Polarization Tests Research Articles

Surface microstructure and corrosion characterization of AZ31 magnesium alloys fabricated by laser surface-modification

This study aimed to improve the corrosion resistance of Mg alloys, and to this end, AZ31 Mg alloy was subjected to laser surface re-melting using a fiber laser. Subsequently, a comparative analysis was conducted on the microstructures of the re-melted surfaces under various laser power settings, and the influence of laser surface re-melting on corrosion characteristics was investigated through a potentiodynamic polarization test. The test results show that laser surface re-melting produced a distinct reduction in the crystallite size of magnesium, ranging from 11.23–15.80 μm within the laser-melted layers. The maximum melted layer thickness of 820 μm was achieved with a laser power of 2100 W. The process of laser surface re-melting notably heightened the hardness, particularly as the power increased, which was attributed to swift solidification. The most noteworthy hardness measurement of 92.1 HV0.02 was recorded at 2100 W. Thus, the study shows that laser surface re-melting significantly enhances the corrosion resistance of Mg alloys, primarily owing to the formation of a corrosion product. The smaller grain size on the surface contributes to the formation of a dense product film.

Corrosion behaviors of single-layer and double-layer nickel alloy coatings fabricated by arc spraying and high-velocity oxy-fuel

This study investigates single-layer and double-layer thermally sprayed nickel alloy coatings (bond and top coatings). Ni-5 wt% Al and Ni-20 wt% Cr were used as bond coatings, whereas highly alloyed Ni-based coatings, Hastelloy C276 or Inconel 625 were used as top coatings. Arc spraying (A) and high-velocity oxy-fuel (HVOF) techniques were used to create the coatings on a 304 stainless steel substrate. The samples were studied by performing potentiodynamic polarization tests in a 20 vol% H2SO4 solution at room temperature. The scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS) and wavelength dispersive X-ray spectroscopy (WDS) techniques were used to investigate the microstructure and chemical composition of the coatings. The arc sprayed coatings are composed of a lamellar microstructure with low porosities, unmelted particles, and high oxides at the intersplats. A uniform and compact coating with minimal oxides and porosity was achieved for all coatings via HVOF technique. In single-layer coatings, arc spray coating surpasses HVOF coating owing to its oxide layers, which impede sulfuric solution penetration and bolster resistance against electrolyte infiltration. Double-layer coatings, comprising a bonding layer and a top coating, using the same thermal spray method have shown to enhance corrosion resistance.

Photoelectrochemical CO2 reduction in tandem photoelectrode cells: Interpretation of apparent photocurrents

Photoelectrochemical reactors harness solar energy to accelerate heterogeneous chemical reactions and reduce power consumption for a given reaction rate. The tandem photoelectrochemical cell design presented here employs a light penetrable TiO2 photoanode||Cu2O photocathode configuration that enables carbon dioxide turnover at limited cell voltages. During polarization tests, the tandem configuration demonstrated a photocurrent density of 0.2 mA/cm2 at a cell voltage of -2.6 V. That is 2-fold higher than the photocurrent density obtained with a solo photoanode (Cu||TiO2) and five orders of magnitude higher compared to the solo photocathode (Cu2O||Ni) design. Moreover, electrolysis under illumination (photoelectrolysis) showed a current density increase of 3.9 mA/cm2 with respect to electrolysis in the dark. However, this photocurrent density was merely apparent and was caused by light-triggered changes in the surface morphology and phase of Cu2O, which in turn affected the catalytic response. Moreover, the apparent partial ethylene photocurrent density and total partial current density during photoelectrolysis was 44 %, the highest among the detected products. That selectivity is attributed to the combined effect of Cu2O photoreduction and the associated local pH rise at the electrode-electrolyte interface.

Selective laser melting of Hastelloy-X alloy and cerium oxide reinforced Hastelloy-X composite: Microstructural examination and corrosion behavior

The study investigated the microstructures and corrosion behaviors of Hastelloy X (HX) and HX reinforced by cerium oxide particles (HX-C) produced by selective laser melting (SLM) and compared to the wrought equivalent (HX-W). The aim was to eliminate hot cracking and investigate the HX's corrosion behavior in the presence of cerium oxide particles. The HX samples showed fine cellular and columnar solidification structures with uniform-size sub-cells and severe microcracking. Incorporating cerium oxide particles (1 wt%) resulted in finer and relatively equiaxed grains without microcracking. The HX-W alloy contained a micron-sized carbide (Mo-rich M6C type) within the matrix. The HX-C sample displayed higher porosities compared to the HX sample (1.8 % against 0.3 %). Potentiodynamic polarization and electrochemical impedance spectroscopy tests were conducted in a standard NaCl solution at temperatures of 25, 50, and 70 °C to assess the corrosion behavior of Hastelloy samples. The HX-C matrix showed superior corrosion resistance compared to the HX-W and HX samples due to its finer grain structure and stable passive layer formation. Cerium oxide particles were found to be efficient in decreasing hot cracking and improving corrosion resistance.

Electrochemical Properties of Nickel-Titanium Rotary Endodontic Instruments

IntroductionNickel-titanium rotary endodontic files have been commercially available for decades, but more recent innovations have introduced heat-treated and surface-treated files. This study investigated the corrosion properties of various nickel-titanium files in normal saline and sodium hypochlorite (NaOCl). MethodsTen different file brands of size 40 with a 0.04 taper were subjected to electrochemical testing in 0.9% NaCl (saline) and 5.25% NaOCl at room temperature. The Open Circuit Potential (OCP) was observed for 1 hour followed by a cyclic polarization test from −300 to 700 mV and back to −300 mV (vs OCP). Nonparametric ANOVA and a pairwise comparison (P < .05) were used for statistical analysis of the OCP at 1 hour and the corrosion current (Icorr) obtained via the cyclic polarization test. ResultsSignificant differences (P < .05) were found between files with respect to OCP and Icorr in both solutions. Nine files exhibited significantly greater (P < .05) Icorrs in NaOCl than in saline. Conversely, pitting corrosion was observed in the saline solution but not NaOCl. Weak and/or moderate correlations existed between OCP and Icorr measures in the 2 solutions. ConclusionSignificant differences in electrochemical properties were observed among the 10 brands of files. Overall, there was not a clear trend between conventional, heat-treated, or surface-treated files among OCP or Icorr in either solution.

Surface modification of biodegradable Mg/HA composite by electrospinning of PCL/HA fibers coating: Mechanical properties, corrosion, and biocompatibility

Mg/HA composite was fabricated using the stir-casting and extrusion processes and coated by electrospun PCL/HA fibers (2.5 and 5 wt.% HA) to enhance the corrosion resistance. The mechanical tests demonstrated an increment of 107% for the compressive yield strength of the composite (151 vs 73 MPa for pure magnesium). SEM, EDS, and XRD analysis illustrated that HA particles distribute in porous coatings. According to the polarization tests, all coated specimens show higher corrosion resistance compared to the uncoated ones. PCL coating reduces the corrosion current density of the sample by two orders of magnitude. The effectiveness of incorporating HA in the coatings was proved by polarization and in vitro corrosion tests. Employment of coatings and subsequent Ca–P layer formation prevents the penetration of simulated body fluid (SBF) and contact with the substrate, thus protecting the surface. PCL/2.5%HA coated sample has the lowest corrosion rate with an average value of 0.98 mm/a by a reduction of 81% compared to the uncoated composite in 14 d. Cell viability enhancement from 43% to 121% was achieved using PCL/2.5%HA coating according to 3 d 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) results. In conclusion, Mg/HA composites coated with PCL/2.5%HA fibers appear promising for bioabsorbable implant applications.

Corrosion behavior of multi-layer friction surfaced structure from dissimilar aluminum alloys

Friction surfacing (FS) is a solid-state coating technology for metallic materials, where the deposition of a consumable material on a substrate is enabled via friction and plastic deformation. The deposited layer material commonly presents a significantly refined microstructure, where corrosion could be an issue due to this grain refinement within the layer deposited, possibly creating micro galvanic pairs. The present work investigates the corrosion behavior of the FS deposited material as well as stud base material and substrate using cyclic polarization tests and open circuit potential (OCP) monitoring. Comparing the FS deposited material and the respective consumable stud base material (both AA5083), the grain size is correlated with the results from the corrosion tests, where the deposited material shows more equiaxed and refined grains in comparison to the stud base material. The cyclic potentiostatic polarization tests showed that the stud base material is more resistant to pitting nucleation presenting smaller pits and a lower amount of pits compared to deposited material and substrate. As a complement to OCP test, the stud base material is also more stable on a chloride solution compared to the substrate and the deposited material.

A study of pomegranate peel extract effect on corrosion inhibition performance on aluminum in HNO3 solution

Green corrosion inhibitors have an important role in reducing the corrosion rate of metals and the effects of toxic chemicals in the environment. In this study, the inhibition effect of pomegranate peel extract (PPE) with concentration of 0.5, 1, 1.5, 2, 2.5 and 3 g/L on the aluminum 1050 alloy corrosion behavior in the nitric acid solution investigates using the weight loss, electrochemical techniques, scanning electron microscope (SEM), atomic force microscope (AFM), contact angle images, gas chromatography-mass spectrometer (GC-MS) analysis, fourier transform Infrared spectroscopy (FTIR) and ultraviolet radiation (UV-IR). And, the (UV-IR), (GC-MS), and FTIR results confirm the presence of many organic compounds (Containing the N, S, and O atoms), which are responsible for inhibitor performance and absorption phenomena. Meanwhile, the electrochemical impedance results (EIS) indicate that the double layer capacity decreases and the corrosion resistance (Corrosion current density (icorr) from 0.128 to 0.009 mA/cm2) increases with the increase of the inhibitor concentration (The inhibition efficiency increased with increasing the inhibitor concentration from % 54.29 to the % 92.58 at (1–3 g/L). In addition, the corrosion current density decreases with the increase of the inhibitor concentration using the potentiodynamic polarization (PDP) test. However, the corrosion rate enhances with increasing the temperature. From the other hand, quantum chemical (QC) calculation and molecular dynamics (MD) simulation perform to investigate the theory of the adsorption mechanism. According to these studies, the adsorption of PPE on the aluminum 1050 alloy surface is agreement with the langmuir isotherm and as a result it is a mixed-type inhibitor. In final the SEM and AFM results show that the corrosion rate of the aluminum 1050 alloy surface is significantly reduced after the addition of the inhibitor to the corrosive environment. Furthermore, the contact angle image shows that the inhibited aluminum surface has a hydrophobic property in an aqueous solution. And, the QC calculation and MD simulation clarify well the thin layer formation due to the good adsorption of inhibitor (PPE) on the surface of aluminum 1050 alloy in the nitric acid solution, theoretically. It is concluded that PPE will inhibit the surface of aluminum against the corrosion agents in acidic environment and can use as a green inhibitor.

Properties and corrosion protection of polypyrrole prepared by electrochemical polymerization on aluminum

AbstractIn a one‐step procedure that did not require any surface preparation, polypyrrole (PPy) films doped with 3‐nitrosalicylic acid (3Nisa) became effectively electropolymerized on the aluminum substrate in aqueous solutions. Fourier transform infrared, scanning electron microscopy, and thermal gravimetric analysis were used to analyze the properties of PPy‐based films. Open circuit potential (OCP), electrochemical impedance spectroscopy, Tafel polarization, and salt spray tests were used to study the corrosion‐resistant efficiency of the coatings. The as‐prepared PPy films performed corrosion resistance on aluminum in the 3% NaCl solution. However, the PPy films prepared in the 0.01 m solution of 3Nisa showed the best protection ability on aluminum. The self‐healing characteristic of the PPy films was recorded by varying the potential in the OCP measurement. The findings indicate the potential of using 3‐nitrosalicylic acid‐doped PPy films for applications as anti‐corrosion coatings for aluminum.

Enhancing wear and corrosion resistance of TiO2–Al2O3 hybrid coatings by the development of TiO2–Al2O3 bilayer film coatings

Sol-gel fabricated TiO2–Al2O3 bilayer coatings were deposited on 316L surfaces with several combinations of layers. Microstructural, corrosion, and wear features of the fabricated film coatings were examined compared to the TiO2–Al2O3 hybrid coating containing 65 % TiO2, which achieved the highest protection against corrosion and wear in the previous study. The electrochemical properties were determined through electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests, whereas dry sliding tests were performed using an Al2O3 ball under 1 N. Regardless of the production parameters, rutile and α-Al2O3 phases were produced in all manufactured coatings with similar thicknesses. The coatings consisting of TiO2 at the top layers showed better anti-corrosive performance due to a dense, low-porosity, and continuous morphology of TiO2 nanoparticles, while the coatings containing Al2O3 at their top layers were determined to exhibit higher wear resistance. All bilayer film coatings increased the anti-corrosion and anti-wear performance of the hybrid coating.

Deposition of nickel-titanium coating on stainless steel 316L by direct current sputtering for bio-implants: Electrochemical, microstructural, and morphological investigations

In general, the application of coatings provides vital protection for medical devices with a host of beneficial properties such as biostability and biocompatibility, chemical barrier, and micro-encapsulation. In the current work, a nickel-titanium (NiTi) system was deposited on stainless steel (SS316L) by the direct current sputtering (DCS) technique to estimate the corrosion behavior in the simulated body fluid (SBF) at 37 °C. The characterization of the coating layer was done using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDX) techniques to know the phases, elemental composition, and structure of the coating that indicated the formation of the Ni3Ti phase as a flake-shaped structure with 2.6 and 0.4 wt% of Ni and Ti, respectively. The results of atomic force microscopy (AFM) showed a decrease in surface roughness from 25.2 to 11.05 nm after coating due to a decrease in the mean diameter of particles from 710.8 to 579.9 nm after coating. The data corrosion test showed the change of corrosion potential to a more noble value with minimizing the corrosion current density as well as the improvement of resistance after coating from 6.91 × 103 to 25.49 × 103 Ω.cm2 to get protection efficiency equal to 73.9 %. In a cyclic polarization test, it can be seen that the passivity region shifts to lower current density values. Microhardness was also measured to show an increase from 187 to 366 HV due to the selected technique of coating that gives more hardness; the measured wettability did not change the contact angle of the uncoated specimen to keep it at 90°; and finally, the histological analysis did not show any severe infection or inflammation. All these observations can suggest the NiTi coating for bio-applications.

Corrosion Resistance of Fe-Based Amorphous Films Prepared by the Radio Frequency Magnetron Sputter Method.

Amorphous thin films can be applied to increase the anti-corrosion ability of critical components. Atomized FeCrNiMoCSiB powders were hot-pressed into a disc target for R. F. magnetron sputtering on a 316L substrate to upgrade its corrosion resistance. The XRD spectrum confirmed that the film deposited by R. F. magnetron sputtering was amorphous. The corrosion resistance of the amorphous film was evaluated in a 1 M HCl solution with potentiodynamic polarization tests, and the results were contrasted with those of a high-velocity oxy-fuel (HVOF) coating and 316L, IN 600, and C 276 alloys. The results indicated that the film hardness and elastic modulus, as measured using a nanoindenter, were 11.1 and 182 GPa, respectively. The principal stresses in two normal directions of the amorphous film were about 60 MPa and in tension. The corrosion resistance of the amorphous film was much greater than that of the other samples, which showed a broad passivation region, even in a 1 M HCl solution. Although the amorphous film showed high corrosion resistance, the original pinholes in the film were weak sites to initiate corrosion pits. After polarization tests, large, deep trenches were seen in the corroded 316L substrate; numerous fine patches in the IN 600 alloy and grain boundary corrosion in the C276 alloy were observed.

Long term performance evaluation of a commercial vanadium flow battery system

This paper describes the results of a performance review of a 10 kW/100 kWh commercial VFB system that has been commissioned and in operation for more than a decade. The evaluation focused on the system efficiencies, useable capacity, electrolyte stability and stack degradation. The analysis shows that the system has stable performance and very little capacity loss for over a decade since commissioning. Only very recently, a slight decrease in system discharge capacity (approximately 5 %) was observed and indicated by changes in the electrolyte valence state. The capacity was restored to the original level after conducting a rebalancing procedure. This demonstrates the advantage that the flow batteries employing vanadium chemistry have a very long cycle life. Furthermore, electrochemical impedance spectroscopy analysis was conducted on two of the battery stacks. Some degradation was observed in one of the stacks reflected by the increased charge transfer resistance. To further investigate the ageing of the stacks, reverse polarity tests were carried out. It is found that reversing the polarity both hydraulically and electrically can restore the stack performance. The study shows that the VFB is a reliable technology for large-scale energy storage applications.

A novel carbon coating by electrochemical deposition in deep eutectic solvent with the assistance of ammonium chloride for stainless steel bipolar plates

In this work, pulse electrodeposition method was proposed to directly deposit amorphous carbon coating (ACC) onto 316L stainless steel substrate in choline chloride-ethylene glycol deep eutectic solvent (DES) mixed with ammonium chloride (NH4Cl) to fabricate bipolar plates. The obtained dense ACC has a thickness of ∼400 nm. Potentiodynamic and potentiostatic polarization tests demonstrated that the corrosion current density of ACC coated 316L steel was of the order of 10−7 A cm−2 in the simulated proton exchange membrane fuel cells (PEMFC) working environment, and the self-corrosion potential of the coating positively shifted by 0.4V, indicating a significant improvement on corrosion resistance of the coated steel plate due to excellent electrochemical stability of ACC. The Rockwell C indentation test showed that the as-obtained ACC was strongly bonded to the substrate and also had high in-plane strength. Further numerical simulation and comparison experiments showed that C was chemically bonded with Fe in the substrate, which was boosted by the assistance of NH4Cl. The intact and strong bonding between ACC and the substrate is highly helpful to improve corrosion resistance. The success in coating stainless steel plate with ACC by pulse electrodeposition method provides a promising alternation for coating of proton exchange membrane electrolyzer cell (PEMEC) and PEMFC metal bipolar plates.

Electrochemical investigation of electrophoretically deposited graphene-oxide coating on AZ31 alloy prepared using in-house synthesized few-layer graphene-oxide nanosheets

Magnesium and its alloys possess low density and superior specific strength making it a potential structural metal to be used in different engineering fields. However, its proneness to corrosion limits its applications. In this novel study, an eco-friendly graphene-oxide coating was prepared on AZ31 magnesium alloy via electrophoretic deposition to enhance its anti-corrosion properties. Scanning electron microscopy coupled with energy dispersive spectroscopy, atomic force microscopy, and scratch test were adopted to investigate surface morphology, roughness, chemical composition, and adherence of the coating. The corrosion behaviour of graphene-oxide coated alloy was studied using potentio-dynamic polarization and electrochemical impedance spectroscopy tests in 3.5 wt% NaCl and Borate Buffer solutions. The obtained results demonstrate that the coating developed on AZ31 alloy is smooth and adherent with the hardness of the as-deposited coating measuring as high as 6.0 GPa. In addition, the electrochemical corrosion behaviour studies revealed that the coating significantly increased the corrosion potential (Ecorr) of the alloy towards more noble values (−0.65 V < Ecorr < −0.35 V), with the coated alloys possessing a charge transfer resistance nearly two orders of magnitude greater than their non-coated counterparts. Consequently, the corrosion rate of the coated alloy decreased substantially, indicating that the coating exhibits exceptional corrosion resistance (0.045–0.09 mm/a in 3.5 wt% NaCl and 0.002–0.006 mm/a in Borate Buffer). These findings challenge the conventional beliefs that graphene exhibits strong cathodic behaviour towards anodic materials such as AZ31 alloy. Thus, the outcomes not only have the potential to revolutionize the advancement of graphene-oxide coatings for corrosion resistance but could also possibly expand AZ31 alloy’s applications in the aerospace and automotive sectors.

Effect of hydrostatic pressure on the anodic dissolution process of X80 steel

Based on the fact that hydrostatic pressure affects chemical potentials of reaction species and the structure evolution of electric double layer (EDL), the authors propose a generalized-BV equation to analyze the anodic dissolution process of X80 steel in deep-sea environment. Combined with the results of potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests, the following conclusions can be drawn: hydrostatic pressure can compress the electric double layer non-uniformly. The CHCD (CD: capacitance of diffused layer; CH: capacitance of compact layer) value increases first and then decreases with increasing hydrostatic pressure and reaches its maximum at 15 MPa, which is sure to influence the difference in electrical potential that drives chemical reaction at interface. Ultimately, the anodic dissolution current increases and then decreases with rising hydrostatic pressure at the same anodic polarized potential. Besides, low hydrostatic pressure may contribute to forming a dense corrosion product film and inducing a good inhibiting effect on further dissolution of X80 steel; However, when the hydrostatic pressure exceeds the critical value of 20Mpa, too high anodic dissolution rate along with promoted Cl− adsorption will deteriorate the protection performance of corrosion product film, and exacerbate local corrosion process.

Corrosion Behavior of 30 ppi TAD3D/5A05Al Composite in Neutral Salt Spray Corrosion

This study created ceramic preforms with a 3D network structure (TAD3D) by using treated aluminum dross (TAD) and kaolin slurry, with 30 ppi polyurethane foam as a template via the sacrificial template method. TAD3D/5A05Al composites were then produced via pressureless infiltration of 5A05Al aluminum alloy into TAD3D. The corrosion behavior and resistance of TAD3D/5A05Al in salt spray were assessed via neutral salt spray corrosion (NSS), scanning electron microscopy (SEM), potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS) tests. The results showed that after 24 to 360 h of NSS corrosion, the corrosion of the 5A05 matrix was primarily pitting, with pits expanding and deepening over time, and showing a tendency to interconnect. The main corrosion products were MgAl2O4, Al(OH)3, and Al2O3. As corrosion progressed, these products increased and filled cracks, pits, and grooves at the composite interface on the material’s surface. Corrosion products transferred to the grooves at the composite interface and grew on the ceramic surface. Corrosion products on the ceramic framework and the Al matrix can form a continuous passivation film covering the composite surface. PDP and EIS results indicated that the composite’s corrosion resistance decreased by 240 h but increased after that time. After 240 h, the surface passivation film can weaken corrosion effects and enhance the composite’s resistance, although it remained weaker than that of the uncorroded samples. Additionally, grooves at the composite interface deepened over time, with loosely structured corrosion products inside, potentially leading to severe localized corrosion.

A new study on the corrosion inhibition mechanism of green walnut husk extract as an agricultural waste for steel protection in HCl solution

In this study, green walnut husk (GWH) extract was explored as a cost-effective (waste-agricultural) and eco-friendly inhibitor to increase the corrosion resistance of carbon steel in a 1 M HCl solution. Electrochemical impedance spectroscopy, weight change, and potentiodynamic polarization (PDP) tests were utilized to examine the electrochemical behavior of steel substrates with and without the inhibitor. Atomic force microscopy (AFM), field emission scanning microscopy, Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) were performed to analyze corroded surface structures with and without the inhibitor. This inhibitor was found to be 27–82 % efficient in increasing the corrosion resistance of the steel substrates. When the temperature of the solution was increased from 303 to 323 K, the retardation coefficient decreased due to the physical adsorption of GWH molecules on the surface. The results indicated that GWH acted as a mixed inhibitor, and its adsorption on the surface followed the Langmuir model. AFM measurements showed that the roughness of corroded surfaces decreased by approximately 22 % when the GWH concentration was at its optimum level of 400 ppm. Thermodynamic studies displayed a decrease in the corrosion reaction's activation energy of about 25 %. FTIR and XRD patterns of corroded surfaces represented that hydrated iron chloride was the dominant corrosion product. Furthermore, the results provided insight into the GWH adsorption mechanism.

Electrochemical Studies of The Corrosion Resistance of Bismuth Titanate Thin Films Deposited by RF Sputtering

Thin films of bismuth titanate were grown on stainless steel (316L) and titanium alloy (Ti6Al4V) substrates using the magnetron sputtering technique. The surface morphology of these films was observed with a scanning electron micrograph (SEM). The electrochemical studies used to evaluate the corrosion resistance of the substrate-coating set were the potentiodynamic polarization (Tafel) tests and electrochemical impedance spectroscopy (EIS), both done in a solution of NaCl (3%) as an electrolyte. The SEM showed that the morphology of the coatings grown on a titanium alloy Ti6Al4V substrate was generally homogeneous with a smooth surface but with unmelted material in some regions, while the morphology of the thin films grown on stainless steel 316L was mainly granular, with the presence of a few holes or craters. The potentiodynamic polarization curves showed that the corrosion resistance of the coated samples was better than that of the bare substrate because the corrosion current obtained from the coated samples was lower by two orders of magnitude than that exhibited by the uncoated substrates, and in addition, the corrosion potential of the coated samples was greater than that of the bare substrate. The EIS test showed the presence of a passive thin film of titanium oxide on the titanium alloy substrate.

Influence of annealing temperature on the mechanical properties and corrosion behavior of Ti-5.5Al-2.0Zr-1.5Sn-0.5Mo-1.5Nb alloy

In this work, the effect of annealing temperature of Ti552 titanium alloy is systematically investigated based on mechanical property tests, electrochemical tests and static immersion tests. The results show that after the annealing treatment, the microstructure morphology of the α-phase transforms from striated to equiaxed, and the intergranular β-phase gradually increases. As the annealing temperature increases, the grain size gradually increases and the volume fraction of α-phase gradually decreases. The tensile strength and Vickers hardness are the maximum and the elongation is the minimum in the hot-rolled condition. With increasing annealing temperature, the strength and Vickers hardness of Ti552 alloy gradually decrease, while the elongation gradually increases. In 3.5 wt% NaCl solution, Ti552 alloy has similar corrosion behavior at different annealing temperatures, although its corrosion resistance varies. In potentiodynamic polarization and EIS testing, the annealed Ti552 alloy shows a low corrosion current density (10-6 A/cm2) and a high polarization impedance (106 Ω·cm2), indicating the formation of a dense and stable oxide film. Under annealing at 800 °C, the corrosion resistance is at its highest and the corrosion rate is the lowest, according to electrochemical and static immersion studies. The comprehensive analysis suggests that the corrosion behavior of Ti552 alloy in NaCl solution may be a result of the combined effect of the volume fraction of the β-phase and the grain size of the α-phase.