In-flight particle states and coating properties of air plasma sprayed ytterbium disilicates

The effects of processing parameters on the in-flight particle behavior, phase composition, and properties of air plasma sprayed ytterbium disilicate (Yb2Si2O7) coatings were investigated in this study. With the increase in plasma enthalpy, in-flight particle temperature increases. Higher particle temperature caused an increase in silica (SiO2) evaporation from the Yb2Si2O7 particles and, as a result, additional Yb2SiO5 phase appears in the Yb2Si2O7 coating. Thermal expansion tests showed the coating containing a higher volume of Yb2SiO5 phase has a larger coefficient of thermal expansion (CTE). Thermal cycling tests in a steam environment indicated that the Yb2SiO5 phase content in the APS Yb2Si2O7 coatings has a significant effect on the EBC's durability. Thermal cycling lives decrease with the increase of Yb2SiO5 phase content in APS Yb2Si2O7 coatings. Analysis of the failed coatings indicated that the predominant EBC failure mechanisms are due to growth of the thermally growth oxides (TGO) as well as the stresses induced by CTE mismatch. Furthermore, Calcium-magnesium-alumina-silicate (CMAS) corrosion tests showed that the recession rate decreases with the increase of Yb2SiO5 phase content in APS Yb2Si2O7 coatings.

Automated summary

The study found that increasing plasma enthalpy increases in-flight particle temperature, affecting the phase composition and durability of the coatings. Additionally, an increase in Yb2SiO5 phase content results in higher thermal expansion coefficient and significant impact on the durability of EBC coatings.