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A study of the penetration treatment of plasma sprayed SUS316L stainless steel coatings by molten MnO–SiO 2 oxides with near-eutectic composition was performed. The penetration treatment was introduced at 1353 K for 5, 20, and 45 min, and the effectiveness of the penetration and the underlying mechanisms of interfacial reactions are discussed on the basis of structural observation (EPMA), high-temperature wetting measurements and further supported by a thermodynamic calculation and analysis. The results indicated that at 1353 K, the MnO–SiO 2 oxides could infiltrate into the stainless steel coating within a depth of approximately 100 μm within 5 min due to the very good wettability of the stainless steel coating by molten MnO–SiO 2 oxides. The oxide could further penetrate to the coating/substrate interface when the treatment was extended to 20 min. During the penetration into the coating, a reaction between the MnO–SiO 2 oxides and adjacent stainless steel particles occurred, which produced MnCr 2 O 4 crystalline particles characterized by a spinel structure. As a result, a variation of the MnO–SiO 2 oxides composition was observed.

A study of the effects of penetration treatments on plasma sprayed SUS316L stainless steel coatings was performed. The stainless steel coatings were sealed using multi-component oxides introduced at the conditions of 1273 K for 20 min, 1273 K for 45 min and 1373 K for 45 min. The effectiveness of the penetration was determined using an electron probe microanalyzer (EPMA). The results indicated that the molten multi-component oxides could seal the open pores near the stainless steel coating surface quickly and effortlessly due to the good wettability. The molten multi-component oxides could pass through the oxide path connected to the inter micro-pores smoothly and infiltrated into the stainless steel coating when the period of impregnation was prolonged to 45 min. The penetration became more effective with increasing temperature because of the reactions between the molten multi-component oxides and the original oxides that occurred in the stainless steel coating around the inter pores. The results of a salt spray test indicated that the penetration treatment could significantly improve the corrosion resistance of the stainless steel coating.

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.