Functionally multilayered Yb‐silicate EBCs fabricated using slurry spraying‐reactive sintering technique

Functionally multilayered environmental barrier coatings (EBCs) with the desired layer sequence of Yb 2 O 3 /Yb 2 SiO 5 /Yb 2 Si 2 O 7 /SiO 2 /Si were obtained using an unconventional yet simple technique of reactive sintering. Yb 2 O 3 slurry was sprayed on polycrystalline silicon (used as a bond coat for SiC f /SiC composites) and reactive sintered to generate graded layers that provide a combination of mitigated thermal expansion mismatch as well as silica activity. The Yb 2 O 3 ‐terpineol slurry produced a uniform deposit of the Yb 2 O 3 topcoat. Reactive sintering of exploratory coatings ( t ∼ 10–20 µm) was carried out in air by varying the temperature (1100–1400°C) and time (2–24 h). X‐ray diffraction and scanning electron microscopy‐energy‐dispersive spectroscopy technique confirmed the in situ formation of X 2 ‐Yb 2 SiO 5 and β‐Yb 2 Si 2 O 7 . Rietveld refinement was performed to know the volume fractions of the respective phases. The set of process parameters identified from the preliminary work was employed to fabricate EBCs with thickness ∼ 250 µm. The X 2 ‐Yb 2 SiO 5 and β‐Yb 2 Si 2 O 7 phases formed next to the Si/SiO 2 interface as two separate layers. Post‐sintering heat treatments in air at 1300, 1350, and 1400°C for 3–50 h elucidated the growth characteristics of the oxide layers to be a function of both temperature and time. The theoretical considerations of diffusional reactive phase formation of the EBC multilayer growth rates are discussed.