Powder synthesis, densification, microstructure, and mechanical properties of HfB <sub>2</sub> ‐HfC ceramic composites
Wenzhou Sun, Yu Tian, Shidiao Xu, Limeng Liu, Youjun Lu
Abstract
Abstract A new route based on HfO 2 + B 4 C + C → HfB 2 + HfC + CO reaction was developed to synthesize HfB 2 ‐HfC hybrid powders. X‐ray diffraction, scanning electron microscopy, energy dispersive spectrometry, and transmission electron microscopy were used to evaluate the powder products. The effects of excess additions of B 4 C and C on the phase constituents of the powder products were investigated. Thermodynamics of relevant reactions for the synthesis of the hybrid powders were calculated to guide the selection of compositions and processing parameters. The results indicated that HfB 2 ‐HfC hybrid powders were obtained by reaction at 1750°C for 1 h. HfB 2 :HfC phase content ratios showed a dependence on B 4 C and C additions. The obtained hybrid powders exhibited good oxidation resistance with an oxidation activation energy of 303 kJ/mol. Good sinterability of the powder products was demonstrated by spark plasma sintering at 2100°C. The consolidated ceramics based on them measured good Vickers’ hardness values (>26.0 ± .5 GPa) and fracture toughness (>3.78 ± .27 MPa·m 1/2 ).