The corrosion behaviors of Ln2Si2O7 (Ln=Yb and Lu) and ASiO4 (A=Ti, Zr and Hf) EBC's
were examined at 1500oC in water vapor environment. These oxides were coated on silicon nitride
specimens by oxidation-bonded reaction sintering technique. Among Ln2Si2O7 system, though the
thermal expansion coefficient of Yb2Si2O7 phase is closer to silicon nitride than that of Lu2Si2O7
phase, the corrosion resistance of silicon nitride with Lu2Si2O7 EBC was higher than that of Yb2Si2O7
EBC sample. In these EBC materials, boundary silica phase was easily corroded by water vapor.
Among ASiO4 system, though the corrosion rate of HfSiO4 bulk was larger than that of ZrSiO4 and
TiSiO4 phases, the oxidation of the silicon nitride substrate for HfSiO4 coated sample was smaller
than that of other two. Many cracks were in ASiO4 EBC layer during the corrosion test. The
introduced crack length in HfSiO4 EBC layer is shorter than in ZrSiO4 EBC layer due to the thermal
expansion mismatch between EBC materials and the silicon nitride substrate.
