Semiconductor Properties Of AISI 316 Austenitic Stainless Steel Modified By Plasma-based Low Energy Nitrogen Ion Implantation

The surface of AISI 316 austenite stainless steel is modified by Plasma-based low energy nitrogen ion implantation. The phase structure is researched by X-ray diffraction analyzes. The correlation of pitting corrosion resistance and semiconductor properties for modified layer in 3.5% NaCl solution is investigated by the measurement of anodic polarization curves, electrochemical impedance spectroscopy and Mott-Schottky curves; and a suitable model is chosen by the fitting analysis of ZsimpWin software, the mechanism of the pitting corrosion resistance of AISI 316 stainless steel modified by Plasma-based low energy nitrogen ion implantation is studied. The results indicate that:The surface of AISI 316 austenite stainless steel treated by plasma-based low-energy nitrogen ion implantation isγN phase modify layer. The anodic polarization curve ofγN phase layer in 3.5% NaCl solution changes from spontaneous passivation-pitting breakdown process into spontaneous passivation-transpassive dissolution process without pitting corrosion, the corrosion potential increase 64 mV, the passivation current density deduce one order magnitude. It proves that theγN phase modify layer have superior pitting corrosion resistance. The equivalent circuit model ofγN phase modify layer is R(QR)(QR) in 3.5% NaCl solution, the passive film resistance R1 of theγN phase layer increases while the value of Yo which reflects the passive film capacitance decreases compared with the original AISI 316 stainless steel, electrode reaction is more difficult and the dense of passive film is increased significantly. As the time of immerse time increased, the risistance of the passive film formed onγN phase layer is about 105 ohm and it was stablize. The passive film of theγN phase layer behaves as n-type (Fe2O3) and p-type (Cr2O3) semiconductors in the potential range above and below the flat band potential Efb. Compared with the original AISI 316 stainless steel, the donor densities ND,acceptor densities NA, and the Efb, of theγN phase layer decreased apparently from 2.4×1021 cm-3,4.57×1021 cm-3 and-547 mV to 6.9×1018 cm-3,6.21×1019 cm-3 and -669 mV, respectively. The oxygen vacancy increase from 4.4×10-17 cm2·s-1to 5.7×10-15 cm2·s-1. It is found that the nitrogen ofγN phase layer mainly occupied the oxygen ion vacancy of n-type semiconductor, leading to form the thickness and the dense of passive film; In addition, when nitrogen contact with solution, it form NH4+, the concentration of OH- increased, prevented the adsorption of Cl" in the passive film, leading to improvement of pitting corrosion resistance of theγN phase layer.