Chemical Vapor Deposition of Dense Hafnium Carbide from HfCl₄–C₃H₆–H₂ System for the Protection of Carbon Fibers

Abstract

Hafnium carbide (HfC) is studied as a promising material for aerospace application at ultra‐high temperatures. The protective HfC coating is deposited on carbon fiber at 1200 °C using a chemical vapor deposition method. Thermodynamic calculation is carried out to optimize process variables in the HfCl 4 –C 3 H 6 –H 2 system. H 2 partial pressure in the system has a significant effect on the yield, composition, and morphology of the HfC coating. When the ratio of H 2 /(HfCl 4 + C 3 H 6 ) is high, a single HfC phase with a porous structure is deposited because of the growth of HfC nanorods. On the other hand, a highly crystalline dense HfC, which contains a small amount excess carbon, is uniformly deposited on the carbon fiber woven fabric at a low H 2 /(HfCl 4 + C 3 H 6 ) ratio.