Effects of thermal spray coating composition and microstructure on coating response and substrate protection at high temperatures

Three thermal spray coatings were subjected to high-temperature corrosion experiments to characterize the operative corrosion mechanism(s) and to examine the effects of coating composition and microstructure. Samples were placed In air and sulfur dioxide (SO2) at 600 degrees C for exposure times up to 1,000 h. The ability of a thermal spray coating to protect its substrate effectively was found to depend upon its tendency to form protective oxides and upon the cross-sectional distance from the coating surface to the substrate via fast diffusion paths such as splat boundaries and voids.