Microstructures and mechanical properties of (Nb0.25Mo0.25Ta0.25W0.25)C and (Nb0.2Mo0.2Ta0.2W0.2Hf0.2)C high-entropy carbide ceramics produced by arc melting

High-entropy ceramics (HECs) become a focus as an innovative design of refractory materials due to their exclusive microstructure, huge adjustable components, some superior properties, and potential applications. Generally, they are manufactured by solid-state synthesis. However, in this paper, (Nb 0.25 Mo 0.25 Ta 0.25 W 0.25 )C (HEC-1) and (Nb 0.2 Mo 0.2 Ta 0.2 W 0.2 Hf 0.2) C (HEC-2) high-entropy carbide ceramics were successfully fabricated through vacuum arc melting using transition metal carbides powders. X-ray diffraction, energy dispersive spectrometer and scanning electron microscope were performed to analyze the phase evolution and microstructure uniformity. The experimental data exhibited that the as-prepared HEC-1 and HEC-2 formed into a single-phase body-centered cubic (BCC) structure. HEC-1 revealed a high compositional uniformity at microscale, while a segregation of molybdenum element was observed in HEC-2. Vickers hardness test results showed that HEC-1 presented a great microhardness of 23.13 GPa at 0.98 N, which was higher than the highest hardness of the individual binary carbides. The significantly enhanced hardness could be attributed to the solid solution strengthening effect. HEC-2 exhibited a good combination of high microhardness and fracture toughness due to the doping of Hf. These broaden the potential applications of HECs towards, such as protective coatings, high temperature structure parts, and machining tools. This study provides a new approach to prepare bulk HECs, and the tuning in toughness by exploring a novel intricated compositions would be of great significance for the further development. • A pioneer study on synthesis of high entropy ceramic by statically pressed and vacuum arc melting. • (Nb 0.25 Mo 0.25 Ta 0.25 W 0.25 )C and (Nb 0.2 Mo 0.2 Ta 0.2 W 0.2 Hf 0.2) C with equimolar concentration has a single crystal structure. • (Nb 0.25 Mo 0.25 Ta 0.25 W 0.25 )C exhibits a relatively high microhardness due to the presence of high-entropy effect and solid solution strengthening effect. • It is beneficial to refine grain size and increase grain boundaries by adding HfC leading a significant improvement of fracture toughness.