Intermediate stage densification kinetics of high-entropy ceramics during spark plasma sintering

The intermediate stage densification kinetics of (Hf, Nb, Ta, Ti, Zr)B2 and (Hf, Nb, Ta, Ti, Zr)C were studied using a Coble creep rate model. (Hf, Nb, Ta, Ti, Zr)B2 was synthesized by boro/carbothermal reduction and (Hf, Nb, Ta, Ti, Zr)C was synthesized by carbothermal reduction. Both ceramics were densified by spark plasma sintering at 1700–1850°C. The activation energies for densification were 575 ± 53 kJ/mol for the high-entropy boride and 646 ± 4 kJ/mol for the high-entropy carbide. The densification mechanisms were grain boundary diffusion for the high-entropy boride and lattice diffusion for the high-entropy carbide. Dissolution of Nb into the high-entropy phase was determined to be the rate limiting mechanism for densification of both the carbide and the boride.

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