Oxidation kinetics of supersonic atmospheric plasma spraying ytterbium oxide doped molybdenum silicide coating

Rare earth oxides usually play an active role in modifying the microstructure and oxidation resistance of silicide coatings, but its modification mechanism has not yet been clarified. In this work, molybdenum silicide (MoSi₂) coating with different contents of ytterbium oxide (Yb₂O₃) was fabricated using supersonic atmospheric plasma spraying, and its microstructural evolution and oxidation behavior were investigated. Experimental results shown that the morphological characteristics of produced SiO₂-rich glass scale varied with the doping of Yb₂O₃, which noticeably affected the oxidation resistance of sprayed MoSi₂-Yb₂O₃ coatings. All coated specimens exhibited a parabolic oxidation behavior, wherein the MoSi₂-10 wt%Yb₂O₃ coating possessed the smallest parabolic constant and the lowest specific mass loss with 100 h oxidation at 1500 °C due to the absence of SiC-depleted region and the formation of continuous multicomponent compound scale. Given this, Yb₂O₃ additive with proper concentration not only guaranteed the sufficient filling of open spaces in SiO₂ network by Yb³⁺ cations, but also strengthened the Si–O bonds to increasing the viscosity of SiO₂ glass, thereby delaying the effective delivery of reactive oxygen species inwardly.