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<p>The selection of coating materials for environmental barrier coatings (EBCs) is primarily governed by their resistance to water vapor corrosion and compatibility with the substrate material’s thermal expansion coefficient (CTE). Research continues to enhance the properties of coating materials. Mostly, the rare-earth-based silicates showed promising results. In this research, compositionally graded coating system that transitions from a mullite-based material at the substrate interface to 100% Y<sub>2</sub>O<sub>3</sub> (yttria) at the outer surface has been chosen due to the gradual compositional change minimizes CTE mismatch while leveraging the advantageous properties of both material systems. To achieve this, mullite and Y<sub>2</sub>O<sub>3</sub> powders are high-energy ball milled with a 25% incremental composition change, resulting in submicron particle sizes. Particle size reduction has aimed silicate formation from mullite and yttria. These powders are then agglomerated via spray drying and sprayed onto C/C composite substrates using plasma spray. Unmilled powders were blended with the same composition and sprayed using the same plasma spray parameters. The coatings were analyzed using SEM and XRD to evaluate their microstructural characteristics and phase formations of silicates (such as Y<sub>2</sub>SiO<sub>5</sub>, Y<sub>2</sub>Si<sub>2</sub>O<sub>7</sub>), and thermal cycle tests were conducted. Object-oriented finite element analysis is applied to SEM microstructure images to further understand the thermal expansion mismatch and numerically simulate stress formation within the coatings. Findings revealed significantly different behaviors between spray-dried powders (SDc) and blended powder (BPc) coatings. Heat treatment at 1000&#xa0;°C for 50&#xa0;h, a relatively low temperature for refractory-based ceramic materials, induced substantial phase transformation in SDc coatings. Thermal cycle tests demonstrated SDc coatings' rapid spallation compared to BPc coatings. These results highlighted the effect of the powder processing route and the reaction mechanism between yttria and sub-micron mullite phases.</p>

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Investigation of In Situ Silicate Formation of Compositionally Graded EBC

  • 期刊论文

  • 发表日期：

    2025年11月4日

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  • Garip Erdogan,
  • Yunus Tokac

摘要

The selection of coating materials for environmental barrier coatings (EBCs) is primarily governed by their resistance to water vapor corrosion and compatibility with the substrate material’s thermal expansion coefficient (CTE). Research continues to enhance the properties of coating materials. Mostly, the rare-earth-based silicates showed promising results. In this research, compositionally graded coating system that transitions from a mullite-based material at the substrate interface to 100% Y2O3 (yttria) at the outer surface has been chosen due to the gradual compositional change minimizes CTE mismatch while leveraging the advantageous properties of both material systems. To achieve this, mullite and Y2O3 powders are high-energy ball milled with a 25% incremental composition change, resulting in submicron particle sizes. Particle size reduction has aimed silicate formation from mullite and yttria. These powders are then agglomerated via spray drying and sprayed onto C/C composite substrates using plasma spray. Unmilled powders were blended with the same composition and sprayed using the same plasma spray parameters. The coatings were analyzed using SEM and XRD to evaluate their microstructural characteristics and phase formations of silicates (such as Y2SiO5, Y2Si2O7), and thermal cycle tests were conducted. Object-oriented finite element analysis is applied to SEM microstructure images to further understand the thermal expansion mismatch and numerically simulate stress formation within the coatings. Findings revealed significantly different behaviors between spray-dried powders (SDc) and blended powder (BPc) coatings. Heat treatment at 1000 °C for 50 h, a relatively low temperature for refractory-based ceramic materials, induced substantial phase transformation in SDc coatings. Thermal cycle tests demonstrated SDc coatings' rapid spallation compared to BPc coatings. These results highlighted the effect of the powder processing route and the reaction mechanism between yttria and sub-micron mullite phases.