Ultrafast synthesis of high-entropy carbides up to 3,273 K for superior oxidation resistance

Exploiting the huge compositional space is significant in achieving the superior oxidation resistance of high-entropy carbides (HECs) yet is challenging with conventional synthesis techniques. Herein, we develop an ultrafast high-temperature synthesis apparatus to reach a heating temperature of 3,273 K within seconds. Based on this apparatus, the equiatomic 4- to 9-cation HECs of the IVB, VB, and VIB groups with compositional uniformity are synthesized via carbothermal reduction. The oxidation resistance of all the as-synthesized HEC samples is then investigated via thermogravimetric analysis. The results show that the 6-cation HEC samples possess the best oxidation resistance. Their superior oxidation resistance is attributed to the formation of (Cr, Me)(Ta, Me)O4 and (Cr, Me)2O3 (Me = Hf, Zr, Ta, Nb, Ti, and Cr) protective layers, which are experimentally and theoretically proved to effectively inhibit the inward diffusion of oxygen. Such superior oxidation resistance enables potential applications in extreme environments.