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

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 (KIC) 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 (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·m1/2, while remaining superior strength (763 MPa) and hardness (24.7 GPa). An ultralow friction coefficient (0.15) coupled with an ultralow wear rate (w, 2.6×10−7 mm3/(N·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 (κ) yet excellent electrical conductivity (σ, 1.3×106 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.