Penetration treatment of plasma spray SUS316L stainless steel coatings by molten MnO-SiO2 oxides

A study of the penetration treatment of plasma sprayed SUS316L stainless steel coatings by molten MnO-SiO2 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-SiO2 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-SiO2 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-SiO2 oxides and adjacent stainless steel particles occurred, which produced MnCr2O4 crystalline particles characterized by a spinel structure. As a result, a variation of the MnO-SiO2 oxides composition was observed.