Pressureless sintering of Ta0.8Hf0.2C UHTC in the presence of MoSi2

Ta0.8Hf0.2C ceramic has the highest melting point among the known materials (4000 °C). However, this high melting point makes the ceramic difficult to be sintered at temperatures lower than 2300 °C, pressurelessly. The purpose of this study is to consolidate Ta0.8Hf0.2C UHTC by pressureless sintering at 2000 °C using MoSi2 as sintering aid. In this regard, effect of different amounts of MoSi2 on sintering behavior of Ta0.8Hf0.2 UHTC was investigated. It was observed that condensation of the UHTC after sintering at 2000 °C was enhanced by increasing MoSi2 content and the highest relative density of 95% was obtained in the presence of 24 vol.% MoSi2. XRD pattern of the sintered UHTC confirmed the formation of single phase TaC–HfC solid solution. SEM micrographs revealed the presence of MoSi2 as a residual phase. Oxidation test of Ta0.8Hf0.2C/24 vol.% MoSi2 sample by oxidized flame at 3000 °C showed the formation of double protective oxide layers on the surface of UHTC.