Corrosion Resistance In Chloride Solutions Research Articles

Effects of Mo and C addition on the microstructure and corrosion behavior of FeNiCrAl duplex alloy

Effects of Mo and C addition on the microstructural evolution and corrosion resistance in chloride solution of FeNiCrAl duplex alloy were investigated. The results showed that α phase stabilizing element Mo increased the α/γ volume ratio and γ phase stabilizing element C decreased its ratio in FeNiCrAl alloy, and the chemical composition of α and γ phases was changed by Mo and C addition, which affected the corrosion resistance of FeNiCrAl alloy. Pitting corrosion mainly occurred in α phase around NbC precipitated at α/γ interface due to the micro-galvanic corrosion (MGC) effect between α (anode), γ (cathode) and NbC (cathode) phases. The pitting corrosion resistance was improved by Mo and C addition, resulting from that Mo and C enhanced the passivity of passive films and decreased the MGC effect between α, γ and NbC phases.

Corrosion performance of wire arc additively manufactured NAB alloy

Nickel–aluminum bronzes (NAB) are vital alloys, known for biofouling resistance, crucial for marine and shipbuilding industries. This study examined corrosion performance of NAB samples fabricated by wire arc additive manufacturing (WAAM) in as-built and heat-treated conditions. Microstructural analysis revealed the WAAM-NAB parts primarily consisted of the α-phase (copper) and three types of κ-phases: κII (spherical Fe3Al), κIII (Ni–Al in lamellar shape) within the interdendritic areas, and iron-rich κIV particles dispersed throughout the matrix. In contrast, casting-produced NAB showed the formation of a rosette-like κI phase as well. Corrosion behavior comparisons between the two NAB fabrication methods were also assessed. The microstructural characterizations revealed a rise in the size of the κIV particles after heat-treated at 350 °C for 2 h (HT1). Heat treatment at 550 °C for 4 h (HT2) resulted in a needle-like κV, coarsening of κII, partial spheroidization of κIII, and reduced κIV precipitation. When heat-treated to 675 °C for 6 h (HT3), κII and κV were coarsened, κIII was completely spheroidized, and κIV precipitation was significantly reduced. These microstructural features in HT2 and HT3 conditions steeply decreased their corrosion resistance compared to the WAAM as-built part. The as-built WAAM sample showed superior corrosion resistance in chloride solution, attributed to fewer κ-intermetallic phases and a finer microstructure. The κ-phases, irrespective of morphology, act as the cathodic areas versus the α-dendritic matrix, fostering microgalvanic cell formation. Consequently, precipitation of all cathodic κ-phases draws a higher galvanic current of the anodic α-phase, meaning a lower corrosion resistance.

Localized corrosion evaluation of newly developed stainless-steel alloys in chloride medium through dynamic and localized micro electrochemical techniques

Novel Fe–Cr SS alloys were fabricated by alloying with 0, 0.10 and 0.20 wt-% Sn respectively to investigate the effect of the Sn addition on the microstructure, passive characteristics and localized corrosion behavior in chloride medium at room temperature. The advanced scanning micro-electrochemical techniques along with the traditional electrochemical methods were used for in-depth investigations. Potentiodynamic and potentiostatic test results exhibited that the addition of Sn in SS alloys increased the resistance against pitting corrosion in NaCl medium. The acquired dynamic impedance data confirmed the effective electrochemical stability of the alloy SS3 (SS with 0.20 wt-% Sn) at applied anodic potential, suggesting the presence of a compact and stable passive film in Sn containing alloys, which contributed to their improved localized corrosion resistance in chloride solution. The scanning electrochemical microscopic results corroborated that the alloy SS3 remained stable even after 24 h of exposure and displayed no noticeable surface heterogeneity. A reduced anodic current density in scanning vibrative electrode technique mapping images was observed even after 24-h of exposure in alloy SS3 compared to other samples, indicating that the anodic metal dissolution was successfully obstructed by forming a compact and dense passive film on this alloy.

Fabrication of Mo-Dispersed Type 304L Stainless Steel By Spark Plasma Sintering and Its Corrosion Resistance in 0.1 M NaCl

Stainless steels are widely used in industries because of their high corrosion resistance. The Cr-rich oxide film on the surface protects the balk metal. For type 316 stainless steel, 2~3 mass% Mo was added to improve corrosion resistance in chloride solutions. The pitting corrosion resistance of type 316 stainless steel is known to be higher than that of type 304 stainless steel1). The role of Mo has been investigated for long time. It was proposed that Mo forms Mo-oxides and inhibits corrosion attack2). In addition, it is suggested that Mo changes the structure of the Cr oxide layers on stainless steels 3).Spark Plasma Sintering (SPS) has been applied to fabricate various types of composite materials. The advantage of the SPS technique is rapid heating and cooling 4). When two metal powders were mixed and sintered, dual-phase materials are expected to be formed because sintering is conducted below the melting points of the metals.In this study, we fabricated Mo-dispersed type 304L stainless steel by spark plasma sintering, and the corrosion resistance was assessed in 0.1 M NaCl.Mo-dispersed type 304L stainless steel was fabricated by SPS. As the starting materials, pure Mo powders and type 304L stainless steel powders were used. Table 1 shows the chemical composition of type 304L stainless powders. Sintering was performed at 1373 K for 20 min. After sintering, the specimen was heat-treated at 1573 K for 5 h in vacuum and quenched in water. After that, the solution treatment was conducted at 1373 K for 30 min and water quenched. The specimen surface was polished down to 1 μm using a diamond paste. Sintered type 304L and type 316L were used as reference materials. The same SPS procedure and heart-treatments were applied to prepare those.The surface of Mo-dispersed type 304L was inspected using an optical microscope. Scanning electron microscope (SEM) was also used. Electron Probe Micro Analyzer (EPMA) analysis of surface was conducted.Potentiodynamic polarization curves were measured in 0.1 M NaCl solution (pH 6.0) at 298 K. Specimens were covered by epoxy resin, with the exception of the electrode area (5 mm × 5 mm).On the basis of the surface observations and X-ray diffraction, it was suggested that the steel matrix of Mo-dispersed type 304L is austenite, but many voids were generated. Mo-rich phase were observed on the entire surface. The size of Mo-rich phase was 100 ~ 200 μm. From EPMA analysis, the average concentration of Mo in Mo-rich phase was determined to be 4.3 mass%. In the steel matrix, the average Mo concentration was 2.8 mass%.In polarization measurements in 0.1 M NaCl, the passive current density of Mo-dispersed type 304L and type 316L was unstable, probably because of the presence of voids. However, the pitting potentials of Mo-dispersed type 304L were found to be higher than those of type 316L. The selective dissolution of Mo-rich phases was thought to prevent the initiation of pitting effectively in chloride environments.References; Nishimoto, I. Muto, Y. Sugawara, N. Hara, J.Electrochem.Soc., 166 (11), C3081-C3089 Hashimoto, K. Asami, K. Teramoto, Corros. Sci., 19 (1979), 3-14. F. Montemor, A. M. P. Simões, M. G. S. Ferreira, M.D.C. Belo, Corros. Sci., 41 (1999), 17-34.Omori, Mater. Sci. Eng., A287 (2000), 183-188. Figure 1

Direct synthesis of layered double hydroxides monolayer nanosheets for co-assembly of nanobrick wall hybrid film with excellent corrosion resistance

Preparation of polymer−clay nanobrick wall film is considered as an ingenious, effective and environment friendly strategy to prevent metal corrosion. The key point is to design and synthesize ultrathin and well dispersed clay nanosheets, which can achieve an orderly orientation in polymer matrix. Herein, we proposed a “bottom-up” strategy to direct synthesis of layered double hydroxides monolayer nanosheets (LDH-NS), and the as-prepared nanosheets was used in a brick wall hybrid film with polyvinyl butyral (PVB) via a straightforward and time-efficient assembly process. The uniform and ultrathin LDH-NS was well aligned along the substrate surface under flow induction and thus forming a highly ordered layered composite film. The present film as a barrier coating for mild steel exhibits excellent corrosion resistance in chloride solutions, because the brick wall structure could effectively inhibit the diffusion of aggressive species. This work provides a new paradigm for designing polymer−clay nanobrick wall hybrid films towards metal anticorrosion applications.

Corrosion resistance in chloride solution of the AlSi10Mg alloy obtained by means of LPBF

The paper deals with the corrosion resistance in chloride solutions of an AlSi10Mg alloy obtained by laser powder bed fusion (LPBF) process. The potentiodynamic tests were carried out in solutions having different chloride contents. The results emphasize the role of chloride concentration on localized corrosion. The increase of concentration reduces pitting potential. In addition, the influence of the post‐processing heat treatment temperature was recognized. Penetrating attacks occurred either on after low temperatures stress relieving or specimens without any treatment, promoted by selective dissolution of the α‐Al phase stimulated by galvanic coupling with noble silicon precipitates at the border of the melt pool. Such penetrating morphology was not observed after heat treatments at high temperature.

Influence of Cold Deformation and Phase Transformation on the Electrochemical Corrosion Behavior of Nitrogen‐Alloyed Stainless Steel in Chloride Solution

Nitrogen‐alloyed stainless steels exhibit outstanding corrosion resistance in chloride solution. However, cold deformation and phase transformation can influence the materials surface properties and, therefore, corrosion behavior. A nitrogen‐alloyed stainless steel with 20 wt% chromium, 0.13 wt% nitrogen, and subject to plastic deformation of up to 36% is electrochemically tested in a 5 wt% sodium chloride solution by linear polarization and electrochemical impedance spectroscopy. The steel's corrosion behavior is distinctly influenced by its deformation state. Before polarization, a negative influence of plastic deformation on the corrosion resistance of the alloy can be determined. However, after anodic polarization, the susceptibility to corrosion due to cold deformation and phase transformation decreases. While the electrochemical resistance of the protective surface film decreases due to deformation‐induced film rupture and the formation of anodes at the surface, the permeability of the double layer also decline. This is caused by the increased activation of the surface due to the formation of local anodes and, therefore, an increase in the formation of protective species that retard further dissolution processes. In addition, increasing plastic deformation results in the surface ratio between anodes and cathodes becoming more favorable, and in a decrease in the anodic current density.

Properties of CrC+(Ni-W) Duplex Layers Produced in Vacuum Chromizing Process Combined With Galvanic Treatment

Abstract Diffusion chromizing was applied to increase the durability of tools, which operate under wear conditions. Vacuum chromizing, as opposed to other known methods, i.e., powder pack, gas, and molten salt baths, is ecological on account of non-toxic substrates, as well as absence of harmful wastes. Vacuum chromizing of tool steel results in hard and wear resistant chromium carbide coatings. However, the obtained carbide layers exhibited rather poor corrosion resistance in chloride media. To improve their corrosion resistance, Ni-W alloy was deposited electrolytically on the steel surface before the chromizing process. This resulted in the formation of CrC+(Ni-W) type duplex layers with modified characteristics. The objective of this paper was to determine the structure of these duplex layers on tool steel surface, their tribological properties and corrosion resistance in chloride solutions. Investigations of layers’ thickness, their morphology, phase composition, hardness, and depth profiles of elements in the layer diffusion zone have been carried out. The chemical composition and distribution of the phases formed in the surface region of the samples were examined by a SEM microscope, equipped with a BSE detector and an EDS spectrometer. Wear resistance tests were carried out by the three-cylinder-cone method. Electrochemical corrosion measurements of obtained layers were performed in a 0.5 M NaCl solution. The tests proved that the wear resistance of duplex layers of the CrC+(Ni-W) type, produced by vacuum chromizing of electrolytically coated steel, is as good as that of carbide layers of the CrC type, produced on bare steel surface, but their corrosion resistance is higher.

Galvacoat – 2015

Zn–Al pack co-cementation was performed on medium carbon steel in a pack mixture containing Zn and Al powders with NH4Cl as activator. An Fe–Zn layer was formed first during pack co-cementation. Fe–Al phases then nucleated locally on the surface of the Fe–Zn layer. With continued reaction, a complete Fe–Al layer was formed and grew at the expense of the Fe–Zn layer. The Fe–Zn was compact, but the Fe–Al layer was porous. The Fe–Al layer had better high-temperature oxidation resistance, while the Fe–Zn layer had better corrosion resistance in chloride solution. Based on microstructural evolution and the chemical reactions associated with Zn–Al pack co-cementation, the growth behavior of Zn–Al pack coating on steel was discussed in detail.

Growth behavior and properties of Zn–Al pack cementation coatings on carbon steels

Abstract Zn–Al pack co-cementation was performed on medium carbon steel in a pack mixture containing Zn and Al powders with NH4Cl as activator. An Fe–Zn layer was formed first during pack co-cementation. Fe–Al phases then nucleated locally on the surface of the Fe–Zn layer. With continued reaction, a complete Fe–Al layer was formed and grew at the expense of the Fe–Zn layer. The Fe–Zn was compact, but the Fe–Al layer was porous. The Fe–Al layer had better high-temperature oxidation resistance, while the Fe–Zn layer had better corrosion resistance in chloride solution. Based on microstructural evolution and the chemical reactions associated with Zn–Al pack co-cementation, the growth behavior of Zn–Al pack coating on steel was discussed in detail.

Effect of Na3PO4 addition in mortar on steel reinforcement corrosion behavior in 3% NaCl solution

The influence of a phosphate inhibitor on the corrosion behavior of steel reinforcement in mortar immersed in 3% NaCl solution was investigated. For this purpose, characterization methods (SEM, XRD), mechanical (flexural strength and compressive strength), electrochemical and acoustic emission measurements were carried out. It was demonstrated that the addition of phosphate inhibitor induces a slight decrease of the mortar compressive strength but no change of the flexural strength. The electrochemical measurements indicate that the addition of Na3PO4 in mortar leads to an improvement of the steel reinforcement corrosion resistance in chloride solution. It was also confirmed by the acoustic emission technique that the phosphate inhibitor decreases the corrosion rate. Furthermore the visual observation of the mortar corroborates these results. Thus it can be concluded that the addition of this phosphate inhibitor in concrete decreases the chloride ions effect on localized corrosion.

Structure and properties of Fe-N-C composites obtained by high-energy ball milling of nitrated iron powders in hydrocarbon environments

Bulk nanocrystalline composites produced by high-energy ball milling of nitrated iron powders followed by dynamic pressing are studied. Composites consist of three phases α-Fe + γ′-Fe4N + Φ, where the nature of the Φ phase is determined by the milling environment (nitrogen, heptane, or xylene). The microhardness of composites is 6–7 GPa at a density of 95–97%. Composites are characterized by a high corrosion resistance in chloride solutions.

Electrochemical and Salt Spray Corrosion Behavior of Copper Alloy Contact Wires in Chloride Solution

The effect of different alloying elements on corrosion behavior of copper alloys was investigated using electrochemical corrosion and salt spray corrosion test in NaCl solution. Cu-Ag has the most stable corrosion current in the potentiostatic scanning test, exhibiting a better corrosion resistant performance. It can be analyzed from corrosion surface morphologies that Cu-Ag presents exfoliation corrosion mechanism while Cu-Sn shows crevice corrosion mechanism. Cu-Mg has a complex corrosion process caused by multiple corrosion mechanism. In the salt spray corrosion test, the corrosion degree of Cu-Ag is lighter than those of Cu-Sn and Cu-Mg after 24h test. Therefore, the Cu-Ag alloy exhibits the best corrosion resistance in chloride solution.

Influence of Step Annealing Temperature on the Microstructure and Pitting Corrosion Resistance of SDSS UNS S32760 Welds

In the present work, the influence of step annealing heat treatment on the microstructure and pitting corrosion resistance of super duplex stainless steel UNS S32760 welds have been investigated. The pitting corrosion resistance in chloride solution was evaluated by potentiostatic measurements. The results showed that step annealing treatments in the temperature ranging from 550 to 1000 °C resulted in a precipitation of sigma phase and Cr2N along the ferrite/austenite and ferrite/ferrite boundaries. At this temperature range, the metastable pits mainly nucleated around the precipitates formed in the grain boundary and ferrite phase. Above 1050 °C, the microstructure contains only austenite and ferrite phases. At this condition, the critical pitting temperature of samples successfully arrived to the highest value obtained in this study.

Examination of Galvanic Action between Fe-Based Bulk Metallic Glass and Crystalline Alloys

Fe-based bulk metallic glasses (amorphous metals) have been developed, and several compositions are shown to have excellent corrosion resistance in chloride solutions. Further, thermal-spray amorphous metals are being developed for use as a barrier coating layer, to protect substrate materials from corrosion. Galvanic action between dissimilar metals and the coating/substrate for the amorphous-alloy coatings is of practical interest for a number of applications. The mixed-potential theory provides a useful approach for examining the corrosion behavior of the component materials in the galvanic couple and is applied in this study. Galvanic action was studied for an Fe-based structurally amorphous metal (SAM) 1651 and several crystalline alloys that included 1018 C-steel, stainless steel (SS) 316L, and alloy 22. Anodic and cathodic polarization curves of each of the metals were measured by potentiodynamic polarization. Based on the mixed-potential theory, the behavior of the component materials in a galvanic cell was predicted. The predictions are compared to the measured behavior of galvanic couples with the crystalline alloys.

Sandvik SAF 2707 HD®(UNS S32707): a hyper-duplex stainless steel for severe chloride containing environments

The new grade has significantly improved corrosion resistance in chloride solutions compared with currently available super duplex stainless steels (e.g. UNS S32750) and the 6Mo austenitic stainless steels (e.g. UNS S31254). Some references in industrial heat exchanger applications are highlighted.