Plasma-Assisted Heat Treatments for Aluminide Coatings Deposition on Ni-Based Superalloys

In this study, hot-dipping aluminizing followed by a novel plasma-assisted heat treatment on Inconel 690 alloy was investigated, with a focus on microstructure, phase transformation, and microhardness. A comparative analysis with thermal heat treatment conducted under identical temperature and duration conditions was performed. X-ray diffraction analysis confirmed the formation of stable α-Al₂O₃ in plasma-treated samples, whereas metastable θ-Al₂O₃ was observed in thermally treated samples. Microstructural examination identified NiAl and α-Al₂O₃ alumina layers in plasma-treated samples, in contrast to Cr₂O₃ precipitates at grain boundaries in thermally treated samples, which were associated with intergranular embrittlement. The plasma-assisted heat treatment effectively mitigated this embrittlement issue as reported in recent studies. Additionally, microhardness measurements were found to align with existing literature, and the applied heat treatment did not impair the bulk properties. These findings highlighted the significant potential of plasma-assisted aluminizing to enhance the performance and durability of Inconel 690 alloy components in nuclear waste management applications. The stable α-Al₂O₃ coating with nickel aluminides was demonstrated as a promising solution to address challenges in joule-heated ceramic melters.