Dense HfB2 Ceramics Fabricated by High-Energy Ball Milling and Spark Plasma Sintering

Abstract The effects of high-energy ball milling (HEBM) on the sintering ability and microstructure of hafnium diboride (HfB2) ultrahigh-temperature ceramics (UHTCs) were investigated. After HEBM, the average particle size range of the HfB2 ceramics decreased to 10–20 nm with a slight alteration in the crystal structure. The microscopic grains of the sintered samples were homogeneous and fine in size. WC removed oxide impurities on the surface of the HfB2 particles by reacting with the oxide impurities, which further improved the sintering ability of the HfB2 ceramics. The densification mechanism of the HfB2 ceramics was also investigated, and nearly fully dense HfB2 (99.1%) was fabricated by reactive spark plasma sintering (R–SPS) at 2100 °C for 35 min under a pressure of 40 MPa. HEBM increased the surface energy of the fine particles, which provided a sufficient driving force to improve the sintering ability and significantly increase the densification of HfB2.