Effects of polymer addition and supercritical drying on sol-gel HfO_2 coating on polycrystalline SiC substrate

摘要

For environmental and thermal barrier coating, sol-gel coatings were carried out to obtain a thick porous HfO_2 film on polycrystalline SiC substrate. HfO_2 precursor solutions with polymer addition were dip-coated on sintered SiC substrate, dried in supercritical CO_2 under 10 MPa at 300 ℃, and fired stepwise at 300 ℃, 400 ℃, and 550 ℃ in air. The polymer addition decreased the temperature where monoclinic HfO_2 particles precipitate from the precursor solution. The obtained HrD_2 film had less cracks than that obtained without polymer addition to precursor solution, and had porous structure with a thickness of 700 nm, which was 3.5 times greater than that of a film without supercritical CO_2 drying. Active oxidation in flowing Ar gas was inhibited by the porous HfO_2 coating.