computational and experimental investigation of Groups V and VI metals in (M,Hf,Ti,Zr)B2-(M,Hf,Ti,Zr)C ceramics

Dual-phase compositionally complex ultra-high temperature ceramics were formulated by incorporating different Groups V and VI metals such as V, Nb, Ta, Cr, Mo, or W into a base composition containing the Group IV elements, Hf, Ti, and Zr. Metal distribution was predicted using first-principles-based thermodynamics simulations and compared with experimental results. Moreover, phase stability, microstructure, and mechanical properties were evaluated for all of the ceramics. Compositions containing Cr, V, Nb, or Ta formed dual-phase ceramics containing only one boride and one carbide phase, while compositions containing Mo or W developed an additional third phase. The experimental metal distribution trends generally aligned with thermodynamic predictions, except for compositions containing V, which showed unexpected segregation behavior that was influenced by complex interactions of the coexistence of boride and carbide structures. From the dual-phase ceramics, the composition containing V exhibited the highest hardness (HV₁ = 25.5 ± 0.6 GPa) combined with smaller grain sizes (0.99 ± 0.33 μm for the boride and 1.15 ± 0.31 μm for the carbide phases). Our findings provide insights into phase formation and elemental segregation and help the design of next-generation dual-phase UHTCs with tailored properties.