Figure 6. (a) SEM image of Micro coating and (b) EDS mapping searching for Cr element. Dark gray phases are Cr rich Cr3C2 splats, while light gray phases are NiCr splats.
Figure 7 gives representative images of Nano and Micro coatings. The sprayed powder builds up a laminar architecture of flat, scattered particles (splats). The size of the splats is according to the size of the powder. The Nano coating microstructure is more refined, therefore containing the higher amount of splat boundaries. Alumina can be seen closer to the interface between the coating and substrate. The alumina is undesirable because it can negatively affect the adhesion of the coating and because it can be a stress riser for fatigue.