High Temperature Ceramic Matrix Composites 8 by Litong Zhang & Dongliang Jiang

Author:Litong Zhang & Dongliang Jiang
Language: eng
Format: epub
ISBN: 9781118933008
Publisher: Wiley
Published: 2014-06-02T16:00:00+00:00

1. INTRODUCTION

Boron carbide plays an important role to improve the oxidation resistance of ceramic matrix composites, such as multilayer self-healing silicon carbide matrix composites1, SiC-B4C oxidation protective coatings2, and oxidation protection matrix in C/C composites3. These composites have received increasing interest in the military and aerospace industries due to the self-healing and oxidation resistant functionality, except for high strength, low density and high melting point.

CVD methods have been extensively studied and developed for boron carbide ceramic. The most researches of CVD B4C are to investigate the deposition mechanism under different deposition conditions, establish the relationship between deposition parameter and deposition mechanism, for example, thermodynamic, mass transfer and kinetic modeling attempts have been studied by several research groups4–5.

Many types of reactive gas mixtures were used for the B4C deposition. Some most commonly adapted mixtures are as follows: BCl3/CH4/H26–8, B2H6/CH4/H29–10, BBr3/CH4/H211 and BCl3/C2H4/H212. The CVD B4C from BCl3/CH4/H2 precursor is a very complex chemical reaction process, and the B4C can be deposited by different mechanisms. Some reasonable deposition mechanisms have been established, such as Moss et al.13, and Karaman et al.14, their experiments were performed under a small variation of deposition parameters. However, all of the B4C deposits had similar microstructure and phase composition, which probably suggests that the B4C coatings were deposited by a single mechanism. The amorphous boron carbide was only fabricated few researcher, for example Berjonneau et al.15. Few characterization and deposition mechanism of amorphous boron carbide were reported.

In this work, the amorphous boron carbide was deposited from BCl3-CH4-H2 mixtures. Firstly, the morphology, composition, phase, bonding state and microstructure were characterized. Then the deposition mechanism was proposed combined with the analysis and characterization results.

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