The photomicrographs above show fairly typical differences in microstructure of coatings produced by plasma spray and combustion powder ( flame ) 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 (flame ) 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.