Thermal spraying consists of
injecting powder particles or wires into a hot jet in which they are
heated and projected towards a substrate. The particles are
molten, impinge on the substrate and form a surface coating.
Because of the decrease in adhesive strength with coating
thickness, the maximum thickness of coatings prepared over
metal surfaces was always less than 500 μm. One of the different
techniques tried to reduce the effect of the mismatch in thermal
expansivity between the coating and the substrate is an under
coat of materials like aluminides