Effects of the pack Al content on the microstructure and hot corrosion behavior of aluminide coatings applied on Inconel-600

In this study, aluminide coatings were successfully synthesized on the nickel-based Inconel-600 superalloy substrates using the pack cementation method. The coatings were produced from the packs containing different amounts of Al in the range of 10 wt% - 30 wt%. For the hot corrosion experiments, the specimens were coated with a thin layer of solid Na2SO4 and subsequently placed in a muffle furnace in static air at 900 degrees C for 96 h. The surface morphology, the elemental composition and the phase composition of the produced coatings before and after the hot corrosion experiments were characterized using different analytical techniques such as SEM, OM, EDS, and XRD. The results indicate that increasing the amount of Al in the packs from 10 wt% to 30 wt% decreased the thickness of the as-formed aluminide coatings from 210.8 +/- 2 mu m to 170.7 +/- 3 mu m. The produced coatings were also composed of three distinct layers including an outer layer, an inner layer, and a narrow inter-diffusion zone (IDZ). Additionally, the coatings consisted of NiAl and Ni2Al3 as major phases and Al86Cr14 and Al13Fe4 as minor phases. During the hot corrosion experiments, an Al2O3 surface scale was developed on the coatings, which resulted in the protection of the substrates. With 10 wt% Al, the Al2O3 surface scale was porous and defective whilst this surface scale peeled off when the Al content in the packs increased to 30 wt%. The best hot corrosion resistance was observed in the presence of 20 wt% Al.