A facile route for the synthesis of high‐entropy transition carbides/borides at low temperatures

Abstract

AbstractAs the main candidates in the field of ultra‐high temperature ceramics, high entropy carbides/borides (HECs/HEBs) have good oxidation resistance properties, high hardness, as well as excellent thermal and electrical conductivities, which are the focused points of research nowadays. In the current study, (Hf,Ta,Zr,Nb,Mo,Ti)C powders were successfully synthesized by a three‐step process, including the mixing process of raw oxides and carbon black with spaying Fe(NO3)3 solution, carbothermal reduction and subsequent calcium posttreatment. For the preparation of (Hf,Ta,Zr,Nb,Mo,Ti)B2 powders, during the calcium posttreatment process, equal stoichiometric ratio of B4C was added for the purpose of boriding reaction. The relevant X‐ray diffraction and SEM characterizations indicate the successful preparations of face‐centered cubic HECs and hexagonal HEBs. However, slight Mo local segregation was found in the prepared (Hf,Ta,Zr,Nb,Mo,Ti)B2 powders. The iron generated from Fe(NO3)3 promotes the solid solution process between monocarbides during the carbothermal reduction process via the dissolution‐diffusion‐precipitation mechanism. In the calcium posttreatment process, the liquid calcium ensures the boriding reaction take place at a low temperature. In addition, the residual carbon could be combined with calcium to generate CaC2 which is easy to be removed by acid leaching, and meanwhile, the added Fe could also be finally eliminated to produce pure HEC/HEB powders. The current method does not require the long‐time high energy ball milling of raw materials, but only simple and mild mixing is enough. Therefore, such a facile route has a great potential application prospect for industrially preparing high entropy phase powders in a large scale.