A gas-phase deposition process for coating a carbonaceous substrate with a tantalum carbide coating, the process includes a coating step. The coating step includes placing a carbonaceous substrate into a reaction chamber, heating the reaction chamber to a temperature between about 1100 C. to about 1500 C. for a duration of between about 1 h to about 24 h. The coating step further includes supplying a process gas to the reaction chamber, the process gas includes a halide containing species and for at least 15 minutes after the start of the process, the process gas includes less than 4 at.-% of carbon and less than 10 vol.-% of H.sub.2. Further, the coating step includes supplying a tantalum containing species to the reaction chamber, or placing a solid comprising tantalum into the reaction chamber. Alternatively, the process includes placing a solid with a tantalum halide into the reaction chamber.