Abstract
In the present study, we optimized the fabrication process, characterized the microstructures and evaluated the mechanical properties of a high entropy carbide ceramic with novel composition, (HfNbTaTiW)C. Our results show that 1700 °C carbon thermal reduction (CTR) and 1800 °C spark plasma sintering (SPS) can yield a single phase (HfNbTaTiW)C with high relative density, low residual C/O and fine grain structure. The nanohardness of (HfNbTaTiW)C is on the lower end (28.16 GPa), but its fracture toughness (4.84 MPa m1/2) is superior to both its constituent monocarbides and most existing multi-cation transition metal carbides. The lattice distortion, bonding strength and stacking fault energy of (HfNbTaTiW)C are compared with (HfNbTaTiZr)C through First Principle Calculations to help understand the observed mechanical properties. The results indicate first, the reduced bonding strength contributes more importantly than the large lattice distortion to the hardness, leading to the observed low hardness of (HfNbTaTiW)C and second, the reduced bonding strength and low intrinsic stacking fault energy synergistically contribute to the observed high toughness of (HfNbTaTiW)C.
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