Comparative Study of Fabrication of HfC-HfB_2-SiC Composites by Spark Plasma Sintering and Hot Pressing

摘要

HfC-HfB_2-SiC composites were fabricated by spark plasma sintering (SPS). The densification behaviour and microstructure evolution were compared with those obtained by hot pressing (HP). Almost fully dense material was produced by SPS in 2 minutes of dwell time at 2100°C, heating rate 100°C/min. In order to achieve high densities by hot pressing (1880°C, 30 MPa and 60 minutes of dwell time), the use of a sintering aid, i.e. silicon nitride, was necessary. The microstructures of the composites processed by the two different techniques were fine and uniform. The distribution of the phases was homogeneous. Besides crystalline HfC and HfB_2, secondary amorphous phases were found in both the composites: HfO_2, Hf-Si-C-O, Hf-Si-C. The amount of SiC decreases slightly in the densest SPS composite, while in the hot-pressed material it increases. The densification behaviour and microstructural evolution of the composites are discussed in terms of the starting composition and of the applied sintering technique.