Corrosion resistance of AISI304 stainless steel treated by hybrid elevated-temperature, low-voltage/high-voltage nitrogen plasma immersion ion implantation

AISI304 stainless steel samples have been treated by a dual process involving low-voltage/elevated-temperature PIII/nitriding and subsequent high-voltage nitrogen PIII. Low-voltage PIII was conducted at 4 kV and about 350 °C, and the ion implant dose was 6×1017 cm−2. Afterwards, three of the treated samples were implanted by high-voltage PIII (25 kV) with an implant dose of about 3.4×1017, 7×1017, and 1.0×1018 cm−2, respectively. Glancing-angle X-ray diffraction (GXRD) patterns reveal that the high-voltage PIII process facilitates the formation of expanded austenite phases, and secondary ion mass spectrometry (SIMS) depth profiling reveals oxygen enrichment in the top surface compared to the sample receiving only the low-voltage treatment. The samples treated by the dual process exhibit excellent corrosion resistance properties as indicated by a higher equilibrium/pitting potential and a lower dissolution current. This improvement may be attributed to the formation of an expanded austenite layer and thicker layer containing chromium oxide as well as nitrogen-enrichment in the top surface, etc.