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Thermal properties and calcium-magnesium-alumino-silicate (CMAS) interaction of novel γ-phase ytterbium-doped yttrium disilicate (γ-YYbSiO) environmental barrier coating material

Advanced Composites and Hybrid Materials, ISSN: 2522-0136, Vol: 7, Issue: 2
2024
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Article Description

Rare-earth disilicates are promising candidates for thermal and environmental barrier coatings (TEBC) in gas turbines that safeguard SiC/SiC ceramic matrix composites (CMCs) from thermal degradation and environmental attacks. Here, we report a systematic investigation on novel TEBC material, γ-YYbSiO. The γ-phase quarter molar ytterbium–doped yttrium disilicate exhibited low thermal conductivity (1.72 W·m·K at 1200 °C) and reduced intrinsic thermal expansion (3.17 ± 0.22 × 10 K up to 1000 °C), ensuring promisingly effective thermal insulation and minimized thermal stress with CMC substrates. Using density functional theory (DFT), the heat capacity of γ-YYbSiO was predicted higher than that of undoped γ-YSiO. Comparing these predictions to results calculated using the Neumann–Kopp (NK) rule revealed only minor variations. A metastable CMAS interaction byproduct, cyclosilicate phase CaRE(SiO), was identified based on energy dispersive X-ray spectrometer (EDS) and electron backscatter diffraction (EBSD) techniques, appearing at 1300 °C but disappearing at 1400 °C. The γ-YYbSiO exhibited good CMAS resistance on both dense pellets and sprayed coatings, forming a protective apatite (CaRE(SiO)O) interlayer that effectively hindered CMAS infiltration at evaluated temperatures. The relatively higher Y:Yb atomic ratio (> 3) in the apatite grains indicate differential reactivity with molten CMAS and provides crucial insights into the CMAS corrosion mechanism. These findings highlight the potential of γ-YYbSiO as a CMC coating material, emphasizing the need for tailored microstructural optimization as a thermal sprayed coating to enhance long-term performance in extreme gas turbine environments.

Bibliographic Details

Buhao Zhang; Ebenezer B. Owusu; Alex Lynam; Acacio Rincon Romero; Tanvir Hussain; Hangfeng Zhang; Mingwen Bai; Aochen Du; Nicholas Curry

Springer Science and Business Media LLC

Materials Science

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