High-temperature oxidation resistance and high emissivity of a novel NbSi2/SiO2-Nb2O5/MoSi2-Yb2O3 multilayer coating on Nb substrate for thermal protection

To develop anti-oxidation and high emissivity coatings on Nb alloys for thermal protection systems, the NbSi2/SiO2-Nb2O5/MoSi2-xYb2O3 (0, 10, 20, and 30 wt%) multilayer coatings are prepared by a two-step method. The NbSi2/SiO2-Nb2O5/MoSi2-20Yb2O3 coating possesses the smallest oxidation mass gain (4.86 mg/cm2) at 1200 °C for 100 h and is the best oxidation resistance of the four coatings. The appropriate Yb3+ filles the SiO2 network voids, enhancing the Si-O bond and raising the viscosity of the SiO2 scale, thus further blocking oxygen diffusion. The coatings with Yb2O3 below 20 wt% achieve an emissivity of ∼0.9 at room temperature and still reach ∼0.7 at 1200 °C, showing excellent radiant thermal protection.