Structure and corrosion behavior of 316L stainless steel coatings formed by HVAF spraying with and without sealing

316L stainless steel (SUS316L) coatings were sprayed on carbon steel substrate by a high-velocity air fuel (HVAF) process. Powder feed rate and particle size were varied systematically to investigate their effects on microstructure, oxide content and adhesion strength of the coatings. When the powder feed rate and particle size increased, the oxide content in the coatings decreased from 7 to 3%, while the adhesion strength decreased from 34 to 17 MPa. The corrosion resistance of the coatings was evaluated for sealed and unsealed coating conditions by salt spray test for up to 500 h. A large amount of corrosion products appeared on the unsealed coatings after 20 h, whereas no corrosion products were observed on the sealed coatings sprayed with the powder of the largest particle size, even after 500 h. Moreover, the above characteristics of the HVAF coatings were compared with those of a SUS316L coating sprayed by a high-velocity oxy-fuel process.