Electrochemical Corrosion Behaviors Of Plasma-Based Low-Energy N Ion Implantation Austenitic Stainless Steel

The surface modification of 316 austenitic stainless steel has been investigated by plasma-based low-energy ion implantatio n apparatus at various temperatures and working atmospheric pressure. The phase microstructure, composition and surface morphology of 316 austenitic stainless steel andγN phase layer are characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM); the changing hardness 316 austenitic stainless steel andγN phase layer are studied by microhardness tester; the electrochemical corrosion behaviors of 316 austenitic stainless steel andγN phase layer are evaluated by using anodic polarization measurements and electrochemical impedance spectroscopy (EIS), based on the result of EIS measurements, appropriate equivalent circuits for the film system were proposed, and using the ZsimpWin software simulate. The results indicate that:Under 7×10^-2 Pa, with the ion implantation temperature increase, the content of N on alloy surface increase, from 14.51% of 320℃increase to 20.14 at.% of 380℃; the maintain passivation current density Ip on the anodic polarization curves in 3.5% NaCl solution decrease and pitting potential Ept increase, the diameter of capacitive arc and the |Z| on EIS increase, the flat roof of phase angle become wider and higher, the corrosion resistence increase. At 380℃, working atmospheric pressure decrease to 3×10^-2 Pa from 7×10^-2 Pa, the content of N on surface increase to 25.12 at.% from 20.14%, the diffraction apices ofγN phase intensify, the anodic polarization curves in 3.5% NaCl solution show self-passivation transpassive dissolve, no pitting corrosion, and the transpassive potential Etp increase by 200 mV, indicateγN phase layer own the excellent pitting corrosion resistance.The optimal working parameters of ECR microwave plasma-based low-energy N ion implantation are 380℃,3×10^-2 Pa,γΝphase layer is about 5μm thick, the average microhardness isΗV0.1N1171 MPa, three times higher than 316 stainless steel.Bode diagrams of 316 stainless steel andγN phase layer in 3.5% NaCl solution indicate that the equivalent circuit is R(QR)(QR), and the flat roof of phase angle become wider and higher when immersion time increase to 3 h from 1 h. The passivation film become uniform and compaction after immersion 3 h, Bode diagrams become similar, passivation film is in equilibrium of dissolve and re-passivation, the passivation film resistance R2 onγN phase layer surface is 662.6 kΩ·cm²,196 kΩ·cm² higher than 316 stainless steel, dispersion coefficient n2 increase to 0.901 from 0.847 for 316 stainless steel, this indicate thatγN phase layer own the intensive capacity of re-passivation.