Sintering of SiC Coating Layer on Graphite Spheres Prepared by Pack Cementation

Abstract

Pack cementation is an effective method in the manufacture of SiC coating on carbon material substrate surface, which is a controllable and simple process. Meanwhile, due to the reactive infiltration process of powder mixture into the substrate, a gradient transition structure layer is formed between the substrate and outer layer. In this paper, SiC was coated on the spherical substrates taken from the matrix graphite pebbles of high temperature gas-cooled reactor (HTR) fuel element. Relations between the Si/C content ratio of the pack mixture and the thickness of SiC layer were studied. Analysis found that Si/C content ratio, powder size and sintering time are factors influenced the thickness of the coating layers. When the Si/C content ratio was higher than 3:1, a uniform thickness coating bonded well with the substrate was obtained. The composition phases and thickness of coating layer etc. also had obvious changes along with the change of the Si/C content ratio in this research.Results also show that sintering atmosphere and particle size of powders are important factors affecting coating microstructure, while a vacuum atmosphere can smaller powder size can help to get a dense structure.