Effect of Electrolyte-Plasma Treatment on the Structure and Surface Properties of Medical-Grade Corrosion-Resistant Steels

This paper presents the results of a study on the effect of Electrolytic-Plasma Treatment (EPT) parameters on the structure and properties of the surface layer of austenitic corrosion-resistant steels AISI 304, AISI 316L, and AISI 321, which are widely used in the production of medical devices. As a result of EPT, inhomogeneities in the form of chromium carbide inclusions appear on the surface of AISI 304 steel samples; their size and quantity decrease with increasing treatment duration and become almost negligible after 10 min. For AISI 321 and AISI 316L steels, EPT primarily leads to surface smoothing through the removal of micro-irregularities without significant structural changes, while small, uniformly distributed titanium carbide particles up to 4 µm in size remain on the AISI 321 steel. The identified features of surface structure formation significantly affect the roughness: its most intensive change is observed at an EPT duration of 3–5 min, after which the dynamics decrease. Due to the relief formed by carbide inclusions, the roughness values of AISI 304 steel samples are higher than those of AISI 316 and AISI 321 steel samples. At voltages of 260–320 V, the roughness parameters remain stable; however, at 340 V, a deterioration in surface quality is observed due to the transition to an electrolytic-discharge mode. With an increase in EPT duration, the corrosion potential of all the studied corrosion-resistant steels shifts to the positive region, and the corrosion current density decreases by 6–7 times. The greatest improvements are observed for AISI 316L steel – the corrosion potential increases from ~184 to ~98 mV. The wetting contact angle increases sharply from ~58° to ~84° after 1–3 min of treatment, then stabilizes in the range of 85–88°, indicating an increase in surface hydrophobicity.