Thermal Spray Coating Microstructures
Effect of Process and Powder Size

Flame spray coarse NiCr powder
Combustion Spray Coarse 80/20 NiCr
Powder
Flame spray fine NiCr powder
Combustion Spray Fine 80/20 NiCr
Powder
Plasma spray NiCr powder
Plasma Spray Coarse 80/20 NiCr
Powder
Plasma spray fine NiCr powder
Plasma Spray Fine 80/20 NiCr
Powder

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.

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