Electrochemical Corrosion Characteristic Of AISI304Austenitic Stainless Steel Modiifed By Plasma-based Low Energy Nitrogen Ion Implantation

The surface of AISI304austenite stainless steel is modified by Plasma-based low energynitrogen ion implantation. The phase microstructure and surface morphology of AISI304austenite stainless steel and the modified layer are characterized by X-ray diffraction andscanning electron microscopy; The concentration-depth of nitrogen atoms for the modifiedlayer cross-section is analysised by electron probe and auger electron spectroscopy. Thechanging hardness of AISI304austenitic stainless steel and modified layer are studied bymicrohardness tester. The pitting corrosion resistance for modified layer in3.5%NaClsolution is investigated by the measurement of anodic polarization curves, electrochemicalimpedance spectroscopy and Mott-Schottky curves. The results indicate that:The surface of AISI304austenite stainless steel treated by plasma-based low-energynitrogen ion implantation isγNphase layer. TheγNphase layer thickness is about13μm, thehighest concentration of nitrogen atoms is up to32at%. The average microhardness of theγNphase layer is five times higher than the original AISI304stainless steel.The anodic polarization curves of the original AISI304stainless steel andγNphase layerin3.5%NaCl solution are spontaneous passivation-pitting breakdown process. The corrosionpotential E_corrand the breakdown potential E_ptof the Nphase layer increased approximatelyfrom-305mV to-155mVand from-30mV to337mV, the self-corrosion current density I_corrand the passivation current density I_ssof the Nphase layer decreased approximately from3×10^-2μA/cm²to3×10^-3μA/cm²and from5×10^-1μA/cm²to5.3×10^-2μA/cm², relative to thatof the original austenitic stainless steel. TheγNphase layer improves the pitting corrosionresisitance.A suitable EIS equivalent circuit R（QR） was chosen by the fitting analysis of ZsimpWinsoftware for the original AISI304stainless steel andγNphase layer in3.5%NaCl solution atdifferent immerse time; the passive film resistance Rp of the γNphase layer increases ofnearly ten times while the value of Y0which reflects the passive film capacitance decreasescompared with the original AISI304stainless steel. As the time of immerse time increase to24h, the risistance of the passive film formed on the original AISI304stainless steel is about5.865×10⁴cm²and it is stablize. Meanwhile, as the time of immerse time increase to10h,the risistance of the passive film formed on theγNphase layer is about3.765×10⁵cm²and itis stabilized. TheγNphase layer improves the ability of passivation and insulation.The passive films on the original AISI304stainless steel and the Nphase layer areobtained as n-type and p-type semiconductors characteristics. The donor and acceptordensities of the Nphase layer decreased approximately from3.94×10²¹/cm³to1.22×10²⁰ /cm³and from5.59×10²¹/cm³to6.76×10²⁰/cm³, and the flat band potential decreasedapproximately from-583mV（SCE） to-614mV（SCE）, relative to that of the originalaustenitic stainless steel. TheγNphase layer enthances the dense of passive film and preventsthe adsorption of Cl-in the passive film.