Microstructural and Phase Evolution of Suspension Plasma-Sprayed Ytterbium Disilicate Environmental Barrier Coatings

Abstract

Suspension plasma spray offers an effective route for depositing coatings with tailored microstructures and phase compositions. In this study, YbDS and YbDS/YbMS EBCs were deposited by varying plasma chemistry specifically the hydrogen content to regulate silica volatilization during the SPS process. Coatings sprayed with zero hydrogen resulted in predominantly YbDS phases, while varying hydrogen content led to the formation of YbDS/YbMS coating with > 70% amorphous content. Post-deposition heat treatment at 1300 °C for 24 h was employed to examine its improved crystallinity and phase distribution for both the coatings. As-sprayed and heat-treated microstructural analysis revealed that post-heat treatment significantly reduced porosity and promoted crack healing, especially in YbDS/YbMS coatings with approximately 45% YbMS content. Further YbDS/YbMS coatings were exposed to long-term (200 h) isothermal oxidation to evaluate microstructural changes and thermally grown oxide (TGO) formation. Finally, the wet corrosion test at 1200 °C for 500 h and erosion tests were performed on the heat-treated YbDS/YbMS coatings to assess their durability in aggressive environmental conditions.