Oxidation Protective Multilayer CVD SiC Coatings Modified by a Graphitic B-C Interlayer for 3D C/SiC Composite

Abstract

A layered graphitic CVD B-C coating was introduced between two CVD SiC coating layers. Microstructure and chemical characterization of the CVD B-C and the hybrid SiC/B-C/SiC multilayer coating was performed using SEM, EDS, XPS and XRD. Oxidation protection ability of the coating for the C/SiC composite was studied using a thermogravimetric analyzer (TGA) in the isothermal mode and by measuring residual flexural strength. The layered graphitic CVD B-C coating middle layer reduced the maximum crack width in the CVD SiC coating. The hybrid SiC/B-C/SiC multilayer coating provided a better oxidation protection for C/SiC composite than a three layer CVD SiC coating due to coating crack control and sealing effects at temperatures up to 1,300°C for 900 min.

Oxidation Behavior of C/SiC Composite with CVD SiC-B4C Coating in a Wet Oxygen Environment

“…The detailed fabrication processes of the substrates were described in reference [11]. Two kinds of specimens were prepared.…”

“…It is proved that the SiC-B-SiC coating was not suitable as oxidation protection coating for C/SiC composite up to 1,300°С in static air [8]. The results of oxidation of 3D C/SiC composites coated with SiC-graphitic (B-C)-SiC coating showed that this coating could provide oxidation protection in air up to 1,300°С for 15 h [11]. The oxidation behavior of SiC-B 4 C-SiC coating protected C/C composite was in static air at 1,300°С for 200 h and showed a residual strength of about 33% [16].…”

“…While, researches on CVD SiC coating showed that cracks resulted from CTE mismatch between composite and coating is also unavoidable [6]. During oxidation, boron bearing materials, such as boron [8], boron doped carbon (BC x ) [3,[9][10][11][12], and B 4 C [13][14][15] formed fluid oxide phases (B 2 O 3 or B-Si-O ternary phase) which can fill cracks and slow down the in-depth diffusion of moisture and oxygen [3,9]. So, boron-containing materials were widely used as internal layer together with CVD SiC as external layer to form a self healing multilayered coating.…”

Preparation and Mechanical Properties of Carbon Fiber Reinforced (BC x –SiC) n Multilayered Matrix Composites

“…Besides the pressure-pulsed CVI, the ordinary CVI could also be employed to fabricate the multilayered matrix. Wu [9] has reported an oxidation protective multilayer CVD coating with the structure of (SiC/B 0.17 C 0.83 /SiC). It is proved that these multilayered coatings were very effective below 1,300°C.…”

“…Boron-containing materials, such as Boron [8], boron doped carbon (BC x ) [3][4][5]9], and Si-B-C [10,11] were widely used in coating, interphase and matrix, in order to form a glassy phase, which can seal the oxygen infiltration path then enhance the oxidation resistance. The coating systems could improve oxidation resistance significantly, while the durability was very limited because of the gasification of the glassy phase at high temperature and/or low pressure.…”