Cyclic Potentiodynamic Polarization Tests Research Articles

Corrosion susceptibility investigation of Ti–O film modified cobalt-chromium alloy (L-605) vascular stents by cyclic potentiodynamic polarization measurement

Ti–O film was deposited on cobalt-chromium alloy (L-605) coronary stents by metal vacuum arc source deposition. The corrosion resistance of the Ti–O film modified and bare L-605 stents was investigated by cyclic potentiodynamic polarization tests in phosphate buffered solution (PBS, 37 ± 1 °C). The optical microscopy and scanning electron microscopy (SEM) images of the modified stents indicated that the surface of all stent cells was very smooth and uniform, and the thickness of Ti–O film was about 10 nm. There were not any cracks and delamination on stent surface after dilation by angioplasty. The polarization results showed that the natural corrosion potential of the Ti–O film modified and bare stents was similar. But the corrosion current density of Ti–O film modified stent was lower than that of the bare stent at all scanned potential range. Compared with Ti–O film modified stent, the bare stent was more susceptible to corrosion. After cyclic potentiodynamic polarization test, the slight localized corrosion was found on the surface of bare stents. But no film flakes or localized pitting can be observed on Ti–O film modified stent. All these results showed that Ti–O film modified stent had the better corrosion resistance, compared with the bare L605 stent.

The effect of shot peening on fatigue and corrosion behavior of 316L stainless steel in Ringer's solution

Abstract Stainless steel 316L is one of the most common biomaterials utilized for producing orthopedic implants. But it has low resistance to fatigue and wear. Therefore surface treatments such as shot peening are used to modify the surface properties. In the present research, the influence of shot peening treatment on hardness, fatigue and corrosion behavior of 316L stainless steel in Ringer's solution was investigated. For this purpose, the steel specimens were shot peened for 5, 10, 15, 20 and 25 min. Hardness, fatigue and electrochemical tests were performed on each specimen before and after shot peening treatment. The open circuit potential (OCP) of the specimens, after 2 h of equilibrium time, was measured in Ringer's solution for 300 s. The cyclic potentiodynamic polarization tests were performed with 5 mV/s scan rate. According to the results, the shot peening treatment increases the surface hardness and fatigue resistance. In addition, this treatment decreases the break-down potential of the passive layer and increases the corrosion current density in shot peened specimens up to 10 min, which shows a reduction in resistance to pitting corrosion. However, the break-down potential of the passive layer begins to increase and the corrosion current density decreases at upper times. This trend continues such that even the conditions of resistance to pitting corrosion improve in comparison with un-shot peened specimens at longer times of shot peening. The morphology of the fractured surfaces of samples was investigated by scanning electron microscopy (SEM).

Characterization and corrosion behavior of hydroxyapatite coatings on Ti6Al4V fabricated by electrophoretic deposition

In order to increase the bone bioactivity of the metallic implants, hydroxyapatite (HA) is often coated on their surface so that a real bond with the surrounding bone tissue can be formed. Plasma spraying of HA coatings is currently the only commercial process in use but long-term stability of plasma sprayed coatings could be a problem because of their high degree of porosities, poor bond strength, presence of a small amount of amorphous phase with non-stoichiometric composition, and non-uniformity. In the present study, cathodic electrophoretic deposition (EPD) has been attempted for depositing HA coatings on Ti6Al4V followed by vacuum sintering at 800 °C. Submicron HA powders with different morphologies including spherical, needle-shaped and flake-shaped were used in the EDP process to produce dense coatings. Moreover, carbon nanotubes (CNTs) were also used to reinforce the HA coating for enhancing its hardness. The surface morphology, compositions and microstructure of the HA coated Ti6Al4V were investigated by electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffractometry, respectively. Electrochemical corrosion behavior of the HA coatings in Hanks’ solution at 37 °C was investigated by means of open-circuit potential measurement and cyclic potentiodynamic polarization tests. Surface hardness, adhesion strength and bone bioactivity of the coatings were also studied. All HA coated specimens had a thickness of about 10 μm and free of cracks, with corrosion resistance higher than that of the substrate and adhesion strength higher than that of plasma sprayed coating. The enhanced properties could be attributed to the use of submicron-sized HA particles in the low-temperature EDP process. Among the three types of HA powder, spherical powder yielded the densest coating whereas the flake-shaped powder yielded the most porous coatings. Compared with monolithic HA coating, the CNT-reinforced HA coating markedly increased the coating hardness without compromising the corrosion resistance or adhesion strength.

Comparison of Crevice Corrosion of Fe-Based Amorphous Metal and Crystalline Ni-Cr-Mo Alloy

The crevice corrosion behaviors of an Fe-based bulk metallic glass alloy (SAM1651) and a Ni-Cr-Mo crystalline alloy (C-22) were studied in 4M NaCl solution at 100 °C with cyclic potentiodynamic polarization and constant-potential tests. The corrosion damage morphologies, corrosion products, and the compositions of corroded surfaces of these two alloys were studied with optical three-dimensional reconstruction, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Auger electron spectroscopy (AES). It was found that the Fe-based bulk metallic glass (amorphous alloy) SAM1651 had a more positive breakdown potential and repassivation potential than crystalline alloy C-22 in cyclic potentiodynamic polarization tests and required a more positive oxidizing potential to initiate crevice corrosion in constant-potential tests. Once crevice corrosion initiated, the corrosion propagation of C-22 was more localized near the crevice border compared to SAM1651, and SAM1651 repassivated more readily than C-22. The EDS results indicated that the corrosion products of both alloys contained a high amount of O and were enriched in Mo and Cr. The AES results indicated that a Cr-rich oxide passive film was formed on the surfaces of both alloys, and both alloys corroded congruently in the crevice corrosion damage areas.

Improvement of pitting corrosion resistance of AISI 444 stainless steel to make it a possible substitute for AISI 304L and 316L in hot natural waters

AbstractThe pitting corrosion resistance of AISI 444, 304L and 316L stainless steels in two tap waters with different chloride concentrations at 80 °C was studied. Cyclic potentiodynamic polarization (CPP) tests were carried out starting from Ecorr − 30 mV until the current density reached 0.1 mA/cm2 (scan rate 0.166 mV/s); the scan was then reversed and continued until new passivity conditions were achieved. The corrosion potential was measured before the polarization experiments. From the E‐log i plots, the values of pitting and protection potential were obtained; from these potentials, the perfect and the imperfect passivity regions were defined to compare the corrosion resistance of the studied steels. CPP tests were performed both on as received stainless steel samples and on samples submitted to different cleaning–passivation treatments to improve their corrosion resistance. The results indicate that, for industrial production, AISI 444 stainless steel can substitute the more expensive AISI 304L or 316L after a cleaning–passivation treatment that reduces the presence of inclusions.magnified image

Pitting Corrosion of Cast Metallurgy Aluminum-Beryllium Alloys in Sulfuric Acid Solutions

Abstract Four casting alloys of aluminum-beryllium ranging in a Be composition from 15 wt% to 68 wt% were tested in sulfuric acid (H2SO4) solutions of pH 2 and 4. Cyclic potentiodynamic polarization tests of the Al-Be alloys demonstrated passive behavior and positive hysteresis. Following cyclic polarization testing, all alloys showed preferential corrosion of the Be-rich phase in the forms of pitting or phase boundary attack with evidence of crystallographic etching. Total pit surface area in the Be phase was proportional to the volume fraction of the Al phase. Immersion test specimens showed uniform corrosion of the Al phase at pH 4, while the Be phase showed phase boundary and crystallographic attack at pH 2. Corrosion potentials were most noble for alloys with the highest Be wt% while corrosion current density decreased with Be wt%. A lower pH increased the corrosion rate for all alloys.

Extremely high pitting resistance of NiTi shape memory alloy thin film in simulated body fluids

In this paper the corrosion behavior of NiTi thin films fabricated by sputtering from Ni and Ti targets has been studied by cyclic potentiodynamic polarization tests in Hank's and Ringer's solution at 310 K. For comparison, bulk NiTi Shape Memory Alloy (SMA) has also been studied to elucidate the different corrosion behavior of bulk and thin film material. The electrochemical experiments reveal that thin film NiTi SMA has comparable corrosion current density ( i corr), much higher pitting corrosion potentials and wider passive range than the bulk NiTi. We show that NiTi SMA vapour deposited thin films are less susceptible to pitting corrosion than the bulk.

The electrochemical behavior of nitinol in simulated physiological solutions

The electrochemical behavior of nitinol in simulated human bile and phosphate-buffered saline (PBS) was examined using electrochemical impedance spectroscopy. In addition, cyclic potentiodynamic polarization tests were performed in the simulated bile and salt-only bile, and the results compared with those obtained previously in PBS. The potentiodynamic tests showed that electropolishing was effective in providing nitinol with a high resistance to pitting corrosion in the bile solutions, as found in PBS. Differences between the breakdown potential and the corrosion potential indicated that mechanically polished nitinol should be more susceptible to pitting corrosion in simulated bile than in the salt-only bile and PBS. The impedance spectra showed near-capacitive behavior in both PBS and simulated bile, and the data could be fitted by a parallel resistance-capacitance (as a constant phase element) circuit associated with the passive oxide film. The thickness of the oxide was determined from the capacitive component and found to be consistent with surface analytical results reported in the literature. Resistivities obtained from resistance values indicated that compositional features of the oxide were similar for PBS and simulated bile.

The Effect of Anions on the Passive Film Properties and Localized Corrosion Behavior of Alloy C-22

This paper investigates corrosion behavior of Alloy C-22 in hot concentrated brines. The passive film behavior and localized corrosion properties of alloy C-22 as a function of nitrate and sulfate anions in concentrated chloride brines was investigated. Cyclic potentiodynamic polarization tests were used to study the general corrosion behavior of the alloy, Electrochemical Impedance Spectroscopy (EIS) and Mott-Schottky (M-S) were used to examine the electronic properties of the passive films, and constant potential tests were done to study crevice corrosion initiation, propagation and stifling of the alloy. The aim was to investigate the correlation between the electronic properties of the alloy's passive film and the localized corrosion susceptibility of the alloy. The results showed that anions had major impact on the repair- repassivation behavior but did not cause significant effect on the properties of passive film when it was intact.

Corrosion Behavior of Metallic Materials in Ethanol-Gasoline Alternative Fuels

Corrosion performances of several metallic materials (Al6061 and Al319 alloys, 304 stainless steel and grey cast iron) in the ethanol-gasoline alternative fuels were investigated. Cyclic potentiodynamic polarization tests were used to study their corrosion behavior. Anodizing and plasma electrolytic oxidation (PEO) techniques were used to produce oxide coatings on the Al6061 and Al319 alloys, and the corrosion properties of these coatings in the alternative fuel environments were also evaluated. The results showed that, the 304 stainless steel, Al6061 and the coating materials are compatible with the alternative fuels. The oxide coatings on both Al alloys provided effective corrosion protection in the alternative fuel environments.

Effect of Fluoride Ions on Crevice Corrosion and Passive Behavior of Alloy 22 in Hot Chloride Solutions

Alloy 22 (UNS N06022) is a Ni-Cr-Mo-W alloy highly resistant to localized corrosion. Alloy 22 may be susceptible to crevice corrosion in pure chloride (Cl−) solutions under aggressive environmental conditions. The effect of the fluoride (F−) over the crevice corrosion induced by chloride ions is still not well established. The objective of the present work was to explore the crevice corrosion resistance of this alloy to different mixtures of fluorides and chlorides. Cyclic potentiodynamic polarization (CPP) tests were conducted in deaerated aqueous solutions of pure halide ions and in different mixtures of chloride and fluoride at 90°C and pH 6. The range of chloride concentration [Cl−] was 0.001 M ≤ [Cl−] ≤ 10 M and the range of fluoride to chloride molar concentration ratio [F−]/[Cl−] was 0.1 ≤ [F−]/[Cl−] ≤ 10. Results show that Alloy 22 was susceptible to crevice corrosion in all the pure chloride solutions but was not in the pure fluoride solutions. Fluoride ions showed an inhibitor behavior only in mixtures with a molar ratio [F−]/[Cl−] > 2. For mixtures with a molar ratio [F−]/[Cl−] of 7 and 10, the inhibition of crevice corrosion was complete.

Effect of interfacial reaction on corrosion behavior of alumina borate whisker reinforced 6061Al composite

Abstract The effect of interfacial reaction on the corrosion behaviors of alumina borate whisker (Al18B4O33w) reinforced aluminum composite has been analyzed in 3.5% NaCl solution at room temperature. The localized corrosion susceptibilities and the stress corrosion cracking behaviors of the composite for each heat treatment were examined by measurement through the cyclic potentiodynamic polarization and double cantilever beam tests. It was found that the degrees of interfacial reaction increase with solution treatment time, and the various degrees of the interfacial reaction led to the difference of composition distribution near the interface between whisker and matrix in the composite. The interfacial reaction plays an important role in the electrochemical corrosion behaviors and stress corrosion cracking behaviors of the composite.

Corrosion behavior between dental implant abutment and cast gold alloy

Two types of HL hexed abutments of a Steri-Oss system, gold/plastic coping and gold coping, were compared in terms of corrosion behavior. The anodic polarization behavior and the galvanic corrosion between abutments and Type III gold alloys, before and after casting, were analyzed. In addition, the crevice corrosion of the casting samples was analyzed with cyclic potentiodynamic polarization tests using the |Er-Ecorr| value and scanning electron microscopy. Before casting, gold/plastic coping and gold coping were shown to have similar corrosion patterns in the anodic polarization test. Type III casting gold alloy was shown to have a lower higher than that of gold coping, but the passive region for the gold/plastic coping was smaller than that of gold coping. The contact current density between the cast gold alloys and gold/plastic before casting was higher than that between gold coping and cast gold alloy. The contact current density of the samples after casting was shown to be similar to that before casting. The crevice corrosion resistance of cast samples using gold coping was lower than that of cast samples using gold/plastic coping, and severe corrosion was observed by SEM at the abutment-casting gold alloy interface.

Electrochemical Evaluation and Surface Characterization of Josephinite as a Natural Analog for Container Materials

AbstractA sample of josephinite, a rock containing predominantly a Ni-Fe metallic phase, was evaluated as a natural metal analog to increase confidence in the assessment of waste package performance for the potential high-level radioactive waste repository at Yucca Mountain, Nevada. The josephinite sample was characterized electrochemically in simulated groundwater environments using cyclic potentiodynamic polarization and potentiostatic tests. The passive surface layers formed potentiostatically were examined by X-ray photoelectron spectroscopy. These results were compared to those obtained with a synthetic Ni3Fe alloy with a chemical composition similar to that of josephinite. Electrochemical studies showed that josephinite exhibited passivity at a slightly higher pH than did the cast Ni3Fe alloy and was found to be slightly more susceptible to pitting corrosion. The passive films formed on the josephinite and the cast Ni3Fe alloy have a duplex structure consisting of an Fe-rich hydroxide outer layer and a Ni-rich oxide inner layer. Results obtained from this study provide an appropriate characterization of the environmental conditions leading to the passivity and localized corrosion of josephinite. Extended persistence of a stable passive film, however, is essential for the long-term stability of the josephinite sample. The relationship between the passive behavior and the formation of alteration layers needs to be established for assessing the survivability of josephinite.

NiTi cladding on stainless steel by TIG surfacing process Part II. Corrosion behavior

Thick NiTi coatings were deposited on AISI 316 stainless steel samples by the tungsten inert gas (TIG) surfacing process. In Part I, the composition, microstructure and cavitation erosion behavior of the NiTi deposit were investigated. In Part II, the corrosion behavior of the NiTi deposit in 3.5% NaCl solution at ambient temperature was studied by electrochemical methods. Based on the results of cyclic potentiodynamic polarization tests, the corrosion resistance of the NiTi deposit in NaCl solution was found to be comparable to, but lower than, that of AISI 316. Compared with bulk NiTi, the corrosion resistance of the TIG-deposited cladding was reduced due to the presence of pores and a more heterogeneous microstructure. The galvanic effect between the NiTi deposit and the 316 steel substrate was minimal, as evidenced by a low galvanic current density relative to the uncoupled corrosion current density for the anodic member. The results of these corrosion tests indicate that TIG-deposited NiTi cladding is compatible with AISI 316 stainless steel and may be employed as local protection against cavitation erosion in NaCl solutions.

Corrosion of Thermal Spray Hastelloy C-22 Coatings in Dilute HCl

The microstructure and corrosion behavior of Hastelloy C-22 coatings produced using the high velocity oxygen fuel (HVOF) method have been determined and related to in-flight measurements of the particle velocity and temperature. Average particle temperatures ranged from 1280–1450 °C and velocities ranged from 565–640 ms−1. All of the coatings were greater than 98% of theoretical density and exhibited passivating behavior in 0.1 M HCl during cyclic potentiodynamic polarization testing. The passive current density was somewhat higher compared with wrought C-22 alloy and an active-passive peak attributed to the formation of a Cr-rich surface layer was observed. Resistance of corrosion and deposition efficiency improved as the particle temperature decreased. There was little effect of particle velocity on the corrosion behavior over the range of deposition conditions examined. Our results suggest that feedback control based on measurement of the particle temperature can be used to process coatings with optimum properties.

Localized corrosion behavior of Al 3Ti–Cr alloys in 3.5 wt.% NaCl solution

Al 3Ti alloys have received a lot of attention as potential light materials because of their low density and high strength at elevated temperatures. The induction melting method followed by thermomechanical treatment was used for preparation of L1 2-typed Al 3Ti–Cr alloys, i.e. Al 67Ti 25Cr 8, Al 66Ti 24Cr 10 and Al 59Ti 26Cr 15. The corrosion behavior of Al 3Ti–Cr alloys in deaerated 3.5 wt.% NaCl solution was investigated by electrochemical corrosion tests and surface analysis. Particular attention was paid to the effects of Cr addition on the surface film composition and its breakdown related to the corrosion behavior. The result of cyclic potentiodynamic polarization test showed that E pit and E prot increased with increasing Cr content. This indicates that Al 3Ti–Cr alloys with higher Cr content are effective in improving relative resistance to pit initiation and propagation. In electrochemical impedance spectroscopy, an increase of Cr content increased polarization resistance ( R p) and decreased the depressed angle, which is strongly related to pitting resistance. Auger electron spectroscopy analyses were performed in order to characterize in-depth distribution of constituents in the passive film. Cr was detected earlier from the outer surface with increasing Cr content. Energy dispersive X-ray spectroscopy techniques were used to examine the effect of alloying elements inside pit. The amount of Ti inside pit was enriched as increasing Cr content.

Effects of N and Mo on the electrochemical behavior of laser-alloyed stainless steels in a 3.5 wt.% NaCl solution

The electrochemical behavior of the laser-alloyed Fe-Cr-Ni-Si-N and Fe-Cr-Ni-Mo-Si-N stainless steels was studied in a 3.5 wt.% NaCl solution. Cyclic potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS) measurements were performed to evaluate the corrosion resistance of the alloyed layers in deaerated 3.5 wt.% NaCl solution at pH 4. The surfaces of the samples after EIS measurements were characterized with X-ray photoelectron spectroscopy. The experimental results showed that the passivation and polarization resistance of laser-alloyed nitrogen-containing stainless steels in chloride-containing solution could be improved by co-alloying molybdenum. The electrochemical behavior in connection with the chemical states of alloying elements on the surfaces of the alloys was discussed.

Microstructure and electrochemical behavior of laser cladded Fe-Cr-Mo-Si-N surface alloys on carbon steel

Laser surface cladding was used in this study to introduce Fe-Cr-Mo, Fe-Cr-Si-N and Fe-Cr-Mo-Si-N stainless steel layers on carbon steel to improve its corrosion resistance. The cladding materials used were Fe/Cr/Mo, Fe/Cr/Si 3N 4 and Fe/Cr/Mo/Si 3N 4 powders which were premixed before laser irradiation. The chemical composition, the microstructure and the electrochemical behavior of the cladded layers were of particular interest and were analyzed. Cyclic potentiodynamic polarization tests and electrochemical impedance spectroscopy measurements were performed to evaluate the corrosion resistance of the cladded layers in a deaerated 3.5 wt.% NaCl solution at pH 4. Experimental results indicated that the Fe-Cr-Mo cladded layers exhibited a lower passive potential range with a higher anodic passive current density, while the Fe-Cr-Si-N and Fe-Cr-Mo-Si-N cladded layers both with a duplex microstructure evidenced a higher passive potential range with a lower anodic passive current density in Cl −-containing solution, as demonstrated by the cyclic potentiodynamic polarization test. The polarization resistance of the laser cladded Fe-Cr-Mo-Si-N layer was higher than that of Fe-Cr-Si-N as determined by electrochemical impedance spectroscopy.

Potentiodynamic Polarization Studies of Candidate Container Materials in Simulated Tuff Repository Environments

ABSTRACTCortest Columbus is investigating the long-term performance of container materials used for high-level waste packages as part of the information needed by the Nuclear Regulatory Commission to assess the Department of Energy's application to construct a geologic repository for high-level radioactive waste. In one task of the program, a cyclic potentiodynamic polarization (CPP) technique was used to evaluate the corrosion behavior of the candidate container materials. In order to evaluate the expected range of environmental variables, a statistical experimental design approach was used. A Resolution IV experimental design for 15 variables was selected. The variables included temperature, pH, species present in the groundwater, and those generated by radiolysis. Complete matrices of CPP tests, which consist of tests in 33 environments, were performed on two candidate container materials; Type 304L Stainless Steel and Incoloy Alloy 825. In these tests, both alloys exhibited a wide range of behavior; including passive behavior, pitting and active corrosion. For each alloy, the environmental variables that affected corrosion behavior were identified.