Processing of Dense High-Entropy Boride Ceramics
Dense (Hf0.2,Zr0.2,Ti0.2,Ta0.2,Nb0.2)B2 high-entropy ceramics with high phase purity were produced by two-step spark plasma sintering of precursor powders synthesized by boro/carbothermal reduction of oxides. The reacted powders had low oxygen (0.404 wt%) and carbon (0.034 wt%) contents and a sub-micron average particle size (∼0.3 µm). Powders were synthesized by optimizing the excess B4C content of the reaction mixture and densified by a two-step spark plasma sintering process. The relative density increased from 98.9% to 99.9% as the final sintering temperature increased from 2000 °C to 2200 °C. The resulting ceramics were nominally single-phase (Hf,Zr,Ti,Ta,Nb)B2 with oxygen contents as low as 0.004 wt% and carbon as low as 0.018 wt%. The average grain size increased from 2.3 ± 1.2 µm after densification at 2000 °C to 4.7 ± 1.8 µm after densification at 2100 °C, while significant grain growth occurred during sintering at 2200 °C. The high relative densities, low oxygen and carbon contents, and fine grain sizes achieved in the present study were attributed to the use of synthesized precursor powders with high purity and fine particle size, and the two-step synthesis-densification process. These are the first reported results for dense high-entropy boride ceramics with high purity and fine grain size.
L. Feng et al., "Processing of Dense High-Entropy Boride Ceramics," Journal of the European Ceramic Society, Elsevier, Apr 2020.
The definitive version is available at https://doi.org/10.1016/j.jeurceramsoc.2020.03.065
Materials Science and Engineering
Keywords and Phrases
Ultra-High Temperature Ceramics; High-Entropy Boride Ceramics; Powder Synthesis; Two-Step Spark Plasma Sintering; Microstructure
International Standard Serial Number (ISSN)
Article - Journal
© 2020 Elsevier, All rights reserved.
09 Apr 2020