Steam oxidation behaviour of electrophoretically deposited (EPD) Yb2Si2O7 environmental barrier coatings (EBCs)

The oxidation behaviour of Yb 2 Si 2 O 7 Environmental Barrier Coatings (EBCs) prepared via Electrophoretic Deposition (EPD) on Si wafers is investigated under low-velocity steam exposure at various temperatures (900 °C-1300 °C) up to 100 hours. The results indicate that the growth of the thermally grown oxide (TGO) silica layer obeys a parabolic growth law at all tested temperatures, exhibits no cracking, suggesting robust structural integrity under the conditions tested. Furthermore, the study reveals that the heat treatment before steam exposure (named sintering for EPD) facilitates the diffusion of topcoat material such as Yb and Al into the TGO, which is further promoted during steam exposure, resulting in a modification of the TGO chemistry, which subsequently slows the TGO growth rate. Furthermore, TEM analysis revealed that diffusion of topcoat to the TGO suppresses the phase transformation, making β-cristobalite stable at room temperature. Indentation interfacial toughness and adhesion strength assessments demonstrate that the chemical bonding between the TGO and the topcoat is strongly adhered post-sintering, and after prolonged steam exposure, regardless of the TGO thickness. These findings underscore the potential of EPD processing for enhanced durability of Yb 2 Si 2 O 7 EBCs in high-temperature steam-rich environments. • EPD EBCs form a chemically bonded and uniformly thick TGO after sintering • Steam results in the diffusion of Yb and Al to the TGO forming a continuous layer • Altering the TGO chemistry by diffusion suppresses the β to α phase transformation • No evidence of delamination or interfacial cracking upon indenting after steam