The photomicrographs above show fairly typical differences in microstructure of coatings produced by plasma spray and combustion powder spray processes and the effect of changing powder particle size.
Plasma sprayed coatings generally have finer, denser microstructures with less oxide inclusions than combustion powder sprayed coatings. Plasma provides rapid heating, low particle flight time, more inert flame and higher velocity than combustion flame.
Generally, coarse powders produce a coarser and more open structured coatings with less oxidation than fine powders. This is mainly due to the differences in surface area of the powder particles exposed in the flame.