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<p>Gas turbines or power generation engines used in transportation, defense, and energy sectors use thermal barrier coatings (TBCs) to protect metallic components exposed to high-temperature conditions. This work focuses on the in situ synthesis during coating deposition by suspension plasma spraying (SPS) from powders mechanoactivated by high-energy ball milling of ZrO<sub>2</sub>-16&#xa0;mol.% YO<sub>1.5</sub>-16&#xa0;mol.% TaO<sub>2.5</sub> (16YTZ) for applications in TBCs. This composition is expected to present a non-transformable tetragonal phase (<i>t′</i> phase), suitable to overcome the thermodynamic limits of the mostly used conventional 6-8 wt.% yttria stabilized zirconia (YSZ). The 16YTZ powder mixtures were mechanoactivated by either planetary ball milling (240 RPM) and high-energy ball milling (1700 RPM). These mechanoactivated powders were used to obtain densified samples through sintering at 1500&#xa0;°C for 2 and 20&#xa0;h, as well as to deposit coatings by SPS at a stand-off distance between 60 and 80&#xa0;mm using Ar/He as the plasma forming gas. The ceramics and coatings were characterized by XRD, SEM, and Raman spectroscopy. The densified ceramics showed a high <i>t′</i> phase content, i.e., &gt; 98% of the 16YTZ system, with an average tetragonality of 1.0267. Coatings deposited at a stand-off distance of 60&#xa0;mm, and a deposition rate of 33&#xa0;µm/min, present a porosity of less than 5%, and a tetragonality of 1.0187, which is higher than that of standard YSZ coatings. Phase quantification by Rietveld refinement revealed a multiphase condition as result of the heat transfer in the plasma plume leading to in situ synthesis of the ZrO<sub>2</sub> base solid solutions, formed by 89.2 wt.% of <i>t′ + c</i> phases (48.4 and 40.8 wt.% of <i>t′</i> and<i> c-</i>ZrO<sub>2</sub>, respectively<i>)</i> 8.1% monoclinic ZrO<sub>2</sub>, 2.4% cubic Y<sub>2</sub>O<sub>3</sub> and 0.4% orthorhombic Ta<sub>2</sub>O<sub>5</sub> on average. Achieving a high percentage of <i>t' + c</i> phases in the coating with a porosity of less than 5% is a significant accomplishment. This success is closely linked to the fact that tetragonality exceeds that of YSZ. These results provide a solid foundation for future experimental designs aimed at optimizing spray parameters.</p>

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Analysis of the t′ + c Phase Content from ZrO2-16 Mol.% Y2O3-16 Mol.% Ta2O5 Mechanoactivated Powder Mixtures in Coatings Deposited by Suspension Plasma Spraying

  • 期刊论文

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  • 发表日期：

    2025年2月20日

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  • Catalina Galeano-Camacho,
  • Iván Bedoya-Trujillo,
  • Sebastián Pérez,
  • Hélène Ageorges,
  • Juan Muñoz-Saldaña

摘要

Gas turbines or power generation engines used in transportation, defense, and energy sectors use thermal barrier coatings (TBCs) to protect metallic components exposed to high-temperature conditions. This work focuses on the in situ synthesis during coating deposition by suspension plasma spraying (SPS) from powders mechanoactivated by high-energy ball milling of ZrO2-16 mol.% YO1.5-16 mol.% TaO2.5 (16YTZ) for applications in TBCs. This composition is expected to present a non-transformable tetragonal phase (t′ phase), suitable to overcome the thermodynamic limits of the mostly used conventional 6-8 wt.% yttria stabilized zirconia (YSZ). The 16YTZ powder mixtures were mechanoactivated by either planetary ball milling (240 RPM) and high-energy ball milling (1700 RPM). These mechanoactivated powders were used to obtain densified samples through sintering at 1500 °C for 2 and 20 h, as well as to deposit coatings by SPS at a stand-off distance between 60 and 80 mm using Ar/He as the plasma forming gas. The ceramics and coatings were characterized by XRD, SEM, and Raman spectroscopy. The densified ceramics showed a high t′ phase content, i.e., > 98% of the 16YTZ system, with an average tetragonality of 1.0267. Coatings deposited at a stand-off distance of 60 mm, and a deposition rate of 33 µm/min, present a porosity of less than 5%, and a tetragonality of 1.0187, which is higher than that of standard YSZ coatings. Phase quantification by Rietveld refinement revealed a multiphase condition as result of the heat transfer in the plasma plume leading to in situ synthesis of the ZrO2 base solid solutions, formed by 89.2 wt.% of t′ + c phases (48.4 and 40.8 wt.% of t′ and c-ZrO2, respectively) 8.1% monoclinic ZrO2, 2.4% cubic Y2O3 and 0.4% orthorhombic Ta2O5 on average. Achieving a high percentage of t' + c phases in the coating with a porosity of less than 5% is a significant accomplishment. This success is closely linked to the fact that tetragonality exceeds that of YSZ. These results provide a solid foundation for future experimental designs aimed at optimizing spray parameters.