Properties and Microstructure of an HfB₂-HfC-SiC Ultra High Temperature Ceramics

Abstract:

HfB2-HfC-SiC ultrahigh temperature ceramics (UHTCs) were prepared and characterized in this paper. It is showed that the densities of the HfB2-HfC-SiC reach 98.5% of the theory density. The room temperature compressive properties of the HfB2-HfC-SiC are good, while those at high temperature decrease rapidly. The volume expansion ratio monotonously increases (up to 2.35% at 2300°C) with increasing temperature. Furthermore, with increasing temperature, the average linear expansion coefficient hardly changes, while the instant linear expansion coefficient decreases first, and followed by an increase. The minimum value of the instant linear expansion coefficient is 5.65×10-6/K at 900°C and that of the mean linear expansion coefficient is 7.39×10-6/K at 1340°C. HfB2-HfC-SiC were burned with the plasma arc heater. After 8-second ablation, part of the SiC particles melted and spurted from the composites, and holes appeared.