High-entropy (HfTaTiNbZr)C and (HfTaTiNbMo)C carbides fabricated through reactive high-energy ball milling and spark plasma sintering

Powders of high-entropy Hf0.2Ta0.2Ti0.2Nb0.2Zr0.2C (HECZr) and Hf0.2Ta0.2Ti0.2Nb0.2Mo0.2C (HECMo) carbides were fabricated through the reactive high-energy ball milling (R-HEBM) of metal and graphite particles. It was found that 60 min of R-HEBM is adequate to achieve a full conversion of the initial precursors into a FCC solid solution for both compositions. The HECZr powder possesses a unimodal particle size distribution (40% d <= 1 mu m, 95% d <= 10 mu m), and the HEC(Zr )powder features a bimodal distribution with a slightly larger particle size overall (30% d <= 1 mu m, 80% d <= 10 mu m). Bulk high-entropy ceramics with a minor presence of an oxide phase were fabricated through the spark plasma sintering of these high-entropy powders at 2000 degrees C with a 10 min dwelling time. The HECZr ceramics possess a relative density of up to 94.8%, hardness of 25.7 +/- 3.5 GPa, Young's modulus of 473 +/- 37 GPa, and thermal conductivity of 5.6 +/- 0.1 W/m.K. HECMo ceramics with a relative density of up to 93.8%, hardness of 23.8 +/- 2.7 GPa, Young's modulus of 544 +/- 48 GPa, and thermal conductivity of 5.9 +/- 0.2 W/m.K were also fabricated. A comparison of the properties of the HECs produced in this study and those previously reported is also provided.