Effect of gas composition on the microstructure and growth behavior of HfC coatings prepared by LPCVD

Hafnium carbide (HfC) coatings were deposited on carbon/carbon (C/C) composites by low pressure chemical vapor deposition (LPCVD) using HfCl4-CH4-H-2-Ar system. The effect of the ratio of CH4 to HfCl4 (input C/Hf ratio) on the deposition of HfC coatings was investigated. It was found that the input C/Hf ratio in the feed gas mixture is a crucial factor in determining the deposition rate, microstructure and growth behavior of HfC coatings. The increased input C/Hf ratio is effective in increasing the linear deposition rate of HfC coating. When deposited with 1:1 input C/Hf ratio, the coating growth is dominated by the crystal growth, the deposited coating exhibits a column-arranged structure. While deposited with 2:1 and 3:1 input C/Hf ratios, the formation of coating is dominated by the nucleation of HfC, the rapid nucleation results in the particle-stacked structure of the deposited HfC coating. Crown Copyright (C) 2013 Published by Elsevier Masson SAS. All rights reserved.