First-principles study, fabrication and characterization of (Zr0.25Nb0.25Ti0.25V0.25)C high-entropy ceramics

The formation possibility of a new (Zr0.25Nb0.25Ti0.25V0.25)C high-entropy ceramics (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 the mixing enthalpy of ZHC-1 was 5.526 kJ/cool and the mixing entropy of ZHC-1 was in the range of 0.693R -1.040R. 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 metal carbides (ZrC, NbC, TiC and VC), it showed a relatively low thermal conductivity of 15.3 +/- 0.3 W/(m.K) 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 MPa m(1/2), which were attributed to the solid solution strengthening mechanism and nanoplate pullout and microcrack deflection toughening mechanism. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.