Microstructural and topographical characterization of the pack cemented aluminide coating applied on Inconel-600

Abstract

Abstract In this research, the pack cementation method was employed to apply a uniform aluminide coating on a substrate of nickel-based superalloy. The obtained intermetallic coating was synthesized using a pack containing 18Al–80Al2O3–2NH4Cl (wt.%) as the main deposition source, an inert filler, and an activator, respectively. The surface morphology and topography, cross-sectional microstructure, the elemental and phase composition, microhardness of the synthesized aluminide coating were studied using atomic force microscopy (AFM), optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), x-ray diffraction (XRD), and Vickers microhardness indenter as the characterization techniques. According to the 3D topography results, the average surface roughness of the Inconel-600 substrate was about 2.446 ± 0.239 nm compared to 43.558 ± 3.876 nm measured for the produced aluminide coating. Additionally, the synthesized coating consisted of NiAl and Ni2Al3 as major phases considering the XRD spectrum. It is also observed that the deposited aluminide coating had a three-layer structure including an outer layer, an inner layer, and a diffusion zone. The Vickers microhardness measurements indicated a significant increase in the microhardness of the substrate (from 185.6 ± 15.8 Hv to 1130.4 ± 42.5 Hv) after applying the aluminide coating. Moreover, the microstructural variations across the deposited aluminide coating led to different microhardness values obtained for each layer. The highest microhardness was observed in the coating diffusion zone, whereas the lowest value belonged to the outer layer.