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.