Generation mechanisms of residual stresses in plasma-sprayed coatings

Stresses generated within plasma-sprayed coatings were evaluated dynamically by measuring the curvature of a strip-shaped substrate throughout the process of deposition. Four kinds of powder, Mo, Ni, Al and 80Ni-20Cr alloy, were plasma-sprayed in the air on five kinds of substrate, Mo, Ni, Al, 80Ni-20Cr alloy and mild steel. It was found that the stress due to deposit build-up is always tensile, whose magnitude mainly depends on powder material, not on substrate material: ranging approximately from 10 to 100 MPa in the order of Al ≽ Mo < Ni < 80Ni-20Cr alloy.. By the curvature change at the onset of spraying, upon which surface treatment of substrate showed significant influence, existence of a higher tensile stress within a boundary layer between a coating and the underlying substrate was suggested.