Corrosion Susceptibility Research Articles

Susceptibility of 316L Stainless Steel Structures to Corrosion Degradation in Salivary Solutions in the Presence of Lactic Acid.

In the field of healthcare and dentistry, 316L stainless steel is widely used for its corrosion resistance. However, the presence of lactic acid in salivary solutions can affect its surface reactivity. This study employed electrochemical methods to investigate the influence of lactic acid on 316L stainless steel's corrosion resistance in Fusayama Meyer saliva and saliva doped with varying lactic acid concentrations. The results revealed a significant decrease in polarization resistance as the lactic acid concentration increased, despite a shift toward more positive corrosion potentials. Consequently, the study suggests that the lactic acid presence in salivary solutions should be considered when evaluating the corrosion susceptibility of 316L stainless steel devices.

Machine-to-machine variability of roughness and corrosion in additively manufactured 316L stainless steel

Numerous studies on the corrosion response of metal AM have been conducted. Nonetheless, the specimens being tested are commonly ground or polished to remove the outer as-built surface. If metal AM is truly going to be employed as a transformative technology that can produce complex shapes that do not require traditional machining, then the material needs to be evaluated in the as-built state. The reality is that AM alloys have shown significant inconsistencies regarding as-built surface texture, topology, and residual stress. One metric that has shown significant unpredictability in the literature is the susceptibility to localized corrosion of typically passive alloys, such as stainless steel (SS). There are a large number of studies that have attempted to understand the corrosion response of metal AM materials, but these studies are typically performed on materials that have been printed on a single machine and often mechanically polished to a smooth finish. This study compares the corrosion response of as-built AM, laser-beam powder bed fusion (LB-PBF), 316L SS parts that have been fabricated on five different machines. The majority of this work focused on understanding the susceptibility to localized corrosion of AM metals with respect to machine-dependent variables, namely surface roughness, and build angle. Surface roughness data was collected using scanning white light triangulation, laser scanning confocal microscopy, and coherence scanning interferometry. The results show that there is significant variability (ptwo-tail < 0.05) in the susceptibility to local corrosion initiation of LB-PBF 316L SS samples built on different machines. Surface oxides were probed with electron dispersive spectroscopy and revealed that variations in local corrosion susceptibility likely arise from differences in the stability of the passive film caused by chemical segregation, unique microstructure, and tortuous roughness features at the as-built surfaces. The variability of roughness and corrosion properties from test samples printed on different machines was corroborated by property measurements performed at five different testing sites, proving reproducibility of the data. Most importantly, this study shows that if the as-built surface layer is removed through grinding or electropolishing the machine-to-machine variation observed in the corrosion susceptibility is reduced.

The effect of plastic strain and temperature on the corrosion resistance of the Al-5.6Zn-2Mg powder metallurgy alloy during hot upsetting

Failure may be expedited or slowed down depending on the way the plastic strain interacts with the corrosive media. Therefore, in the present study, the Al-5.6Zn-2Mg alloy produced by the powder metallurgy process was subjected to hot deformation at different plastic strain levels and temperatures (300 °C–500 °C) on a hydraulic press, and then the impact on Corrosion susceptibility was studied using electrochemical corrosion tests in a 3.5% NaCl solution at room temperature. The results of potentiodynamic polarization showed that as deformation levels increased, the corrosion current density decreased and the pitting potential increased. The corrosion resistance of Al-5.6Zn-2Mg increased considerably with an increase in upsetting temperature, due to increasing grain size and a decrease in pore content. Icorr of 2.4982 (μA cm−2) and Epit −0.876 V have been found for the highly deformed preforms under 500 °C condition. EIS results showed a high contact resistance of 2659 Ohm.cm2 for the sample deformed under 500 °C. After the deformation process, densification behaviour is related to the electrochemical behaviour. Pitting corrosion occurred in all deformed samples, while intergranular corrosion was found only in the severely deformed samples.

A Study of Crevice Corrosion Susceptibility of Zn-Al Alloys in a High-pH Environment

This paper aims to clarify the effect of polymer coating damage of dual polymer–zinc coating used to protect rebar reinforcement from corrosion. The coating damage can result in crevices between the two materials. At these crevices, corrosion–passivation plays an important role in the integrity of the intended coating and the protectiveness of the steel base metal. An experimental design was developed to replicate a crevice of Zn-2%Al alloy. This alloy is commonly used for the dual coating protection of rebars. Experiments in this investigation were performed to test several crevice sizes and conditions to assess the state of crevice corrosion. Prepared electrodes were submerged in a 1 M NaOH solution and connected to a data logger to monitor the potential. A special reference electrode was prepared using activated titanium, against which the potential was measured. Additionally, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization were carried out to assess the corrosion rate of the different specimens. The results suggest that, in the absence of a crevice, corrosion occurred on bare specimens. However, whenever a crevice was present, a shift in potential and corrosion rate values indicated that the specimen shifted from an active corrosion regime to a passive one. This shift (gain) in potential was measured as approximately 0.9 V, resulting in a shift in the electrode potential to −0.6 V (SCE). The analysis showed that the solution inside the crevice shifted toward lower pH values, with pH = 12 suggested as the level that supports more passivity inside the crevice according to the Pourbaix diagram.

Simultaneous Effect of Welding Current with PostWeld T6 Heat Treatment on Corrosion Susceptibility of Al6013 Alloy Joined by GTAW

Al6013 base metals were joined successfully with ER4047 weld metal by using the GTAW method under different welding currents. Post-weld T6 heat treatment effects on corrosion properties were investigated in terms of open circuit potential (OCP), potentiodynamic polarization (PDS), and electrochemical impedance spectroscopy (EIS) tests. It was determined that corrosion resistance of the post-weld samples increased with increasing welding current, while T6 heat-treatment only effective on 110A and 140A welding current samples (3.61 to 2.08, 2.95 to 2.40, and 1.38 to 2.15 µA·cm-2 for 110, 140, and 170A welding current before and after T6 heat-treatment). The characteristics of the oxide films on the surfaces are revealed with EIS analysis by a two-constant equivalent circuit model which observed that while the passive film originating from Al is formed on the surfaces, on the other hand, it contains a pittings on the surface. It was determined that the pitting resistance of the T6 heat-treated 110A samples increased (3075 to 4562 Ω). Post-corrosion SEM surface morphologies showed that low welding currents lead to more damage with increased exposure to corrosion.

Corrosion of food grinding discs in gastro-intestinal environment

The need for food size reduction before consumption has led to the use of motorized grinding machine which operates on energized rubbing of two grooved cast-iron discs, and this unintentionally results in tribological degradation and corrosion of grinding discs into the ground food. The objective of this study was to carry out an assessment of corrosion susceptibility of grinding discs from different manufacturing methods in simulated gastro-intestinal environment. Six grinding discs from three states in Nigeria were selected for this study, based on manufacturing methods namely: rotary, cupola, and pit furnaces. Experimental techniques used for the study included: X-Ray Fluorescence spectroscope for determination of chemical composition and X-Ray Diffractometer was used for phase identification. Corrosion susceptibility of grinding discs on interaction with pseudo-body fluid was studied using potentiodynamic polarization scan and product analysis (gasometric) methods in simulated gastro-intestinal environment, typical of human stomach, as electrolyte. The electrolyte contained 2 g/L NaCl acidified to pH of 1.7 with HCl and regulated at 37 °C. Optical microscopy of the electrochemical samples was done for corrosion damage assessment. The key finding from the study was that all the grinding discs contain iron and silicon as dominant alloy elements, which existed predominantly as iron carbide and ferrosilicon phases. Corrosion of the discs in simulated gastric solution was well profound irrespective of the manufacturing method, though, with varying degree among the discs. The outcome of this study is applicable to food industries where cognitive measures may have to be taken on materials selection to minimise the risk of food contamination from materials corrosion.

Study on Variable Stress Corrosion Susceptibility of Four Typical High-Strength Sucker Rods in High-Salinity Well Fluids

Study on Variable Stress Corrosion Susceptibility of Four Typical High-Strength Sucker Rods in High-Salinity Well Fluids

Influence of the Manufacturing Process on the Corrosion and Mechanical Behavior of Esophageal Stents

Esophageal nitinol stents are an established method for treating swallowing difficulties caused by obstructing cancer. This raesearch investigates the influence of different qualities of raw metal alloys in combination with production technology on corrosion resistance in standardized simulated gastric fluid (SGF). Four different international stent manufacturers produced samples of their standard stents from nitinol sourced from three different alloy manufacturers. The stents were subjected to a 6-week immersion in SGF. During the immersion, the surface was studied at specified intervals using microscopy. The surface of the samples was also studied by X-ray Photoelectron Spectroscopy and after immersion the released ions were analyzed. Results demonstrated that both raw material and certain steps in the manufacturing process negatively affect corrosion resistance. Analysis of the SGF showed that the amount of nickel released is proportional to the degree of corrosion attack. Finally, current accepted standard test methods are inadequate for assessing susceptibility to corrosion by gastric acid and should take the low pH of the implanted environment into account. Conversely, certain measures in the manufacturing process are able to reduce the impact of the base material on corrosion susceptibility.

An Electrochemical Approach to Accelerate Mechanically Assisted Crevice Corrosion Damage on Modular Implant Interfaces

Abstract Corrosion within the crevice of modular tapers is one of the major mechanisms that leads to orthopedic device failures. However, the currently used fretting corrosion test methods involve extended test durations and are often burdensome. This study evaluates the feasibility of adding micromotion to crevices while being simultaneously subjected to cyclic polarization in order to accelerate corrosion damage. The addition of micromotion was intended to induce crevice and fretting corrosion between metals in a washer-rod combination geometry. Three commonly used orthopedic metals (316L stainless steel, SS316L; grade 5 titanium, Ti6Al4V; and cobalt-chromium-molybdenum per ASTM F1537-20, Standard Specification for Wrought Cobalt-28Chromium-6Molybdenum Alloys for Surgical Implants [UNS R31537, UNS R31538, and UNS R31539], CoCrMo) were used to form crevices in this study to evaluate the test method. A cyclic polarization control group in which no micromotion was present was used to determine the effect of the cyclic polarization alone. In addition, a fretting control group in which no cyclic polarization was conducted was used to assess the effect of micromotion without cyclic polarization. The results of this study showed that fretting corrosion damage can be achieved on Ti6Al4V and SS316L washer crevices when subjected to micromotion alone. The test method did not induce more corrosion on Ti6Al4V samples when crevices were tested with cyclic polarization alone. Furthermore, the results found that cyclic polarization in combination with micromotion did not achieve the same fretting corrosion damage on the CoCrMo samples as observed in explants. Still, electrochemical test methods have potential for accelerating corrosion damage within crevices when combined with existing fretting corrosion testing and therefore could potentially reduce test durations for fretting corrosion susceptibility evaluations for medical devices having modular taper connections.

Enhancing pitting corrosion inhibition of AISI 304 stainless steel using a green frankincense-modified ferric chloride solution

Abstract To inhibit pitting corrosion of AISI 304 stainless steel (SS), the effect of different percentages of frankincense addition to a 0.5 M ferric chloride solution was explored in this work for the first time. The samples were investigated for pitting corrosion susceptibility via electrochemical noise (EN) tests, where the current and potential noises were recorded for 10000 seconds, and potentiodynamic polarization. The frequency domain of EN data was analyzed using power spectral density (PSD). Frankincense addition to the ferric chloride solution effectively reduced the pitting corrosion of AISI 304 SS. The pitting inhibition was concluded from the high fluctuations in current noises over the test period, its decreasing amplitude, the greater positive potential, the lower current values, and the lower spectral noise and noise resistances with increasing frankincense additions. Optical microscope images supported pitting inhibition with frankincense addition, where pits decreased in number per mm2 and size. A significant decrease in the pit size and pits mm−2 was observed with the 10 wt.% frankincense addition. It was attributed to the adsorption of the inhibitor on the stainless steel surface, inhibiting the adsorption of chloride ions. Additionally, frankincense addition reduced the corrosion current and increased the corrosion potential positively.

In-situ electrochemical testing and fluid dynamics simulation of pipeline defects under flow accelerated corrosion

The pipeline defects of flow accelerated corrosion (FAC) on the corrosion behaviors and localized corrosion mechanisms on different locations of the depressions and the welded joint with weld reinforcements were investigated using wire beam electrode (WBE) techniques and fluid dynamics simulations. The results revealed that the swirling vortex inside the depression and the local jet impact by the fluid separation in the weld reinforcement can accelerate the localized corrosion. Also, the depressed upper and trailing edge regions and the weld toes on both sides of the weld reinforcement experience considerable pressure fluctuations, enhancing interfacial mass transfer processes and inducing cavitation for severe localized corrosion failure. Furthermore, the galvanic corrosion strength factor (g) indicated an enhanced susceptibility of localized corrosion in depression and welded joints with weld reinforcement.

Corrosion failure of nitinol stents in the upper gastrointestinal tract: The role of surface finishes and the importance of an appropriate test environment

Esophageal nitinol stents are an established method for treating swallowing difficulties caused by obstructing cancer. As a consequence of improved patient survival, stent failure and an increasing need for re-intervention is a rapidly emerging problem. This research investigates the influence of different quality of raw metal alloys in combination with production technology on corrosion resistance. Four different international stent manufacturers produced samples of their standard stents from nitinol sourced from three different alloy manufacturers. The corrosion resistance was evaluated by cyclic potentiodynamic scans according to the ASTM standards in phosphate buffered saline solution. Because of targeted application of the stent in gastrointestinal tract, the simulated gastric fluid was also used for corrosion measurement. In addition, the surface of the samples was studied by X-ray Photoelectron Spectroscopy and Mott-Schottky analysis. Results demonstrated that both, raw material and certain steps in the manufacturing process affects corrosion resistance. Conversely, other certain measures in the manufacturing process are able to reduce the impact of the base material on corrosion susceptibility. Furthermore, we could demonstrate that a key factor influencing corrosion resistance is the concentration of nickel on the surface. Current accepted standard test methods with phosphate buffered saline solution are inadequate for assessing susceptibility to corrosion by gastric acid and should take the low pH of the implanted environment into account. Understanding the corrosive process and the impact of surface finishes is key to developing stents suitable for long-term palliation.

Effect of Grain Structure and Quenching Rate on the Susceptibility to Exfoliation Corrosion in 7085 Alloy.

The influence of grain structure and quenching rates on the exfoliation corrosion (EXCO) susceptibility of 7085 alloy was studied using immersion tests, optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and scanning transmission electron microscopy (STEM). The results show that as the cooling rate decreases from 1048 °C/min to 129 °C/min; the size of grain boundary precipitates (GBPs); the width of precipitate-free zones (PFZ); and the content of Zn, Mg, and Cu in GBPs rise, leading to an increase in EXCO depth and consequently higher EXCO susceptibility. Meanwhile, there is a linear relationship between the average corrosion depth and the logarithm of the cooling rate. Corrosion cracks initiate at the grain boundaries (GBs) and primarily propagate along the HAGBs. In the bar grain (BG) sample at lower cooling rates, crack propagation along the sub-grain boundaries (SGBs) was observed. Compared to equiaxed grain (EG) samples, the elongated grain samples exhibit larger GBPs, a wider PFZ, and minor compositional differences in the GBPs, resulting in higher EXCO susceptibility.

Corrosion susceptibility of the nanophases of the Al-based amorphous-nanocrystalline coatings

The influence of the size and types of nanophases on the corrosion behavior for Al86Ni6Y4.5Co2La1.5 amorphous-nanocrystalline coatings in a chloride-containing environment were systematically studied. Results revealed that when the two coatings contained only α-Al nanophase with different size, it was the combined effects of the carrier density and the thickness for the passive film that determined the stability of the passive film. Moreover, with the presence of Al-TM and Al-RE nanophases, the origin of localized corrosion on the coating was ascribed to the weak passive film stability on Al-RE nanophase, which was preferentially dissolved by the interaction with chloride ions.

Hexafluoroisopropanol based silk fibroin coatings on AZ31 biometals with enhanced adhesion, corrosion resistance and biocompatibility

Biomacromolecule coating on biomedical magnesium alloys have generated considerable interest for the improved corrosion resistance and biocompatibility. Silk fibroin (SF) based on aqueous solvent has been demonstrated to be a promising coating for magnesium alloy, but pretreatment process is necessary due to the corrosion susceptibility to water. Herein, the SF coating with hexafluoroisopropanol(HFIP) solvent was prepared without preteatment for simplified processing and enhanced adhesion. Ethylene glycol diglycidyl ether(EGDE) was applied to stabilize the coating with more chemical crosslinking. The morphologies and nano-scratch test verify that the compactness and adhesion strength of HFIP based SF are better than that of aqueous based SF. The electrochemical evaluation and in vitro degradation in simulated body fluid indicated that the HFIP based SF coating exhibited significantly enhanced corrosion resistance. Moreover, the application of EGDE post-treatment significantly improved corrosion resistance (the corrosion current density Icoor of the SF-HFIP-EGDE samples stands at 9.93*10−10A cm−2, representing a reduction by two orders of magnitude in comparison to pure SF samples). Cytoskeleton, cell adhesion and cytotoxicity tests with MC3T3-E1 cells verifies the improved cell adhesion and biological activity of silk coating. This study provides a simple method for physical deposition of biomacromolecule coatings on magnesium alloys, while improving adhesion and corrosion resistance.

Corrosion Behavior of AA70 Reinforced Zea mays Husk Particle in NaCl/H2SO4 Concentrations

The effects of Zea mays husk particle and heat treatment on the corrosion behavior of AA70 matrix composite in 1.5 wt.% NaCl/0.0125 M H2SO4 concentrations were studied using an electrochemical technique and optical microscopy. Results showed that the samples had similar anodic-cathodic polarization behavior after heat treatment, with no passivation. However, the heat-treated AA70 matrix composites were more corrosion-resistant than the untreated AA70 matrix composite material in 1.5 wt.% NaCl/0.0125 M H2SO4 concentrations. The composite with 15 wt.% Zea mays husk and a particle size of 300 μm reinforced AA70 matrix revealed the least corrosive tendency and is the most thermodynamically stable in chloride and sulphate ions conditions. Therefore, the corrosion behavior of heat-treated AA70 matrix composites was better compared to that of AA70 material in 1.5 wt.% NaCl/0.0125 M H2SO4 solution. Furthermore, the presence of a high concentration of aggressive chloride ions increases the corrosion susceptibility, and the Zea mays husk particle breaks down the stable oxide film, resulting in increased chloride ion adsorption. The optical microscopy examination suggested the presence of localized corrosion on the material surface.

Susceptibility of Zr-2.5 (wt. %) Nb alloy to undergo nodular corrosion in water and steam environments: Effect of surface, cold work, temperature

Nodular corrosion can severely affect the service life of zirconium alloys in water cooled nuclear reactors. In this study, the susceptibility of pressure tube alloy to undergo nodular corrosion in water-steam with air surroundings at 250°C and 300°C is investigated. Accelerated corrosion has been studied in single phase steam at 500°C. The effect of specimen surface condition and cold work on nodular corrosion susceptibility has been studied in detail. The results indicate that surface condition of the specimen plays primary role in determining the propensity of the alloy to undergo nodular corrosion. Cold work has negligible effect on the initiation as well as growth of oxide nodules in Zr-2.5 (wt. %)Nb alloy. The effect of temperature is highly localized and is visible on the size of the nodules. Presence of non-uniform or discontinuous autoclave layer increases the susceptibility of pressure tube alloy to undergo nodular corrosion.

Unexpectedly high corrosion susceptibility near fusion boundaries of Inconel 625 manufactured by laser powder bed fusion

The intergranular corrosion (IGC) resistance of Inconel 625 produced by laser powder bed fusion was investigated according to ASTM-G28 method A. Unexpected severe corrosion near fusion boundaries was found. The initiation and expansion of corrosion along fusion boundaries and the relationship between microstructure and corrosion behavior were analyzed. This unusual corrosion behavior was related to the Volta potential variation near fusion boundaries. This Volta potential difference was caused by the Al2O3 nanoparticles and Mo, Nb-rich precipitates near the fusion boundaries. This finding may enhance the understanding of corrosion behavior of LPBFed nickel alloys.

Electrochemical investigation of the corrosion susceptibility of hybrid reinforced Al6063 with SiC and PKSA in 1.0 M sulfuric acid environment

AbstractThe recycling of agro‐waste as complementary reinforcements has received significant recognition in the development of aluminium matrix composites. Hence, this study examines the corrosion behavior of Al6063 reinforced with hybrid SiC/PKSA (palm kernel shell ash) particles. Through various ratios of SiC and PKSA particles in Al6063 alloy, composites were fabricated by double stir casting. Samples were cut and metallographically prepared for 1 M H2SO4 solution corrosion experiments. Gravimetric, potentiodynamic polarization and electrochemical impedance spectroscopic analyses were employed. The composites corroded initially at relatively high rates, gradually declining during long immersion times in the acidic solution. The intersection of reinforcements at the general surfaces of the composites where flawed oxide skins predominate acted as active sites for corrosion initiation. From potentiodynamic polarization studies, the corrosion currents increased with time for all specimens, with A9 being 1075.65 μA/cm2 at 72 h as against 857.99 μA/cm2 at 24 h of measurement. The corrosion potentials for all the specimens hovered around −654.00 to −647.22 mV. Bode plots revealed similar electrochemical reactions over all the substrates' surfaces. The relative corrosion resistance by the specimen depends on the oxide films' nature as the cathodic interfacial reinforcements dropped off into the acidic environment.

Preparation of corrosion‐resistant composite coating on AZ91D magnesium alloy through hydrothermal method

AbstractThe high corrosion susceptibility of magnesium alloy has become a practical problem which restricts its wide application in many fields. To improve its surface properties, a composite coating has been successfully prepared on the surface of AZ91D magnesium alloy using a one‐step hydrothermal method. The coating surface possesses a dense structure in the form of scales and has an adhesion strength of 3B. The effect of different preparation conditions on the coating thickness and corrosion resistance is discussed. The coating heated at 180°C for 2 h showed the best corrosion resistance in a 3.5 wt% sodium chloride solution, with a reduction in corrosion current density of 5 orders of magnitude compared to the bare sample. This solution significantly improved the corrosion resistance of the magnesium alloy and helped to further realize the application of magnesium alloys in corrosive environments.