Comparison of thermal shock behavior of SiC coating deposited on graphite substrates by chemical vapor reaction and physical vapor transport

Abstract

The thermal shock behavior of α-SiC coatings deposited using the chemical vapor reaction (CVR) and the physical vapor transport (PVT) methods on graphite substrates was investigated. The correlation between the physical properties such as crystallinity, surface roughness, etc. and the thermal shock behavior of the coated specimens was evaluated. Analyses of the SiC-coating layers deposited by CVR and PVT were carried out by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron probe microanalysis (EPMA). A better quality of crystal growth was observed on the surfaces prepared by PVT. The surface morphology of the α-SiC-coated substrate obtained by the PVT method was denser than that obtained by CVR. More crystal facets were observed on the surface coated by PVT, which indicates that the crystallinity of the surface coated by PVT is much higher than that by CVR. Judging from confocal laser scanning microscope (CLSM) observation, the surface roughness of the layer coated by CVR looks much smoother than that by PVT. In terms of the thermal shock behavior, the PVT specimen looked more stable as compared to the CVR specimen. The crystallinity and microstructure of the α-SiC-coated surface play an important role in the thermal shock properties of the SiC coatings; the greater the degree of crystallinity and the greater the surface roughness, the more resistant the coating is to thermal shock.