Plasma Treatment of Stainless Steel Alloys

Both 316L stainless steel (69.3 wt.% Fe, 16.38 wt.% Cr, 10.7 wt.% Ni, 2 wt.% Mo) and 410 martensitic SS (12.5 wt.% Cr, 0.30 wt.% Ni, Bal. Fe) were purchased from China Baosteel Co., Ltd. (Shanghai, China). Fe-Cr alloys with varying Cr content were homemade using a powder metallurgical method. Other pure metals, including Al (99.9%), Ti (99.5%), Cr (99.9%), and Fe (99.5%), are also treated with the same processing. Prior to the plasma treatment, 10 mm × 6 mm × 3 mm bars of bulk metals or alloys were ground and polished with 0.5 µm diamond. The samples were then ultrasonicated in ethanol for 15 min and subsequently cleaned using pure alcohol and distilled water. After cleaning, the samples were dried under compressed air and then placed in a dielectric barrier discharge (DBD) system (See Figure S1). To prevent the metal surface from damage caused by ion bombardment, the discharge gap between the parallel barriers was limited to 8 mm. A sinusoidal voltage was applied between electrodes by a high voltage generator. The input voltage was 30 to 50 V, and the input current was 1.0 to 2.0 A. The ambient atmosphere, with humidity ranging from 20% to 45%, was introduced into the system at room temperature. The temperatures of metal surfaces during processing were 80–110 °C. Treatment time, ranging from 10 min to 10 h, was varied to investigate the effects of corrosion behavior from the thin film.