Electrochemical Corrosion Characteristic Of Direct Current Pulsed Plasma Sourse Nion AISI 304 Stainless Steel

The surface modification of AISI 304 austenitic stainless steel has been investigated by direct current pulsed plasma source ion nitriding (DCPPSIN) apparatus LDL-50. The phase microstructure, composition and surface morphology of AISI 304 austenitic stainless steel andγN phase layer were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy spectrum analysis; the changing hardness AISI 304 austenitic stainless steel andγN phase layer are studied by microhardness tester; The passivation of high-nitrogen f.c.c. (γN) phase formed on AISI 304 austenitic stainless steel, the pitting resistance and semiconductor characteristics of the passive film were studied by using anodic polarization, electrochemical impedance spectroscopy (EIS), and Mott-Schottky plot, and based on the result of EIS measurements, using the ZsimpWin software simulate to chose reasonable equivalent circuits and achieve the dynamics and electrode boundary informations. The results indicate that:The high-nitrogen f.c.c. phase isγN, and the nitrid temperature is 14.51 at.%, the average microhardness is V0.1N0.690 GPa, five times higher than AISI 304 stainless steel.The anodic polarization curves of AISI 304 austenitic stainless steel in 3.5% NaCl solution show 'self-passivation-pitting corrosion', and the Ept is -81 mv;γN phase shows 'self-passivation -transpassive dissolve', no pitting corrosion.The Mott-Schottky plot of AISI 304 austenitic stainless steel shows that the films of behave as p-type semiconductor below the flat band potential and above flat band potential is the n-type semiconductor, which are consist of Fe2O3 outside and Cr2O3 inside. And ND is 4.23×1021 cm-3, NA is 6.02×1021 cm-3, the flat band potential is -702 mv; The Mott-Schottky plot ofγN shows that the behave of film is mainly n-type semiconductor character, and the p-type semiconductor character is weak, the passivation film is mainly with Fe2O3, and ND is 5.64×1020 cm-3, the flat band potential is -753 mv, so the density of current carrier is decreased, and the passivation film surface adsorption of Cl- is weaken.The Nyquist figure of AISI 304 austenitic stainless steel/yN in 3.5% NaCl solution 1h shows single capacitive loop offset transverse axis, the diameters of theγN capacitive loop is increased; and in Bode figure, AISI 304 austenitic stainless steel shows two time constants, butγN shows one time constant, besides the phase angle enhanced; the results of EIS and Mott-Schottky plot prove that the equivalent circuit of AISI 304 austenitic stainless steel is R(QR)(QR), and the equivalent circuit ofγn is R(QR), besides compared with AISI 304 austenitic stainless steel, the deep space resistance ofγn increased by 1 orders, and the speed of electrode reaction is decreased. With the extension of soaking time from 1h to 48h,γN has superer pitting corrosion resistance than AISI 304 austenitic stainless steel.