Comparison of hot-dip and slurry aluminizing of Inconel 718 followed by short time induction heating

This study demonstrates the successful application of very fast induction heating after two competitive and cost effective aluminizing process, namely, hot dip aluminizing (HDA) and slurry aluminizing (SA) on Inconel 718 superalloy. Induction heating for 20 s after the HDA process results in a 330 mm thick aluminide coating on the surface, while a 43 mm thick coating was achieved by the SA process. Morphological, structural and chemical characterizations of the coatings were made and compared to each other. In the HDA coating, main aluminide phase is aluminium rich Ni₂Al₃, while the SA process also encourages the formation of Ni rich aluminides in the form of NiAl and Ni₃Al. Both coatings are well-adhered to the substrate and free from any apparent discontinuity. Beside the aluminide phases, the HDA coating has also a needle like Cr₂Si phase at the coating – substrate interface, which might be beneficial for improving service life of the coating by limiting inward diffusion of aluminium. Similarly, EBSD examination revealed that the SA coating has uniform grain size and random grain orientation, which is promising for improved oxidation resistance. Also, the obtained results from the SA process in this study prove that successive application of the slurry and induction heating could be completed within very short period of time for partial and complete aluminizing of large industrial parts.