Dense, highly textured, hydrophobic ZrO₂-TiO₂ (1:1) coatings with amorphous structure were prepared using the sol-gel method. Both organic and inorganic zirconium precursor salts were used. The present study dealt with the investigation of their protective ability in a selected model corrosive medium with chloride ions as corrosion activators. The coatings showed good anticorrosion performance during the test, which was demonstrated both by the weight loss method and potentiodynamic polarization curves. The samples were characterized by means of X-ray diffraction (XRD), Atomic Force Microscopy (AFM), contact angle measurements, Infrared spectroscopy (IRS), Scanning Electron Microscopy (SEM), Differential Thermal analysis (DTA-TG) and X-ray photoelectron spectroscopy (XPS). It was established that the extent of influence of some factors, like treatment temperature (T_tr) and type of zirconium precursor, was different. The PD curves of samples treated at 400 °C (A4 and B4, respectively) demonstrated an increased effect of the precursor in comparison to T_tr, since the application of organic Zr salt led to deterioration of the anodic passivation zones. Contrary to this, the coatings obtained from both the organic and inorganic Zr precursor salts with T_tr = 500 °C had similar corrosion efficiency, i.e., the influence of the precursor was minimized. All investigated coatings had no visible corrosion damage. It seems that some complex structural and surface parameters, such as amorphous dense structure, surface smoothness, hydrophobicity and the surface chemical composition (low hydroxyl groups content), were responsible for the increased anticorrosion properties of the composite films.

The construction of anticorrosion coatings containing antifouling agents is an effective way to ensure the long-term durability of marine steel infrastructures. In this work, an innovative hybrid coating was prepared by introducing biocide CuO nanoparticles in ordinary zinc coating to improve its protective ability for steel in aggressive salt water environments. The CuO nanoparticles were embedded inside the matrix of chitosan/alginate complexes to prevent spontaneous copper leaching during corrosive attacks. Two procedures were applied for the electrodeposition of hybrid/composite zinc-based coatings on low-carbon steel substrates (DC current): first—the co-electrodeposition of encapsulated CuO nanoparticles with zinc on a cathode (steel) electrode from a sulfate electrolyte with a relatively low pH value of about 4.5–5.0 and second—the encapsulated CuO nanoparticles were electrodeposited from aqueous solution as an intermediate layer between two zinc deposits. The particles size and stability of suspensions were evaluated using dynamic light scattering. Both hybrid coatings were compared in terms of surface morphology and hydrophilicity (SEM and AFM analysis, contact angle measurement) and corrosion resistance (potentiodynamic polarization curves, polarization resistance). The protective characteristics of the coatings were compared in a 3.5% NaCl solution and artificial sea water. The hybrid coating showed 2–4 times higher polarization resistance than the bare zinc coating during a 30 day immersion in artificial sea water, indicating that this coating has the necessary characteristics to be used in a marine environment.

Enhanced corrosion efficiency of low-carbon steel was achieved by newly developed hybrid multilayers, composed of low-carbon steel coated with an electrodeposited zinc sublayer (1 µm), a chitosan (CS) middle layer and ZrO₂ coating by the sol–gel method (top-layer). The middle chitosan layer was obtained by dipping galvanized steel substrate in 3% tartatic acid water solution of medium molecular-weight chitosan, composed of β-(1–4)-linked D-glucosamine and N-acetyl-D-glucosamine with a deacetylation degree of about 75–85% (CS). The substrates were dipped into CS solution and withdrawn at a rate of 30 mm/min. One part of the samples with the CS layer was dried at room temperature for 2 weeks, and another part at 100 °C for 1 h, respectively. After CS deposition treatment, the substrates were dipped into an isopropanol sol of zirconium butoxide with small quantity of polyethylene glycol (PEG400). The dipping-drying cycles of the ZrO₂ coatings were repeated three times. After the third cycle, the final structures were treated at 180 °C. The samples were denoted as T25, which consists of the CS middle layer, and dried at RT and T100 with the CS middle layer treated at 100 °C, respectively. The samples were characterized by means of differential thermal analysis (DTA-TG), XRD analyses, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Hydrophobicity properties were evaluated by measuring the contact angle with a ramé-hart automated goniometer. Two electrochemical tests—potentiodynamic polarization technique (PD) and electrochemical impedance spectroscopy (EIS)—have been used to determine the corrosion resistance and protective ability of the coatings in a 5% NaCl solution. The results obtained by both methods revealed that the applied “sandwich” multilayer systems demonstrate sacrificial character and will hopefully protect the steel substrate in corrosion medium containing chloride ions as corrosion activators. The newly obtained hybrid multilayer coating systems have dense structure and a hydrophobic nature. They demonstrated positive effects on the corrosion behavior at conditions of external polarization independent of their various characteristics: morphology, grain sizes, surface roughness and contact angle. They extend the service life of galvanized steel in a chloride-containing corrosion medium due to their amorphous structure, hydrophobic surface and the combination of the positive features of both the chitosan middle layer and the zirconia top layer.

The presented investigations demonstrate the corrosion behavior and protective ability of hybrid zinc coatings specially designed for combined protection of low-carbon steel from localized corrosion and biofouling. Polymer-modified copper oxide (CuO) nanoparticles as widely used classic biocide are applied for this purpose, being simultaneously electrodeposited with zinc from electrolytic bath. The corrosion behavior of the hybrid coatings is evaluated in a model corrosive medium of 5% NaCl solution and in artificial sea water (ASW). Scanning electron microscopy (SEM) and atomic force microscopy (AFM) are used to characterize the surface morphology of pure and hybrid zinc coatings. Contact angle measurements are realized with an aim to determine the hydrophobicity of the surface. X-ray photoelectron spectroscopy (XPS) is applied for evaluation of the chemical composition of the surface products appearing as a result of the corrosion treatment. Potentiodynamic polarization (PDP) curves and polarization resistance (Rp) measurements are used to estimate the protective characteristics in both model corrosive media. The results obtained for the hybrid coatings are compared with the corrosion characteristics of ordinary zinc coating with the same thickness. It was found that the hybrid coating improves the anticorrosion behavior of low-carbon steel during the time interval of 35 days and at conditions of external polarization. The tests demonstrate much larger corrosion resistance of the hybrid coating in ASW compared to 5% NaCl solution. The obtained results indicated that the proposed hybrid zinc coating has a potential for antifouling application in marine environment.

This study aimed to present the differences in the corrosion properties and protective ability of two bi-layer systems obtained on low-carbon steel in a model corrosive medium of 5% NaCl solution. These newly developed systems consist of Zn-Co (3 wt.%) or Zn-Ni (10 wt.%) alloy coatings as under-layers and a very thin TiO₂ sol-gel film as a top-layer. Scanning electron microscopy (SEM) is used for characterization of the surface morphology of the samples indicating that some quantitative differences appear as a result of the different composition of both zinc alloys. Surface topography is investigated by means of atomic force microscopy (AFM), and the hydrophobic properties are studied by contact angle (CA) measurements. These investigations demonstrate that both sample types possess grain nanometric surface morphology and that the contact angle decreases very slightly. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) are used for characterization of the chemical composition and electronic structure of the samples. The roughness R_q of the Zn-Ni/TiO₂ is 49.5 nm, while for Zn-Co/TiO₂, the R_q value is 53.4 nm. The water contact angels are 93.2 and 95.5 for the Zn-Ni/TiO₂ and Zn-Co/TiO₂ systems, respectively. These investigations also show that the co-deposition of Zn and Ni forms a coating consisting entirely of Ni₂Zn₁₁, while the other alloy contains Zn, Co and the intermetallic compound CoZn₁₃. The corrosion resistance and protective ability are estimated by potentiodynamic polarization (PDP) curves, as well as polarization resistance (R_p) measurements for a prolonged test period (35 days). The results obtained are compared with the corrosion characteristics of ordinary zinc coating with an equal thickness. The experimental data presents the positive influence of the newly developed systems on the enhanced protective properties of low-carbon steel in a test environment causing a localized corrosion—lower corrosion current density of about one magnitude of order (~10⁻⁶ A.cm⁻² for both systems and ~10⁻⁵ A.cm⁻² for Zn) and an enhanced protective ability after 35 days (~10,000–17,000 ohms for the systems and ~900 ohms for Zn).

The mechanical properties, structure, and morphology of milled and 3D-printed Ti-6Al-4V alloys produced by selective laser melting were investigated in this study. The mechanical properties were investigated by means of nanoindentation, a tensile test, and a three-point bending test. An Atomic Force Microscope (AFM) was used to study the surface topography and roughness of both titanium alloys. The surface structure and phase analyses were studied by a scanning electron microscope (SEM) and through powder X-ray diffraction (XRD). The results from the nanoindentation experiments showed that the 3D-printed sample has higher indentation hardness and modulus than the milled one. The AFM observation of the surface topography of the samples showed that the milled sample has a higher roughness than the 3D-printed one. The tensile test results showed that the 3D-printed sample by means of Selective Laser Melting (SLM) technology has about 26% higher tensile strength and smaller elongation than the milled one. The three-point bending test revealed that the 3D-printed Ti-6Al-4V sample has higher flexural strength than the milled one. It was found that the 3D-printed sample has a smaller crystal size than the milled one, which, according to the Hall–Petch relationship, leads to its higher indentation hardness.