Synthesis of (HfZrTiNbTa)N powders via nitride thermal reduction with soft mechano-chemical assistance

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 (Si3N4)) thermal reduction with soft mechano-chemical assistance. The results show that metal oxides like hafnium dioxide (HfO2), zirconium dioxide (ZrO2), titanium dioxide (TiO2), niobium pentoxide (Nb2O5), and tantalum pentoxide (Ta2O5) can all be transformed into the corresponding metal nitrides in the presence of Si3N4 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 (Rw) of 94.31%±0.76%, Vickers hardness of 21.00±0.94 GPa, and fracture toughness (KIC) of 3.18±0.16 MPa·m1/2 are obtained with submicron-sized powders, which are superior to those obtained with micron-sized powders.