Abstract
There has been growing interest in the high-entropy ceramic (HEC) recently owing to its tailorable compositions and microstructures, versatile properties, together with promising structural and functional applications. However, inferior fracture toughness (<i>K</i><sub>IC</sub>) and damage tolerance restricted many practical applications of the HEC. Herein, we addressed this challenge by incorporating a three-dimensional graphene–carbon nanotube (3D G–CNT) as toughening agent in (Hf<sub>0.2</sub>Nb<sub>0.2</sub>Ta<sub>0.2</sub>Ti<sub>0.2</sub>Zr<sub>0.2</sub>)C. The resulting enhanced 3D G–CNT/(Hf<sub>0.2</sub>Nb<sub>0.2</sub>Ta<sub>0.2</sub>Ti<sub>0.2</sub>Zr<sub>0.2</sub>)C featured an outstanding toughness of 8.23 MPa·m<sup>1/2</sup>, while remaining superior strength (763 MPa) and hardness (24.7 GPa). An ultralow friction coefficient (0.15) coupled with an ultralow wear rate (<i>w</i>, 2.6×10<sup>−7</sup> mm<sup>3</sup>/(N·m)) in the 3D G–CNT/(Hf<sub>0.2</sub>Nb<sub>0.2</sub>Ta<sub>0.2</sub>Ti<sub>0.2</sub>Zr<sub>0.2</sub>)C was obtained primarily as a function of lubricating scrolls, in which two-dimensional (2D) graphene acted as a tribolayer, and one-dimensional (1D) carbon nanotubes acted as nano ball bearings embedded inside. Strikingly, the 3D G–CNT/(Hf<sub>0.2</sub>Nb<sub>0.2</sub>Ta<sub>0.2</sub>Ti<sub>0.2</sub>Zr<sub>0.2</sub>)C exhibited rather low thermal conductivity (<i>κ</i>) yet excellent electrical conductivity (<i>σ</i>, 1.3×10<sup>6</sup> S/m) in comparison with the pure (Hf<sub>0.2</sub>Nb<sub>0.2</sub>Ta<sub>0.2</sub>Ti<sub>0.2</sub>Zr<sub>0.2</sub>)C. This study provided great potential for maximizing the physical and functional properties of the HEC for various applications.
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