Production and Properties of the Porous Layer Obtained by the Electrochemical Method on the Surface of Austenitic Steel

Anticorrosive properties of chitosan-derivatives coatings on Mg AZ31 alloy in Hank's Balanced Salt Solution

This study describes the preparation of chitosan-derivatives coatings on AZ31 Mg alloy for corrosion protection in Hank's Balanced Salt Solution (HBSS). The derivatives were prepared by reacting chitosan with natural aldehydes (vanillin, benzaldehyde and cinnamaldehyde) and the coatings were characterized by means of water contact angle, scanning electron microscopy and swelling essays. The corrosion behavior of the samples was investigated using potentiodynamic polarization, electrochemical impedance spectroscopy and hydrogen evolution essays. All derivatives present superior corrosion protection than neat chitosan and the best performance is observed for the vanillin derivative with the highest modification degree, which present hydrogen evolution rate of 0.05 mL cm-2 day-1, below the tolerance limit for biomedical application, and |Z|max in the order of 104.6 Ω cm2 even after 14 days of exposure to the corrosive solution.

Corrosion Behavior of Different Types of Stainless Steel in PBS Solution

Anodic and spontaneous corrosion of different types of stainless steel (AISI 304L, AISI 316L and 2205 DSS) in phosphate-buffered saline solution (PBS, pH = 7.4) at 37 °C (i.e., in simulated physiological solution in the human body) were examined using open circuit potential measurements, linear and cyclic polarization, and electrochemical impedance spectroscopy methods. After the anodic and spontaneous corrosion, the surface of the tested samples was investigated by light and scanning electron microscopy (SEM) with EDS analysis. It has been established that the tendency of the examined steel materials towards local corrosion decreases in the order: AISI 304L < AISI 316L < 2205 DSS. Namely, the possibility of repassivation and the resistance to local corrosion increases in the same order. The corrosion resistance of steel samples at open circuit potential is a consequence of forming a natural oxide film with a bi-layer structure and consists of an inner barrier and an outer porous film. The inner barrier film has a small thickness and extremely high resistance, while the outer porous film is much thicker but also has significantly lower resistance. The inner barrier layer mainly prevents corrosion of examined steel samples in order: AISI 304L < AISI 316L < 2205 DSS. Light microscopy and SEM/EDS analysis after pitting and spontaneous corrosion showed damage on the AISI 304L and AISI 316L surface, while the surface of 2205 DSS was almost undamaged by corrosion.

Evolution of the Geometric Structure of X39Cr13 Steel upon Thermochemical Treatment Specific to Medical-Grade Steels

This paper presents the results of the multi-aspect surface characterization of X39Cr13 steel samples subjected to technological processes specific to medical instrumentation, such as heat and thermochemical treatment, as well as sterilization, which are implemented in corrosion resistance measurements. The application of numerical methods of fractal analysis to averaged profiles obtained from SEM images resulted in double-log plots of structure function, from which the determination of the fractal parameters of interest was possible. The discussion was focused on the fractal dimension D, which governs relative height variations upon scaling in length, and corner frequency fc, which separates the scaling behavior of different-order structures (particles and their aggregates). The obtained results show that the heat treatment leaves behind a granular structure of steel (D2 = 2.43; fc2 = 1.97 nm), whereas corrosion tests reveal the appearance of pits (D1 = 2.17; fc1 = 0.303 nm; D2 = 2.59; fc2 = 4.76 nm). In turn, the ion nitriding improves the resistance of steel X39Cr13 to local corrosion. The fractal analysis also shows that the structure of the nitrided layer differs insignificantly from that of the untreated material, seen only as a shortening of the radius of the self-similarity area by a factor of two (fc2 = 1 nm).