Electrochemical impedance spectroscopy study of the passive film for laser-beam-melted 17-4PH stainless steel

The passive films formed on laser-beam-melted (LBM) and conventional 17-4PH martensitic stainless steels were studied by electrochemical impedance measurements in a 0.5 M NaCl solution at the corrosion potential. The passive films were described as dielectric layers, and impedance data showed that the Young model was the most appropriate to describe their electrical properties. Fitting of the impedance data led to lower capacitance values, associated with a thicker oxide layer, and higher resistivity values at the oxide-electrolyte interface for the LBM samples. While the differences were subtle, impedance measurements served to explain the better pitting corrosion resistance of LBM samples.