Effect of graphite addition on the microstructure, mechanical properties and oxidation resistance of HfB2-SiC composites prepared by the SPS method

Among the intermediate metal diborides, HfB2 and ZrB2 are the most suitable options for high temperature applications. Compounds such as borides, carbides and nitrides of the IV-V group intermediate metals, which have melting temperatures above 3000 °C [1], are known as ultra high temperature ceramics (UHTCs). In this study, HfB2-SiC-graphite composites have been fabricated using spark plasma sintering at 1900 ℃ for 10 min. The effect of graphite content on microstructure, mechanical properties were studied and also oxidation resistance of prepared composites was investigated at 1400 ℃ for 32 h. Weight changes and the thickness of formed oxide layer was measured. The relative density, toughness and strength of SPSed composites were increased with inccraesing of graphite up 2.5 wt% and then decraesed. The hardness of composites were decreased when graphite was added. The oxidation resistance of composite improved after graphite addition up 2.5 wt%, while ecessive quantity of graphite caused to poor oxidation resistance of composite.