Corrosion Potential Research Articles

Effect of CNTs concentration on the microstructure and properties of B, Ni, CNTs co-doped diamond like carbon films

B, Ni, and CNTs co-doped diamond-like carbon (B, Ni, CNTs co-doped DLC) films were synthesized on the surface of AZ91D magnesium alloy by electrodeposition with low cost. The effect of CNTs concentration on the microstructure, microhardness, tribological properties and corrosion behavior of B, Ni, CNTs co-doped DLC films were evaluated. Results revealed that the B, Ni, CNTs co-doped DLC films were hydrogenated amorphous carbon films. Raman spectra showed that the D and G peaks of DLC films appear near 1330 cm−1 near 1580 cm−1, respectively. When the concentration of CNTs was 0.25 g/L, the CNTs were evenly distributed, making the structure of co-doped DLC films uniform, dense and flat. At this time, since the combined synergistic effect of reticulation of CNTs and the network-like structure of DLC films, the microhardness of the co-doped DLC films reached the maximum of 248.3 HV. The tubular structure of CNT supports and lubricates the substrate, which weakens the frictional resistance between the friction partners and reduces the friction coefficient to the lowest value of 0.128. The wear loss was the minimum with 0.1 × 10−5 kg/m, which is the result of CNTs exerting their self-lubricating properties to improve the wear resistance of the DLC film so that less wear occurs during the repeated friction process. Meanwhile, the positive corrosion potentials of B, Ni, CNTs co-doped DLC films indicate that the three elements co-doped DLC films can improve the corrosion resistance of magnesium alloy substrates.

The spontaneous passivation of (CoFeNi)(1-x)/3Crx alloys in sulfuric acid

The influence of at% Cr on the spontaneous passivation of (CoFeNi)(1-x)/3Crx alloys in 0.1 M H2SO4 was investigated. During spontaneous passivation, Cr enrichment occurs due to the selective dissolution of the matrix elements. The quantity of Cr enrichment is relatively constant with at% Cr while the total quantity of alloy dissolved decreases with increasing at% Cr. Element resolved polarization curves predict spontaneous passivation by comparing the critical dissolution rate with the cathodic kinetics near the corrosion potential. The stoichiometric relationships between the spontaneous dissolution rate, Cr enrichment, and the open circuit potential were determined and discussed.

Waterborne robust superhydrophobic PFDTES@TiO2-PU coating with stable corrosion resistance, long-term environmental adaptability, and delayed icing functions on Al–Li alloy

Aluminum–Lithium (Al–Li) alloys widely used in aerospace manufacture are highly susceptible to corrosion, which limits their industrial applications. Herein, 1H,1H,2H,2H-perfluorodecyltriethoxysilane (PFDTES) is used as a modifier for low-surface-energy treatment of TiO2 nanoparticles. The water-based polyurethane (PU) is made as a binder to achieve a tight bonding between modified ceramic particles and Al–Li alloy, thus resulting in the extremely-feasible air-spraying preparation of a superhydrophobic coating with strong abrasion resistance. The water contact angle (CA) of as-prepared coating achieves 160 ± 0.83°, and the rolling angle (SA) is as low as 5.95 ± 0.59°. The surface structure, organization and composition are further characterized using SEM, EDS, XPS and laser confocal microscopy. Meanwhile, the electrochemical impedance and potentiodynamic polarization tests are performed for corrosion characterization. The results show that the corrosion potential of such coating increases by 170 mV compared with substrate, the corrosion current density decreases by two orders of magnitude, and the impedance modulus increases by two orders. The corrosion inhibition rate of the as-prepared coating is 98.8%, indicating that the corrosion resistance has been significantly enhanced. In addition, the mechanical robustness and stability of the coating is evaluated and confirmed using a sandpaper rubbing test. It also possesses great self-cleaning, anti-pollution and thermostable behaviors, thereby allowing them to work in extreme manufactures. Moreover, the as-prepared coating exhibits excellent adaptability to various materials and anti-icing property. This work sheds positive insights in enlarging industrial applications of multifunctional ceramic coatings in aerospace fields.

Durability of Alkali activated concrete made using multiple precursors as primary binders

Alkali-activated binders (AABs) have been and continue to be extensively explored as an alternative to ordinary Portland cement (OPC), addressing environmental and sustainability issues. A large number of studies that were conducted earlier focused mainly on the mechanical properties and some durability aspects of industrial waste-based AABs. However, chloride migration and diffusion causing reinforcement corrosion in AAB-based concrete (AAC) have not been thoroughly investigated. The present study focuses on the durability of AAC produced using multiple precursors that included industrial waste materials and natural minerals such as limestone powder (LSP), red mud (RM), silicomanganese fume (SMF), and natural pozzolan (NP) activated by alkali. Firstly, the dosages of all four precursors were optimized through trials and then NP was partially replaced by 10, 20 and 30% OPC to enhance the performance of the AABs. The AAC mixtures were prepared and cured under different conditions and tested for compressive strength and durability characteristics related to chloride permeability, chloride migration, chloride diffusion, and chloride-induced reinforcement corrosion to evaluate the performances of the mixtures. The results show that the composition of the AABs and curing regimes significantly influenced the performance of the AAC. The inclusion of the OPC resulted in a very significant enhancement of the strength and durability characteristics of the AAC. In addition, there is a sharp increase in the performance of the AAC mixtures when the OPC content of the precursor was increased from 10 to 20%, irrespective of the curing method. Therefore, an optimum dosage of the OPC in the precursor can be considered as 20%, allowing utilization of 80% waste materials and natural minerals as the precursor with much higher strength and durability characteristics than traditional OPC concrete, thus saving energy and reducing environmental pollution leading to a cleaner production of concrete. Lastly, electrochemically measured corrosion potential (Ecorr ) and corrosion current density (Icorr ) values for the reinforcing bars (rebars) embedded in AAC mixtures were found to be misleading, as confirmed by visual inspection of the extracted rebars in addition to gravimetric test results. Hence, there is a need for further research to develop corrective measures before the utilization of the electrochemical-reinforced corrosion monitoring methods in the case of AACs.

Amino polycarboxylic acid complex agent modified Fe0 enhanced activation of H2O2 double decomposition pathways for tetracycline removal under neutral condition

The summary of this study explores the modification of Fe0 with amino polycarboxylic acid complex agents (APCAs) to enhance H2O2 catalysis for tetracycline (TC) removal under neutral conditions. The ethylenediaminetetraacetic acid-modified Fe0/H2O2 system (EDTA-Fe0/H2O2) achieved a removal efficiency of 90.2 % for 50 mg/L TC, significantly higher than the 23.9 % efficiency of the traditional Fe0/H2O2 system. The removal rate of various pollutants by the EDTA- Fe0/H2O2 process is 2.9 to 8.4 times higher than that of the Fe0/H2O2 process. After four cycles of use, the removal rate of TC by the EDTA-Fe0/H2O2 system can still reach 76.3 %. Additionally, the effect of treating TC in natural freshwater can also achieve 80.1 %. Characterization revealed that EDTA-Fe0 had a larger Fe(II) proportion, better hydrophobicity, and lower corrosion potential than Fe0, indicating higher activity. Quenching experiments and electron paramagnetic resonance tests confirmed that •OH was the major reactive species. Shell-isolated nanoparticle-enhanced Raman spectroscopy indicated the presence of *OOH species, suggesting the involvement of a dioxygen coordination reaction. Density functional theory calculations showed that both dioxygen and single oxygen coordination H2O2 decomposition pathways played significant roles, and EDTA-Fe0 exhibited high catalysis ability for H2O2 in both pathways. Analysis of the relationship between APCAs’ group structure and APCAs-Fe0 properties indicated that the number of carboxyl groups was crucial for enhancing catalytic activity, while the number of amino groups also impacted antibiotic removal efficiency. Overall, this study provides a solid theoretical foundation for further Fe0 applications and suggests a new method to improve TC removal.

Effects of Nb and Mo Alloying Elements on the Corrosion Characteristics of Sintered Cobalt-Chromium Alloys in Hanks Solution for Biomedical Application

This study investigates the influence of molybdenum and niobium on the corrosion characteristics of spark plasma-sintered cobalt–chromium (Co–Cr) in Hank’s solution for their biocompatibility for potential biomedical applications using spark plasma sintering (SPS). The results indicated that the Co–Cr binary alloy was highly susceptible to corrosion in the Hanks solution due to its low corrosion potential and high current density. Compared to Co–Cr–7Mo, the ternary compositions of Co–Cr–5Mo and Co–Cr–6Mo exhibited a somewhat higher susceptibility to corrosion more than 10%, showing a high corrosion potential and current density. While the Co–Cr–3Mo–3Nb composition had a high current density and a negative corrosion potential. The Co–Cr–2.5Mo–2.5Nb composition was only moderately susceptible to passive corrosion. The highest corrosion resistance was found in the Co–Cr–3.5Mo–3.5Nb alloy, indicating that uniform corrosion may occur in this alloy, albeit slowly. This study explores the impact of Nb and Mo on the corrosion resistance of sintered cobalt-chromium alloys in a biologically relevant environment. Hence, it is noteworthy that the development of next-generation biomaterials and medical devices depends on this breakthrough in surface functionalization.

Preparation and properties of multiphase composite enhanced functional organosilicon nano-coatings

BackgroundTo improve the inherent stability and environmental compatibility of traditional organosilicon coatings, nano-reinforced composite materials were innovatively designed and synthesized to improve the performance of organosilicon coatings. MethodologyThe silicon dioxide (SiO2) clusters on the surface of graphene oxide (GO) incorporated with calcium carbonate (CaCO3) and dicyclohexylamine nitrite (Dn) nanocomposites (GO@SiO2/CaCO3/Dn) were prepared successfully. Then nanocomposites were integrated into the coating matrix to comprehensively assess their effects on morphology, mechanics, corrosion resistance, and anti-fouling properties. Significant findingsScanning Electron Microscopy (SEM) observations revealed that 4.0 wt.% of the nanocomposite reinforcement led to stratification within the organosilicon coating. The mechanical properties test shows that the hardness, bonding strength, and maximum impact resistance of SiNC2.0 coating is 10.3 HV, 2.8 MPa, and 75 kg·cm, respectively. Electrochemical assessments confirmed that SiNC2.0 displayed superior corrosion resistance, with a corrosion potential (Ecorr) of 0.199 V and a corrosion current density (Icorr) of 7.308 × 10–6 A/cm2. Furthermore, the surface free energy of the nano-coatings is calculated in the range of 20–30 mN/m by contact angle measurement, indicating the anti-fouling and self-cleaning of the organosilicon nano-coatings. Long-term immersion in natural lake water further confirms the stability and durability of the SiNC2.0 coating in real environments.

Effect of Zr content on the microstructure, mechanical properties, electrochemical behavior, and biocompatibility of Mg–3Zn–xZr alloy using powder metallurgy

Abstract In this study, Mg–3Zn–xZr (x = 0, 0.5, 1, 2 and 3) alloy were produced using powder metallurgy incorporating high-energy ball milling. Scanning electron microscope (SEM), energy dispersive X-ray (EDX) analyzer and X-ray diffraction (XRD) have been used to investigate the microstructure, chemical composition and phase distribution of the samples. XRD results show that the Mg solid solution wholly formed, and the milled powders were single phase, and no secondary phase was observed. While the secondary phases were formed after sintering. Hardness of Mg–Zn–xZr sample increased from 58.8 Hv (for Zr = 0) to 87.81 Hv with addition of 3 wt.% Zr. The result shows that the corrosion potential of Mg–Zn–Zr alloy was more positive than Mg–3Zn. However, the Mg–3Zn–Zr alloy exhibited higher corrosion current than Mg–3Zn due to galvanic effect of Zr rich area. All of Mg–3Zn–Zr alloys showed better antibacterial and biocompatibility properties than Mg–3Zn alloy due to the presence of Zr as additive. According to the mechanical, corrosion, and biological evaluations in this study, it can be concluded that the Mg–3Zn–1Zr alloy can be used as a suitable biomaterial for the use of orthopedic implants.

Trace ruthenium dioxide stabilize active center of CoFe-LDH for efficient water electrolysis

It is immensely meaningful to design efficient electrolysis for water electrolysis and realize green hydrogen production. Herein, a ruthenium dioxide modified CoFe-Layered double hydroxides (LDHs) catalyst (RuO2/CoFe-LDH/NF) was synthesized by combining the advantages of RuO2 and CoFe-LDHs for driving alkaline water and seawater. RuO2/CoFe-LDH/NF display impressive activity and stability at 10 mA cm−2, which only need an overpotential of 59 and 270 mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) respectively. Meaningfully, the catalyst only required a small cell voltage of 1.58 V as a bifunctional catalyst, what is superior to commercial RuO2/NF||Pt/C/NF (1.66 V). In addition, RuO2/CoFe-LDH/NF exhibited excellent HER and OER performance with overpotentials of 119 and 260 mv in alkaline seawater at 10 mA cm−2, respectively. Additionally, RuO2/CoFe-LDH/NF displays a larger corrosion potential, smaller corrosion and improved oxygen evolution capacity than CoFe-LDH/NF. Moreover, there is electron transfer between Ru and Co or Fe, which can improve the micro-coordination environment and enhance the stability for RuO2/CoFe-LDH/NF. The method with integration of RuO2 and CoFe-LDH could be broadened to explore other robust bifunctional catalysts for water/seawater electrolysis.

The Galvanic Corrosion of AM60B Coupled with DC01 in Simulated Environments with Varying Water Salinity.

The galvanic corrosion performance of AM60B coupled to DC01 was characterized in simulated environments with varying water salinity. The results showed that the coupled DC01 effectively accelerated the corrosion rate of AM60B, and the increased salt concentration had a significant effect on the deterioration process. The corrosion of AM60B mainly exhibits metal dissolution, and the formed Mg(OH)2 has weak a protective effect on the alloy substrate. Furthermore, the distributions of the corrosion potential and the corrosion current density of the AM60B/DC01 couple were simulated and intensively discussed.

Study on microbiologically influenced corrosion of HSLA-65 steel

In the current study, the corrosion behavior of HSLA-65 steel was investigated in a simulated marine environment inoculated with P. aeruginosa. In the electrochemical measurements, the negative shift in OCP, lower values of corrosion potential, pitting potential, and increased corrosion current density of the HSLA-65 steel in the biotic medium signified its low corrosion resistance in the presence of P. aeruginosa. The observation of the surface morphology revealed biofilm formation on the steel surface in the P. aeruginosa-inoculated culture medium, which significantly accelerated the pitting corrosion of the steel. The pit observed on the steel surface in the biotic medium was about 3.9 times deeper than in the sterile medium. In addition, the weight loss of the steel in the biotic medium was about 2.4 times higher compared to that in the sterile medium. These findings suggest that the P. aeruginosa biofilm significantly accelerated the corrosion of HSLA-65 steel in the simulated marine environment.

The effect of three types of heat treatment on the hardness and corrosion resistance of Al 2014 alloy

AbstractAl 2014 is a high‐strength aluminum alloy widely used in the aerospace and automotive industries for its mechanical strength. This research examines the effects of three heat treatment processes—retrogression and re‐aging (RRA), T6 standard aging, and a modified RRA with high‐temperature pre‐aging—on the hardness and corrosion resistance of Al 2014. Polarization studies using potentiodynamic electrochemical methods in a 3.5 wt% sodium chloride solution were conducted to evaluate the corrosion resistance. The results showed that heat treatment, which causes precipitation hardening, shifted the corrosion potential (E) toward a more noble direction. The formation of Al2Cu precipitates is associated with improved corrosion resistance. Additionally, samples treated with the T6 process exhibited a higher corrosion current density compared to untreated Al 2014 alloy samples, indicating superior corrosion resistance. Analysis of corroded surfaces using scanning electron microscopy (SEM) with energy‐dispersive X‐ray spectroscopy (EDS) showed evidence of general and pitting corrosion, with distinct patterns among the three heat treatment processes. A comparison of the results revealed that the T6 standard aging process provided the best combination of hardness and corrosion resistance. This was likely due to the formation of stable precipitates during aging. The results also indicated that the RRA process showed good performance, suggesting it is a viable alternative when a balance between hardness and toughness is required. The modified RRA with high‐temperature pre‐aging resulted in lower performance, likely due to overaging, which reduced hardness and corrosion resistance. These findings highlight the significance of heat treatment in improving the corrosion resistance of Al 2014 alloy. This suggests that particular processes can enhance the alloy's durability in corrosive environments, potentially leading to a longer lifespan and reduced maintenance costs. The T6 standard aging process offers the best balance of enhanced hardness and corrosion resistance for Al 2014 alloy, making it ideal for extending lifespan and reducing maintenance costs in corrosive environments. Careful selection of heat treatment is crucial based on specific alloy performance requirements.

The time evolution of electrical and thermodynamic characteristics of surface dielectric barrier discharge caused by dielectric degradation

Abstract The degradation of the dielectric layer is a common issue in dielectric barrier discharge (DBD). The performance of DBD devices may suffer from instability due to potential corrosion of the dielectric layer caused by discharge, which could even result in structural failure. To gain a comprehensive understanding of the degradation of DBD devices during discharge, the evolution of the performance of DBD devices with various dielectric materials over time is studied. Periodic patterns are found to form on the dielectric surface along the edge of the high-voltage electrode. The electrical data, emission spectra, and surface morphologies of DBD devices with three different dielectric materials, namely ceramics, glass, and PCB, are obtained during an eight-hour discharge. The electrical and thermodynamic characteristics of DBD devices with the three dielectric materials are found to initially decrease by about 20~40%. Subsequently, they remain stable in devices with ceramics and PCB dielectric layers but increase in devices with glass dielectric layers until the end. Surface morphologies reveal that periodic patterns consisting of metal accumulations, etching pits, and metal depositions form on the surfaces of ceramics, glass, and PCBs, respectively. Some organic compounds vaporize from the surface of PCBs. The deposition, etching, and vaporization could be reasons for changes in the electrical and thermodynamic characteristics. It shows that degradation occurs not only in organic dielectrics like polymers but also in inorganic dielectrics such as ceramics and glass. To enhance stability and prevent potential failures and overestimations, electrical and optical measurements could be utilized as diagnostic methods in applications involving DBD devices.


Fatigue and corrosion‐fatigue behavior of the β‐metastable Ti‐5Al‐5Mo‐5V‐3Cr alloy processed by laser powder bed fusion

AbstractWe performed rotating bending tests and axial (tension‐compression) load‐increase and constant amplitude high‐cycle fatigue tests in air and Hanks' balanced salt solution (HBSS) on the β‐metastable titanium alloy Ti‐5Al‐5Mo‐5V‐3Cr, processed by laser powder bed fusion (LPBF‐M), solution‐treated and aged, and shot‐peened. Rotating bending loading in air revealed a strong influence of process‐induced flaws on fatigue endurance. Especially in the high‐cycle fatigue range and the transition region, the stochastic distribution of the flaws and flaw sizes led to a high scatter of the number of cycles to failure. The axial load‐increase tests yielded a good fatigue life estimation, with a negligible difference between air and HBSS. The cyclic deformation behavior in HBSS was also strongly influenced by the local microstructure and defect distribution, and, thus, by crack formation and propagation. Plastic deformation and microcrack growth interact, and their relative amount resulted in different progressions of the plastic strain amplitude over the number of cycles for different specimens. Changes in the free corrosion potential and the corrosion current were highly sensitive indicators for fatigue‐induced damage on the rough surfaces, which was correlated to the microscopic examination, fracture surface features, and the fatigue crack development.

EIS Investigation of a Single Pit on Cantor Alloy in Acidic Environment

High-entropy alloys (HEA) are an emerging class of materials with promising properties such as high strength and ductility, improved fatigue resistance, fracture toughness, and thermal stability. They show considerable potential for use as corrosion resistant alloys to support our infrastructure especially for use in extreme environments. In this work, we mainly focused on the typical Cantor alloy, which consists in a mixture of 5 elements CrMnFeCoNi in equimolar proportion. A huge amount of works has already been devoted to the study corrosion resistance of alloys in sulfuric acid [1] or in chloride containing solutions [2,3]. For the latter, the study of the pitting propagation remains challenging since this kind of corrosion initiates as a stochastic process.Electrochemical impedance spectroscopy (EIS) is intensively used as a tool for corrosion research and is well suited for the identification of complex mechanisms. However, data analysis remains difficult in the case of pitting studies, which can be described schematically as n anodic sites in parallel at different states of evolution. In this work we report on EIS analysis performed on a single pit (Fig. 1a) in order to describe the various step of its evolution as a function of time, but also as a function of various parameters such as the chloride ion concentration or the corrosion potential. Single pits were obtained by studying the breakdown of the passive film using the pumped-micropipette delivery/substrate collection (Pumped-MD/SC) mode of scanning electrochemical microscopy (SECM). A detailed mechanism is proposed to account for EIS results obtained on a single pit (Fig. 1b) in order to explain results on usuals EIS measurements.[1] J. Yang, J. Wu, C. Y. Zhang, S. D. Zhang, B. J. Yang, W. Emori et J. Q. Wang, « Effects of Mn on the electrochemical corrosion and passivation behavior of CoFeNiMnCr high-entropy alloy system in H2SO4 solution », Journal of Alloys and Compounds, 819, avril 2020, p. 152943, https://doi.org/10.1016/j.jallcom.2019.152943[2] Camila Boldrini Nascimento, Uyime Donatus, Carlos Triveño Ríos et Renato Altobelli Antunes, « Electronic properties of the passive films formed on CoCrFeNi and CoCrFeNiAl high entropy alloys in sodium chloride solution », Journal of Materials Research and Technology, 9, no 6, novembre 2020, p. 13879-92, https://doi.org/10.1016/j.jmrt.2020.10.002[3] Mengjiao Li, Qingjun Chen, Xia Cui, Xinyuan Peng et Guosheng Huang, « Evaluation of corrosion resistance of the single-phase light refractory high entropy alloy TiCrVNb0.5Al0.5 in chloride environment », Journal of Alloys and Compounds, 857, mars 2021, p. 158278, https://doi.org/10.1016/j.jallcom.2020.158278 Figure 1

(Dielectric Science and Technology Division Poster Award, 3rd Place) Radical Oxidation for Enhancing Polishing-Rate and Improving Slurry Stability in Ag-Film Chemical–Mechanical-Planarization

Recently, Ag-film has been utilized as a reflective layer in organic-light-emitting- diode on silicion(OLEDoS). The formation of a reflective Ag-film layer was conducted by Ag-film deposition and following Ag-film chemical-mechanical planarization (CMP). The Ag-film has ductility property (i.e., hardness of 0.3 GPa) so that a reletively soft CMP pad should be used to minimize the generation of the CMP induced scratches. However, using a soft CMP pad, it is notably difficult to achieve a high Ag-film polishing-rate (i.e., 300 nm/min). Thus, to enhance Ag-film polishing-rate, a Fenton reaction between ferric ions and H2O2 has been applied. Although, a Fenton reaction enhancing dissolved oxygen concentration can increase remarkably the Ag-film polishing-rate, the CMP slurry using Fenton reaction has produced a detrimental slurry stability after mixing with H2O2 (i.e., extremely low H2O2 pot life time. In this study, as a solution, the Ag-film CMP slurry was designed via radical oxidation on the Ag-film surface during CMP, without using Fenton reaction (i.e., mixing ferric ions with H2O2). The radical oxidation was achived by using halide oxidant (i.e., H5IO6), which radical oxidation degree principally depended on halide oxidant concentration and slurry pH, showing a notable high Ag-film polishing-rate (i.e., 400 nm/min) without the precence of corrosion. Without using Fenton reaction, the secondary diameter of colloidal abrasives in the designed Ag-film CMP slurry was not changed for several months. In our presentation, we will prove the mechanism of the radical oxidation on the polished Ag-film surface. In addition, we will present the dependencies of the chemical dominant polishing properties (i.e., OH radical, chemical oxidation degree of the Ag-film surfcae, chemical composition of chemical oxidation, slurry adsortion degree, and corrosion potential and current) as well as the mechanical dominant polishing properties (i.e., electrostatic force between abrasives and Ag-film surface) on the halid oxidant concentration.

Corrosion Evaluation of Metal Binder-Jetted Stainless Steel Parts: Influence of Printing Parameters on Performance

Additive manufacturing is a rapidly expanding fabrication process in both research and industry, capable of constructing parts layer by layer from a 3D CAD model. ASTM recognizes seven distinct additive manufacturing processes, with the majority capable of producing metal components. Among these technologies, binder jetting stands out, offering the potential to create a variety of metallic parts for applications in the biomedical and energy sectors at reduced costs and shorter lead times. Achieving acceptable corrosion resistance is crucial for such applications. Binder jetting exhibits advantages such as relatively high part density (~99%) and good surface roughness (~6μm for as-sintered parts), making it an ideal candidate for investigating corrosion behavior, given the general correlation between low surface roughness, high density, and improved corrosion performance. Despite its promise, binder jetting lacks standardized procedures for producing parts with specific properties, necessitating users to determine parameters through trial and error. The corrosion behavior of parts created through binder jetting remains uncertain due to various influencing parameters. This study focuses on two key printing factors: layer thickness and binder saturation, chosen due to their impact on surface roughness, density, and thereby on corrosion. Existing literature suggests that increased layer thickness may reduce powder bed density, potentially affecting green part density and causing more significant shrinkage during sintering. Simultaneously, binder saturation is recognized as a critical factor influencing final part quality. Predicting the combined impact of layer thickness and binder saturation on corrosion performance proves challenging. To unravel this relationship, we conducted experiments using an ExOne Innovate Plus metal binder jetting machine and 316L stainless steel metal powder (mean powder size of 22μm) which is widely recognized as the most common powder in research. A number of test runs were conducted by varying layer thickness and binder saturation, offering insights into their nuanced interplay in the context of corrosion performance. Initially, to address insufficient green strength, printer drying time and curing cycle time were optimized by conducting a series of experiments changing the drying time and curing time. Subsequent printing involved changing binder saturation parallel to the layer thickness variations, resulting in distinct parts with varying properties. Then the predetermined curing cycle was executed, followed by de-powdering, and sintering in a furnace. Sintering is imperative to increase the part density and enhance the overall strength of the final product. However, it's essential to acknowledge that sintering may adversely impact corrosion resistance due to the remaining porosity and surface fissures. The choice of sintering profile becomes crucial, necessitating careful consideration to minimize elemental migration during sintering and mitigate porosity. Scanning electron microscopy and optical microscopy are used to analyze sintered parts and interpret corrosion mechanisms. Electrochemical tests were conducted to identify corrosion rates, corrosion potential, passivation behavior, pitting potential, etc. in contrast with conventionally manufactured 316L in M NaCl solution. This study offers insights and recommendations aimed at enhancing the corrosion resistance of binder jetted stainless steel parts.

Galvanic Corrosion Behavior of Zn and Al Couples in NaCl Solution

Multi-materialization is being promoted in automotive structural materials, and fuel economy is being improved by replacing steel with aluminum and other lightweight metallic materials. Automotive steel is often galvanized for corrosion protection, and galvanic corrosion of aluminum and zinc in an atmospheric environment is a very important issue in evaluating automotive durability. Zinc is usually considered to be an anode when combined with aluminum, but its galvanic corrosion behavior can be complicated by environmental conditions because the corrosion potentials of the two are relatively close. Therefore, the objective of this study is to investigate the galvanic corrosion behavior of the couples consisting of zinc and aluminum under corrosive environmental conditions.The galvanic couple used in this study was fabricated from AA1050 Al and zinc plates. The width and length of both plates are 10 mm and 15 mm, respectively. After connecting lead wires to each plate, both plates were embedded in epoxy resin. To fabricate coplanar galvanic couples in this study, both plates were placed separately along the surface from a gap size of 500 um. The surfaces of the galvanic pairs were polished with SiC paper to JIS 2000 grit and cleaned with EtOH. The test solutions used in this study were aqueous NaCl solutions of various concentrations from 0.01 to 2 M, prepared with Milli-Q water and reagent grade chemicals. Galvanic currents and corrosion potentials were measured to investigate the galvanic corrosion behavior of the couples after 72 hours of galvanic corrosion experiments in the test solutions.The results of the galvanic corrosion test showed that the immersion potentials of the galvanic couples were lower at higher NaCl concentrations. The galvanic current decreased with immersion time, finally reaching about 1 uA in all NaCl solutions. The results of the electrochemical impedance measurements for galvanic couples in various NaCl concentrations showed that the impedance gradually increased with immersion time. It was also found that the impedance can be expressed as an electrical equivalent circuit consisting of two time constants, and that the impedance increases at intermediate frequencies between 0.1 and 1 Hz, which is thought to correspond to the dissolution reaction of Zn. This was the same trend as the behavior of the galvanic current. These results suggest that prolonged immersion reduces the galvanic current and the dissolution rate of zinc due to the passivation of the A1050 surface and the suppression of cathodic reactions.

Comparing the Corrosion Behavior and Microstructure of a WE43 Mg Alloy in Simulated Body Fluids Under Different CO2 Conditions

With the low density and high specific strength, magnesium (Mg) alloys are lightweight alloys with various applications. In addition, combined with biocompatibility, similar mechanical properties to human bones, and unique biodegradability, Mg alloys are promising biodegradable implant materials for orthopedic surgeries. However, the degradation rates of Mg alloys are too fast in physiological environments, which limits the clinical applications of Mg implants. Therefore, understanding the corrosion behavior in physiological environments is crucial for developing biodegradable Mg alloys.During Mg alloy degradation, hydroxide (OH-) ions are generated, and the pH near the alloy surface increases. Since carbonate-bicarbonate (CO3 2--HCO3 -) is a vital pH buffer system in the human body, the corrosion behavior of Mg alloys would be affected by the CO2 concentrations of the test environments. In this study, we performed electrochemical and corrosion tests of a solution heat-treated WE43 (Mg-4 wt%Y-3 wt%Nd) alloy in Hanks’ balanced salt solutions (HBSS) at 37°C. By performing the tests in air and in an incubator maintained at 5% CO2, the effect of carbonate-bicarbonate pH buffering on the corrosion behavior and corrosion microstructure of the WE43 Mg alloy was investigated.When testing the WE43 Mg alloy in air, a general corrosion morphology was observed during the 24-hour immersion. In contrast, WE43 Mg alloy tested in the incubator shows a more active surface potential and localized corrosion initiates on the alloy surface in the early stages of immersion. Electrochemical impedance spectroscopy (EIS) analysis shows that WE43 Mg alloy tested in air has better corrosion resistance than in the incubator. Furthermore, the corrosion resistance of the alloy tested in air increases with immersion time but decreases when tested in the incubator. Potentiodynamic polarization curves after 24-hour immersion confirm that the corrosion current density (i corr) of the WE43 Mg alloy tested in the incubator is higher than that when tested in air. The difference in corrosion behavior is owing to the carbonate-bicarbonate pH buffering effect and will be discussed based on corrosion microstructure characterizations. Figure 1

Corrosion behavior of steel bar in magnesium oxysulfide cement-based materials: The role of chloride and nitrite

Magnesium oxysulfide (MOS) cement has emerged as a promising cementitious material due to the high strength and excellent durability, but research on its rust inhibition remains limited. In this study, the chloride and nitrite were introduced in the MOS cement composites, aiming to investigate the corrosion properties and reveal the rust inhibition mechanism of steel bar under different W/C ratio. Experimental results show that the corrosion area ratios reach the largest value of approximately 98% and the lowest value of approximately 3%, respectively, as the chloride and nitrite contents increase to 2%. Compared with chloride, the effect of W/C ratio on the mass loss of steel bar is gradually weakened when the nitrite content is larger than 0.5%. Based on the natural potential, the change of corrosion degree mainly occurs after 28d. In addition, the corrosion potential of steel bar decreases and corrosion rate increases with the increase of chloride content in MOS cement composites. Conversely, the presence of Mg(NO2)2 from nitrite engenders an opposite effect. Besides, the increase of W/C ratio results in higher electrochemical parameters. At this time, the rust inhibition mechanism is revealed based on the micro-structure analysis.