Salt Spray Environment Research Articles

Adhesive, reflective, and conductive films comprised of graphene nanosheets decorated with Ag nanoparticles for flexible electronics

A highly adhesive, reflective and conductive graphene-silver composite film has been fabricated on the modified surface of polyethylene terephthalate (PET) substrate. Graphene nanosheets (GNS) were decorated with silver nanoparticles (AgNPs-GNS) by electroless plating and co-deposited onto the polymer surfaces by spray-spin-spray technique. Peel test results showed that peeling strength between composite films and substrate increased from 1.2 N/cm to 4.8 N/cm by grafting. The average reflectance of composite films was reached 98% from results of the spectrometer, which was much higher than commercial Ag films. Owing to the co-deposition with AgNPs-GNS, the composite films exhibited a sheet resistance of 40 mΩ/sq, which was 80.3% lower than pristine silver films. In addition, AgNPs-GNS/Ag composite films maintained their conductive stability even after over 1000 times of bending tests and several hours of salt spray environment, indicating the application possibility of flexible circuits. Meanwhile, these composite films were used to produce several electronic components integrating on target circuit and the composite films could maintain a good stability of electrical conductivity even after being bending compression and bending tension. These results indicate that these high-quality, highly conductive and flexible composite films prepared by the spray-spin-spray method could be applied to real flexible electronics.

Study on surface characteristics and stochastic model of corroded steel in neutral salt spray environment

To study the surface morphology characteristic of corroded steel in a neutral salt spray environment, an artificial accelerated corrosion tests were carried out and eight batches of specimens with different corrosion ages were obtained. The corroded steel surface morphologies were collected by a non-contact 3D profiler, and the characteristic parameters were extracted by a special analysis program. The results showed that the corrosion depth of steel surfaces generally follows a normal distribution, while the pit depth and aspect ratio follow a lognormal distribution. As the degree of corrosion increases, the average value and standard deviation of corrosion depth, and logarithm mean value of the pit depth increase, while the logarithm mean value of the pit aspect ratio decreases. In addition, the pit density fluctuates in the range of 20–30 and the conical pits on the steel surface account for the largest proportion in the neutral salt spray corrosion environment. Based on the statistical results and parameter change laws, the stochastic field model of corrosion depth and the random distribution model of corrosion pit were established, and the corroded surfaces were reconstructed in the neutral salt spray corrosion environment.

Research on corrosion performance of 6061 aluminum alloy in salt spray environment

AbstractSalt spray corrosion test was carried out on 6061 aluminum alloy, and quasi‐static tensile test at room temperature was carried out on the sample with universal testing machine. The effect of salt spray corrosion on the mechanical properties of 6061 aluminum alloy was studied by scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and electrochemistry. The corrosion rate of 6061 aluminum alloy was quantitatively characterized by different corrosion parameters. It was found that local corrosion of 6061 aluminum alloy occurred in salt spray environment, mainly pitting corrosion and intergranular corrosion. With the increase of corrosion time, the polarization resistance of 6061 aluminum alloy decreases, and the corrosion rate significantly increases. The average corrosion rate and the maximum corrosion rate of 6061 aluminum alloy were characterized by corrosion weight loss and corrosion pit depth. And they can be transformed into each other. The mechanical properties of 6061 aluminum alloy were mainly affected by the depth of corrosion pit. With the increase of corrosion time, the tensile strength and fracture strain decreased, resulting in poor plasticity of the sample. At the same time, the change of elongation of 6061 aluminum alloy can be accurately predicted by the depth of corrosion pit.

(Keynote) Sensor Design, Construction and Validation for in-Situ Water Layer Thickness Determination during Accelerated Corrosion Testing

The design, construction, validation, and application of a sensor to determine water layer (WL) thickness in the range of 0 to 5 mm in salt spray testing using finite element modeling (FEM) and experimental methods is presented. The sensor determines WL thickness based on electrical resistivity, which is a function of the width of the sensor, distance between the electrodes, and solution conductivity. Sensor design, and validation under known WL thicknesses, was informed by FEM results. The utility of the sensor was shown by measuring WL thickness in a continuous salt spray test similar to ASTM B117 (3.5 wt % NaCl at 35 ˚C) and the range of specifications allowed within the standard were explored. Within the realms of accelerated corrosion testing, the angle of exposure played the largest role in WL thickness. Furthermore, it was found that above an angle of 20˚ from vertical the WL experiences semi-periodic run-off events causing a transient decrease in the WL by up to 80%. Finally, the angle of sample exposure in salt spray environments determines if thin film conditions are achieved, influencing the rate of corrosion. The large allowances for sample angle present in most standards for laboratory corrosion chamber testing pose a large source of test-to-test and chamber-to-chamber variability. Acknowledgements SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. This document is SAND2020-5133 A

Characterizing the damage behavior of thin sheets for fuselage based on in situ corrosion fatigue test and digital image correlation technique

The effect of salt spray and salt solution on the fatigue properties of 2024-T3 aluminum alloy plate used for aircraft fuselage structure have been investigated by combining Digital Image Correlation (DIC) technology with in-situ corrosion fatigue test. For this purpose, an in-situ corrosion fatigue platform was designed for gas and liquid phases. Fatigue experimental investigation was carried out in salt spray and salt solution environments respectively, the crack propagation process was monitored by the DIC technology and the influences of NaCl concentration on fatigue life and crack growth rate were analyzed under the two kinds of corrosive environments. Moreover, the failure mechanism is discussed based on the micro-morphology of fracture and the composition of corrosion products. Experimental results demonstrated that for the corrosion fatigue in salt spray environment, there is a competition between the hydrogen embrittlement and the crack tip closure effect caused by corrosion products, which results in fatigue life decreasing with the increase of NaCl concentration first and then increasing. The fatigue life (with 3.50 wt.% NaCl salt spray) is the lowest, which is 82.9% of that in air, while the fatigue life (with 5.00 wt.% NaCl salt spray) is 112.6% of that in air. But for the corrosion fatigue in the NaCl salt solution environment, there is no obvious crack tip closure effect. In the 5.00 wt.% NaCl salt solution environment, fatigue life is 74.2% of that in air. The microfractures and strain nephogram of specimens revealed the stress concentration caused by corrosion pits, which might be the main factor for the decrease of fatigue life.

Effect of phosphate-based sealing treatment on the corrosion performance of a PEO coated AZ91D mg alloy

This study investigated the effect of sealing treatment on the corrosion performance of plasma electrolytic oxidation (PEO) coated AZ91D Mg alloy with and without addition of corrosion inhibitor. The microstructure, phase composition and corrosion property of the sealed and unsealed coatings were evaluated by using scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), polarization, and electrochemical impedance spectroscopy (EIS) tests. Electrochemical experiments and salt spray tests showed that, after sealing in phosphate solution containing corrosion inhibitor, the corrosion current density of PEO-coated AZ91D decreased more than 10-fold and the anti-corrosion time in a salt spray environment increased more than three-fold. The corrosion rate of the PEO coating slowed down due to the releasing and adsorbing of the corrosion inhibitors in the pores and cracks of the coating during the corrosion process.

Corrosion Resistance of Nickel-Based Composite Coatings Reinforced by Spherical Tungsten Carbide

Nickel-based composite coatings reinforced by spherical tungsten carbide were deposited on 42CrMo alloy steel using plasma transfer arc welding (PTAW) process. Their electrochemical corrosion properties in NaCl solution under atmospheric and high pressure were studied by polarization curve, electrochemical impedance spectroscopy. The corrosion and erosion resistance of the coatings were also investigated by salt spray corrosion and erosion corrosion tests. The results show that the self-corrosion potential of the composite coatings increased with the increase of tungsten carbide content, and the Cr element in Ni60 sample formed a stable and compact passivation film. Compared with corrosion at atmospheric pressure, the adsorption and penetration of Cl- on the coating surface enhanced due to the increase of Cl- activity under pressure, thereby to weaken the corrosion resistance. The Samples that passivated in salt spray environment, cannot completely hinder the corrosion of the coating, just only to slow down the corrosion. This study can provide theoretical basis for deep-sea oil drilling and production engineering equipment.

Corrosion Behavior of Pressure Infiltration Diamond/Cu Composites in Neutral Salt Spray.

Diamond particle-reinforced copper matrix composites (Diamond/Cu) are recognized as promising electronic packaging materials due to their excellent thermophysical properties. It is necessary to investigate the reliability of Diamond/Cu composites under extreme environmental conditions. The corrosion behavior of Diamond/Cu composites was studied in a 5 wt% NaCl neutral salt spray. Surface morphology, thermal conductivity, bending strength, corrosion rate, and corrosion depth resulting from corrosion were researched in this paper. The results showed that the corrosion phenomenon mainly occurs on the copper matrix, and the diamond and interface products do not corrode. The corrosion mechanism of Diamond/Cu composites was micro-galvanic corrosion. The corrosion product formed was Cu2Cl(OH)3. The salt spray environment had a great influence on the composite surface, but the composite properties were not significantly degenerated. After a 168-h test, the bending strength was unaltered and the thermal conductivity of gold-plated composites showed a slight decrease of 1–2%. Surface gold plating can effectively improve the surface state and thermal conductivity of Diamond/Cu composites in a salt spray environment.

Raman and XPS depth profiling technique to investigate the corrosion behavior of FeSiAl alloy in salt spray environment

Abstract As a promising material for electromagnetic microwave absorption, FeSiAl (FSA) alloy always suffers from inadequate corrosion resistance in the marine environment. Herein, the Raman and X-ray photoelectron spectroscopy (XPS) depth profiling techniques are adopted to investigate the basic corrosion behavior of FSA in salt spray environment. The Raman analysis contributes to the understanding of the composition change at various corrosive periods while the XPS depth profiling reveals the corrosion process of Fe0→Fe2+→Fe3+ in a sequence. The observed corrosion rates (CRs) of FSA immersed in 5 wt% NaCl solution for 1, 24 and 48 h are 2.99 × 10−12, 4.90 × 10−12 and 5.85 × 10−12 m/s, respectively. The increasing value of CRs as a function of time demonstrates the accelerated corrosion tendency. Moreover, to suppress the corrosive behavior of FSA alloy, carbon is decorated on its surface by catalytic chemical vapor deposition method using acetylene as the carbon source. The carbon coating restrains the corrosion process by impermeability and hydrophobicity of carbon materials in corrosive mediums. This study will help in the designing of microwave absorbers which can resist corrosion in harsh reaction conditions as well as available at commercial level to save the economy.

Numerical and Experimental Study on the Steel Strands under the Coupling Effect of a Salt Spray Environment and Cyclic Loads.

Composed of multi-strand parallel high-strength wires or steel strands, the stayed cables have been widely used recently in stayed bridges or suspension bridges owing to their light weight and high bearing capacity, especially the steel strands. Meanwhile, chloride-induced corrosion of steel strands is one of the most considerable factors for the durability of the stayed cable exposed to marine environments. The fatigue caused by both cyclic loading and corrosion can affect the life of the steel strands. Besides, the current studies related to the effects of the aforementioned two impact factors on the life of the steel strands either considered the fatigue only, or took the two impact factors into account separately. The coupling effects of fatigue and corrosion on the life of the steel strands are required to be further explored and discussed. Consequently, it is essential to create a model to predict the life of the steel strands with the coupling effects taken into consideration. In this paper, an indoor physical experiment of the steel strand specimens exposed to marine tidal environment was carried out. To avoid accidental errors, the whole specimens were divided into 20 groups, with each group having two steel wires with a 5 days, 10 days, and 15 days cycle for the test. The corrosion of steel strands was observed at various exposure times and it was found that the pits were formed on the surface with the chloride ion erosion to the steel strands. Deeper and sharper pits result in greater pitting-local stress and a shorter fatigue life, which is also the main reason for reducing the carrying capacity of the steel strands. However, a detailed description for this problem is lacking in current domestic and foreign literature, because the pit is hard to predict owing to its complex nature. In order to simulate the evolution of the pits, the stochastic pitting-corrosion model was set up by the neural network method to evaluate the pit evolutions over time. In addition, an empirical formula consisting of length–width ratios, length–depth ratios, and depth-to-width ratios of the pits was obtained to determine the stress concentration factor based on the multi-dimensional linear regression method. The fatigue notch factor of components can be deduced by the stress concentration factor, and the life of the steel strands can be deduced by both of them. The findings are expected to be useful in realistically predicting the durability of wire structures.

Corrosion-resistant plasma electrolytic oxidation coating modified by Zinc phosphate and self-healing mechanism in the salt-spray environment

Aluminum alloys are widely used in many industrial applications. However, they are susceptible to corrosion especially in aggressive media such as high salinity which can expedite the corrosion reactions. In this work, zinc phosphate modified plasma electrolytic oxidation (PEO) coatings are fabricated and demonstrated to have excellent corrosion resistance for a much longer duration (>11,000 h) than conventional PEO coatings (<1,000 h). Insoluble zinc phosphate is distributed in the pores of the coating serving as a barrier against the high-salinity medium. A self-healing mechanism is discovered as zinc phosphate migrates from the surface to pores continuously wetting the corrosion droplets on the super-hydrophilic coating until all the zinc phosphate is consumed.

Perfect Combination of LBL with Sol-Gel Film to Enhance the Anticorrosion Performance on Al Alloy under Simulated and Accelerated Corrosive Environment.

Given their outstanding versatile properties, multilayered anticorrosion coatings have drawn great interest from researchers in the academic and engineering fields. However, the application of multilayered coatings is restricted by some limitations such as low interlayer compatibilities, the harsh preparation process, etc. This work introduced a composite film fabricated on a 2A12 aluminum alloy surface, including an anodic oxide film, a sol–gel film, and a layer-by-layer (LBL) self-assembling film from bottom to top. The microstructure and elemental characterization indicated that the finish of the coating with the LBL film resulted in a closely connected multilayered coating with a smoother surface. The anticorrosion performance was systematically evaluated in the simulated corrosive medium and neutral salt spray environment. The integrated coating with the LBL film presented an excellent anticorrosion ability with system impedance over 108 Ω·cm2 and a self-corrosion current density two orders of magnitude lower than that of the other coatings. After the acceleration test in a salt spray environment, the multilayered coatings could still show a good protective performance with almost no cracks and no penetration of chloride ions. It is believed that the as-constructed multilayered coating with high corrosive properties and a fine surface state will have promising applications in the field of anticorrosion engineering.

Effects of Relative Humidity on Crevice Corrosion Behavior of 304L Stainless-Steel Nuclear Material in a Chloride Environment

In the dry cask storage of spent nuclear fuels, a stainless-steel canister acts as an important barrier for encapsulating spent fuels. As a result, local corrosion behavior of 304L stainless steel has become an issue of concern in the wet coastal region and salt spray environment. The test was conducted after deposition of simulated sea salt particles on the 304L stainless-steel specimen. It was first covered with a crevice former, and then kept at 45 °C with a relative humidity of 45%, 55%, and 70%, respectively. The surface morphologies and electron back scatter diffraction (EBSD) analysis of the corroded region for the 304L stainless-steel specimen are presented in this paper. The goal of this work was to investigate the crevice corrosion behavior of 304L stainless steel under different chloride concentrations and relative humidity conditions. From the experimental results, a threshold relative humidity for stress corrosion cracking (SCC) initiation of 304L stainless steel was proposed.

Corrosion behavior of 316L stainless steel coatings on ZE41 magnesium alloy in chloride environments

The corrosion behavior of the ZE41 magnesium alloy with a HVOF 316L stainless steel coating was electrochemically evaluated in 3.5 wt% NaCl solution and by salt spray testing. Electrochemical Impedance Spectroscopy (EIS) allowed determining the resistance of the coatings deposited, the growth of compact corrosion products on the ZE41 Mg alloy and the failure of the non-optimized coatings. The best coating resisted the chloride attack for long times in immersion and in salt spray environments, and it drastically reduced galvanic couple formation. Its behavior is associated with its reduced porosity and its higher compactness and mechanical stability.

Anode characteristics of Al/Ti galvanic couple in a salt spray environment

AbstractThe galvanic corrosion behavior of a 2A12 aluminum alloy and a Ti‐15‐3 titanium alloy in a salt spray environment was investigated. The results indicated that the galvanic effect accelerated the dissolution rate of the anodes significantly; however, the corrosion of the anode was not uniform. The region adjacent to the coupled joint experienced the most significant corrosion, with galvanic corrosive action emerging as dominant. The corrosion of the region distant from the joint was slight and was dominated by the self‐corrosion process. A new model for the current difference distribution of the galvanic couple was established to illuminate the nonuniform corrosion phenomenon of the anode.

Microstructure and Electrochemistry of Al-Rich Primer

The Al-rich primer, developed by NAVAIR is designed to be anodic relative to high strength Al alloys such as AA2XXX and AA7XXX, so that it drives the mixed potential of the Al alloy substrates into a cathodic region below the breakdown potentials of Al alloys, preventing localized corrosion. The Al-rich primer under study is composed of spherical Al-Zn-In pigments and epoxy binder. The spherical pigments are achieved from atomization of Al-Zn-In bulk sacrificial anode used on hulls of boats operating in seawater. The size of spherical pigments in the primer ranges from with size ranging from a few hundreds of nanometers to tens of microns. The average size of the pigments is around 7 µm in diameter. The active Al-Zn-In pigments are further treated with trivalent chromium passivation (TCP) solution for different dwell times to reduce the self-corrosion of the pigments. In this study, the Al-rich primer coated on TCP-treated AA2024-T3 substrate provided by NAVAIR was investigated. The microstructure of the Al-rich primer was studied using a combination of X-ray microscopy (XRM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. 3D reconstruction microstructure of the Al-rich primer was acquired by XRM, showing that the primer contains Al-Zn-In particles with various sizes, epoxy and a significant volume of voids. The planar and cross-section views of the Al-rich primer were also examined by SEM. Since mechanical polishing damaged the pigments and smeared epoxy, so ion polishing was used to prepare the planar and cross-sectional samples of the Al-rich primer to reduce materials damage and achieve a less-damaged surface. Similar to what was found in XRM results, voids were also found in the primer. In addition, some relatively large Al-Zn-In pigments with size of tens of microns were surrounded by some very fine Al-Zn-In pigments with size of a few hundred of nanometers to form agglomerates. The cross-section view examined by TEM showed that some fine pigments directly contacted large pigments, and others bonded with epoxy. Heavy elements enriched at grain boundaries in the pigments. STEM-EDS mapping will be conducted on the pigments. To understand the electrochemistry of Al-Zn-In pigments, the microstructure and electrochemistry of Al-Zn-In bulk alloy were studied. Zn enriched along grain boundaries in bulk alloy. Large intermetallic particles with size of tens of microns located at grain boundaries. Some intermetallic particles were enriched with Fe and Si, and some were enriched with In. In situoptical microscopy was used to observe the pitting initiation and growth on the both polished and TCP-treated Al-Zn-In bulk alloy during anodic potentiodynamic polarization in 3.5% NaCl solution. Pits initiated around some intermetallic particles. The composition of these particles will be determined. When the primer is exposed to bulk solution or salt spray environment, electrolyte saturates the epoxy. Thus, the environment in which the substrate and Al-Zn-In pigments are surrounded is not bulk solution or electrolyte layer on the primer surface, but electrolyte saturated in epoxy. To simulate the environment of the primer, the special coplanar electrodes were designed. Ag/AgCl electrode was used as reference electrode; pure Ni was chosen as counter electrode; working electrode was AA2024 or Al-Zn-In bulk alloy. Three electrodes were mounted in epoxy and then polished. The neat primer without pigments were applied on the polished surface of coplanar electrodes. The coplanar electrodes were immersed in 3.5 wt% NaCl solution. The neat primer was saturated with electrolyte after 24 h of immersion. Potentiodynamic polarization and electrochemical impedance spectroscopy tests were conducted to measure the electrochemistry under the neat primer. Galvanic corrosion between the AA2024 substrate and Al-Zn-In bulk alloy was also studied. Each alloy was connected with electrical wires, and then both of them were put side by side with around 2 mm separation and then mounted in epoxy. The galvanic panels were polished and then exposed to NaCl solution or salt spray chamber. Galvanic currents between them were measured during exposure. The experiments are ongoing.

Aspects regarding corrosion and mechanical tests for metallic parts obtained by Powder Metallurgy

The researches for this paper were made for knowing the corrosion behavior and mechanical resistance of some metallic powder’s specimens obtained by powder metallurgy. This technology was chosen because of the technical and economic advantages, and the obtained parts can be used in all domains. The parts were obtained from iron powders by pressing at different pressures and sintered in an inert atmosphere. The innovation was to obtain metallic composites, having as a matrix an iron powder type Ancorsteel 1000B and as a reinforcement a spring steel wire. The specimens were tested in different solutions and environments and also two mechanical tests. This paper presents a part of tests that were the corrosion in salt spray environment and bending tests, aiming to compare the results for the types of proposed specimens. For the morphological characterization (size, shape, surface) and chemical composition of the material used, SEM electronic microscopy was used using an FEI Inspect S microscope. The sintering was made in a neutral controlled atmosphere (argon) furnace.

Polyphenol-reduced graphene oxide toward high-performance corrosion inhibitor

Graphene as a physical barrier in organic coating exhibits good anticorrosion property, whereas its agglomeration would greatly debase such performance. Here, functionalized graphene was prepared via a green/facile method with tea polyphenol as reductant and graphene oxide (GO) as precursor. The anticorrosion performance of polyphenol-reduced graphene oxide (T-rGO) in waterborne epoxy coating was evaluated according to the electrochemical impedance spectroscopy, polarization curve, water absorption and salt spray test. Results indicate that the T-rGO/epoxy coating has the largest impedance modulus and corrosion potential, and the corrosion current density is an order of magnitude lower than that of pure epoxy coating. The T-rGO/epoxy coating displays excellent corrosion protection under continuous high salt spray environment, with pure epoxy coating as a comparison. T-rGO greatly enhances the corrosion resistance of waterborne epoxy coating, which is attributed to its good dispersibility and intrinsic characteristics.

Influence of electric current on the corrosion behavior of Cu for the electric contact in the isolation switch

AbstractThe flow of electric current through the conductor has a far‐reaching effect on its corrosion behavior. In this paper, the effect of current on the corrosion behavior of Cu is investigated. The accelerated corrosion test of Cu with various external currents from 1 A to 5 A are carried out in 5% NaCl neutral salt spray environment. The results show that the samples with external current exhibit a faster corrosion rate than those without current. The corrosion kinetics and underlying mechanism are also discussed in this paper.

Experimental study and 3D cellular automata simulation of corrosion pits on Q345 steel surface under salt-spray environment

The evolution laws of Q345 steel pitting corrosion are introduced using a salt-spray corrosion test. The number and maximum depth of corrosion pits are counted and a mathematical model is established. 3D cellular automata is adopted to reproduce the initiation and growth processes of corrosion pits simultaneously. The results demonstrate that the cellular automata model can better reflect the evolution randomness and time-dependent laws. Within the cellular automata model, the maximum depths are controlled mainly by the corrosion reaction probability Pc and probability of downward movement Pd, whereas the pitting shapes are governed by the passivation reaction probability Pp.