Corrosion Resistance of Aluminum Alloy AA2024 with Hard Anodizing in Sulfuric Acid-Free Solution

In the aeronautical industry, Al-Cu alloys are used as a structural material in the manufacturing of commercial aircraft due to their high mechanical properties and low density. One of the main issues with these Al-Cu alloy systems is their low corrosion resistance in aggressive substances; as a result, Al-Cu alloys are electrochemically treated by anodizing processes to increase their corrosion resistance. Hard anodizing realized on AA2024 was performed in citric and sulfuric acid solutions for 60 min with constant stirring using current densities 3 and 4.5 A/dm². After anodizing, a 60 min sealing procedure in water at 95 °C was performed. Scanning electron microscopy (SEM) and Vickers microhardness (HV) measurements were used to characterize the microstructure and mechanical properties of the hard anodizing material. Electrochemical corrosion was carried out using cyclic potentiodynamic polarization curves (CPP) and electrochemical impedance spectroscopy (EIS) in a 3.5 wt. % NaCl solution. The results indicate that the corrosion resistance of Al-Cu alloys in citric acid solutions with a current density 4.5 A/dm² was the best, with corrosion current densities of 2 × 10⁻⁸ and 2 × 10⁻⁹ A/cm². Citric acid-anodized samples had a higher corrosion resistance than un-anodized materials, making citric acid a viable alternative for fabricating hard-anodized Al-Cu alloys.     

Local Electrochemical Corrosion Properties of a Nano-SiO2/MAO Composite Coating on an AM60B-Mg Alloy

In order to improve the corrosion resistance of the automotive AM60B-Mg alloy, a nano-SiO₂/MAO composite coating was prepared on the surface of the alloy. The electrochemical properties were studied in an 80 °C corrosion environment using potentiodynamic polarization tests. Local Electrochemical Impedance Spectroscopy (LEIS) was used to study the corrosion mechanisms of coating defect zone. The microstructure and phase of the samples were observed by confocal laser microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Macroscopic electrochemical test results showed that the impedance of the nano-SiO₂/MAO coating was much higher than that of the MAO coating, by about 433 times. Local electrochemical test results showed that the minimum impedance of the nano-SiO₂/MAO coating was 1–2 orders of magnitude higher than the maximum impedance of the MAO coating. The defective SiO₂/MAO coating still had high corrosion resistance compared to the defective MAO coating. A physical model of local corrosion mechanisms was proposed.     

Optimization of Alumina Ceramics Corrosion Resistance in Nitric Acid

The development of ceramic materials resistance in various aggressive media combined with required mechanical properties is of considerable importance for enabling the wider application of ceramics. The corrosion resistance of ceramic materials depends on their purity and microstructure, the kind of aggressive media used and the ambient temperature. Therefore, the corrosion resistance of alumina ceramics in aqueous HNO₃ solutions of concentrations of 0.50 mol dm⁻³, 1.25 mol dm⁻³ and 2.00 mol dm⁻³ and different exposure times—up to 10 days—have been studied. The influence of temperature (25, 40 and 55 °C) was also monitored. The evaluation of Al₂O₃ ceramics corrosion resistance was based on the concentration measurements of eluted Al³⁺, Ca²⁺, Fe³⁺, Mg²⁺, Na⁺ and Si⁴⁺ ions obtained by inductively coupled plasma atomic emission spectrometry (ICP-AES), as well as density measurements of the investigated alumina ceramics. The response surface methodology (RSM) was used for the optimization of parameters within the experimental “sample-corrosive media” area. The exposure of alumina ceramics to aqueous HNO₃ solutions was conducted according to the Box–Behnken design. After the regression functions were defined, conditions to achieve the maximum corrosion resistance of the sintered ceramics were determined by optimization within the experimental area.     

Investigation of MAO Coatings Characteristics on Titanium Products Obtained by EBM Method Using Additive Manufacturing

Coatings with a thickness from 27 to 62 µm on electron beam melted Ti-6Al-4V have been formed by micro-arc oxidation (MAO) in a silicate-hypophosphite electrolyte. MAO tests in the anode-cathode mode (50 Hz) with an anode-to-cathode current ratio of 1:1 and sum current densities 10 and 20 A/dm² were carried out. The duration of the MAO treatment was 30 and 60 min. The effect of the processing parameters on the structural properties of the MAO treated coatings was studied. The current density and treatment time significantly affect the coating thickness and surface roughness. The values of these characteristics increase as the current density increases. The effect of thermal cycling tests on surface morphology, thickness and roughness, and elemental and phase composition of MAO coatings was analyzed. After 50 cycles of thermal cycling from +200 °C to −50 °C, no cracking or delamination of coatings was observed. Coatings formed in 30 min at a current density of 20 A/dm² turned out to be the best in terms of such indicators as surface morphology, thickness, and roughness.     

Glass-Forming Ability and Corrosion Resistance of Al88Y8−xFe4+x (x = 0, 1, 2 at.%) Alloys

The effect of iron and yttrium additions on glass forming ability and corrosion resistance of Al₈₈Y_8-xFe_4+x (x = 0, 1, 2 at.%) alloys in the form of ingots and melt-spun ribbons was investigated. The crystalline multiphase structure of ingots and amorphous-crystalline structure of ribbons were examined by a number of analytical techniques including X-ray diffraction, Mössbauer spectroscopy, and transmission electron microscopy. It was confirmed that the higher Fe additions contributed to formation of amorphous structures. The impact of chemical composition and structure of alloys on their corrosion resistance was characterized by electrochemical tests in 3.5% NaCl solution at 25 °C. The identification of the mechanism of chemical reactions taking place during polarization test along with the morphology and internal structure of the surface oxide films generated was performed. It was revealed that the best corrosion resistance was achieved for the Al₈₈Y₇Fe₅ alloy in the form of ribbon, which exhibited the lowest corrosion current density (j_corr = 0.09 μA/cm²) and the highest polarization resistance (R_p = 96.7 kΩ∙cm²).     

The Influence of Casein Coatings on the Corrosion Behavior of Mg-Based Alloys

This article discusses the influence of conversion casein coatings with a thickness of about 20 µm on the structure and the corrosion behavior of two magnesium alloys: MgCa2Zn1 and MgCa2Zn1Gd3. Casein is a protein that, along with whey protein, is a part of milk. Casein coatings are appropriate for bone growth because they contain high amounts of calcium and phosphorus. In this work, casein coatings and casein-free coatings were applied on Mg-based alloys using the conversion process. The structure and topography observations were presented. The corrosion behavior was determined by electrochemical and immersion tests, and electrochemical impedance spectroscopy (EIS) in chloride-rich Ringer solution. The obtained results show that conversion casein coatings effectively protect Mg-based alloys against corrosion. This was confirmed by higher corrosion potentials (E_corr), polarization resistances (R_p) derived from Tafel’s and EIS analysis, as well as low hydrogen release. The volume of hydrogen released after 216 h of immersion for casein coatings applied to MgCa2Zn1 and MgCa2Zn1Gd3 alloys was 19.25 and 12.42 mL/cm², respectively. The improvement in corrosion resistance of casein coatings was more significant for Mg alloy dopped with gadolinium. The lower corrosion rate of casein conversion coatings is explained by the synergistic effect of the addition of Gd in the Mg-based alloy and the formation of dense, tight conversion casein coatings on the surface of this alloy.     

Investigation of the Structure and Corrosion Resistance of Novel High-Entropy Alloys for Potential Biomedical Applications

High-entropy alloys are a new generation of materials that have attracted the interest of numerous scientists because of their unusual properties. It seems interesting to use these alloys in biomedical applications. However, for this purpose, the basic condition of corrosion resistance must be fulfilled. In this article, selected corrosion properties of self-composed high-entropy alloys are investigated and compared with conventional biomedical alloys, that is titanium alloys and stainless steels. Corrosive parameters were determined using the potentiodynamic method. X-ray diffraction studies were performed to characterize the crystal structures. Microstructures of the prepared materials were examined using a scanning electron microscope, and surface hardness was measured by the Vickers method. The results show that investigated high-entropy alloys are characterized by simple structures. Three out of four tested high-entropy alloys had better corrosion properties than conventional implant alloys used in medicine. The Al_0.7CoCrFeNi alloy was characterized by a corrosion potential of −224 mV and a corrosion current density of 0.9 μA/cm²; CoCrFeNiCu by −210 mV and 1.1 μA/cm²; TiAlFeCoNi by −435 mV and 4.6 μA/cm²; and Mn_0.5TiCuAlCr by −253 mV and 1.3 μA/cm², respectively. Therefore, the proposed high-entropy alloys can be considered as potential materials for biomedical applications, but this requires more studies to confirm their biocompatibility.     

Surface Treatment of Zn-Mn-Mg Alloys by Micro-Arc Oxidation in Silicate-Based Solutions with Different NaF Concentrations

Newly developed Zn-Mn-Mg alloys can be invoked as biomedical materials because of their excellent mechanical properties. However, the corrosion behavior of Zn-Mn-Mg alloys was still lacking in research. It had grown to be a hot research topic to improve the corrosion behavior of Zn alloys by surface treatment to meet the application of degradable Zn alloys in biomedical applications. Micro arc oxidation (MAO) is a simple and effective method to improve the corrosion behavior of the alloy. MAO coatings were successfully prepared on the surface of Zn-Mn-Mg alloys by MAO in silicate-based solutions with different NaF concentrations. The microstructure and phase composition of MAO coatings prepared on Zn-Mn-Mg alloys with different NaF concentrations in the electrolyte was examined by a scanning electron microscope and X-ray diffraction. The results showed that the MAO coatings are porous and mainly composed of ZnO. With the increasing NaF concentration in the electrolyte, the average thickness increases. The distribution of the micro/nanopores was uniform, and the pore size ranged from the submicron scale to several micrometers after MAO treatment in the electrolyte containing different concentrations of NaF. Potential dynamic polarization curves and electrochemical impedance spectroscopy were employed to assess the corrosion behavior of MAO coatings in Hank’s solution. The highest corrosion rate can be achieved after MAO treatment, with an electrolyte concentration of 1.5 g/L NaF in Hank’s solution. These results indicated that MAO coating can accelerate the corrosion resistance of a Zn-Mn-Mg alloy.     

Statistical Optimisation of Chemical Stability of Hybrid Microwave-Sintered Alumina Ceramics in Nitric Acid

The goal of this research is the statistical optimisation of the chemical stability of hybrid microwave-sintered alumina ceramics in nitric acid. The chemical stability of ceramic materials in corrosive media depends on many parameters, such as the chemical and phase composition of the ceramics, the properties of the aggressive medium (concentration, temperature, and pressure), and the exposure time. Therefore, the chemical stability of alumina ceramics in different aqueous nitric acid solution concentrations (0.50 mol dm⁻³, 1.25 mol dm⁻³, and 2.00 mol dm⁻³), different exposure times (up to 10 days), as well as different temperatures (25, 40, and 55 °C), was investigated, modelled, and optimised. The chemical stability of high purity alumina ceramics (99.8345 wt.% of Al₂O₃) was determined by measuring the amount of eluted ions (Al³⁺, Ca²⁺, Fe³⁺, Mg²⁺, Na⁺, and Si⁴⁺) obtained by inductively coupled plasma atomic emission spectrometry. The changes in the density of alumina ceramics during the chemical stability monitoring were also determined. The Box–Behnken approach was employed to reach the optimum conditions for obtaining the highest possible chemical stability of alumina at a given temperature range, exposure time, and molar concentration of nitric acid. It was found that an increase in exposure time, temperature, and nitric acid concentration led to an increase in the elution of ions from hybrid microwave-sintered alumina. Higher amounts of eluted ions, Al³⁺ (14.805 µg cm⁻²), Ca²⁺ (7.079 µg cm⁻²), Fe³⁺ (0.361 µg cm⁻²), Mg²⁺ (3.654 µg cm⁻²), and Na⁺ ions (13.261 µg cm⁻²), were obtained at 55 °C in the 2 mol dm^{− 3} nitric acid. The amount of eluted Si⁴⁺ ions is below the detection limit of inductively coupled plasma atomic emission spectrometry. The change in the alumina ceramic density during the corrosion test was negligible.     

The Effect of Increasing Nickel Content on the Microstructure,Hardness, and Corrosion Resistance of the CuFeTiZrNix High-Entropy Alloys

In recent years, high-entropy alloys (HEAs) that contain fine grains of intermetallic compounds (IMCs) have gained increasing attention as they have been shown to exhibit both high mechanical strength and strong corrosion resistance. One such class of HEAs is that of CuFeTiZrNi alloys. In this study, we have investigated the effect of increasing Ni content on the microstructure, hardness, and corrosion resistance of the CuFeTiZrNi_x alloys (where x = 0.1, 0.3, 0.5, 0.8, 1.0 in a molar ratio). The alloys used in this study were prepared in an arc melting furnace and then annealed at 900 °C. First-principles calculations of the bulk modulus were also performed for each alloy. The results revealed that increasing the Ni content had several effects. Firstly, the microstructure of the CuFeTiZrNi_x alloys changed from B2_BCC and Laves_C14 in the CuFeTiZrNi_0.1 and CuFeTiZrNi_0.3 alloys to FCC, B2_BCC, and Laves_C14 in the CuFeTiZrNi_0.5 alloys; and to FCC, B2_BCC, Cu₅₁Zr₁₄, and Laves_C14 in the CuFeTiZrNi_0.8 and CuFeTiZrNi_1.0 alloys. Secondly, IMCs arising from a combination of the refractory elements (Ti and Zr) and atomic size differences were found in the interdendritic region. Thirdly, as the Ni content in the CuFeTiZrNi_x alloys increased, the hardness decreased, but the corrosion resistance increased.     

Influence of the Nb and V Addition on the Microstructure and Corrosion Resistance of the Fe-B-Co-Si Alloy

The paper presents a comparison of the results of the corrosion resistance for three Fe-B-Co-Si-based newly developed alloys with the addition of Nb and V. The corrosion performance differences and microstructure variations were systematically studied using scanning electron microscope, electric corrosion equipment, X-ray diffractometer, and differential calorimeter. It has been shown that each alloying addition increased the corrosion resistance. The highest corrosion resistance obtained by potentiodynamic polarization was found for the alloy with both Nb and V addons (Fe₅₇Co₁₀B₂₀Si₅Nb₄V₄) and lowest in the case of the basic four-element Fe₆₂Co₁₅B₁₄Si₉ material. This shows that the proper choice of additions is of significant influence on the final performance of the alloy and allows tailoring of the material for specific applications.     

Effect of (NH4)2ZrF6, Voltage and Treating Time on Corrosion Resistance of Micro-Arc Oxidation Coatings Applied on ZK61M Magnesium Alloys

The effects of (NH₄)₂ZrF₆ concentration, voltage and treating time on the corrosion resistance of ZK61M magnesium alloy micro-arc oxidation coatings were studied by orthogonal experiments. The SEM result shows that the surface roughness and porosity of MAO coatings increased with (NH₄)₂ZrF₆ concentration, voltage and treating time as a whole, except the porosity decreased with treating time. EDS, XRD and XPS analysis show that (NH₄)₂ZrF₆ was successfully incorporated into coatings by reactive incorporation, coatings are dominantly composed of ZrO₂, MgO, MgF₂ and amorphous phase Mg phosphate. Potentiodynamic polarization was used to evaluate the corrosion property of coatings. When the concentration of (NH₄)₂ZrF₆ is 6 g/L, the voltage is 450 V, and the treating time is 15 min, the coating exhibits the best corrosion resistance which corrosion current density is four magnitudes lower than substrate attributed to the incorporation of ZrO₂ and the deposition of MgF₂ in the micropores.     

Corrosion Behavior of CrFeCoNiVx (x = 0.5 and 1) High-Entropy Alloys in 1M Sulfuric Acid and 1M Hydrochloric Acid Solutions

CrFeCoNiV_x high-entropy alloys were prepared by arc-melting, and the microstructures and corrosion properties of these alloys were studied. The CrFeCoNiV_0.5 alloy had a granular structure; the matrix was a face-centered cubic (FCC) structure, and the second phase was a σ phase with a tetragonal structure. The CrFeCoNiV alloy had a dendritic structure; the dendrites in this alloy showed an FCC phase, and the interdendrities had a eutectic structure of FCC and σ phases. Therefore, CrFeCoNiV was much harder than the CrFeCoNiV_0.5 alloy due to the dendritic structures. The potentiodynamic polarization test and electrochemical impedance spectroscopy were used to evaluate the corrosion behavior of the CrFeCoNiV_x high-entropy alloys in deaerated 1M sulfuric acid and 1M hydrochloric acid solutions. The results indicated that the CrFeCoNiV_0.5 alloy had a better corrosion resistance because of the granular structure.     

Corrosion Behavior of Ultrafine-Grained CoCrFeMnNi High-Entropy Alloys Fabricated by High-Pressure Torsion

The influence of the nanocrystalline structure produced by severe plastic deformation (SPD) on the corrosion behavior of CoCrFeMnNi alloys with Cr contents ranging from 0 to 20 at.% was investigated in aqueous 0.5 M H₂SO₄ and 3.5% NaCl solutions. The resistance to general corrosion and pitting became higher in both the solutions, with higher passivation capability observed with increasing Cr content, and it is believed that the high corrosion resistance of CoCrFeMnNi alloys can be attributed to the incorporation of the Cr element. However, the impact of the nanocrystalline structure produced by SPD on the corrosion behavior was negligibly small. This is inconsistent with reports on nanocrystalline binary Fe–Cr alloys and stainless steels processed by SPD, where grain refinement by SPD results in higher corrosion resistance. The small change in the corrosion behavior with respect to grain refinement is discussed, based on the passivation process of Fe–Cr alloys and on the influence of the core effects of HEAs on the passivation process.     

Comparative Study on the Corrosion Resistance of 6061Al and SiC3D/6061Al Composite in a Chloride Environment

Interface problems and the destruction of the continuity of the oxide film in the Al matrix usually reduce the corrosion resistance of the material. In this paper, the corrosion resistance of Al matrix composites (AMCs) was improved by introducing the silicon carbide skeletons (SiC_3D) obtained with polymer replica technology. SiC_3D/6061Al was fabricated by infiltrating molten 6061Al alloy in the oxidized SiC_3D using the low-pressure casting method. The corrosion resistance performances of 6061Al and SiC_3D/6061Al in NaCl solution were studied by electrochemical, neutral salt spray corrosion (NSS), and salt leaching (SL) tests. Results show corrosion resistance of SiC_3D/6061Al is higher than that of 6061Al alloys by open circuit potential (OCP), potentio-dynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS) tests. However, NSS and SL tests show the corrosion resistance of SiC_3D/6061Al is lower than that of 6061Al alloy. The reason is a corrosion resistant and anti-oxidation network macrostructure with large interface recombination, few concentrated interfaces, and a small specific area that formed in SiC_3D/6061Al. SiC_3D cannot damage the continuity of the Al₂O₃ passivating film, and the network macrostructure greatly improves the corrosion resistance performance.     

Influence of Hydrated Lime on the Chloride-Induced Reinforcement Corrosion in Eco-Efficient Concretes Made with High-Volume Fly Ash

The main objective of this study was to analyze the influence that the addition of finely ground hydrated lime has on chloride-induced reinforcement corrosion in eco-efficient concrete made with 50% cement replacement by fly ash. Six tests were carried out: mercury intrusion porosimetry, chloride migration, accelerated chloride penetration, electrical resistivity, and corrosion rate. The results show that the addition of 10–20% of lime to fly ash concrete did not affect its resistance to chloride penetration. However, the cementitious matrix density is increased by the pozzolanic reaction between the fly ash and added lime. As a result, the porosity and the electrical resistivity improved (of the order of 10% and 40%, respectively), giving rise to a lower corrosion rate (i_CORR) of the rebars and, therefore, an increase in durability. In fact, after subjecting specimens to wetting–drying cycles in a 0.5 M sodium chloride solution for 630 days, corrosion is considered negligible in fly ash concrete with 10% or 20% lime (i_CORR less than 0.2 µA/cm²), while in fly ash concrete without lime, corrosion was low (i_CORR of the order of 0.3 µA/cm²) and in the reference concrete made with Portland cement, only the corrosion was high (i_CORR between 2 and 3 µA/cm²).     

Effect of Pre-Oxidation Treatment on Corrosion Resistance of FeCoSiBPC Amorphous Alloy

In this paper, the corrosion resistance of FeCoSiBPC amorphous alloy after pre-oxidation and non-oxidation heat treatment is investigated. The corrosion behaviors of Fe₈₀Co₃Si₃B₁₀P₁C₃ amorphous alloys in 1 mol/L NaCl solution were investigated by the electrochemical workstation. The pre-oxidation heat treatment can improve the corrosion resistance of FeCoSiBPC amorphous alloy through an increase in the Ecorr value from −0.736 to −0.668 V, which makes it easy to reach a passive state. The corroded morphology and products of amorphous alloys were tested by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The SEM/TEM analysis showed that, after pre-oxidation treatment, the oxide layer was divided into two layers: the inner layer was amorphous, the outer layer appeared crystalline, and the main oxide was Fe₂O₃. During the oxidation process, Co and P elements diffused from the inner layer to the outer layer, forming phosphorus and cobalt oxides with high corrosion resistance on the surface of the ribbon, thereby improving the corrosion resistance of the ribbon.     

The Microstructure Evolution and Electrochemical Corrosion Behavior of 7A46 Aluminum Alloy in Different Quenching Conditions

The quenching condition of aluminum alloy can affect the mechanical property and corrosion resistance of the profile. This paper is aimed at the low quench sensitivity of aluminum alloys. Scanning electron microscopy and transmission electron microscopy were used to analyze precipitate behaviors of the 7A46 aluminum alloy under different isothermal cooling conditions and microstructure evolutions of quench-induced precipitations. The effect of the different isothermal time on the corrosion resistance of the alloy, and the relationship between microstructure and corrosion resistance after quenching were revealed through electrochemical impedance spectroscopy and potentiodynamic polarization tests. Results show that corrosion sensitivity of the quenching-aged alloy is much higher than that of the double-aged (DA) alloy, and the corrosion resistance of the quenched alloy decreases firstly and then increases. Due to the high density of the matrix precipitates, the increased content of the impurity element, the discontinuity of the grain boundary precipitates and the widening of the precipitates free zone, the most serious degree of corrosion performance among the quenched alloys is 295 °C at 800 s, and the self-corrosion potential and self-current density is −0.919 V and 2.371 μA/cm², respectively.     

Effect of Cr on Aqueous and Atmospheric Corrosion of Automotive Carbon Steel

This study investigated the effect of Cr alloying element on the corrosion properties of automotive carbon steel (0.1C, 0.5Si, 2.5Mn, Fe Bal., composition given in wt.%) in aqueous and atmospheric conditions using electrochemical measurement and cyclic corrosion tests. Three steels with 0, 0.3, and 0.5 wt.% Cr were studied by electrochemical impedance spectroscopy. Polarization resistance (R_p) of 0.3 Cr and 0.5 Cr steels was higher than that of 0 Cr steel, and the R_p also increased as the Cr content increased. Therefore, Cr increases the corrosion resistance of automotive carbon steel immersed in a chloride ion (Cl⁻)-containing aqueous solution. In the cyclic corrosion test results, Cl⁻ was concentrated at the metal/rust interface in all of the steels regardless of Cr content. The Cl⁻ was uniformly concentrated and distributed on the 0 Cr steel, but locally and non-uniformly concentrated on the Cr-added steels. The inner rust layer consisted of β-FeOOH containing Cl⁻ and Cr-goethite, while the outer rust layer was composed of amorphous iron oxyhydroxide mixed with various types of rust. FeCl₂ and CrCl₃ are formed from the Cl⁻ nest developed in the early stage, and the pitting at CrCl₃-formed regions are locally accelerated because Cr is strongly hydrolyzed to a very low pH.     

Influence of Surface Modification of Titanium and Its Alloys for Medical Implants on Their Corrosion Behavior

Titanium and its alloys are often used for long-term implants after their surface treatment. Such surface modification is usually performed to improve biological properties but seldom to increase corrosion resistance. This paper presents research results performed on such metallic materials modified by a variety of techniques: direct voltage anodic oxidation in the presence of fluorides, micro-arc oxidation (MAO), pulse laser treatment, deposition of chitosan, biodegradable Eudragit 100 and poly(4-vinylpyridine (P4VP), carbon nanotubes, nanoparticles of TiO₂, and chitosan with Pt (nano Pt) and polymeric dispersant. The open circuit potential, corrosion current density, and potential values were determined by potentiodynamic technique, and microstructures of the surface layers and coatings were characterized by scanning electron microscopy. The results show that despite the applied modifications, the corrosion current density still appears in the region of very low values of some nA/cm². However, almost all surface modifications, designed principally for the improvement of biological properties, negatively influence corrosion resistance. The reasons for observed effects can vary, such as imperfections and permeability of some coatings or accelerated degradation of biodegradable deposits in simulated body fluids during electrochemical testing. Despite that, all coatings can be accepted for biological applications, and such corrosion testing results are presumed not to be of major importance for their applications in medicine.