Ultrahigh-temperature stability and SiC decomposition behaviour in HfC-SiC ceramics derived from non-oxygen precursor

HfC-SiC ceramics are promising for ultrahigh-temperature applications, yet their structural degradation due to SiC decomposition at 2500 °C remains underexplored. In this study, HfC-SiC nanocomposites with a uniform nanoscale microstructure were successfully fabricated via the polymer-derived ceramics route using a liquid, non-oxygen PHNCS precursor. Upon heat treatment at 2500 °C, significant SiC decomposition occurs, and the volatilization of silicon promotes the deposition of residual carbon as graphitic layers on HfC particles, forming a HfC@C structure. Commercial SiC exhibits much less decomposition than the HfC-SiC nanocomposites. This may be attributed to nano-sized HfC particles that precipitate on the SiC surface above 1900 °C, which act as defects and accelerate SiC decomposition at extreme temperatures. These findings elucidate the structural degradation mechanisms of HfC-SiC ceramics at ultrahigh temperatures and provide valuable insights for defining their upper service temperature and guiding the design of optimized multiphase architectures.