Effect of Si addition on the phase formation of Ni2Al3 and NiAl in plasma paste aluminizing of IN-738 superalloy

Ahmad Reza Rastkar
Laser and Plasma Research Institute, Shahid Beheshti University, Tehran 1983969411, Iran
Taha Shariati
Laser and Plasma Research Institute, Shahid Beheshti University, Tehran 1983969411, Iran

Article ID: 4049

Keywords: IN-738 superalloy, plasma aluminizing, diffusion coatings, NiAl, Ni2Al3

Abstract

Ni superalloys are mostly used in turbine engines. But they suffer from high temperature oxidation. So, many investigations have been tried to protect the surface of these materials by pack aluminizing. A plasma paste process was used to aluminize the surface of superalloy IN-738. Nickel aluminum phases were created on the surface of the nickel-based superalloy IN-738 by plasma paste aluminizing with pure aluminum and Al-Si mixtures. Specimens were plasma-paste aluminized at 750–900 ºC for 1 h in low pressures of 10 mbar argon gas without Si and with 5–10% Si. Microstructural and compositional evaluations were studied using optical and scanning electron microscopes, EDS, X-ray diffraction (XRD) techniques, and Vickers microhardness tests. A mixture of fine or coarse equiaxed-grained microstructure of NiAl, Ni₂Al₃ with precipitates of Al4Cr phases were observed in the coating layers. The addition of silicon showed the transformation of the NiAl and Ni₂Al₃ phases in the compound layers from fine-grained structures to nearly coarse equiaxed grains. In this plasma paste process, the silicon can be dissolved in the coating up to 10 at.% of the total coating composition and is mostly concentrated in some phases. Average Vickers microhardness analysis across the transverse cross section of aluminized samples under 500 g force revealed mostly an increase in hardness from approximately 250–300 HV0.5 in the substrate to 550–600 HV0.5 in the coating layers.

Published

2026-06-17

How to Cite

Rastkar, A. R., & Shariati, T. (2026). Effect of Si addition on the phase formation of Ni2Al3 and NiAl in plasma paste aluminizing of IN-738 superalloy. Materials Technology Reports, 4(1). https://doi.org/10.59400/mtr4049

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Vol. 4 No. 1 (2026)

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Article

This work is licensed under a Creative Commons Attribution 4.0 International License.

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