FABRICATION AND EVALUATION OF SiC/C FUNCTIONALLY GRADIENT MATERIAL

Abstract
A plate-like deposit having a compositional gradient from carbon (C) to silicon carbide (SiC) (SiC/C FGM) was obtained on a graphite substrate with chemical vapour deposition (CVD) by changing the Si/C molar ratio in input gas during deposition. Cracking due to heat flux was investigated using a CO₂ laser setup. Heat flux which resulted in cracking in SiC-coated graphite (SiC NFGM) was 5.8 MWm^-2 at a surface temperature (T_s) of 1300 K and a reverse surface temperature (T_b of 1220 K. In the case of SiC/C FGM, heat flux occurred cracking was 7.4 MWm^-2 at a T_s of 1650 K and a T_b of 1080 K. The temperature difference between T_s and T_b was 570 K in FGM and 80 K in NFGM. Thermal stress calculation showed that in cracking caused by hoop stress, the stress was close to the fracture strength of SiC. It was clear that SiC/C FGM has effective thermal shock resistance and thermal barrier characteristics.