Effect of microstructure on impact resistance of chemical vapor deposited SiC coating on graphite substrate

SiC coatings were prepared by chemical vapor deposition at 1050 degrees C, 1100 degrees C, 1150 degrees C, and 1200 degrees C by using methyltrichlorosilane (MTS, CH3SiCl3) as the precursor. The compositions, microstructures, and deposition kinetics of the coatings were studied. The results show that the main constituent of the as-prepared coatings is 3C-SiC with a small amount of free C at deposition temperatures above 1100 degrees C. The coating has a regular fine-grain structure at 1050 degrees C, umbrella-shaped structure at 1100 degrees C, and columnar structure at 1150 degrees C and 1200 degrees C with the deposition process being controlled by surface kinetics and diffusion kinetics, respectively. The impact resistance was tested using a Split Hopkinson Pressure Bar system. The impact resistance of the graphite substrate is improved by the as-prepared SiC coating evidently. The impact strength of the coating sample increases with increasing deposition temperature, reaching the maximum at 1150 degrees C, and declines slightly at 1200 degrees C. The stress-strain curves under dynamic impact resistance loading, and the surface morphologies and microstructures resulting from the impact tests of the different SiC coatings are discussed in detail. The factors affecting impact resistance are mainly the thickness and hardness values of the as-prepared coatings.