As 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(NO 3 ) 3 solution, carbothermal reduction and subsequent calcium posttreatment. For the preparation of (Hf,Ta,Zr,Nb,Mo,Ti)B 2 powders, during the calcium posttreatment process, equal stoichiometric ratio of B 4 C 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)B 2 powders. The iron generated from Fe(NO 3 ) 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 CaC 2 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.
High-entropy carbides (HECs) possess superior properties such as favorable corrosion resistance and marvelous hardness and are widely applied in specific extreme environments. Herein, a novel method was proposed for synthesizing HECs powders with raw materials of corresponding oxides and carbon black, which was composed of steps of ball-milling in stainless jar, carbothermic reduction at 1873 K, as well as the following calcium posttreatment at 1273 K to remove residual carbon by generating CaC 2 . Finally, pure HECs powders could be fabricated after acid leaching treatment. Under the current experimental conditions, besides HfC-TaC-ZrC-NbC quaternary system, a homogeneous solid solution could be fabricated by adding Mo or/and Ti, but it could not be achieved for systems with addition of V, W, or Cr, owing to the low lattice constant or different crystal structure of corresponding carbides. In the reduction step, iron resulted from ball milling process acted as the diffusion channel to promote the mutual diffusion of different components. Meanwhile, the calcium treatment temperature had a weak effect on particle size of HEC powders. HfC-TaC-ZrC-NbC-MoC-TiC powders prepared at the calcium posttreatment temperature of 1273 K had an oxygen content of .302% and an average grain size of 252 nm.
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