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<p>Aluminizing enhances the oxidation resistance of Ni-based superalloys, with reactive air aluminizing (RAA) using a slurry route being particularly effective for high-temperature applications. This study employed a halide activator-free slurry with an environmentally friendly organic binder (PVA) and Al particles, which was sprayed onto IN625 samples and heat-treated in air at temperatures ranging from 700°C to 1100°C for up to 2&#xa0;h to deposit aluminide coatings. The formation mechanism was investigated, and phase stability was evaluated through isothermal oxidation in static air at 1000°C for 100&#xa0;h. FE-SEM and SEM imaging was used to analyze the surface morphology and cross-sectional microstructures, while XRD identified the present phases. Elemental compositions were determined via EDS and analyzed using Al-Cr-Ni ternary phase diagrams. The results showed that the RAA method successfully formed aluminide coatings on IN625, with the microstructure varying by temperature and duration. Lower temperatures formed Al-rich aluminides (Al<sub>3</sub>Ni<sub>2</sub>), while higher temperatures favored β-NiAl. Oxide scale formation was observed, with γ-Al<sub>2</sub>O<sub>3</sub> at lower temperatures (700–900°C) and α-Al<sub>2</sub>O<sub>3</sub> at higher temperatures (&gt; 1000°C). The best oxidation performance was noted for coatings formed at 1000–1100°C, attributed to α-Al<sub>2</sub>O<sub>3</sub> formation and enhanced β-NiAl phase stability.</p>

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Microstructure Evaluation of IN625 Aluminide Coatings Produced by Reactive Air Aluminizing (RAA) Process: Impact of Temperature and Process Duration

  • 期刊论文

  • 发表日期：

    2025年7月14日

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  • Pargol Rooygari,
  • Omid Bakhtiary,
  • Zahra Alizadeh,
  • Shayan Sarraf,
  • Mansour Soltanieh

摘要

Aluminizing enhances the oxidation resistance of Ni-based superalloys, with reactive air aluminizing (RAA) using a slurry route being particularly effective for high-temperature applications. This study employed a halide activator-free slurry with an environmentally friendly organic binder (PVA) and Al particles, which was sprayed onto IN625 samples and heat-treated in air at temperatures ranging from 700°C to 1100°C for up to 2 h to deposit aluminide coatings. The formation mechanism was investigated, and phase stability was evaluated through isothermal oxidation in static air at 1000°C for 100 h. FE-SEM and SEM imaging was used to analyze the surface morphology and cross-sectional microstructures, while XRD identified the present phases. Elemental compositions were determined via EDS and analyzed using Al-Cr-Ni ternary phase diagrams. The results showed that the RAA method successfully formed aluminide coatings on IN625, with the microstructure varying by temperature and duration. Lower temperatures formed Al-rich aluminides (Al3Ni2), while higher temperatures favored β-NiAl. Oxide scale formation was observed, with γ-Al2O3 at lower temperatures (700–900°C) and α-Al2O3 at higher temperatures (> 1000°C). The best oxidation performance was noted for coatings formed at 1000–1100°C, attributed to α-Al2O3 formation and enhanced β-NiAl phase stability.