Abstract
Formation of a ceramic coating layer (Al₂O₃ + 13% TiO₂) takes place by a gradual deposition (overlapping) of non-uniformly deformed particles irregularly distributed over the NiAl surface layer and then over the ceramic layer surfaces. This results in a layer with a rough surface and containing some microvoids (pores). This generally applies also to other types of metallic and ceramic layers (coatings). Surface roughness of a metallic or ceramic layer depends first of all on the powder granularity. Under the given conditions, the surface roughness is stabilized at values around R_a = 6-8 µm (NiAl) or R_a = 3-5 µm (Al₂O₃ + 13% TiO₂). The effect of substrate surface roughness on surface roughness of the NiAl layer (and also the effect of metallic layer surface roughness on surface roughness of the ceramic layer) depends on the difference between the surface roughness of substrate surface (NiAl layer) and a stabilized surface roughness of the NiAl layer (Al₂O₃ + 13% TiO₂ layer) as well as on the required layer thickness. The surface roughness of the ceramic layer (R_a = 3-5 µm) can be improved by polishing (R_a = 1-2 µm) or grinding (in the given conditions R_a = 0.8-0.9 µm). A better surface roughness can be achieved by altering the grinding conditions but mainly by the use of a diamond grinding wheel with smaller dimensions of abrasive grain size.

Key words
ceramic coating layer (Al₂O₃ + 13% TiO₂)

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