Reactive Interaction in Hf–Nb–B₄C and Hf–Nb–B₄C–C Systems

The reactive interaction in Hf–Nb–B₄C and Hf–Nb–B₄C–C systems was studied at 1750°C, isothermal holding times of 30 and 60 min, and a residual argon pressure of 100 Pa. Different sequences of the interaction of reactants were found. The HfB₂, NbB₂, HfC, and NbC phases are formed in a Hf–Nb–B₄C system due to the diffusion saturation of Hf and Nb with boron and carbon from B₄C. The presence of elemental carbon in a Hf–Nb–B₄C–C system predetermines the primary synthesis of carbides HfC and NbC. The diffusion boronation of carbides from B₄C occurs along with their formation and results in the formation of borides HfB₂ and NbB₂. The conclusions are confirmed by thermodynamic calculations.