First-Principles Study, Fabrication and Characterization of (Zr0.25Nb0.25Ti0.25V0.25)C High-Entropy Ceramic
39 Pages Posted: 12 Dec 2018 First Look: Accepted
The formation possibility of a new (Zr0.25Nb0.25Ti0.25V0.25)C high-entropy ceramic (ZHC-1) was first analyzed by the first-principles calculations and thermodynamical analysis and then it was successfully fabricated by hot pressing sintering technique. The first-principles calculation results showed that ZHC-1 was an entropy stabilized solid solution due to its high mixing enthalpy of 5.526 kJ/mol. The thermodynamical analysis results showed that ZHC-1 was thermodynamically stable above 959 K owing to its negative mixing Gibbs free energy. The experimental results showed that the as-prepared ZHC-1 (95.1% relative density) possessed a single rock-salt crystal structure, some interesting nanoplate-like structures and high compositional uniformity from nanoscale to microscale. By taking advantage of these unique features, compared with the initial binary metal carbides (ZrC, NbC, TiC and VC), it showed a relatively low thermal conductivity of 15.3 0.3 W/(mK) at room temperature, which was due to the presence of solid solution effects, nanoplates and porosity. Meanwhile, it exhibited the relatively high nanohardness of 30.3 0.7 GPa and elastic modulus of 460.4 ± 19.2 GPa and the higher fracture toughness of 4.7 ± 0.5 MPam1/2, which were attributed to the solid solution strengthening mechanism and nanoplate pullout and microcrack deflection toughening mechanism.
Keywords: High-entropy ceramics, metal carbides, first-principles calculations, mechanical performances, thermal physical properties
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