Thermodynamics equilibrium analysis on the chemical vapor deposition of HfC as coatings for ceramic matrix composites with HfCl_{x(x = 2–4)}-C_yH_z(CH₄, C₂H₄ and C₃H₆)-H₂-Ar system

A detailed thermodynamic equilibrium analysis in the chemical vapor deposition of HfC as coatings for ceramic matrix composites with HfCl_{x(x = 2–4)}-C_yH_z(CH₄, C₂H₄ and C₃H₆)-H₂-Ar system has been investigated using the FactSage code. To protect the excellent performance of the composites, we demand a suitable composition and yield of condensed phases. They have been examined as functions of the inject reactant ratios of HfCl_x/(HfCl_x + C_yH_z) and H₂/(HfCl_x + C_yH_z), temperatures, and pressures. The results show that the HfCl₄ species are the optimal Hf-source in the deposition process. The ideal ratio parameters for production of single phase HfC are Log[H₂/(HfCl₄ + C_yH_z)] = 2 and Hf/C = 1. And the optimum temperature condition is above 1200 K. A lower pressure of 5 kPa is found to be more favorable for the deposition of a pure HfC phase. The co-deposition of HfC with C or Hf will be easily obtained by only controlling the ratios of HfCl₄/(HfCl₄ + C_yH_z) and H₂/(HfCl₄ + C_yH_z). The HfCl₄-C₃H₆-H₂ precursor system should be the best choice in the experiment due to a higher yield of HfC at the same deposition conditions. The results in this work will be helpful for the further experiment investigation under different deposition conditions and put forward a new idea in exploration of the preparation method of coatings for ceramic matrix composites. [Figure not available: see fulltext.]