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Mechanisms of formation of slurry aluminide coatings from Al and Cr microparticles

  • Grégoire, Benjamin
  • Bonnet, Gilles
  • Pedraza, Fernando
Publication Date
Feb 01, 2019
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The mechanisms of formation of nickel aluminide coatings from alternate deposition of Al and Cr microparticles and subsequent heat treatment in Ar were studied on pure nickel. For this purpose, tailored amounts of Al and Cr water-based slurries were successively deposited on pure nickel following two different architectures (Al/Cr and Cr/Al double-layer systems). Regardless of the coating architecture, the addition of Cr microparticles was foundto decrease the thermodynamic activity of Al upon aluminizing through the formation of Alx Cry phases. This considerably limited the inward diffusion of Al towards the substrate at low temperature (e.g. 650 °C). Whereas the formation of δ-Ni2Al3 was still observed with the Al/Cr double-layer system, its formation was completely suppressed with the Cr/Al one. By adjusting the composition of the deposited layers, i.e. the thickness of both Cr and Al layers, it was possible to directly form the β-NiAl phase with a further annealing at high temperature (e.g. 1000 °C for 3 h). This fostered the outward diffusion of nickel and the dissolution of synthesized AlxCry phases. Undissolved Cr-rich phases were also observed in the diffusion layers, which confirmed the outward growth of the coating typical of low-activity aluminizing

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