AVS 47th International Symposium
    Surface Engineering Tuesday Sessions
       Session SE-TuA

Paper SE-TuA4
Enhanced Passivity of Austenitic AISI 304 Stainless Steel by Low-Temperature Ion Nitriding

Tuesday, October 3, 2000, 3:00 pm, Room 201

Session: Surface Engineering: Surface Preparation to Postcoating Surface Finishing
Presenter: S. Rudenja, Tallinn Technical University, Estonia
Authors: S. Rudenja, Tallinn Technical University, Estonia
I. Odnevall Wallinder, Royal Institute of Technology, Sweden
C. Leygraf, Royal Institute of Technology, Sweden
P. Kulu, Tallinn Technical University, Estonia
V. Mikli, Tallinn Technical University, Estonia
Correspondent: Click to Email
Low-temperature ion-nitriding introduces interstitial nitrogen into the austenitic stainless steel matrix. The passivity and anodic oxidation of a nitrided AISI 304 stainless steel have been studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in 0.1 M H@sub 2@SO@sub 4@ + 0.05 M HCl solution. The chemical composition of the oxidized surface film on the stainless steel was analyzed by X-ray photoelectron spectroscopy (XPS), including angle-resolved spectra of the elements. The distribution of the chemical elements beneath the oxide- metal interface was studied with Auger depth profiling. Defects of crystalline structure nearby the surface were studied with transmission electron microscopy (TEM). An enhanced passivity of the nitrided stainless steel was detected by anodic polarization. Capacitance measurements by EIS revealed a 3-4 nm thick oxide film on the surface of nitrided specimens, that is 2-3 times thicker than on blank specimens. XPS analyses and Auger depth profiles indicate increased chromium uptake into the oxide film on nitrided surface, supposedly through the kinetically stable oxide-metal interface enriched with nitrogen and nickel. Several possible mechanisms influencing passivation of the nitrided stainless steel may operate simultaneously. Among these mechanisms, austenite strengthening by interstitial nitrogen near the oxide/alloy interface and associating with structural defects like dislocation branches are most likely explanation for the enhanced passivity of the nitrided stainless steel.