High-performance multifunctional (Hf0.2Nb0.2Ta0.2Ti0.2Zr0.2)C high-entropy ceramic reinforced with low-loading 3D hybrid graphene-carbon nanotube

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 (K-IC) and damage tolerance restricted many practical applications of the HEC. Herein, we addressed this challenge by incorporating a threedimensional graphene-carbon nanotube (3D G-CNT) as toughening agent in (Hf0.2Nb0.2Ta0.2Ti0.2Zr0.2)C. The resulting enhanced 3D G-CNT(Hf0.2Nb0.2Ta0.2Ti0.2Zr0.2)C featured an outstanding toughness of 8.23 MPa center dot m(1/2), while remaining superior strength (763 MPa) and hardness (24.7 GPa). An ultralow friction coefficient (0.15) coupled with an ultralow wear rate (w, 2.6x10(-7) mm3/(N center dot m)) in the 3D G-CNT/(Hf0.2Nb0.2Ta0.2Ti0.2Zr0.2)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/(Hf0.2Nb0.2Ta0.2Ti0.2Zr0.2)C exhibited rather low thermal conductivity (kappa) yet excellent electrical conductivity (sigma, 1.3x10(6) S/m) in comparison with the pure (Hf0.2Nb0.2Ta0.2Ti0.2Zr0.2)C. This study provided great potential for maximizing the physical and functional properties of the HEC for various applications.