Mechanical and thermal properties of a Hf2[Al(Si)]4C5 ceramic prepared by in situ reaction/hot-pressing

Predominantly single-phase Hf2[Al(Si)]4C5 ceramic has been fabricated by an in situ reaction/hot-pressing method using Hf, Al, Si and graphite as starting materials. Hf2[Al(Si)]4C5 shows comparable mechanical properties to Zr2[Al(Si)]4C5, and lower hardness and stiffness but higher strength and toughness than HfC. The stiffness decreases slowly with temperature and at 1600 °C it remains 83% of that at ambient temperature. Compared to Zr2[Al(Si)]4C5 and HfC, however, Hf2[Al(Si)]4C5 exhibits a relatively higher coefficient of thermal expansion, an intermediate specific heat capacity and a lower thermal conductivity.