Comparative evaluation of microstructure and electrochemical, high-temperature corrosion rates of titanium- and aluminum-modified black chromium coatings on AISI 304 stainless steel

A comparative assessment of the microstructure and the rate of electrochemical high-temperature corrosion of black chromium coatings modified with titanium and aluminum, applied to AISI 304 stainless steel, has been conducted. Elemental analysis confirmed the presence of oxygen, chromium, titanium, and aluminum in the coatings. The EDX element mapping method demonstrated that modifying the coating with aluminum oxide positively affects the distribution of elements and reduces the number of cracks. X-ray diffraction (XRD) analysis revealed that the coatings mainly consist of chromium, with the addition of TiO 1.04 and Al 2 O 3 phases, which enhances the coating's resistance. This study presents potentiodynamic polarization curves illustrating the current-voltage dependencies of steel with Cr · CrO x , Cr · CrO x · TiO y , and Cr · CrO x · AlO z coatings, highlighting their electrochemical behavior and enhanced protective properties against pitting corrosion. Furthermore, electrochemical impedance spectroscopy (EIS) analysis reveals the complex equivalent circuit models for these coatings, showing significant increases in impedance and resistance values, particularly for aluminum oxide-modified coatings, which exhibit corrosion resistance. The effectiveness of protective coatings on steel operating as part of a galvanic pair with a zinc anode in a 6 wt% sodium chloride solution was evaluated by measuring the currents in the electrochemical pair, corrosion rates, and the protective influence of zinc in the Zn – AISI 304/coating galvanic pair. The results demonstrated a significant reduction in contact corrosion currents when the coating was modified with titanium or aluminum oxides, reducing the current density by 6–7.5 times after 5 days of exposure. The appearance of the modified coatings remained unchanged even after prolonged testing, highlighting their high level of protective properties. High-temperature corrosion tests at temperatures up to 800 °C revealed that coatings modified with titanium or aluminum oxides exhibit lower weight gain compared to uncoated samples, emphasizing the superior protective properties of these coatings. • Black chrome coatings are formed on AISI 304 steel. • The compositional protective effect is due to the modification of coatings by the introduction of Ti and Al oxides and additional processing of the coatings. • Contact corrosion tests show a reduction in the corrosion rate of zinc. • CrO x ·MO y coatings increase the corrosion resistance properties of the material.