Electrochemical and X-ray investigation of austenitic 304L and 316L stainless steels treated by a gliding arc in humid air

Austenitic 304L and 316L stainless steel discs are exposed to the abundant highly reactive hydroxyl radicals radical dotOH with respect to radical dotNO, generated by a non-thermal gliding arc plasma in humid air. The plasma–surface interaction presumably provokes oxidation of the stainless steel surface and induces corrosion phenomena and/or phase transformation on the alloy surface which is electrochemically controlled using the linear sweep voltammetry in aqueous NaOH (0.025 M) solution by looking at the iron hydroxide Fe(OH)3 reduction. Corrosion potential (Ecorr) and current (Icorr), in 10−2 M nitric acid solution, of the plasma-treated samples with respect to exposure time increase and decrease respectively to a constant value after a treatment time threshold suggesting the formation a passive barrier layer. Grazing incidence X-ray diffraction analysis of the treated samples show a decrease of the less predominant ferrite phase (α-Fe), suggesting the transformation of this phase into hydroxides or to the other predominant (γ-Fe) phase with the treatment time. The application of the gliding arc plasma in humid air to the surface treatment of austenitic 304L and 316L stainless steels is found to improve their corrosion resistance in aggressive environments by forming more resistant barrier layers.