Hafnium and silicon carbide multilayer coatings for the protection of carbon composites

The low pressure chemical vapor deposition (LPCVD) process developed here allows multilayer HfC/SiC depositions. The HfC coatings have various morphologies and thicknesses depending on the experimental conditions (temperature, pressure, dilution). This carbide has been firstly deposited over flat graphite substrates and carbon single fibers. Secondly, the multilayer coating deposition over a C/C composite and over carbon single fibersis studied. Finally, HfC layers have been infiltrated inside carbon fiber tows. To avoid the notch effect on the carbon fibers, a thin layer of pyrocarbon (50 nm thick) has been deposited prior to the growth of the carbides. All the coatings were done in a hot wall CVD reactor and their morphologies and chemical compositions characterized by scanning electron microscopy.