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<p>Gadolinium zirconate Gd<sub>2</sub>Zr<sub>2</sub>O<sub>7</sub> (GZ<sub>2</sub>) has excellent thermal stability up to 1530°C, low thermal conductivity (1.1 W ∙ m<sup>–1</sup> ∙ K<sup>–1</sup>), a low sintering rate, and a higher coefficient of thermal expansion (CTE) (10.4 ∙ 10<sup>–6</sup> K<sup>–1</sup>, 293–1373 K) compared with LZ<sub>2</sub>. Therefore, GZ<sub>2</sub> is a very promising candidate for new thermal barrier coatings (TBCs). However, the relatively low fracture toughness of GZ<sub>2</sub>, which promotes crack propagation, limits its application as a TBC. In addition, GZ<sub>2</sub> tends to react with aluminum oxide to form the porous GdAlO<sub>3</sub> phase. For this reason, the implementation of the two-layer coating concept will retain the advantageous properties of GZ<sub>2</sub> and mitigate its weaknesses. Analysis of published sources on the production and properties of two- and multilayer GZ<sub>2</sub>/YSZ TBCs shows that two-layer GZ<sub>2</sub>/YSZ coatings can be successfully applied employing all established techniques: atmospheric plasma spraying (APS), electron-beam physical vapor deposition (EB–PVD), plasma spray–physical vapor deposition (PS–PVD), solution precursor plasma spray (SPPS), and suspension plasma spray (SPS). Such coatings endure a greater number of thermal cycles than the single-layer 8YSZ coating at 1550°C. Two-layer GZ<sub>2</sub>/YSZ TBCs are capable of increasing the operating temperature up to 1400°C and have a longer service life than similar LZ<sub>2</sub>/YSZ TBCs. Nevertheless, the CTE mismatch between the layers and the low fracture toughness remain a serious problem for such coatings. The interaction between the GZ<sub>2</sub> and YSZ layers does not critically affect the TBC properties. Reduction in Young’s modulus of TBCs appears promising to achieve excellent characteristics. Multilayer TBCs demonstrate significantly longer thermal shock lives at both 1100 and 1200°C. Doping the GZ<sub>2</sub> topcoat with Yb<sub>2</sub>O<sub>3</sub> increases the thermal cyclic life and CTEs of two-layer TBCs. At 1050°C, GZ<sub>2</sub>-based coatings are more thermally and chemically stable than YSZ and show better hot corrosion resistance. The key factors that influence the properties of the GZ<sub>2</sub> layer in the two-layer APS GZ<sub>2</sub>/YSZ coatings include the specific microstructure of the GZ<sub>2</sub> topcoats, particularly a higher density of defects and a higher proportion of unmelted particles compared with conventional YSZ coatings. In the post-sprayed state, the roughness of GZ<sub>2</sub> coatings is lower than that of YSZ coatings with the same porosity. The GZ<sub>2</sub> layers examined do not show higher resistance to sintering at 1100°C.</p>

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Multilayer Coatings as a New Stage in the Development of Modern Highly Effective Thermal Barrier Coatings II. Two-Layer Gd2Zr2O7/YSZ Thermal Barrier Coatings

  • 期刊论文

  • 发表日期：

    2025年7月1日

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  • S. M. Lakiza,
  • M. I. Hrechaniuk,
  • A. O. Makudera,
  • I. O. Marek,
  • O. K. Ruban,
  • V. P. Red’ko,
  • V. B. Shmybelskii,
  • O. V. Dudnik

摘要

Gadolinium zirconate Gd2Zr2O7 (GZ2) has excellent thermal stability up to 1530°C, low thermal conductivity (1.1 W ∙ m–1 ∙ K–1), a low sintering rate, and a higher coefficient of thermal expansion (CTE) (10.4 ∙ 10–6 K–1, 293–1373 K) compared with LZ2. Therefore, GZ2 is a very promising candidate for new thermal barrier coatings (TBCs). However, the relatively low fracture toughness of GZ2, which promotes crack propagation, limits its application as a TBC. In addition, GZ2 tends to react with aluminum oxide to form the porous GdAlO3 phase. For this reason, the implementation of the two-layer coating concept will retain the advantageous properties of GZ2 and mitigate its weaknesses. Analysis of published sources on the production and properties of two- and multilayer GZ2/YSZ TBCs shows that two-layer GZ2/YSZ coatings can be successfully applied employing all established techniques: atmospheric plasma spraying (APS), electron-beam physical vapor deposition (EB–PVD), plasma spray–physical vapor deposition (PS–PVD), solution precursor plasma spray (SPPS), and suspension plasma spray (SPS). Such coatings endure a greater number of thermal cycles than the single-layer 8YSZ coating at 1550°C. Two-layer GZ2/YSZ TBCs are capable of increasing the operating temperature up to 1400°C and have a longer service life than similar LZ2/YSZ TBCs. Nevertheless, the CTE mismatch between the layers and the low fracture toughness remain a serious problem for such coatings. The interaction between the GZ2 and YSZ layers does not critically affect the TBC properties. Reduction in Young’s modulus of TBCs appears promising to achieve excellent characteristics. Multilayer TBCs demonstrate significantly longer thermal shock lives at both 1100 and 1200°C. Doping the GZ2 topcoat with Yb2O3 increases the thermal cyclic life and CTEs of two-layer TBCs. At 1050°C, GZ2-based coatings are more thermally and chemically stable than YSZ and show better hot corrosion resistance. The key factors that influence the properties of the GZ2 layer in the two-layer APS GZ2/YSZ coatings include the specific microstructure of the GZ2 topcoats, particularly a higher density of defects and a higher proportion of unmelted particles compared with conventional YSZ coatings. In the post-sprayed state, the roughness of GZ2 coatings is lower than that of YSZ coatings with the same porosity. The GZ2 layers examined do not show higher resistance to sintering at 1100°C.