Oxidation of refractory metallic coatings on carbon fibers heated up to 1850 °C

A method for testing high refractory metallic coatings at high temperature (up to 1850 °C) in controlled atmosphere (inert or oxidizing), at low pressure (around 4 kPa) and with an exposure time of 5 s maximum is developed here. Metallic coatings on carbon fibers are deposited using the PVD (physical vapor deposition) process. The sample is then heated by Joule effect (electrical resistivity). Cooling is not controlled, so the material undergoes quenching and keeps the microstructure and chemical composition produced at very high temperature under controlled atmosphere. PVD coatings on carbon fibers are sufficiently continuous and thick to be used as protective coatings during the oxidation tests at high temperature. This test allows studying the diffusion of carbon at the fiber/coating interface and of oxygen at the interface of external environment/coating at high temperatures. The aim of this study is to highlight the effect of a modification of composition on the carburization and on the oxidation mechanism, from the testing at high temperatures on these metallic coatings. Pure Hf and Hf–Ta metal alloys are considered.