Fused coatings are different. These are remelted and completely metallurgically bonded with the substrate and its self. A large proportion of thermal spraying is conducted in air or uses air for atomisation. Chemical interactions occur during spraying, notably oxidation, Metallic particles oxidize over their surface forming an oxide shell. This is evident in the coating microstructure as oxide inclusions outlining the grain or particle boundaries.
Coatings show lamellar or flattened grains appearing to flow parallel to the substrate.
Strength in the longitudinal direction can be 5 to 10 times that of the transverse direction. The coating structure is heterogeneous relative to wrought and cast materials. This is due to variations in the condition of the individual particles on impact. It is virtually impossible to ensure that all particles are the exact same size and achieve the same temperature and velocity. Cooling and solidification of most materials is accompanied by contraction or shrinkage.