Pitting Corrosion Resistance Research Articles

Pitting Corrosion in AA7075 Friction Stir Welds on Minor Additions of Silver

AA7075 is extensively used in aerospace, defense, automotive applications because of its high strength to weight ratio. Issues related to fusion welding and corrosion resistance are key problems associated with these alloys. Friction stir welding is an alternative welding technique that overcomes problems associated with fusion welding. In the present investigation, preliminary studies were done on pitting corrosion behavior of AA7075 friction stir welds by adding silver along the weld joint line. Silver paste was applied along the longitudinal direction of AA7075-T6 rolled plates of 6-mm thickness and cured at 130 °C for 30 seconds. Weld joints were prepared at two different tools rotational speeds, i.e., 750 rpm and 1000 rpm, while keeping other parameters fixed. Welded joints were cut as per the required sizes to study the hardness, microstructure, and pitting corrosion resistance in various regions. It was observed that the hardness was not much affected, but pitting corrosion resistance substantially improved by trace addition of silver. In the stir zone and the thermo-mechanically affected zone, onion ring type marks were observed. Grain refinement in the stirred zone (SZ) was higher at 750 rpm compared to 1000 rpm. The increased hardness in the welds was due to grain refinement. All the observed results were correlated with microstructural features as evidenced by optical microscopy.

High-throughput preparation and electrochemical screening of nanocrystalline Fe-Cr-Ni material libraries with homogeneous element distribution

Magnetron co-sputtering has been widely used for high-throughput preparation of combinatorial material library. However, a large number of alloy compositions in the fabricated material libraries are interconnected with each other, and their element distribution is uneven. Here, we present a high-throughput strategy where 97 independent nanocrystalline alloy samples with homogeneous element distribution can be prepared simultaneously through multi-station rotary sample stage. Using this approach, we synthesized 22 nanocrystalline Fe-Cr-Ni alloy samples covering 10.65–28.36 wt% Cr and 7.47–24.57 wt% Ni and studied their pitting corrosion resistance by electrochemical measurements, thereby quickly establishing the relationship between chemical compositions and corrosion resistance.

Effect of Grain Refinement on the Corrosion Resistance of 316L Stainless Steel.

The effect of hydrostatic extrusion (HE) on the microstructure, uniform corrosion, and susceptibility to a localized attack of 316L stainless steel was studied. Both qualitative and quantitative analyses of inclusions before and after HE were carried out. The multiplication of non-metallic inclusions after HE lowered the stability of the passive film over a broad range of pH, while refinement of the matrix had a minor effect on it. The refined materials were prone to metastable pitting, but their pitting corrosion resistance was improved.

Optimizing And Comparative of Polymer-45S5BG and Polymer- HA Coating by Electrophoretic Deposition (EPD)

In this study, two systems of bio-ceramic coating (45S5 bioactive glass and hydroxyapatite) were used in order to compare between them for biomedical applications. Each system consists from two layers of coating done by electrophoretic deposition (EPD) technique on 316L stainless steel material as substrate. Two types of biopolymer were used (Chitosan with Gelatin) as first layer of coating. Taguchi approach with L9 array was used in order to choose the best conditions (concentrations, voltage and time) for coating layers. Each system consists of two layer (biopolymer (first layer) and bioceramic (second layer)) materials. The optimum parameters for first layer of biopolymer was (3g/L concentration, 20 voltage and 3 minute) while optimum parameter for second layer (6g/L concentration, 30 voltage and 1 minute) for two bioceramic group. Zeta potential test were employed to measure suspensions stability. The tape test method was used to evaluate the adhesion between substrate and coating layers, the results show that the percentage of removal area for optimum coating layer (biopolymer, 45S5 BG and HA 8.06%, 10.668%, 6.23% subsequently). XRD inspection was used for identify the phases of coating layers. The Cyclic polarization test was used for evaluation of pitting corrosion resistance, the results show all layers gives good corrosion resistance but 45S5BG gives the best corrosion resistance when compared with HA system.

Laser-assisted removal of weld heat tints from stainless steel surface

The heat generated during the welding of stainless steel results in the oxidation of the surface that, apart from aesthetics, adversely affects its corrosion property too. This communication reports the successful removal of heat tint generated by the gas tungsten arc welding process off a stainless steel surface in addition to an improvement in its pitting corrosion resistance by exposure to the emission of a nanosecond pulsed fiber laser. The laser cleaning experiments, conducted with six different laser pulses having different temporal shapes and duration that varied from 20 to 1020 ns, revealed that removal of the weld heat tint was possible in all conditions provided the effective laser fluence exceeded a definite threshold value. This threshold value, in turn, was found to increase with an increase in pulse duration. The laser cleaned specimens were subsequently analyzed for surface morphology, roughness, and pitting corrosion resistance. The pitting corrosion resistance of the laser-treated specimens was compared with the as-welded specimens and welded specimens with heat tint removed using conventional methods like wire brush cleaning and chemical pickling. The superior quality of tint removal, improved pitting corrosion resistance, and the ease of noncontact operation indicates the significant potential of the fiber laser-based weld tint removal method to substitute the conventional mechanical or chemical cleaning methods currently in use in the manufacturing industry.

Wear and corrosion behavior of nano carbide dispersed AISI304 stainless steel by laser surface processing

In this study, dispersion of tungsten carbide on AISI 304 stainless steel substrate has been carried out by laser melting of the sand blasted substrate using a 5 kW continuous wave (CW) Nd:YAG laser (with the beam diameter of 3 mm) with an output power ranging from 1.5–2 kW, and scan speed varying from 12 to 16 mm s−1 and simultaneous feeding of premixed WC + Co powders in the ratio (wt) of 1:4 (with a flow rate of 10 mg s−1). The microstructure of the composite zone is dendritic or cellular in morphology and consists of nano-tungsten carbide (both WC and W2C) and M23C6 precipitates. There is an enhancement in hardness due to carbide dispersion from 220 VHN of the as-received substrate to 290–400 VHN. The wear resistance is improved significantly with a maximum enhancement observed in the sample processed with an applied power of 2 kW and a scan speed of 12 mm s−1. The corrosion rate in a 3.56 wt% NaCl solution is significantly reduced due to laser processing in most samples except when processed with 2.5 kW applied power and 12 mm s−1 scan speed. However, pitting corrosion resistance is found to be improved (shifting of Epit towards noble direction) for the sample processed with an applied power of 2 kW and a scan speed of 12 mm s−1.

Wear and corrosion behavior of AA6061 metal matrix composites with ilmenite as reinforcement

Aluminum matrix composites (AMCs) are extensively using in different fields such as defense automotive, marine, electronics and automobile sectors because of their impressive mechanical properties. This study aims to investigate the tribological and corrosion behavior of AA6061 alloy with the reinforcement of ilmenite (FeTiO3) particles. AA 6061-(FeTiO3) composites were fabricated througha stir casting process with AA 6061 as matrix material and ilmenite (FeTiO3) particles in different wt.% (5%, 10% and 15%) as reinforcement. In this investigation, the composites' properties like hardness, wear behavior, coefficient of friction and pitting corrosion behaviour were evaluated. From these tests, it is noticedthat hardness increased and wear rateand coefficient of friction decreased with the addition of ilmenite as reinforcement in AA6061 alloy. Pitting corrosion resistance of composites with 10%ilmenite is better than remaining composites and base metal.

Enhanced wear, corrosion, and corrosive-wear resistance of the biocompatible Ti-based bulk metallic glass by oxidation treatment

In the present study, effects of the oxidation treatment on microstructures, wear, electrochemical, and corrosive-wear performances of a TiZrCuPd bulk metallic glass (BMG) were investigated. After annealing at 300 ℃ and 400 ℃, the Ti-based BMG showed Cu2O particles on the surface and ZrCu and Cu3Ti2 crystalline phases. The oxidation treatment improved the wear resistance of the Ti-based BMG under both dry- and wet-friction conditions. As the annealing temperature increased, the pitting-corrosion resistance of the Ti-based BMG in the phosphate buffer saline (PBS) was enhanced, which was mainly due to the relative enrichment of corrosive-resistant elements Ti, Zr, and Pd in the alloy surface. The tribocorrosion result showed that the corrosion- and passivation-current-density of the oxidized-Ti-based BMG under the sliding condition decreased with the increase in the oxidation temperature, which contributed to the enhanced corrosive-wear resistance.

Investigation of corrosion behavior on plastically deformed aa 7075 t651 by shot peening process

As AA 7075 T651 comprehensively is used in the marine naval vessels, the factor of corrosion performance always plays a significant role. In this work, an investigation is carried out to study the effect of corrosion behavior of shot peened AA 7075 T651 in 3.5% solution. From the potentio-dynamic polarization study, a 27.72% decrease is ascertained in the Icorr in shot peened specimen in correlation to unpeened aluminium alloy. A drop in Icorr from 1.883 to 1.480 mA cm−2 in shot peened specimen, indicates enhanced pitting corrosion resistance. An electrochemical impedance spectroscopy reveals a surge in the oxide layer formation on the peened surface aiding the drop in corrosion rate. Resistance to pit formations and improvement in oxygen deposition in the peened specimen is observed availing a Scanning Electron Microscopy (SEM) and Energy Dispersive x-ray analysis (EDX). The micro structures of the peened and unpeened specimen are captured using optical microscopy and Transmission electron microscopy (TEM). Micro-strain, dislocation density is also calculated from the x-ray diffraction analysis (XRD), in which grain size reduces by 28.07%, dislocation density surges by 38.65% and micro strain increases by 21.95% in peened specimen in correlation to unpeened AA 7075 T651. As a result of these improvements the corrosion resistance by 27.92% in the peened specimen in correlation to unpeened aluminium alloy.

Roles of Alloying Elements in the Corrosion Resistance of Equiatomic CoCrFeMnNi High-Entropy Alloy and Application to Corrosion-Resistant Alloy Design

The equiatomic CoCrFeMnNi alloy and the equiatomic quaternary alloys with no addition of one element of the CoCrFeMnNi alloy were fabricated, and the roles of the alloying elements in corrosion resistance were clarified. In 1 M H2SO4, the passivity of the CoCrFeMnNi alloy was mainly due to Cr. The Co and Fe additions also contributed the decrease in the passivity current density. While Ni addition was found to suppress active dissolution, Mn addition increased the active dissolution rate. The quaternary alloy without Mn indicated superior pitting corrosion resistance in 0.1 M NaCl. To improve the corrosion resistance of the CoCrFeMnNi alloy, Mn was replaced with Mo, and the effect of the Mo content on the pitting corrosion resistance and the role of Co addition were assessed in 1 M HCl.

Corrosion behavior of AlCuFeMn alloy in aqueous sodium chloride solution

Medium Entropy Alloy AlCuFeMn possesses high room temperature strength and oxidation endurance. In present work, the aqueous corrosion resistance of the as-cast as well as low temperature oxidized AlCuFeMn alloy in 3.5 wt% NaCl solution, is explored. Equimolar proportions of high purity copper, manganese, iron, and aluminum were arc melted and cast in a copper mold. The alloy primarily consists of a face-centered cubic and a body-centered cubic phase. Potentiodynamic polarization tests on the alloy after low temperature surface oxidation reveal an aqueous corrosion resistance comparable to AISI 304 steel and CoCrFeMnNi high entropy alloy. The X-ray photoelectron spectroscopic studies confirmed that the free surface in the as-cast alloy is in partially oxidized state. The same completely oxidizes after low-temperature surface oxidation. Such low temperature surface oxidation improves pitting corrosion resistance in AlCuFeMn alloy due to increased metal/oxide layer resistance. The electrochemical impedance spectroscopy tests coupled with microscopy confirmed that the principal corrosion mechanisms in the alloy are of the uniform and pitting type. The energy dispersive spectroscopy experiments indicate that a copper oxide enriched layer is formed on the surface oxidized specimen during corrosion.

Improvement of corrosion resistance and biocompatibility of 316L stainless steel for joint replacement application by Ti-doped and Ti-interlayered DLC films

Titanium was incorporated and interlayered into diamond-like carbon (DLC) films deposited on 316L stainless steel using a filtered cathodic vacuum arc. The local bonding structure, corrosion, and biocompatibility of non-doped DLC (ta-C), Ti-interlayered (ta-C/Ti), Ti-doped (ta-C:Ti), and Ti-doped and Ti-interlayered (ta-C:Ti/Ti) DLC films were thoroughly investigated. ta-C:Ti/Ti (0.55 at.%Ti) exhibited not only the highest corrosion resistance performance, including the lowest corrosion rate (7.34 × 10 −8 mm yr −1 ), the highest pitting potential (1672.97 mV), and the highest polarization resistance (5.97 MΩ cm 2 ), owing to the formation of TiO 2 on its surface, as confirmed by X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy, but also the highest amount of hydroxyapatite , an indicator for biocompatibility, on its surface as determined with Fourier transform infrared spectroscopy and scanning electron microscopy. Two barrier layers, namely, outer and inner layers, were observed in ta-C/Ti and ta-C:Ti/Ti, while only one barrier layer was in ta-C and ta-C:Ti, as demonstrated by electrochemical impedance spectroscopy . Therefore, ta-C:Ti/Ti is an alternative promising DLC film for joint replacement biomaterials . • ta-C:Ti and ta-C:Ti/Ti notably increased sp 2 bonding fractions. • All DLC films notably improved 316L corrosion resistance in PBS + 1 g L −1 of HA. • Ti interlayer enhanced pitting corrosion resistance while Ti dopant increased R p . • ta-C:Ti/Ti exhibited the most corrosion resistance and biocompatibility due to TiO 2 . • TiO 2 manifested as a barrier layer and a preferred site for HAp formation.

Understanding the efficacy of concentrated interstitial carbon in enhancing the pitting corrosion resistance of stainless steel

By introducing a high fraction of interstitial carbon through low temperature carburization, the pitting corrosion resistance of austenitic stainless steel can be significantly improved. Previous work attributed this to strengthening of the passive film by carbon. Here, however, we present a paradigm shift by showing that carbon actually weakens the passive film but strengthens the bonding within the alloy by forming localized (covalent) bonds with the metal atoms (Fe, Cr, Ni). Accordingly, the enhancement in pitting resistance is a result of carbon reducing the metal dissolution rate in a local pit environment by many orders of magnitude, which extremely decreases the growth stability of a pit and prevents it from transitioning into stable growth. Electronic structure calculations confirm that carbon bonds to the metal atoms and that the metal–carbon bonds are 1.4 to 2.0 times stronger than the metal–metal bonds. These results suggest a new strategy for the design of corrosion resistant alloys, namely surface engineering by infusion of concentrated interstitials that form strong bonds with the matrix atoms.

Beneficial Effects of Cerium Addition to Sulfide Inclusions on Pitting Corrosion Resistance of Stainless Steels

The pit initiation sites for commercial stainless steels have been attributed to sulfide inclusions such as MnS. The chemical composition of the inclusions affects the pitting corrosion resistance of stainless steels. It is known that the inclusion solubility in aqueous solutions affects pitting corrosion resistance. The dissolution of sulfide inclusions produces S species and exposes the bare surface of the steel matrix, resulting in high pitting susceptibility near the inclusions.1 Cerium is expected to be an additive element for insolubilizing water-soluble inclusions because Ce tends to form sulfides and Ce-sulfides exhibit low solubility in aqueous solutions. Additionally, Ce ions have been shown to be effective in the corrosion inhibition of stainless steel. In this study, a microelectrochemical technique was applied to analyze the effect of Ce addition to sulfide inclusions on the pitting corrosion resistance of stainless steels.2,3 To analyze the effect of Ce addition on water solubility of CaS inclusions, spark plasma sintering was used in the facile fabrication of stainless steel specimens containing artificial Ce-added and Ce-free inclusions.3,4,5 The pit initiation resistance at the Ce-added CaS inclusions was higher than that at the Ce-free CaS inclusions. The surface of the Ce-free CaS inclusions largely dissolved during immersion in 0.1 M NaCl, while a large part of the Ce-added CaS inclusions remained undissolved. Thermodynamic calculation showed that CeS is less soluble than CaS.To analyze the effect of Ce ions on pitting at sulfide inclusions, a type 304 stainless steel (Fe-18Cr-8Ni-1.5Mn-0.02S) was prepared by vacuum induction melting. Manganese sulfide inclusions existed in the specimens. Polarization curves were measured in 3 M NaCl and 2.97 M NaCl-0.01 M CeCl3. Pitting occurred at the MnS inclusions in the Ce3+-free solution, whereas no stable pit was generated in the Ce3+-containing solution even when metastable pitting events were observed.It was found that Ce addition inhibits the dissolution of water-soluble inclusions and improved pitting corrosion resistance. Moreover, the Ce3+ ions are expected to inhibit the pitting even after the dissolution of Ce-added inclusions.

Pitting Corrosion Resistance and Electrochemical Properties of Equimolar CoCrFeMnNi and Non-Equimolar Alcocrfeni High-entropy Alloys

Equimolar CoCrFeMnNi high entropy alloy (HEA) exhibits excellent mechanical properties, but the corrosion resistance is relatively poor because of high Mn content. Thus, this study focused on Al addition and non-equimolar AlCoCrFeNi HEAs were fabricated. To investigate the effect of alloy composition on corrosion resistance, non-equimolar HEAs, Al8Co19Cr23Fe32Ni18 and Al25Co14Cr10Fe19Ni32, were fabricated by arc-melting. Their pitting corrosion resistance was studied by polarization in 0.1 M NaCl. Moreover, Al-containing HEAs have great potential to develop high corrosion resistant alloys by anodizing. Thus, the properties and the pitting corrosion resistance of passive oxide film formed by polarization from -0.55 to 0.5 VSCE in H2SO4 were also investigated.On the basis of the XRD results and surface images, Al8Co19Cr23Fe32Ni18 alloy was single phase alloy. On the other hand, equimolar AlCoCrFeNi and Al25Co14Cr10Fe19Ni32 alloys have multi-phase structures of Al and Ni rich phase and Cr and Fe rich phase. The pitting potential of Al8Co19Cr23Fe32Ni18 alloy was higher than that of equimolar CoCrFeMnNi alloy. After H2SO4 treatment, both alloys have apparent increase in their pitting potential. In the case of multi-phase alloy, Al25Co14Cr10Fe19Ni32 alloy has a lower pitting potential than that of equimolar AlCoCrFeNi alloy. After H2SO4 treatment, the Al and Ni rich phase was dissolved, and a Cr rich oxide layer was formed. This was likely to contribute the improvement of pitting corrosion of both AlCoCrFeNi and Al25Co14Cr10Fe19Ni32 alloys.

Fabrication of Type 304L Containing Mo-rich Areas and Corrosion Behavior

Stainless steels are widely used because of their high corrosion resistance. Mo is main alloying elements that can improve pitting corrosion resistance. Although the role of Mo has been investigated for a long time, there is no unified theory about it.In stainless steels, Mo is added as solid solution. However, in this study, we tried to fabricate a type 304L stainless steel containing Mo-rich areas, and effects of Mo-rich areas on corrosion resistance was investigated1). For fabrication of samples, spark plasma sintering (SPS) was used. The effect of heat-treatments after sintering was also investigated.Type 304L stainless steel containing Mo-rich areas was fabricated by sintering mixed powders of type 304L gas atomized powders and 2.5mass% of Mo powders. Sintering temperature was 1100℃, and it kept for 20 min. After sintering, the sample was heat-treated at 1300℃ for 5 h and water-quenched. After that, a solution-treatment was conducted at 1100℃ 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 heat-treatment of the Type 304L stainless steel containing Mo-rich areas was applied to those specimens. After sintering, the same heat-treatment of the heat-treatment of the Type 304L stainless steel containing Mo-rich areas was performed. In addition, type 304L and type 316L sheets were used.Surface observation of the samples were conducted using an optical microscope, a scanning electron microscope (SEM), a transmission electron microscope (TEM). Electron probe micro analyzer (EPMA) analysis of surface was also conducted.From the observation of the sample surface of the Type 304L stainless steel containing Mo-rich areas, it was found that the sintered samples contained many voids. Mo-rich areas were also observed. In addition to Mo, Cr was found to be rich in the Mo-rich areas.To assess the corrosion resistance, potentiodynamic polarization curves were measured in 0.1 M NaCl (pH 6.0). Specimens were covered by epoxy resin except for the electrode area (5 mm × 5 mm).Polarization curves of sintered samples did not show stable value because of the presence of voids. During the polarization measurements of Type 304L (SPS) and type 316L (SPS), current density increased with increasing potential, and no passivation occurred. On the other hand, in the case of type 304L containing Mo-rich areas (SPS), re-passivation occurred at 0.3 V. After that, current density increased at 0.83 V because of pitting growth. Type 304L containing Mo-rich areas (SPS) showed higher corrosion resistance than the other samples.The effect of heat-treatments after sintering was also investigated. Type 304L powders and Mo powders (2.5 mass%) were mixed and sintered. After sintering, four different heat-treated samples were prepared.Polarization measurements of each sample were performed. Passivation occurred in the polarization of the sample heat-treated at high temperature, and it showed the highest corrosion resistance of the four samples.Reference; Saito, I. Muto and Y. Sugawara, Mater.Trans., 61 (2020), 2248-2251

Dissolution Behavior of Hydrated Tungsten Chlorides in Chloroaluminate Ionic Liquids and It's Application in Aluminum–Tungsten Alloy Electrodeposition

Introduction The demand for aluminum (Al) alloys as coating materials have increased owing to their high corrosion and oxidation resistance. In addition, electrodeposition technique has attracted attention for obtaining Al alloy coatings, and various non-aqueous electrolytic baths for Al alloy electrodeposition, including ionic liquids, have been developed. Alloying Al with refractory metals, such as tungsten (W) and molybdenum (Mo), significantly improves the pitting-corrosion resistance of Al. However, the salts of these metals have relatively low solubility in Al electrodeposition baths, and thus, it is difficult to obtain Al alloys with a high content of these metals.In our previous study, we reported that a W(II) salt, namely W6Cl12, which is dissolved in 1-ethyl-3-methylimidazolium (EMIC)–AlCl3 ionic liquids at a higher concentration than other salts such as WCl4, enables the electrodeposition of Al–W alloy films with a high W content[1]. However, the W6Cl12 used previously turned out to contain water due to the synthesis process, which may have increased the solubility of W6Cl12.In this study, we investigated the effect of water content on the solubility of W precursors in ionic liquids. Herein, three W precursors with different water contents were employed, namely anhydrous W6Cl12 and hydrated complexes W6Cl12·2H2O and (H3O)2[W6Cl14]·7H2O (Figure 1). Al–W alloy was electrodeposited using baths containing different W precursors. In addition, the chemical speciation of the hydrated complexes in the ionic liquids was conducted using, Raman, and Fourier transform infrared (FT-IR), ultraviolet-visible (UV-Vis) spectroscopy. Experimental Herein, three electrolytic baths were prepared by adding anhydrous salt W6Cl12, hydrated complex W6Cl12·2H2O, and (H3O)2[W6Cl14]·7H2O to an EMIC–AlCl3 ionic liquid with EMIC:AlCl3 molar ratio of 1:2. The saturation concentrations of W precursors were determined using inductively coupled plasma atomic emission spectroscopy (ICP-AES). Potentiostatic electrodeposition was performed on copper substrates at a bath temperature of 80 °C under an Ar atmosphere in a glove box. The W content, current efficiency, and impurity content derived from the hydration water in the electrodeposited material were evaluated by energy dispersive X-ray spectroscopy (EDX), ICP-AES, and X-ray photoelectron spectroscopy (XPS), respectively. The dissolved species in the baths were analyzed by Raman, FT-IR, and UV-Vis spectroscopy. Results and Discussion The saturation concentration of each W ion source in the EMIC–AlCl3 ionic liquid was less than 1 mM for anhydrous W6Cl12; however, it increased to ~80 and 120 mM for W6Cl12·2H2O and (H3O)2[W6Cl14]·7H2O, respectively. Potentiostatic electrodeposition at potentials lower than 0 V (vs. Al/Al(III)) produced films consisting of Al and W. The W content increased to ~1 and 15 at.% from the anhydrous salt bath and hydrated complex bath, respectively. The current efficiency for electrodeposition was close to 100%, even in baths with hydrated precursors. EDX and XPS measurements of Al–15 at.% W alloy film obtained from the hydrated complex bath showed that Al and W existed in metallic states in the film.The Raman spectra of each bath showed that the Al2Cl7 − concentration decreased and AlCl4 − concentration increased in the hydrated complex bath compared to the anhydrous salt bath. This suggests that the hydrated W complex reacted with AlCl3 to form other Al species, thereby decreasing the apparent AlCl3/EMIC ratio in the bath. The FT-IR spectra of baths with the addition of hydrated complex or liquid water showed that both the hydrated water and liquid water reacted with Al anions to produce Al–OH–Cl species[2]. The UV-Vis spectra of the anhydrous salt bath and hydrated complex baths showed two prominent peaks: one at 240 nm (λ1) and the other at ~270–300 nm (λ2). λ1 was almost constant for all the W precursors, whereas λ2 shifted to a lower wavelength for the hydrated complex baths. The dissolved W species estimated from these spectroscopic data and their relationship with solubility are discussed at the meeting.

Pitting corrosion behavior of friction-surfaced 17-4PH stainless steel coatings with and without subsequent heat treatment

Improvement in pitting corrosion resistance of the friction-surfaced (FSed) 17-4PH stainless steel coatings was mainly attributed to fragmentation of sulfide inclusions during friction surfacing (FS). Formation of vermicular δ-ferrite and grain refinement of martensitic matrix around the δ-ferrite affected the distribution of pits. FS parameters had a negligible effect on the pitting corrosion resistance of the FSed 17-4PH coatings. However, the decrease in pitting corrosion resistance of the FSed coatings after aging (H900) was due to the higher dislocation density for facilitating the metastable pit initiation and promoting the transition of metastable pits to the stable ones.

Microstructure and Corrosion Behavior of Functionally Graded Wire Arc Additive Manufactured Steel Combinations

Functionally graded materials (FGM) have gained many interests for various applications and are designed to match special requirements in local properties (e.g., corrosion behavior), which highly determines the component's lifetime. The corrosion behavior is strongly dependent on the chemical composition and the microstructure of the designed materials. Therefore, two FGM combinations are designed using wire arc additive manufacturing (WAAM) with a linear changing material deposition from G 3Si1 to G 19 9L Si (combination 1) and G 18L Nb to G 19 9L Si (combination 2). The microstructure at different positions is analyzed using optical light microscopy (OLM), scanning electron microscopy with attached energy dispersive X‐ray spectroscopy (SEM/EDS), and X‐ray diffraction (XRD). The electrochemical corrosion behavior in 0.6 m NaCl solution is determined by cyclic potentiodynamic polarization (CPDP) including SEM imaging after CPDP to determine the pit size and morphology. The phase formation sequences of ferrite (α and δ), martensite, and types of austenite are discussed regarding the chemical gradient. The pitting corrosion resistance is enhanced for both combinations in direction to G 19 9L Si due to the increase in Cr and/or Ni, while the pit morphology changes in dependence of the presence of various microstructures.

Oxygen impurity improving corrosion resistance of a Zr-based bulk metallic glass in 3.5 wt% NaCl solution

The effect of oxygen impurity on corrosion behavior of as-cast Zr61Ti2Cu25Al12 bulk metallic glasses (BMGs) is clarified using electrochemical measurements, microstructure characterization and surface analyses. We find unexpectedly that oxygen impurity (≤1200 ppm) improves pitting corrosion resistance when a fully amorphous structure is attained. The oxygen-induced annihilation of free volume enhances passive film protectiveness and hence accounts for the improved corrosion property. In contrast, adding more oxygen impurity (1800 ppm) deteriorates pitting corrosion resistance by assisting the formation of highly-reactive crystalline phases. The finding herein provides an avenue for designing new low-cost Zr-based BMGs with superior properties by oxygen microalloying.