Correlation between surface roughness of plasma-sprayed chromium oxide coatings and powder grain size distribution: a fractal approach

Attempts were made to correlate the arithmetic mean surface roughness Ra and the 10-point height values Rz of atmospheric plasma-sprayed (APS) chromium oxide coatings with fractal properties such as the relative area for 2 μm2 patch size (RAPS), the smooth-rough crossover (SRC) and the area-scaled fractal complexity (ASFC). In particular, the measured surface roughness of the coatings correlates with high statistical probability with the grain size distribution of the selected spray powders. It was found that the SRC value is useful to characterize the low and high cutoff values of the grain size distribution of thermal spray powders. Hence fractal analysis is a potential analytical tool to quantify the geometric complexity of the surface structure of plasma-sprayed coatings as a function of scale of observation.