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<p>Solid-particle contaminants rich in CaO–MgO–Al<sub>2</sub>O<sub>3</sub>–SiO<sub>2</sub> (CMAS) remain a dominant life- limiting factor for thermal-barrier coatings (TBCs) in modern gas turbines. Standard 8 wt.% yttria-stabilized zirconia (YSZ) topcoats, although thermally efficient, permit molten CMAS to penetrate their splat network, triggering phase destabilization and accelerated spallation. To counter this weakness, we designed a multilayer architecture that marries YSZ with a lanthanum pyrochlore lanthanum phosphate (LPZ) composite expected to neutralize CMAS chemically while preserving thermal insulation. Four variants were fabricated by atmospheric plasma-spraying pure YSZ (200 µm) and three hybrid stacks containing 50, 100, or 150 µm of LPZ beneath progressively thinner YSZ caps over NiCrAlY bond-coated INCONEL 718 substrates. All specimens were exposed to a 10 mg&#xa0;cm<sup>-2</sup> CMAS overlay at 1200°C for 8–48h. Pre- and post-exposure characterization employed 3-D profilometry, scanning electron microscopy with energy-dispersive spectroscopy, and X-ray diffraction. Increasing the LPZ fraction systematically reduced columnar gap width, porosity, and roughness growth. The richest LPZ coating (50 µm YSZ/150 µm LPZ) curtailed CMAS ingress to ~50 µm after 48 h one quarter of the depth measured in monolithic YSZ and retained &gt;90% of its initial hardness. X-ray analysis revealed the <i>in situ</i> formation of a dense apatite layer, Ca<sub>3</sub>La<sub>7</sub>(PO<sub>3</sub>)(SiO<sub>3</sub>)<sub>5</sub>O<sub>2</sub>, that sealed residual pathways and blocked further attack. The study confirms that integrating a reactive LPZ sub-layer transforms a conventional YSZ topcoat into a reactive protective layer formation, offering a viable route to longer component life and higher permissible firing temperatures in CMAS-laden environments.</p>

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Investigation of lanthanum pyrochlore-lanthanum phosphate (La2Zr2O7.LaPO4) composite coatings for high-temperature CMAS corrosion resistance in TBCs

  • 期刊论文

  • 发表日期：

    2026年3月26日

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  • Karthikeyan Kumarasamy,
  • Umapriya Rohan,
  • Manisha Vidyavathy Sudandaradoss

摘要

Solid-particle contaminants rich in CaO–MgO–Al2O3–SiO2 (CMAS) remain a dominant life- limiting factor for thermal-barrier coatings (TBCs) in modern gas turbines. Standard 8 wt.% yttria-stabilized zirconia (YSZ) topcoats, although thermally efficient, permit molten CMAS to penetrate their splat network, triggering phase destabilization and accelerated spallation. To counter this weakness, we designed a multilayer architecture that marries YSZ with a lanthanum pyrochlore lanthanum phosphate (LPZ) composite expected to neutralize CMAS chemically while preserving thermal insulation. Four variants were fabricated by atmospheric plasma-spraying pure YSZ (200 µm) and three hybrid stacks containing 50, 100, or 150 µm of LPZ beneath progressively thinner YSZ caps over NiCrAlY bond-coated INCONEL 718 substrates. All specimens were exposed to a 10 mg cm-2 CMAS overlay at 1200°C for 8–48h. Pre- and post-exposure characterization employed 3-D profilometry, scanning electron microscopy with energy-dispersive spectroscopy, and X-ray diffraction. Increasing the LPZ fraction systematically reduced columnar gap width, porosity, and roughness growth. The richest LPZ coating (50 µm YSZ/150 µm LPZ) curtailed CMAS ingress to ~50 µm after 48 h one quarter of the depth measured in monolithic YSZ and retained >90% of its initial hardness. X-ray analysis revealed the in situ formation of a dense apatite layer, Ca3La7(PO3)(SiO3)5O2, that sealed residual pathways and blocked further attack. The study confirms that integrating a reactive LPZ sub-layer transforms a conventional YSZ topcoat into a reactive protective layer formation, offering a viable route to longer component life and higher permissible firing temperatures in CMAS-laden environments.