Water vapour corrosion of rare earth monosilicates for environmental barrier coatings application

Water vapour corrosion resistance of five rare earth monosilicates Y2SiO5, Gd2SiO5, Er2SiO5, Yb2SiO5, and Lu2SiO5 was investigated during testing at 1350 ˚C for up to 166 h in static air with 90% water vapour. Four of the RE-silicates showed little weight gain (0.859 mg cm-2) after 166 h of exposure. Prior to testing the microstrucre consists of equiaxed grains of 4- 7 ± 0.4 µm. XRD analysis showed that after 50 h exposure to water vapour corrosion Y, Er, Yb and Lu-silicates had both mono and disilicates present on their surfaces as a result of the reaction between monosilicate and water vapour to form disilicate, while Gd-silicate has converted completely to G4.67Si3O13 making it less stable for environmental barrier coatings application. The microstructures of corroded Y, Er, Yb and Lu-silicates contain ridges and cracks, while that of Gd-silicate contains rounded grains suggesting melting along with striped contract grains