Si3N4 and SiC are good candidates as substrate materials because of their good matching. But if you only want to investigate the properties of SiC coating, you can choose graphite as substrate because it is easy to cut graphite into different shapes and size. And after deposition, you can remove the graphite substrate easily, for example, by grinding and polishing.
Thank you very much for your suggestion. Could you please tell me the substrate materials used in automotive and aircraft industries with ceramic coating specially silicon carbide as a top coating.