Electrochemical Corrosion Performance Research Articles

Use of Multi-Modal Synchrotron Analytical Techniques Combined with Electrochemical Analysis to Understand Anomalous Localized and General Corrosion Behavior of Additively Manufactured 316L Stainless Steel

Additive manufacturing (AM) of alloys such as stainless steels has the potential to be a disruptive technology for design of complex structures which eliminates the potentially damaging effects of mechanical failure and localized corrosion associated with interfaces between separate parts (which can now be printed as part of a single assembly). In addition, increasingly complex geometries can be manufactured with nearly as much ease as simple ones, and new mechanisms for optimization and generative design can allow manufacturers to achieve significant material and weight savings. However, challenges remain, in particular due to the potential for material variability both between parts made with the same nominal build parameters and even within a single build, as the consistency in properties inherent in the commercial-scale forging of alloys to be machined into components is exchanged for the considerable advantages of on-site, distributed custom parts production. Our studies and related work by other groups indicates that this is clearly true in the case of corrosion susceptibility in AM alloys. By studying the relationship between build parameters and electrochemical properties, we propose that it will be possible to tailor alloys for enhanced corrosion properties.AM processes produce materials with hierarchical microstructures containing fusion boundaries at the macroscale, irregular grains and grain boundaries at the microscale, and subgrain dislocation structures at the nanoscale. In laser powder bed fusion (LPBF) formed 316L stainless steel structures, corrosion performance has been discussed in the context of chemical heterogeneities formed in the presence of these hierarchical microstructures. Furthermore, localized corrosion (pitting) is closely related to microstructural defects including dislocation structures, inclusions, and localized elemental segregation which has been found to occur during the very rapid heating and cooling which occurs during laser fusion AM processes.In this presentation, we explore multi-modal synchrotron X-ray techniques for quantifying hierarchical microstructures and their connection to the underlying chemical distribution in 316L stainless steel, as well as localized heterogeneities in the passive film structure. Our results show that the dislocation density depends on the printing conditions with implications for the chemical distribution at the nanoscale, which in turn may play a key role in inconsistent corrosion behavior. Furthermore, we discuss the correlation between this print-formed alloy surface microstructure (dislocation structures, Mn inclusions, and elemental segregation), and local heterogeneities in the passive film formed on LPDF 316L in Cl-containing media. These heterogeneities observed in the passive layer may in turn impact repassivation and other processes critical in localized cession phenomena.Samples formed at varying speeds using pulsed and continuous laser deposition are compared via cyclic polarization in 3.5% NaCl and 0.1M HCl solutions, as well as using Mott-Schottky analysis of passive layers formed in 0.1M HCl. Surface corrosion layers are characterized using laboratory-based X-ray photoelectron spectroscopy to determine the impact on passivity of the aforementioned microsegregation associated with process-induced microstructures. Corrosion rates and pit densities are then discussed to build a connection between printing conditions and corrosion performance vis-à-vis microstructural and chemical information from synchrotron measurements performed at Brookhaven National Laboratory (BNL), including high energy X-ray diffraction using the X-ray Powder Diffraction (XPD) beamline at the National Synchrotron Light Source-II (NSLS-II) which provided data on minor precipitate population(s), atomic structure and dislocation microstructures critical to corrosion behavior. In addition, heterogeneities in elemental composition data is provided by 2D X-ray fluorescence (XRF) and 2D X-ray Absorption Spectroscopy (XAS) nanometer resolution-mapping obtained at the Hard X-ray Nanoprobe (HXN) beamline at the NSLS-II and correlated with process-induced hierarchal structures via use of the microscopy facilities at the Center for Functional Nanomaterials (CFN). X-ray photoemission microspectroscopy/low energy electron microscopy (XPEEM/LEEM) conducted at the Electron Spectro-Microscopy beamline at the NSLS-II provides evidence that the passive layer itself contains inhomogeneities, including areas enriched in oxidized Cr and Mn, as well as microstructural boundaries, reflecting the inhomogeneities in the microstructure of the alloy surface beneath. Mott-Schottky analysis of the passive layer provides further evidence that these inhomogeneities, correlated with alloy microstructure, impact the semiconducting character (and hence protective properties) of the passive layer.By employing a combination of multi-modal synchrotron characterization techniques, electron microscopy, and baseline testing protocol combined with electrochemical polarization experiments, we are able to study the role of microstructure across multiple length scales on electrochemical properties and corrosion performance. Understanding the impact of microstructure and chemical heterogeneities on the susceptibility to pitting and intergranular attack will enable microstructurally-informed process optimization and materials design for enhancing the corrosion resistance of LPBF 316L stainless steel, with implications for AM and subsequent durability of alloys in general.

Effects on Al2O3 and La2O3 additions on electrochemical performances of laser‐cladded WC10Co4Cr coatings

AbstractAl2O3 and La2O3‐reinforced WC10Co4Cr coatings were fabricated on Cr12MoV steel by laser cladding (LC). The microstructure and phases of obtained coatings were analyzed using a digital microscopic system (DMS) and X‐ray diffraction (XRD), respectively. The effects of Al2O3 and La2O3 mass fractions on the electrochemical corrosion performances of WC10Co4Cr coatings in 3.5% NaCl solution were investigated on an electrochemical workstation. The results show that the WC10Co4Cr with the different Al2O3 mass fractions are composed of Co4W2C, WC, Al2O3, W2C, and Fe‐Cr phases, and the La2O3‐reinforced WC10Co4Cr‐Al2O3 coatings are composed of WC, W2C, Al2O3, La2O3, LaAlO3, and Fe‐Cr phases. The corrosion current density icorrof the substrate, WC10Co4Cr‐Al2O3, and WC10Co4Cr‐Al2O3‐La2O3 coatings decreases from 2.424 × 10−5 to 6.840 × 10−7 A•cm−2; and the corresponding polarization resistance Rp and charge transfer resistance Rct increase from 1371 to 64 536 Ω•cm2 and from 1568 to 14 020 Ω•cm2, respectively. The La2O3‐reinforced WC10Co4Cr‐Al2O3 coatings have higher electrochemical corrosion resistance than the Al2O3‐reinforced WC10Co4Cr coatings, and the WC10Co4Cr‐6%Al2O3‐9%La2O3 coating presents the highest electrochemical corrosion resistance among all the experimental coatings.

Response surface and corrosion behavior analysis of nanosecond laser patterned ZK60A magnesium alloy

Parallel groove patterns were fabricated on ZK60A magnesium alloy surface using nanosecond laser technology. In order to study the influence of laser processing parameters on the groove size, firstly, the single factor test was used to preliminarily determine the range of laser parameters, and then the mathematical models between processing parameters and groove width (W), depth (D) were established by response surface methodology. The morphologies, elements, hardness and phases of the magnesium alloy with different scanning distances were characterized by lanthanum hexaboride scanning electron microscope (SEM), environmental SEM, microhardness tester and X-ray diffractometer (XRD), respectively. The electrochemical corrosion performances of polished and laser patterned magnesium alloy samples in hanks' balanced salt solution (HBSS) were analyzed and compared using electrochemical experiments. The results show that W first increases and then decreases with the decrease of laser scanning speed (v) or the increase of repetition frequency (f), while D shows an increasing trend; the regression model obtained by the response surface methodology is in good agreement with the experimental values, and it accurately predicts the groove size. The wavy accumulation on the groove surface is caused by the sputtering of liquid materials when the laser acts on the sample surface. Compared with the polished sample, the hardness of samples with scanning distances of 80, 120 and 160 μm is significantly improved, which are 40.30, 30.69 and 29.18% respectively. Ecorr values of polished sample and patterned samples with scanning distances of 80, 120 and 160 μm are −1.4481, −1.6398, −1.5712 and −1.5142 V, respectively; and the corresponding Icorr values are 5.2209 × 10–6, 1.2378 × 10–5, 2.7849 × 10–5 and 6.3782 × 10–6 A•cm−2, respectively. The hydrophilicity of laser patterned magnesium alloy is enhanced, which is conducive to cell adhesion, however, the probability of contact between corrosive medium and samples increases at the same time. In addition, the grain refinement increases crystal defects, thereby reducing the corrosion resistance of laser patterned samples.

CHARACTERIZATION AND ELECTROCHEMICAL CORROSION ANALYSIS OF HEAT-TREATED REINFORCED HA COATINGS DEPOSITED BY VACUUM PLASMA SPRAY TECHNIQUE

Herein, a biomimetic coating of hydroxyapatite (HA)–Al2O3 and HA–ZrO2 was deposited on Ti–6Al–4V-alloy using vacuum plasma spray (VPS) technique. The bond-coat of ZrO2 has been introduced between the substrate and reinforced HA coatings to study the effect of bond-coat on structural, mechanical properties and electrochemical corrosion performance of the developed coatings. In addition, the impact of thermal treatment of coating was investigated on these properties too. Coating characteristics, such as morphology, porosity, surface roughness, and crystallinity were investigated. The corrosion performance of coatings was tested in Hank’s-based salt solution (HBSS). Significant enhancement in crystallinity and surface-hardness has been witnessed after heat treatment; nevertheless, porosity reduced. The electrochemical corrosion study revealed that the corrosion resistance of heat-treated samples was better than the as-sprayed coatings samples. The intensity of XRD peaks of all coatings increased after 24[Formula: see text]h immersion in HBSS for the electrochemical test in comparison to the intensity of peaks before the corrosion test.

Nano dual-phase CuNiTiNbCr high entropy alloy films produced by high-power pulsed magnetron sputtering

Dual-phase high entropy alloys have been proved to have the ability to overcome the strength-ductility trade-off. However, high-entropy alloy films are difficult to obtain a dual-phase structure due to the extremely high cooling rate during the preparation process and the high-entropy effect of the film itself. In this paper, the dual-phase CuNiTiNbCr high-entropy alloy films were prepared by high-power pulsed magnetron sputtering at different working pressures. The composition, microstructures, mechanical properties and electrochemical corrosion performance were tested by energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), nano-indentation, Vickers indentation and electrochemical polarization. The CuNiTiNbCr films exhibited a dual-phase structure composed of FCC matrix phase and Cu-rich BCC precipitated phase. The film presented a two-layer structure, the single FCC phase structure near the substrate and the FCC + BCC structure above. Comparing with FCC phase, the dual-phase structure exhibited higher hardness. With the increase of deposition pressure, the structure of the film became looser, and the hardness, toughness and corrosion resistance were all decreased due to the influence of the structure. It is proved that high-power pulsed magnetron sputtering is a feasible way for the phase structure regulation and performance improvement of high-entropy alloy films.

Electrochemical performance and corrosion mechanism of Cr–DLC coating on nitrided Ti6Al4V alloy by magnetron sputtering

A Cr–DLC coating was deposited on nitrided Ti6Al4V alloy (TA) by magnetron sputtering (MS) using CrN as an interlayer. The characterization processes of obtained coating were performed on scanning electron microscopy (SEM), energy dispersive spectroscope (EDS), X-ray diffraction (XRD), Raman spectroscopy and transmission electron microscopy (TEM), and the hardness and bonding strength were also measured by nanoindentation and scratch testers. The electrochemical corrosion performances of TA, nitrided TA and Cr–DLC coating in 3.5% NaCl solution were systematically investigated using an electrochemical workstation, and the corrosion mechanisms were discussed in detail. The results show that the amorphous carbon atoms are uniformly distributed on the in–situ grown Cr–DLC coating, and the CrN interlayer plays an important connection role between the Cr–DLC coating and the nitrided TA. After the electrochemical corrosion test, the O mass fraction on the Cr–DLC coating is lower than those on the TA and nitrided TA, and the nitrided TA is effectively protected from electrochemical corrosion. The Cr–DLC coating presents the smallest corrosion current density icorr and the largest polarization resistance Rp among the TA, nitrided TA and Cr–DLC coating, showing the outstanding electrochemical corrosion resistance. Meanwhile, the capacitive arc radius, impedance |Z| and phase angle of Cr–DLC coating are also the maximum, exhibiting that its electrochemical corrosion resistance is higher than the TA and nitrided TA.

Corrosion resistance of 45 carbon steel enhanced by laser graphene-based coating

In this study, a directly growing graphene layer on carbon steel and its corrosion performance is reported. The graphene-based coating was now prepared on carbon steel by combining electroplating and laser preparation of graphene. Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were used to characterize the structure and composition, confirming the possibility of directly preparing few layers of graphene on carbon steel materials. The graphene-based substrate showed the highest Vickers hardness of coatings studied using the polarization curve and electrochemical impedance spectroscopy corrosion performance. The graphene-based coating's dynamic polarization curve's corrosion rate is much lower than that of pure Ni-coating and pure carbon steel material. A supplement of electrochemical impedance spectroscopy also showed the highest charge transfer resistance and the minimum double-layer capacitance. The excellent anti-corrosion performance of the laser graphene-based coating protects the carbon steel material from corrosion.

Corrosive wear and electrochemical corrosion performances of arc sprayed Al coating in 3.5% NaCl solution

PurposeThe purpose of this paper is to investigate the effects of load and speed on the corrosive wear performance of Al coating in 3.5% NaCl solution, which provided an experimental reference for the anti-corrosion engineering on offshore platforms.Design/methodology/approachA layer of Al coating was prepared on S355 steel using an arc spraying. The corrosive wear test was carried out with CFT–1 type surface property tester. The effects of load and speed on the corrosive wear performance of Al coating were investigated and the wear mechanism was also discussed. The electrochemical tests were conducted using a CHI660E type electrochemical workstation, the anti-corrosion mechanism was analyzed.FindingsThe average coefficient of frictions (COFs) of Al coating under loads of 1.5, 2.5 and 3.5 N are 0.745, 0.847 and 0.423, the wear mechanism is abrasive wear. The average COFs of Al coating at the speeds of 200, 400 and 600 rpm are 0.745, 0.878 and 0.617, respectively, the wear mechanism at the speeds of 200 and 400 rpm are abrasive wear, while that at the speed of 600 rpm is abrasive wear and fatigue wear. The anti-corrosion mechanism is the isolation of Cl– corrosion and cathodic protection of sacrificial anode.Originality/valueThis paper mainly studied corrosive wear and electrochemical corrosion performances of Al coating. This study hereby confirms that this manuscript is the original work and has not been published nor has it been submitted simultaneously elsewhere. This paper further confirms that all authors have checked the manuscript and have agreed to the submission.

Characterization of Waste-Integrated Multi-hybrid Structure for Enhancing Corrosion Resistance of High-Carbon Steel

Due to their exceptional properties, low-cost high-carbon steels have long been extensively utilized in many industrial applications. However, their corrosion resistance is poor for many applications and requires further enhancement. Various methods have been developed to achieve this, but they suffer from some limitations. In the work presented herein, a single-stage heat treatment process was applied at low temperature and utilizing waste materials for comparison as new resources, being shown to be a cost-effective approach. In the framework of this study, a multi-hybrid coating structure was developed on the surface of high-carbon steel by applying a single-step heat treatment process and utilizing various waste materials, namely metallurgical slag, glass, and automotive shredder residue (ASR). The results reveal that not only was the process completed in a short time but significant enhancements in the corrosion resistance and hardness performance were achieved. Analyses were performed by high-resolution laser scanning confocal microscopy, electron probe microanalysis (EPMA), focused ion beam-scanning electron microscopy (FIB-SEM), and atomic force microscopy (AFM) in peak force quantitative nanomechanical (PF-QNM) mode. The electrochemical corrosion performance was tested using Tafel method. Both the Young’s modulus and corrosion resistance of the steels treated using the waste materials were improved compared with the base material. This approach opens a new perspective for utilizing waste materials to obtain environmentally sustainable products in a cost-effective fashion, thereby reducing reliance on new resources as well as disposal of waste materials in landfill.

Novel Biocompatible Zr-Based Alloy with Low Young's Modulus and Magnetic Susceptibility for Biomedical Implants.

The microstructure, mechanical properties, magnetic susceptibility, electrochemical corrosion performance, in vitro cell compatibility and blood consistency of Zr-16Nb-xTi (x = 0, 4, 8, 12 and 16 wt.%) materials were investigated as potential materials for biomedical implants. X-ray diffraction (XRD) and Transmission electron microscopy (TEM) analyses revealed the secondary phase martensite α’ formed during the quenching process. The phase composition contained metastable β and martensite α’, resulting from Ti addition. These phase constitutions were the main causes of a low Young’s modulus and magnetic susceptibility. The in vitro cytocompatibility analysis illustrated that the MG63 cells maintained high activity (from 91% to 97%) after culturing in Zr-16Nb-xTi extraction media for 12 days due to the high internal biocompatibility of Zr, Nb and Ti elements, as well as the optimal corrosion resistance of Zr-16Nb-xTi. On the basis of Inductively coupled plasma optical emission spectrometry (ICP-OES) ion release studies, the concentration of Zr, Nb and Ti was noted to reach the equipment detective limit of 0.001 mg/L, which was much lower than pure Ti. With respect to the corrosion behavior in Hank’s solution, Zr-16Nb-16Ti displayed superior properties, possessing the lowest corrosion current density and widest passivation region, attributed to the addition of Ti. The blood compatibility test illustrated that the Zr-16Nb-xTi materials were nonhemolytic, and the platelets maintained a spherical shape, with no aggregation or activation on Zr-16Nb-xTi. Overall, Ti addition has obvious effects on the developed Zr-16Nb-xTi alloys, and Zr-16Nb-4Ti exhibited low magnetic susceptibility, low modulus, good biocompatibility and proper corrosion properties, demonstrating the potential of use as implant biomaterials.

Surface alteration of biomedical alloys by electrical discharge treatment for enhancing the electrochemical corrosion, tribological and biological performances

In the current research, the electrical discharge treated (EDT) biomedical alloys substrates such as cobalt-chromium (F90), stainless steel (316L) and titanium (Beta type) have been investigated for their in-vitro biocompatibility, corrosion resistance and tribological performance. The alloys substrates were machined by copper tungsten tool electrode in a deionized water tank at 10A current, 200μs pulse on-time, 60μs pulse off-time. To examine the corrosion rate of the substrates, the electrochemical potentiodynamic test was executed in which Tafel slopes were designed. Further, cytocompatibility and hemocompatibility tests were performed on the substrates to study the in-vitro biocompatibility. Moreover, the tribological characteristics such as wear rate and coefficient of friction were investigated on a pin-on-disc tribometer. The results revealed that the modification of the substrate was perceived to be effective in increasing the corrosion resistance of cobalt-chromium alloy, titanium alloy and stainless steel alloy by 86.39%, 62.15% and 56.21%, respectively in comparison to the unmachined substrates. Similarly, the tribological results exhibited that the altered substrates have improved friction-reducing characteristics and higher wear-resistance. The cytocompatibility and hemocompatibility outcomes validating the higher %cell viability and low RBC-lysis on treated substrates. The existence of titanium carbide (TiC), niobium carbide (NbC) and tungsten carbide (WC) phases on EDT substrates were detected from X-ray diffraction examination favors the synthesis of the hard and wear-resistant surface. Although, the formation of oxides, nitrides and phosphides during the EDT process lead to developing bio-inert surfaces and also ameliorates the corrosion resistance of the alloy. However, the F-90 cobalt-chromium alloy substrate showed improved corrosion, wear and biocompatibility responses as compared to titanium and stainless steel alloy. Therefore, the metallurgical alteration during EDT and the inherent bulk properties of base alloy contributed towards its biocompatibility and surface properties. These results promote the EDT biomedical alloys in bulk in the biomedical field.

Alumina Reinforcement of Inconel 625 Coatings by Cold Gas Spraying

Reinforced Inconel625 coatings have been successfully deposited by means of cold gas spray (CGS). Alumina has been simultaneously sprayed achieving a homogeneous distribution along the deposit with good cohesion between particles. The aim of this study was to investigate whether ceramic reinforcement could improve the mechanical and tribological properties of Inconel625 cold-sprayed coatings, while keeping the oxidation and corrosion resistance capacity. Furthermore, alumina particles were found to improve the spraying feasibility, by avoiding WC nozzle clogging during the process. A proper optimization of the spraying conditions was carried out in order to obtain the lowest possible porosity and best embedment of the alumina. Then, the mechanical and tribological properties as well as corrosion and oxidation behavior were characterized. Alumina acts as a reinforcement, improving the effects of abrasive and sliding wear. Regarding the oxidation and corrosion behavior, the coatings exhibit reasonably good oxidation resistance at temperatures up to 900 °C. The electrochemical corrosion performance in NaCl solution showed potentially lower noble corrosion values and corrosion current densities than bulk Inconel.

Corrosive-wear and Electrochemical Performance of Laser Thermal Sprayed Co30Cr8W1.6C3Ni1.4Si Coating on Ti6Al4V Alloy

Co30Cr8W1.6C3Ni1.4Si coatings were fabricated on Ti6Al4V alloy using a laser thermal spraying (LTS). The surface and cross-section morphologies, phases and bonding strength of obtained coatings were investigated using scanning electronic microscopy (SEM), X-ray diffraction (XRD), and scratch test, respectively. The effects of laser power on the coefficients of friction (COFs) and corrosive-wear behaviors of Co30Cr8W1.6C3Ni1.4Si coatings were investigated using a wear tester in 3.5% NaCl solution, and the electrochemical corrosion performance was analyzed using an electrochemical workstation. The experimental results show that the Co30Cr8W1.6C3Ni1.4Si coating is bonded with the substrate in the metallurgical form, and the bonding strengths of Co30Cr8W1.6C3Ni1.4Si coatings fabricated at the laser power of 1 000, 1 200, and 1 400 W are 76.5, 56.5, and 55.6 N, respectively. The average COFs of Co30Cr8W1.6C3Ni1.4Si coatings fabricated at the laser power of 1 000, 1 200, and 1 400 W are 0.769, 0.893, and 0.941, respectively; and the corresponding wear rates are 0.267 × 105, 0.3 1 78 × 105, and 0.325 × 105 µm /Nm, respectively, which increases with the increase of laser power, the wear mechanism is primarily abrasive wear. The corrosion potential of Co30Cr8W1.6C3Ni1.4Si coatings fabricated at the laser power of 1 000, 1 200, and 1 400 W is −0.05, −0.25, and −0.31 V, respectively, higher than −0.45 V of substrate which enhances the electrochemical corrosion resistance of substrate.

Electrochemical corrosion behavior and surface passivation of bulk nanocrystalline copper in alkaline solution

PurposeThis paper aims to focus on an assessment of the electrochemical corrosion performance of bulk NC copper in a variety of corrosion environments.Design/methodology/approachThe electrochemical corrosion behavior of bulk nanocrystalline (NC) copper prepared by inert gas condensation andin situwarm compress technique was studied by using potentiodynamic polarization and electrochemical impedance spectroscopy tests in de-aerated 0.1 M NaOH solution.FindingsNC copper exhibited a typical active-passive-transpassive behavior with the formation of duplex passive films, which was qualitatively similar to coarse-grain (CG) copper. Although a compact passive film formed on NC copper surface, the corrosion resistance of NC copper was lower in comparison with CG copper. The increase in corrosion rate for NC copper was mainly attributed to the high activity of surface atoms and intergranular atoms. These atoms led to an enhancement of passive ability and an increase of dissolution rate of passive film in oxygen-deficiency solution. For NC copper, the corrosion resistance decreased as grain size increased in NC range.Originality/valueThe difference in corrosion resistance between bulk NC copper and its CG counterpart is dependent upon the corrosion solution. In a previous work, the potentiodynamic polarization tests revealed that NC copper bulks (grain size 48, 68, 92 nm) had identical corrosion resistance to CG copper bulk in naturally aerated 0.1 M NaOH solution. The results might be related to the dissolved oxygen in the medium.

Comparison on electrochemical corrosion performances of arc and laser thermal sprayed Al–Ti–Ni coatings in marine environment

Al–Ti–Ni coatings were fabricated on S355 structural steel using an arc spraying (AS) and laser thermal spraying (LTS), and their electrochemical corrosion performances in 3.5% NaCl, 0.1 M H2SO4 and 0.1 M NaOH solutions were comparatively investigated. The results show that the obtained coatings are composed of crystalline and amorphous phases, and the metallurgical bonding is formed at the interface of laser thermal sprayed coating. The polarization resistance Rp and charge transfer resistance Rct of laser thermal sprayed coating are higher than those of arc sprayed coating in 3.5% NaCl, 0.1 M H2SO4 and 0.1 M NaOH solutions, while the corrosion current density jcorr is opposite, its electrochemical corrosion resistance is better than the arc sprayed coating. The Rp and Rct of laser thermal sprayed coating in 0.1 M NaOH solution are the highest among the three kinds of solutions, showing the highest electrochemical corrosion resistance.

Effect of graphene addition on composition, morphology and corrosion behavior of ZnNiFe-graphene composite coatings

Graphene reinforced, Zn-rich, Zinc-Nickel-Iron (ZnNiFe-G) coatings were deposited on mild steel substrate by electrolyzing the Zn-Ni-Fe acidic sulphate bath containing different amounts of dispersed graphene layers. Effect of graphene incorporation on composition, microstructure, morphology and electrochemical corrosion performance of coatings was investigated. X-ray diffraction studies revealed ZnNiFe coatings consists η Zn, γ Ni2Zn11 and Fe phases but the concentration of γ Ni2Zn11 phase increased with increasing graphene content in the coating. Incorporation of graphene enhanced the coating compactness and reduced the micro-pores and surface defects. Presence of graphene increased the Ni and Fe content in the coatings. The electrochemical corrosion behavior of the composite coatings was determined using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. Increase in γ Ni2Zn11 phase concentration, compact and defect free ZnNiFe-G composite coatings exhibited >50% better corrosion resistance performance when compared to the corrosion resistance exhibited by the graphene free Zn-Ni-Fe coating. Among the ZnNiFe-G coatings, the composite coating with combination of highest Ni and graphene content showed the best corrosion resistance performance.

Use of Multi-Modal Synchrotron Analytical Techniques to Understand Anomalous Localized and General Corrosion Behavior of Additively Manufactured 316L Stainless Steel

Additive manufacturing (AM) of alloys such as stainless steels has the potential to be a disruptive technology for design of complex structures which eliminates the potentially damaging effects of mechanical failure and localized corrosion associated with interfaces between separate parts (which can now be printed as part of a single assembly). In addition, increasingly complex geometries can be manufactured with nearly as much ease as simple ones, and new mechanisms for optimization and generative design can allow manufacturers to achieve significant material and weight savings. However, challenges remain, in particular due to the potential for material variabilities both between parts made with the same nominal build parameters and even within a single build, as the consistency in properties inherent in the commercial-scale forging of alloys to be machined into components is exchanged for the considerable advantages of on-site, distributed custom parts production. Our studies and related work by other groups indicates that this is clearly true in the case of corrosion susceptibility in AM alloys. By studying the relationship between build parameters and electrochemical properties, we propose that it will be possible to tailor alloys for enhanced corrosion properties.AM processes produce materials with hierarchical microstructures containing fusion boundaries at the macroscale, irregular grains and grain boundaries at the microscale, and subgrain dislocation structures at the nanoscale. In laser powder bed fusion (LPBF) formed 316L stainless steel structures, corrosion performance has been discussed in the context of chemical heterogeneities formed in the presence of these hierarchical microstructures. However, the large variability in reported measurements underscores the need for statistically significant microstructural data, which is often difficult to access via electron microscopy alone. In this presentation, we explore multi-modal synchrotron X-ray techniques for quantifying hierarchical microstructures and their connection to the underlying chemical distribution in 316L stainless steel. Our results show that the dislocation density depends on the printing conditions with implications for the chemical distribution at the nanoscale, which in turn may play a key role in inconsistent corrosion behavior.LPDF 316L samples formed at varying speeds using pulsed and continuous laser deposition are compared via cyclic polarization in 3.5% NaCl and 0.1M HCl solutions, as well as using standard methods for characterizing sensitization. Surface corrosion layers are characterized using laboratory-based X-ray photoelectron spectroscopy to determine the impact on passivity of the aforementioned microsegregation associated with process-induced microstructures. Corrosion rates and pit densities are then discussed to build a connection between printing conditions and corrosion performance vis-à-vis microstructural and chemical information from synchrotron measurements performed at Brookhaven National Laboratory (BNL), including high energy X-ray diffraction using the X-ray Powder Diffraction (XPD) beamline at the National Synchrotron Light Source-II (NSLS-II) which provided data on minor precipitate population(s), atomic structure and dislocation microstructures critical to corrosion behavior. In addition, heterogeneities in elemental composition data is provided by 2D X-ray fluorescence (XRF) and 2D X-ray Absorption Spectroscopy (XAS) nanometer resolution-mapping obtained at the Hard X-ray Nanoprobe (HXN) beamline at the NSLS-II and correlated with process-induced hierarchal structures via use of the microscopy facilities at the Center for Functional Nanomaterials (CFN).By employing a combination of multi-modal synchrotron characterization techniques, electron microscopy, and baseline testing protocol combined with electrochemical polarization experiments, we are able to study the the role of microstructure across multiple length scales on electrochemical properties and corrosion performance. Understanding the impact of microstructure and chemical heterogeneities on the susceptibility to pitting and intergranular attack will enable microstructurally-informed process optimization and materials design for enhancing the corrosion resistance of LPBF 316L stainless steel, with implications for AM and subsequent durability of alloys in general.

Corrosion resistance of amorphous carbon film in 3.5 wt% NaCl solution for marine application

In this work, we fabricated the tetrahedral amorphous carbon (ta-C) films with thicknesses of 20 nm, 40 nm and hydrogenated diamond-like carbon (DLC:H) film with thickness of 1.1 μm on 316 stainless steel substrate (316SS). The electrochemical corrosion performances of two typical amorphous carbon (a-C) films in 3.5 wt% NaCl solution were focused. Results revealed that both ultrathin ta-C films exhibited superior corrosion resistance than that of DLC:H film, because the high content of sp3 bonded carbon and low porosity in ta-C films significantly suppressed the diffusion of corrosion media. However, a thickness threshold beyond 20 nm was proposed to obtain the superior corrosion resistance for ta-C films due to the emerged pitting of 316SS. For DLC:H film, the deterioration of corrosion resistance could be attributed to the hydrogen-containing interface, the large sp2 clusters with high electron transport, and the higher porosity density in carbon matrix.

Production of Mg-Ca-Zn-Zr-Cu alloy for resorbable compression screw in bone fixation applications

ABSTRACT In this work, biodegradable Mg-Ca-Zn-Zr-Cu alloy specimens were manufactured for temporary implant (compression bone screw or interference screw) applications in the bone fixation applications. Mg-Ca-Zn-Zr-Cu alloy specimens were produced by the metal (powder) injection moulding (MIM/PIM) method. Small and complex parts can be manufactured with the metal (powder) injection moulding (MIM) technique. The metal powder mixtures were mechanically alloyed to prepare the Mg alloys. A mixture consisting of paraffin wax, polyethylene and stearic acid was used as a multi-component polymer binder. Electrochemical corrosion performance of the Mg alloy samples was investigated in the simulated body fluid solution. The experimental findings demonstrated that the electrochemical corrosion resistance of the samples was enhanced with the alloying the Mg. Biodegradation (resorption) performance of the specimens was investigated by using weight change and metal (Mg) ion release measurements. Effect of the alloying elements on the Young’s (elastic) modulus of the alloy was also studied.

Electrochemical corrosion performances of laser thermal sprayed amorphous Al–Ti–Ni coatings in marine environment

PurposeThe purpose of this paper is to investigate the effects of laser power on the electrochemical corrosion performance in 3.5% NaCl, 0.1 M H2SO4 and 0.1 M NaOH solutions, which provided an experimental basis for the application of Al–Ti–Ni amorphous coating in marine environment.Design/methodology/approachAmorphous Al–Ti–Ni coatings were fabricated on S355 structural steel by laser thermal spraying (LTS) at different laser powers. The surface and cross-section morphologies, chemical element distribution, phases and crystallization behaviors of obtained coatings were analyzed using a scanning electron microscope, energy-dispersive X-ray spectroscope, X-ray diffraction and differential scanning calorimetry, respectively. The effects of laser power on the electrochemical corrosion performances of Al–Ti–Ni coatings in 3.5% NaCl, 0.1 M H2SO4 and 0.1 M NaOH solutions were investigated using an electrochemical workstation.FindingsThe crystallization temperature of Al–Ti–Ni coatings fabricated at the laser power of 1,300 and 1,700 W is ∼520°C, whereas that fabricated at the laser power of 1,500 W is ∼310°C. The coatings display excellent corrosion resistance in 3.5% NaCl and 0.1 M NaOH solutions, while a faster dissolution rate in 0.1 M H2SO4 solution. The coatings fabricated at the laser power of 1,300 and 1,700 W present the better electrochemical corrosion resistance in 3.5% NaCl and 0.1 M NaOH solutions, whereas that fabricated at the laser power of 1,500 W exhibits the better electrochemical corrosion resistance in 0.1 M H2SO4 solution.Originality/valueIn this work, Al-wire-cored Ti–Ni powder was first on S355 steel with the laser power of 1,300, 1,500 and 1,700 W, and the effects of laser power on the electrochemical corrosion performance in 3.5% NaCl, 0.1 M H2SO4 and 0.1 M NaOH solutions were investigated using an electrochemical workstation.