Synthesis of (HfZrTiNbTa)N powders via nitride thermal reduction with soft mechano-chemical assistance
Xiang Liu, Youjun Lu, Qian Xu, Lutong Yang, Hongfang Shen, Wenzhou Sun, Xiao Zhang, Yanmin Wang
Abstract
High-entropy nitride powders are one of prerequisite materials for the preparation of high-performance high-entropy nitride ceramics. In this paper, high-entropy (HfZrTiNbTa)N powders were synthesized via nitride (i.e., silicon nitride (Si<sub>3</sub>N<sub>4</sub>)) thermal reduction with soft mechano-chemical assistance. The results show that metal oxides like hafnium dioxide (HfO<sub>2</sub>), zirconium dioxide (ZrO<sub>2</sub>), titanium dioxide (TiO<sub>2</sub>), niobium pentoxide (Nb<sub>2</sub>O<sub>5</sub>), and tantalum pentoxide (Ta<sub>2</sub>O<sub>5</sub>) can all be transformed into the corresponding metal nitrides in the presence of Si<sub>3</sub>N<sub>4</sub> at 1700 ℃, and solid solution of the metal nitrides can be formed as the temperature increases to 2100 ℃. The high-entropy (HfZrTiNbTa)N powders with submicron-sized particles, a narrower size distribution, and a single face-centered cubic (fcc) structure are obtained from raw material mixtures ground for 10 h and subsequently sintered at 1800 ℃. In addition, the high-entropy bulk nitride ceramics with relative density (<i>R</i><sub>w</sub>) of 94.31%±0.76%, Vickers hardness of 21.00±0.94 GPa, and fracture toughness (<i>K</i><sub>IC</sub>) of 3.18±0.16 MPa·m<sup>1/2</sup> are obtained with submicron-sized powders, which are superior to those obtained with micron-sized powders.