Cyclic Polarization Research Articles

Anodizing of AA2024 Aluminum–Copper Alloy in Citric-Sulfuric Acid Solution: Effect of Current Density on Corrosion Resistance

Al–Cu alloys are widely used as a structural material in the manufacture of commercial aircraft due to their high mechanical properties such as hardness, strength, low density, and tolerance to fatigue damage and corrosion. One of the main problems of these Al–Cu alloy systems is their low corrosion resistance. The purpose of this study is to analyze the influence of anodizing parameters on aluminum–copper alloy (AA 2024) using a bath of citric-sulfuric acid with different anodizing current densities on the thickness, microhardness, and corrosion resistance of the anodized layer. Hard anodizing is performed on AA 2024 Al–Cu alloy in mixtures of solutions composed of citric and sulfuric acid at different concentrations for 60 min and using current densities (i) of 0.03, 0.045, and 0.06 A/cm2. Scanning electron microscopy (SEM) was used to analyze the surface morphology and thickness of the anodized layer. The mechanical properties of the hard anodized material are evaluated using the Vickers hardness test. The electrochemical techniques use cyclic potentiodynamic polarization curves (CPPC) according to ASTM-G6 and electrochemical impedance spectroscopy (EIS) according to ASTM-G61 and ASTM-G106, respectively, in the electrolyte of NaCl at 3.5 wt. % as a simulation of the marine atmosphere. The results indicate that corrosion resistance anodizing in citric-sulfuric acid solutions with a current density of 0.06 A/cm2 is the best with a corrosion current density (jcorr) of 1.29 × 10−8 A/cm2. It is possible to produce hard anodizing with citric and sulfuric acid solutions that exhibit mechanical properties and corrosion resistance similar or superior to conventional sulfuric acid anodizing.

Influence of tin additions on the corrosion passivation of TiZrTa alloy in sodium chloride solutions

Abstract In this study, the fabrication of Ti-12%Zr-4%Ta-2%Sn alloy, Ti-12%Zr-4%Ta-4%Sn alloy, and Ti-12%Zr-4%Ta-6%Sn alloy using powder metallurgy fabrication technique has been carried out. The influence of Sn addition on the corrosion of these alloys after 30 min and 3 days in 3.5% NaCl solution using various techniques has been reported. The Nyquist spectra revealed that boosting Sn content from 2 to 4% and further to 6% increases the corrosion resistance of the alloy through increasing the diameter of the obtained semicircle. Bode spectra also elucidated that the increased percentage of Sn increases the values of the impedance of the interface |Z| and the maximum degree of the phase angle (Φ). It was indicated from the cyclic polarization curves that the increased Sn content increases the passivation of the alloy through decreasing its rate of corrosion and increasing its corrosion resistance. The measured current over time at −0.10 V showed that the alloy with low Sn content, 2%, records the highest currents, which pronouncedly decreases when Sn content increases to 4% and further to 6%. Prolonging the time of exposure from 30 min to 3 days greatly enhances the passivation of the TiZrTaSn alloys due to the formation of mixed oxides of TiO2, ZrO2, TaO2, and SnO2. The results of these electrochemical measurements were confirmed by the surface investigations carried out by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results collectively proved that the uniform corrosion remarkably decreases with the increase in the Sn% and that the pitting corrosion is not likely to take place.

A Comparative Study on Dip Coating and Corrosion Behavior of Ti-13Zr-13Nb and Commercially Pure Titanium Alloys Coated with YSZ by Taguchi Design

This work evaluates experimentally the corrosion and tip testing of Ti-13Zr-13Nb joint implant alloys and commercially pure titanium (cp-Ti) covered with YSZ nanoceramic. Through the use of the Taguchi design of experiments (DOE) approach, the dip coating process produced a thin sticky covering. The effects of temperature, YSZ concentration, duration, and the level of Ti alloy substrate grinding during dip coating were investigated using a L9-type orthogonal Taguchi array to determine the deposition yield. The thickness and adhesion tests that were utilized to optimize the dip coating conditions served as the input data, and the Ti alloys were coated using the ideal dip coating technique parameters as previously mentioned. For commercial Ti, the ideal values for YSZ coating thickness and adhesion were 60°C, 10 seconds, 10% concentration, and 250 degrees of grinding; correspondingly, for Ti-13Zr-13Nb, the ideal values were 60°C, 10 seconds, 15% concentration, and 400 degrees of grinding. For both Cp-Ti and Ti-13Zr-13Nb, the obtained thickness and removal area (adhesion) were 58.5µm and 11.45%, respectively, and 69.5µm and 9.33%, respectively. High-resolution scanning electron microscopy (FE-SEM) images were used to study the coated alloys; optical microscopy and AFM were used to identify the microstructure and thickness measurements of the coated surfaces; EDAX was used to analyze the coating composition; and XRD was used to analyze the formed phases. The optimized coated Ti alloys' corrosion resistance was investigated in simulated body fluid (SBF) using electrochemical methods such as cyclic polarization and Tafel polarization, and the adhesion strength of the coatings was measured using a tip tester. The following corrosion-resistant values were used to compare Ti-13Zr-13Nb and coated Cp-Ti: In Ringer's solution at 37°C, both coating alloys—Cp-Ti and Ti-13Zr-13Nb—improved corrosion resistance; however, the coated Ti-13Zr-13Nb alloy demonstrated greater corrosion resistance than the coated Cp-Ti alloy (5.417×10-3 and 1.042×10-2, respectively).

ELECTROCHEMICAL REDUCTION OF ELEMENTAL SULFUR IN ETHYLENE GLYCOL ELECTROLYTE

The work is devoted to the study of the mechanism of reduction of elemental sulfur from ethylene glycol. For this purpose, linear and cyclic voltampere polarization curves were recorded. The influence of sulfur concentration in ethylene glycol electrolyte, potential unfolding rate and temperature on the sulfur reduction process was investigated. By recording the cyclic polarization curve, the range of potentials at which the reduction of elemental sulfur and its anodic oxidation occur was determined. It has been established that an increase in the concentration of sulfur in the electrolyte and temperature raises the speed of its reduction, and the process itself is controlled by the diffusion of sulfur ions to the cathode surface. In addition, the polarization curves on the platinum rotating disc electrode were recorded. The obtained data, namely the rectilinear dependence of ip on the rotation speed of the electrode (ω) to the power of 0.5, confirm the proposal that the process of reduction of elemental sulfur is accompanied by diffusion polarization. The dependence of the current density on the rotation speed of the electrode to the power of 0.5 at different potentials showed that the process of reduction of elemental sulfur in non-aqueous ethylene glycol at potentials of (0.25÷0.4 V) is accompanied by diffusion polarization, whereas at potentials above 0.4 V, it is accompanied by electrochemical polarization. Keywords : Sulfur ions, electroreduction, polarization, scanrate.

Electrochemical characteristics and damage mechanism in scrubber washing water of UNS N08367 with plasma ion nitriding and electropolishing

In this investigation, electropolishing and plasma ion nitriding are applied to super austenitic stainless steel for the purpose of improving its corrosion and pitting resistance. Electrochemical experiments are conducted with washing water collected directly from the ship’s scrubber. After electropolishing, the surface roughness is improved by about 73.6% compared to mechanical polishing. After plasma ion nitriding, CrN (precipitate), Fe4N (compound), and γN (solid solution) are observed on the surface. The thickness of the layer formed on the surface is measured to be about 10 μm. A hysteresis loop is observed in the cyclic potentiodynamic polarization curves of mechanical polishing and electropolishing, and the areas are calculated as 23.33 mW cm−2 and 0.17 mW cm−2, respectively. The polarization curve of plasma ion nitriding presents perfect passivation characteristics. Accordingly, mechanical polishing and electropolishing reveal local corrosion, whereas plasma ion nitriding presents a tendency towards general corrosion. In the mechanical polishing, electropolishing, and plasma ion nitriding, the corrosion current densities are 0.665 μA cm−2, 0.093 μA cm−2, and 16.47 μA cm−2, respectively, and the maximum damage depth is observed to grow progressively smaller from plasma ion nitriding to electropolishing and then mechanical polishing.

Effect of surface roughness on corrosion behavior of AISI 4340 high-strength steel in sodium chloride solutions

In this work, an AISI 4340 high-strength steel alloy was surface machined to have four different grades of roughness (Ra). The impact of changing Ra on the corrosion of the steel alloy in 3.5% NaCl solutions after 40 min and 24 h was performed using various electrochemical techniques. The cyclic polarization experiments showed that an increase in Ra increases the steel corrosion via enhancing the corrosion current of the alloy. The electrochemical impedance plots also indicated that an increase in Ra reduces the corrosion resistance of the alloy by decreasing the diameter of the semicircle obtained by the Nyquist spectra. The change in potentiostatic current vs time measurements, which were obtained at −350 mV (Ag/AgCl), confirmed that pitting attack occurs and its intensity further increases with increasing Ra for all steel samples. An increase in immersion time also reduces the resistance to corrosion due to the iron dissolution from the surface of the steel alloy. After corrosion, the surface was analyzed using a scanning electron microscope and energy dispersive spectroscopy investigations.

Development of electrophoresed anti-corrosion coating for copper from functionalized multi layered graphene nano-sheets synthesized through anionic acidic electrochemical exfoliation

Following the discovery of graphene, a two-dimensional carbonaceous substance, numerous possibilities in materials science domain have evolved, one being its function as a corrosion inhibitor. This investigation undertakes the synthesis of functionalized multi-layered graphene nanosheets (FMLGNs) from pyrolytic graphite sheets through electrochemical exfoliation involving four distinct acid-based solutions (H2SO4, HCLO4, HNO3 and combination of the above three in 1:1:1 ratio). Post-exfoliation analysis of FMLGNs included X-ray diffraction (XRD) wherein 2θ values were reported at 26° confirming graphene's presence. Raman spectroscopy reiterated the same observation along with an increase in ID/IG ratio to ≈ 1 hinting at the presence of functional groups and defects. UV–visible spectroscopy indicating π-π* transitions, Fourier transform infrared spectroscopy (FTIR) showing CO stretching and X-ray photoelectron spectroscopy (XPS) with a C/O ratio = 3.12 gave an idea about the functionalization in FMLGNs. Average particle sizes of FMLGNs was in the range of 400–500 nm and zeta potential measurements showed stable dispersion behaviour (≈−40 mV). Utilizing scanning electron microscopy (SEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM), authors observed a layered (10–15 layers), overlapping shape of FMLGNs. Electrophoretic deposition (EPD) method was employed to coat FMLGNs onto copper substrates under various iterative conditions (number of layers and time of deposition) which produced depositions of ≈20–30 μm. SEM images displayed adequate coverage of graphene sheets on copper surfaces, backed by energy-dispersive x-ray spectroscopy (EDS). Crack propagation resistance (CPR) values of 34.03 N highlighted better adherence than other similar coatings. The coated copper samples were subjected to cyclic voltammetry (CV), potentio-dynamic polarization (PDP) and electrochemical impedance (EIS) tests in 3.5 wt% NaCl solution for analysing the inhibitory impacts of coatings. An inhibition efficiency of 85 % and charge transfer resistance of 5535 Ω.cm2 was observed, which highlighted better corrosion mitigation than reported literatures. The authors also identified that 1 layered coatings showed better reliability than two layered coatings.

Beneficial effect of 4% Ta addition on the corrosion mitigation of Ti–12% Zr alloy after different immersion times in 3.5% NaCl solutions

Abstract The recent study reports the fabrication and corrosion behavior of two Ti alloys, 88% Ti–12% Zr and 84% Ti–12% Zr–4% Ta, in 3.5% NaCl electrolyte. These alloys were manufactured using powder metallurgy, where the powders were mixed, ball milled, and sintered. The corrosion behavior of these alloys was examined using various electrochemical and spectroscopic tests. Cyclic polarization experiments indicated that adding 4% Ta reduces corrosion of the TiZr alloy by suppressing anodic dissolution, resulting in a lower corrosion rate. The Nyquist and Bode impedance spectra for the tested alloys revealed that the presence of 4% Ta within TiZr alloy highly decreases the corrosion by increasing the impedance of the interface, the maximum degree of phase angle, and polarization resistance. The chronoamperometric current measured at −0.10 V (Ag/AgCl) proved that the presence of 4% Ta powerfully alleviates both uniform and pitting corrosion for TiZr alloy by lowering the obtained absolute currents. The surface investigation using scanning electron microscopy confirmed the homogeneity of the surfaces. The elemental analysis performed on the surface using energy dispersive spectroscopy revealed that the surface of TiZr alloy forms a top film including different oxides such as TiO2 and ZrO2, and for TiZrTa alloy, the surface has TiO2 + ZrO2 plus TaO2. Experiments demonstrated that Ta has the ability to increase the corrosion passivation of TiZr alloy.

Reduced graphene oxide (rGO) reinforced CoCrFeNiMn high entropy alloy: Microstructure, mechanical properties, and corrosion behavior

The CoCrFeMnNi high entropy alloy (Cantor), and its variant incorporating 0.2 wt% reduced graphene oxide (rGO), denoted as Cantor + rGO, were successfully synthesized using mechanical alloying followed by spark plasma sintering. Comprehensive characterization utilizing FESEM, XRD, and TEM provided detailed insights into the microstructural features of the materials. The addition of rGO reduced crystallite size from 209 nm to 169 nm, promoted a uniform distribution of carbide phases of smaller size, and enhanced microhardness from 421.8 HV to 510 HV for Cantor and Cantor + rGO, respectively. The incorporation of rGO into the Cantor structure led to an increase in compressive yield strength (CYS) from 1100 MPa for Cantor to 1250 MPa for Cantor + rGO sample. A significant decrease in corrosion current density of samples from 6.1 ± 1.5 μA/cm2 for Cantor to 1.4 ± 0.9 μA/cm2 for Cantor + rGO was observed due to the addition of rGO reinforcement. Moreover, the pitting corrosion resistance was increased in rGO-reinforced Cantor, as revealed by cyclic polarization test. This research underscores the potential for utilizing rGO as a reinforcing agent to optimize the mechanical and corrosion resistance characteristics of HEAs, offering promising avenues for advanced materials in diverse applications.

Effect of Artificial Aging in the Microstructure and Corrosion Performance of Superduplex UNS S32750 Stainless Steel

Superduplex stainless steels have great mechanical and corrosion properties. However, its chemical composition makes it prone to intermetallic phase precipitation during thermal processing. Sigma (σ), chi (χ), and chromium nitrides (Cr2N) remove Cr and Mo from the matrix, reducing the corrosion and mechanical resistance. Understanding the effects of thermal processing on the secondary phase’s precipitation and depletion of the material’s performance is crucial to its applications. Thus, this work aims to analyze the behavior of the corrosion performance of the UNS S32750 after thermal treatment at 800°C, for 60, 180, 300, and 420 minutes, in comparison to the as-received material. Optical emission spectrometry, X-ray diffraction, and SEM with backscattered electrons (BSE) were used to evaluate the material. The corrosion performance was evaluated with the cyclic potentiodynamic polarization technique. The main results and conclusions obtained in the study were a decomposition of the ferrite phase into the χ and σ phases, with the formation of the χ phase being predominant in shorter times, while for longer aging times σ formed in greater quantities. It was also possible to verify a more aggressive corrosion trend for aged samples in the regions adjacent to the formation of the χ and σ phases. It was also possible to observe that the losses generated in corrosion resistance were greater for aging times longer than 60 minutes. The aging treatment significantly reduced the material’s corrosion resistance in conjunction with the formation of precipitates.

Alternating C- and Ti-dominated sublayers on bipolar plates achieve enhanced corrosion resistance under high potentials toward proton exchange membrane fuel cells

High cathodic transient potentials accelerate the dissolution of metal bipolar plates, and developing corrosion-resistant coatings is imperative. A multilayer coating that C and Ti alternatively dominated the sublayers is fabricated on SS316L (C/Ti/SS). Such an optimized composition and structure significantly expands transpassive potential to 1.6 V and thus offers full protection within the entire working potential range of proton exchange membrane fuel cells. After 10,000 cyclic polarizations with Epeak of 1.6 V, a conductive TiO2 nanofilm forms on the surface and C/Ti/SS achieves a noticeable interfacial contact resistance of 9.43 mΩ∙cm2, highlighting the remarkable commercial application of the novel coating.

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.

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.

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.

Investigation of the Effect of Bioactive Glass Coating on the Corrosion Behavior of Pre-treated Ti6Al4V Alloy

Titanium alloys, especially Ti6Al4V, are widely used in in-body implants due to their superior mechanical properties, corrosion resistance and biocompatibility. However, due to their higher modulus of elasticity than bone, they do not bond well with the bone structure, leading to loosening. In addition, they contain the elements Al and V, both of which are dangerous when released into the body. Therefore, these alloys are subjected to a number of surface treatments to improve their surface properties. In this study, Ti6Al4V alloys were produced by selective laser melting in dimensions of 10x10x2 mm3 and then surface treated. The alloy surfaces were first anodized and then coated with 45S5 bioglass powder. After all surface processes, structural analyzes were performed and the effectiveness of the coating was examined. The untreated and coated samples were subjected to corrosion tests by cyclic polarization method and their corrosion behaviors were investigated.

Effect of hydrochar-doping on the performance of carbon felt as anodic electrode in microbial fuel cells.

In this study, the feasibility of using hydrochars as anodic doping materials in microbial fuel cells (MFCs) was investigated. The feedstock used for hydrochar synthesis was metal-polluted plant biomass from an abandoned mining site. The hydrochar obtained was activated by pyrolysis at 500 °C in N2 atmosphere. Under steady state conditions, the current exerted by the MFCs, as well as the cyclic voltammetry and polarization curves, showed that the activated hydrochar-doped anodes exhibited the best performance in terms of power and current density generation, 0.055 mW/cm2 and 0.15mA/cm2, respectively. These values were approximately 30% higher than those achieved with non-doped or doped with non-activated hydrochar anodes which can be explained by the highly graphitic carbonaceous structures obtained during the hydrochar activation that reduced the internal resistance of the system. These results suggest that the activated hydrochar materials could significantly enhance the electrochemical performance of bioelectrochemical systems. Moreover, this integration will not only enhance the energy generated by MFCs, but also valorize metal polluted plant biomass within the frame of the circular economy.

Effect of endogenous chloride ion on the corrosion behavior of reinforcement embedded in sea-sand UHPC matrix in different immersion environments

Ultra-high performance concrete (UHPC) is an innovative cement-based composite material characterized by extremely high durability and mechanical properties, which provides a potential possibility of using non-desalted sea-sand as aggregate. However, the long-term steel corrosion behavior in UHPC prepared by simulated sea-sand under different immersion environments remains unclear, which is of great significance for the application of sea-sand UHPC in practical engineering. In this study, the pore structure of sea-sand UHPC matrix was measured using nitrogen adsorption/desorption method. The corrosion behavior of rebar in sea-sand UHPC with different endogenous chloride ion contents soaking in pure water and NaCl solution was characterized by linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS) and cyclic polarization (CP). The experimental results show that the initial UHPC pore structure is refined by incorporation of sea-sand, and is similar to that of ordinary UHPC at the later hydration. Regardless of the endogenous chloride ion content and immersion environment, the corrosion rate evaluated by corrosion current density (icorr) and polarization resistance (Rp) of reinforcement in UHPC is extremely low. The measurement of EIS shows that UHPC group has higher matrix resistance (Rc) and charge transfer resistance (Rct), while lower electric double layer capacitance (CPEdl) of reinforcement, which indicates that the steel in UHPC made of sea-sand is still in a state of passivation. However, the steel bar in comparison specimen OPC soaking in NaCl solution is in the corrosion stage. Furthermore, sea-sand UHPC possesses of excellent ability of anti-pitting corrosion of reinforcement after 180 days of immersion in NaCl solution.

Мырыш электродын өндірістік айнымалы токпен натрий хлориді ерітіндісінде поляризациялау арқылы мырыш оксидін алу

The purpose of the work is to dissolve the zinc electrode during polarization with an alternating current with a frequency of 50 Hz and to obtain zinc oxide. It is shown that the pre-recorded anode-cathode cyclic potentiodynamic polarization curves allow to predict to a certain extent the processes occuriing on the zinc electrode during alternating current polarization. It has been established that when two zinc electrodes are polarized in sodium chloride with an alternating current with a frequency of 50 Hz, they do not dissolve, but when one electrode is replaced with a titanium one, zinc dissolves intensively with the production of zinc hydroxide. It is shown that the rate of zinc dissolution directly depends on the current density at the titanium electrode. When the values of the current density on the titanium electrode change in the range of 5-10 kA/m2, the zinc dissolution current efficiency exceeds 100%. Based on the results of the research, it was established that zinc (II) hydroxide is produced during electrolysis, and zinc oxide can be obtained by dehydration. The composition of the resulting compound was identified by X-ray phase and elemental analyses

Influence of laser power on mechanical properties and pitting corrosion behavior of additively manufactured 316L stainless steel by laser powder bed fusion (L-PBF)

316L stainless steel parts were additively manufactured via laser powder bed fusion under different laser powers. We investigated the influence of laser power on the microstructure and mechanical properties of the printed parts by conducting scanning electron microscopy, X-ray diffraction, microhardness and tensile tests. In addition, we performed electrochemical corrosion tests including cyclic potentiodynamic polarization and electrochemical impedance spectroscopy in 3.5 wt% NaCl solution to study the influence of laser power on the corrosion behavior of as-printed parts. The results indicate that as-printed parts exhibit a preferential orientation of (220) direction, and increasing the laser power results in grain refinement of the samples, but excessive laser power can lead to a re-increase in the grain size of the samples. Excessively low laser power can result in the formation of lack of fusion pores, while excessively high power can lead to the formation of keyhole pores. These defects lead to a reduction in tensile performance. Significant differences in corrosion resistance are observed for the parts printed with different laser powers, and between the building direction and normal direction. Some defects, such as micropore, MnS inclusions and boundaries of melt pools, have an impact on the pitting corrosion resistance of printed parts. However, due to low content of MnS inclusions, the presence of pore defects remains the major factor in the pitting corrosion process. Laser powers in the range of 300–375 W can effectively reduce pore defects and improve the resistance of pitting corrosion. These findings emphasize the importance of optimizing the laser power to enhance the overall performance and pitting corrosion resistance of 316L stainless steel parts.

Synergistic protection of borate and silicate salts composite for controlling the chloride-induced pitting and uniform corrosion of steel reinforcement bars embedded in mortars

In this study, the efficacy of the combined effect of borate and silicate alkali metal salts added to mortars for controlling the chloride-induced uniform and localized corrosion of embedded steel rebars is examined. The individually added salts in mortars are found to have insignificant effects in terms of reducing the uniform corrosion rate and localized damage. However, their combination (0.50% sodium tetra borate + 0.10% sodium silicate added with respect to the weight of the binder) provides complete protection to reinforcements tested for long durations under wet/dry treatments with mortars in saline water and laboratory atmospheres. Electrochemical impedance spectroscopy, direct current cyclic polarization, polarization resistance, and visual observations are used for quantitative and qualitative evaluations of the protective effects of the tested additives. X-ray diffraction analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy analysis of the corrosion products formed on the embedded steel surfaces help explain the possible mechanisms behind the considerable improvement in the inhibitive effects of a mixed composition of borate and silicate. This combination also improves the compressive strength and workability of the mixed concrete. The results reveal that the synergistic protection provided by a mixture of borate and silicate can be attributed to the co-deposition of an iron-boron + ferrosilicate + cortensitite (an iron-silicon phase) film on the rebar surface.