Deposition Rate, Texture, and Mechanical Properties of SiC Coatings Produced by Chemical Vapor Deposition at Different Temperatures

Abstract

Silicon carbide (SiC) coatings were produced on carbon/carbon (C/C) composites substrates using chemical vapor deposition (CVD) at different temperatures (1100°C, 1200°C, and 1300°C). The deposition rate was found to increase with deposition temperature from 1100°C to 1200°C. From 1200°C to 1300°C, the deposition rate decreased. SiC coating produced at 1200°C exhibited a strong (111) texture compared with the coatings produced at other temperatures. Both hardness and Young's modulus were also found to be higher in the coating produced at 1200°C. The variation in mechanical properties with the increase in temperature from 1100°C to 1300°C showed a direct correlation with the change in deposition rate and (111) texture. Microstructure analysis shows that the change in CVD temperature leads to the change in grain size, crystallinity, and density of stacking faults of SiC coatings, which appears to have no significant effect on mechanical properties of SiC compared with the texture observed in SiC coating. For the coating deposited at 1200°C, both the hardness and Young's modulus increased gradually from the substrate/coating interface to the top surface. The nonuniformity of mechanical properties along the cross-section of the coating is attributed to the nonuniform microstructure.

Influence of SiC grain boundary character on fission product transport in irradiated TRISO fuel

“…The images in Figure 2 show that most of the grain boundaries are high angle with relatively few low-angle grain boundaries present. Qualitatively, the grain size in the inner area (Figure 2a and d) appears to be smaller than in the areas from the center and outer samples, as expected from SiC grown by chemical vapor deposition (CVD) methods [23][24][25] and in agreement with the variation in grain size of SiC in unirradiated, baseline TRISO fuel particles as reported by Kirchhofer [26].…”

Deposition Mechanism and Thickness Control of CVD SiC Coatings on NextelTM440 Fibers

“…That is to say, pure SiC coatings can hardly be prepared via CVD process, and they will always be rich in silicon or free carbon. It is reported in the literature that coatings deposited on carbon plate, fibers or composites by CVD using MTS at temperatures above 1200 • C are usually composed of SiC, and Si impurities form at lower deposition temperature [25][26][27]. In this study, the coatings deposited on Nextel TM 440 fibers by CVD using MTS at 1100 • C were composed of SiC and free carbon.…”

Evidence of twin mediated growth in the CVD of polycrystalline silicon carbide

“…The mechanical properties, for example, of polycrystalline SiC films are affected by this preferential orientation. <111> oriented films exhibit both greater hardness [13][14][15] and a higher Young modulus [13,16] than <110> oriented ones. Grain size also plays a role [13][14][15].…”

“…<111> oriented films exhibit both greater hardness [13][14][15] and a higher Young modulus [13,16] than <110> oriented ones. Grain size also plays a role [13][14][15]. Consequently, it is important to understand how this preferential orientation occurs.…”