Thermodynamic Analysis of Metal Segregation in Two Metal Boride-Carbide Ceramics Containing V With Cr, Hf, Ti, or Zr

Dual-phase carbide-boride ceramics in different vanadium-Me (Me = Cr, Hf, Ti, and Zr) binary systems were synthesized by boro/carbothermal reduction under stoichiometric and carbon-deficient conditions and densified by spark plasma sintering. Thermodynamic analysis was used to evaluate the influence of composition on the phase stability and metal segregation between phases, along with the resulting effects on microstructure and hardness. Pairing vanadium with Group IV elements (Hf, Ti, and Zr) consistently formed one boride and one carbide phase, while the Cr-V system formed a monoboride phase and a carbon-deficient carbide. Metal segregation trends depended on composition. Vanadium preferentially segregated to the carbide phase in the Ti-V and Cr-V systems, while it was enriched in the boride phase in Hf-V and Zr-V systems. Hardness measurements showed a higher hardness for the Ti-V sub-stoichiometric system, reaching 27.7 ± 0.9 GPa at 9.8 N, while the Cr-V sub-stoichiometric system presented the lowest hardness at 18.8 ± 0.3 GPa at the same load. Notably, in the Zr-V system, thermodynamic predictions based solely on standard Gibbs energy deviated from experimental observations. However, when combined with first-principles calculations that accounted for non-stoichiometry in vanadium carbide, the predictions aligned more closely with experimental observations, qualitatively indicating a preference for vanadium segregation to the boride phase and zirconium to the carbide phase. These results suggest that elemental distribution between phases results from complex interactions beyond simple Gibbs free energy minimization, especially in systems like Zr-V with strong carbide-to-boride ratio dependence. The optimized systems were characterized with nominal compositions of (Ti0.61,V0.39)B2-(Ti0.39,V0.61)C0.9, (Hf0.12,V0.88)B2-(Hf0.88,V0.12)C0.9, (Zr0.29,V0.71)B2-(Ti0.71,V0.29)C0.9 and (Cr0.60,V0.40)B-(Cr0.40,V0.60)C0.8. Their thermodynamic interactions provided insights into metal segregation in dual-phase ceramics, demonstrating its strong composition dependence.

Duke Scholars

Author Simon Divilov Thomas Lord Department of Mechanical Engineering and Materia ...

Author Stefano Curtarolo Thomas Lord Department of Mechanical Engineering and Materia ...