Induction assisted hot-dip and slurry aluminizing of Inconel 718

This study compares the effect of very fast induction heating for two competitive and cost effective aluminizing process, namely, hot dip aluminizing (HDA) and slurry aluminizing (SA) of Inconel 718 superalloy. Each process produced well adhered coating layers, which comprise two or more layers. Morphological, structural and chemical characterizations of each layer were extensively studied, and formation mechanisms of the coatings were discussed in comparison to each other. The HDA process performed in a molten Al-11 wt. Si bath at 700 °C formed a 120 μm coating layer, mostly comprising of NiAl₃. The induction heating for 20 s at 1000 °C increased the coating thickness more than two times (250 μm), transformed the aluminides to Ni₂Al₃, made the elemental distribution more uniform within the coatings, and also formed CrSi₂ precipitates, which might be beneficial for an improved oxidation resistance. In the SA process, the induction heating forms a coating of 43 μm in thickness, which is more uniform than the HDA coatings, and also comprises of two layers having Ni₂Al₃ and NiAl type aluminides. EBSD examination revealed that the SA coating has a uniform grain size and random grain orientation, which are promising for improved oxidation resistance. Evaluation of the results in comparison to each other provided a better understanding of the effect of induction heating on different aluminizing processes. For example, a coating uniformity similar to that of the SA coating can be achieved only after the application of the induction heating in the HDA coatings. Also, the SA process assisted with the induction heating can be applied to various substrates without subjected them to a high temperature for a long time, and would be a promising method for partial and complete aluminizing of Ni-based substrates.