The effect of different pH values of artificial sea water on the passivation behavior and the pitting corrosion resistance of Ni70Cr21Si0.5B0.5P8C≤0.1Co≤1Fe≤1 (VZ1) and Ni72.65Cr7.3Si6.7B2.15C≤0.06Fe8.2Mo3 (VZ2) glassy alloys were studied using impedance spectroscopy measurements (EIS), cyclic polarization, and electrochemical frequency modulation techniques. The results showed that the alloys undergo a general corrosion process and tend to form an oxide film on the alloy surface, developing a stable protective layer in the artificial seawater solution. In both alloys, the lower corrosion current density was observed at a pH of 8.5 but had less pitting corrosion resistance. The VZ1 alloy had a relatively lower passive current density value, having a smaller anodic hysteresis loop area compared to the VZ2 alloy. The effect of the medium’s pH on corrosion potential, corrosion current density, pitting potential, and repassivation potential was investigated and discussed, as was surface morphology.
More than 70% of the earth’s surface is covered by seawater and it is considered the most corrosive of all naturally-occurring electrolytes . For many common metals structures used in marine environments and sea water, corrosion is a major cause of structural deterioration, causing problems in desalination plants, and with pipelines, leakage, and product loss . The corrosivity of seawater has increasingly gained attention. The most significant factors that determine seawater corrosivity can be placed into three categories: physical factors, such as the content of dissolved oxygen, temperature, and pH; chemical factors, such as high chloride ion concentration; and other factors, such as biological activity .
Nickel and its alloys have been reported to corrode in sea water environments [3,4,5,6,7]. Additionally, it was studied in a different type of aqueous, i.e., in 1.0, 3.0, 6.0, 9.0, 12.0 M NaOH solutions . They have been intensively studied, especially to further improve their corrosion resistivity property, e.g., the passive films formed on its surface in 1.0, 3.0, 6.0, 9.0, 12.0 M HCl solutions . Metallic materials, in bulk form with thicknesses of over several millimeters, have been limited to a crystalline structure. These non-equilibrium bulk alloys have attracted increased attention worldwide as an innovative metal with both scientific and technological applications. Nickel-based glassy alloys, though comparative newcomers to the bulk metal–glass (BMG) family, are considered as one of the most important BMG systems . They have many advantages, including high thermal stability due to their high glass transition temperature, ultrahigh strength (up to ~ 3 GPa), and excellent corrosion resistance [11, 12].
Therefore, our study aimed to investigate the corrosion resistance of two Ni-based glassy alloys in artificial seawater. Electrochemical tests were completed to understand how a shift in pH from 7.5 to 8.5 would influence the pitting corrosion resistance and the formation of the protective film on Ni70Cr21Si0.5B0.5P8C≤0.1Co≤1Fe≤1 (VZ1) and Ni72.65Cr7.3Si6.7B2.15C≤0.06Fe8.2Mo3 (VZ2) glassy alloys in marine environments.
The artificial seawater used had all biological factors removed, to provide a reproducible solution of known composition on the pitting corrosion and had a density (ρ) of 1.027464 g cm−3, salinity (S) of 34.481‰ , chlorinity (Cl) of 19.086‰, and a pH in the range of 7.5–8.5.
Experimental Materials and Methods
The two Ni-based BMG alloys with nominal compositions (wt%) of Ni70Cr21Si0.5B0.5P8C≤0.1Co≤1Fe≤1 (VZ1) and Ni72.65Cr7.3Si6.7-B2.15C≤0.06Fe8.2Mo3 (VZ2), were investigated in this work. These were produced by rapid solidification as ribbons with a width of about 40–74.5 mm and a thickness of 25 µm. The electrochemical measurements were carried out in artificial sea water. A solution of artificial sea water was prepared using the Lyman and Fleming formula (Table 1), by dissolving analytical grade reagents and double distilled water. All chemicals were obtained from Aldrich Chemical Co., KSA.
For electrochemical testing, the BMG alloy specimens were evaluated under the same conditions with a working area of 100 mm2. One side, the bright face, of the sample was exposed to the corrosive environment as a working electrode. The other side was coated with epoxy resin. Before each measurement, this working electrode was degreased with acetone, rinsed with double distilled water, cleaned in an ultrasonic bath, and immersed in the test solution without drying. The measurements were performed in a typical three-compartment glass cell containing working electrode (WE), the counter-electrode (CE), which was a platinum wire, and the reference electrode (RE), which was a saturated silver/silver chloride (Ag/AgCl) electrode. The measurements were conducted by means of an Interface 1000TM, Gamry Potentiostat/Galvanostat/ZRA, USA analyzer. This analyzer includes a Gamry Framework system based on the ESA400, supports all Gamry electrochemical application software, including the DC105™ for direct current (DC) corrosion measurements, EIS300 for electrochemical impedance spectroscopy measurements (EIS), and EFM140 for electrochemical frequency modulation (EFM) measurements.
The potential of the examined alloy was recorded as a function of time over 1 h until it stabilized. For the EFM technique, the baseline frequency (b.f.) was 0.1 Hz, and input frequencies of 2 and 5 Hz were used, with amplitudes of 10 mV over 4 cycles. The EIS measurements were performed with a sinusoidal voltage of 10 mV and 10 points per decade. The frequency range was from 800 kHz to 0.1 Hz. For cyclic polarization curves, the potential was swept from the cathodic to the anodic direction after the impedance run in the range of − 800 mV to 1.200 mV, with a sweep rate of 1 mV s−1. X-ray photoelectron spectroscopy (XPS) measurements were collected using a monochromatic Al Kα X-ray source operating at 300 W (Kratos Axis Ultra DLD, USA).
After cyclic polarization, the surface condition and chemical composition of the alloy surface were examined using a JEOL JSM-6000 scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDS) microanalysis hardware. The acceleration voltage was 15 kV, and the working distance was 10 mm. To provide superior topographic images, Atomic Force Microscopy (AFM) measurements were performed using a Veeco digital instrument CP-׀׀ in contact mode.
Results and Discussion
Electrochemical Impedance Spectroscopy Measurements in Artificial Sea Water
EIS experiments were performed on the VZ1 and VZ2 alloys in the artificial seawater media at different pH values of 7.5, 8, 8.2, and 8.5, at 27 °C, at their respective open circuit potential (OCP). Nyquist plots (Fig. 1a, b) show depressed semicircular capacitive loop formation with an angle of (1 − n) × 90°, owing to surface heterogeneity, where n is a component of the constant phase element (CPE) . These spectra end with a long diffusion tail in low frequency (LF). The arc of the capacitive loops increases in size with an increase in the pH value. The change in the dimension of the capacitive arcs indicate that the state of corrosion rate resistance changes with pH.
The Bode phase plots (Fig. 2a, b) show two humps or peaks corresponding to the two capacitors (CPE1 and CPE2), and the three depressions corresponding to the three resistors (Rs, Rct, and Rf) in the circuit. This suggests that the presence of two time constants representing the electrode processes. A small decay of the phase angle was also observed in the medium to low frequency range, implying a high corrosion resistance behavior due to the protective film formed on the alloy surface.
To interpret electrochemical behavior, the electrical circuit presented in Fig. 3 was chosen because it had the smallest error of fit of about χ2 × 10−3. It consisted of a parallel combination of a capacitor (CPE1), and a charge transfer resistor (Rct), in series with a resistor (Rs). The diffusion model included another (Q2(Rf ZW)) combination of a passive film capacitor (CPE2), a passive film resistance (Rf), and Warburg impedance (Zw). The relevance of the use of this diffusion/migration impedance was to describe the passive film system . The results of the fitting parameters are summarized in Table 2. The time constant at high frequencies was due to the parallel combination of the charge transfer resistance and the double layer capacitance (RctCPE1), while that at low frequencies was initiated from the combination of Rf and CPE2.
On the basis of the EIS, an equivalent circuit was applied that to distinguish between the cases, in which the charge transfer resistance was determined by the nature of the alloy (Rct) or by the passive layer on the alloy surface (Rf). The first resistance, Rct, corresponds to the oxidation of the alloying elements (chromium and/or nickel). After this oxidation, the oxide film, formed as a corrosion product that had been adsorbed at the interfaces, blocked the alloy surface. This film had a higher resistance, Rf, due to its passive characteristics. The consequence of this process was an increase in charge transfer resistance (Rct) of the alloy surface with increasing pH values.
From Table 2, the Rct increases with increasing pH due to the presence of the passive film, which prevents the penetration of the electrolyte to the alloy surface. The lower Rct indicates the high charge transfer across the passive film/electrolyte interface for the VZ2 alloy. As a result, more current-carrying pathways will be generated, as the electrolyte reaches the underlying alloy through the less stable passive film, leading to lower Rct values . The CPE1 decreased with increasing pH, because the available area of alloy during the passivation process decreased due to the presence of the oxide layer. The n1 and n2 values of the VZ1 alloy of 0.8 and 0.6, respectively, show that the behavior of this element is not clearly defined but is situated between the behavior of capacitive (n1) and the Warburg diffusion element (n2). This reflects the reactivity of oxide layer . The obtained values of n1 and n2 for the VZ2 alloy were close to 0.8, indicating high homogeneity of the film surface .
The stability of the passive film is due to a higher chromium (Cr) percentage of 21% in the VZ1 alloy compared to that of the VZ2 alloy, at 7.3%, leading to the low diffusion of ionic species and/or low charge transfer and their accumulation across the passive layer/solution interface  for the VZ1 alloy.
Cyclic Polarization Measurements in Artificial Sea Water
The cyclic polarization (CP) curve for pH 7.5 is presented in Fig. 4a, b to show more information about the pitting corrosion resistance of VZ1 and VZ2, respectively. The curves recorded for other pH values were similar and have been omitted due to space constrictions. The corrosion parameters are listed in Table 3. The VZ1 and VZ2 alloys exhibit a similar CP behavior with spontaneous passivation without the active passive transition. This reveals their high corrosion-resistant nature at all pH values. Table 3 shows that the VZ1 alloy showed marginally lower Ecorr values than the VZ2 alloy under identical conditions. This is due to the ease of passive film formation by higher Cr content in the VZ1 alloy. The more positive potential indicates a negative reaction thermodynamic trend .
The pH of seawater has direct effect on corrosion rate. The higher corrosion current density was observed at pH 7.5. This behavior can be attributed to the low pH value accelerating corrosion by providing a supply of hydrogen (H+) ions. The partial cathodic reaction of the corrosion process is likely to be the reduction of the hydrogen ion and water molecule, according to the following equations :
The passive current density (ipass) for the VZ1 alloy was relatively low in comparison to the VZ2 alloy. This is related to the higher Cr present (21%) in the VZ1 alloy, which enhances the Cr2O3 formation, as XPS analysis later confirmed, in this region. The beginning of the rapid increase of anodic current density in the passive region indicates pit growth in the alloys.
The repassivation potential, Erep, Ecorr, and Epit values provide an indication of the resistivity of the VZ1 and VZ2 alloys against pitting corrosion. The tendency of VZ1 and VZ2 alloys to pitting can be evaluated by the anodic hysteresis loop area, where it is associated with the current density that has been consumed during the pitting corrosion process . The potential difference (Erep − Epit) values (Table 3), increase as the pH of the environment increased from 7.5 to 8.5. Due to containing a sufficient amount of alloying elements, such as Cr, reverse portions of the scan rate for the VZ1 alloy showed a small positive hysteresis with a high repassivation potential. The hysteresis area in VZ2 alloy was bigger and positive with repassivation potential (Erep) slightly nobler than the corrosion potential (Fig. 4b). The trends toward localized corrosion is attributed to the migration of the Cl− through the passive film formed on VZ2 alloy, leading to the production of Ni2+ and Cr3+ ions, and the formation of pits . So, the solution turned greenish yellow at the end of the polarization test.
The resistance pitting range, which is the difference in potential difference (Epit − Ecorr) decreased, as a result of dissolving the protective oxide layer by forming soluble complexes influencing the oxide film’s solubility, which is pH-dependent. The main reason for these variations is the influence of the various halide anions (Cl−, Br−, and F−), which exist in artificial sea water, and also their role in spreading the pits in the alloy. The presence of specifically adsorbed halide ions on the weak parts of the oxide surface caused pitting, which subsequently resulted in the initiation of pits. Pitting proceeds by an autocatalytic process in which there is a local increase in chloride and acid concentrations, due to corrosion product hydrolysis in cavities, where the adsorbed anions can transform Ni(OH)2 to more soluble nickel halide (NiX2) [20, 22] according to Eq. (3):
This acidic chloride environment is aggressive to most metals and tends to prevent repassivation, thereby promoting continued propagation of the pit .
Electrochemical Frequency Modulation (EFM) Measurements in Artificial Sea Water
To validate the corrosion parameters measured by cyclic polarization and EIS methods, the EFM technique was used in artificial seawater for each pH value at 27 °C (obtained curves not shown here). The values of the kinetic parameters, such as icorr, βc, and both Causality Factors (CF-2 and CF-3), used to corroborate the reliability of the acquired data , are given in Table 4. The smaller icorr values obtained at all pH values clearly indicate the high corrosion resistance of the VZ1 alloy compared to VZ2. The corrosion rate for VZ1 and VZ2 alloys were directly proportional to pH and exhibited an outstanding corrosion resistance by having low corrosion rate of less than 0.02 mmpy. The results obtained from the EFM measurements complement the AC and DC studies and are in agreement with the trend observed in the EIS and polarization measurements. The icorr calculated from the EFM data are much lower than the polarization and EIS measurements regardless of whether the corrosion process under investigation is passive. The reason for this might be the calculation of corrosion rates was measured in a narrow frequency range based on the resistance of the passive surface (Rf) instead of Rct, a wide frequency range in the capacitive region of the spectrum. As a consequence, the calculated impedance values are much too high and corrosion rates much too low .
X-ray Photo-electron Spectroscopy Analysis
For both alloys, the XPS-surveyed spectra of the passive film, formed in artificial seawater at pH 7.5 showed the presence of mainly nickel, chromium, oxygen, and iron signals (obtained curves not shown). The Nim 2p3/2 spectrum of the VZ1 alloy (Fig. 5a) shows a peak representing the metallic state Nim at a binding energy of about 852.3 eV. Also, a peak of Niox 2p3/2 at 853.3 eV was observed, characteristic of divalent nickel oxide species (NiO). The Crox 2p3/2 spectrum constitutes a large peak at 576.3 eV and a small one at 577.4 eV (Fig. 5b), due to trivalent (Cr(III)) species in chromium oxide Cr2O3 and chromium hydroxide Cr(OH)3, respectively . The spectra for Oox 1s (Fig. 5d) can be fitted with the components corresponding to the oxide of nickel (529.9 e), chromium oxide (530.3 eV), and the chromium hydroxide Cr(OH)3 (531.1 eV) , in alignment with the Ni 2p3/2 and Cr 2p3/2 regions. Hence, the improved corrosion resistance of the VZ1 alloy was attributed to enrich the protective chromium oxide and/or hydroxide layer formation in the inner part of the passive film, and the NiO species will be considered as an outer part of the passive layer in artificial seawater solution.
The VZ2 alloy in artificial seawater solution process mainly induced the formation of chromium oxide (Cr2O3) and/or chromium hydroxide (Cr(OH)3) as an inner passive layer and nickel oxide as the outer passive layer. In addition to these components, other components, including passive layer on the VZ2 alloy, can be observed in the Feox 2p3/2 spectrum at the binding energy of 711.6 eV (Fig. 5c). This was assigned to ferric compounds, such as Fe2O3 and/or FeOOH . In fitting the Oox 1s spectrum, additional peaks at 531.3 eV and .7 eV appeared, due to the O−2 groups in Fe2O3 and OH− groups in FeOOH, respectively (Fig. 5d). This suggests that the ferric compounds are present in the outer part of passive layer in the case of the VZ2 alloy, which appear to be responsible for the lower corrosion resistance observed in the electrochemical behavior, compared with the results of the VZ1 alloy. The present results for the Ni-based glassy alloys agree with the earlier observation results from the EIS and polarization measurements.
Scanning Electron Microscope, Energy Dispersive X-ray Spectroscopy (SEM/EDS) Analyses
The SEM/EDS analyzed the surface morphology and confirmed the nominal composition of the VZ1 alloy in seawater of pH 7.5, 8, 8.2, and 8.5 after the cyclic polarization measurements (Fig. 6). The as-received surface of bulk glassy alloy (Fig. 6a) shows a smooth and uniform surface morphology, as the alloy was formed by cooling an alloy liquid with high cooling rates to avoid crystallization. Figure 6b–e exhibit the passivating nature and high homogeneous oxide film as result to presence the chromium oxide on its surface , indicating high corrosion resistance. According to the EDS analysis (obtained curves not shown), the precipitate was mainly composed of Ni, O, Cr, C, and P elements and they were uniformly distributed along the surface. The mass fractions of the chemical elements of the passive film (wt%) were as follows: Ni 49.16, O 19.57, Cr 17.11, and C 7.91; the atom ratio was about 2:4:1:3, of which the compositions can be expressed as NiO + CrOx. These compositions were found in all of the samples with EDS results which showed similar elemental mapping, proving that no other major corrosion product existed.
The corrosion current density decreased with increasing pH of artificial sea water, but the pitting corrosion resistance decreased with increasing pH. The alloys exhibited a spontaneous passivation without the active passive transition in cyclic polarization behavior. The VZ1 alloy showed a smaller passive current density value and better corrosion resistance. This was attributed to the higher Cr content (21%) which enhanced the Cr2O3 formation.
S.A. Al-Fozan, A.U. Malik, Effect of seawater level on corrosion behavior of different alloys. Desalination 228, 61–67 (2008)
J. Bhandari, F. Khan, R. Abbassi, V. Garaniya, R. Ojeda, Modelling of pitting corrosion in marine and offshore steel structures—a technical review. J. Loss Prev. Process Ind. 37, 39–62 (2015)
J. Grosseau-Poussard, J. Dinhut, J. Silvain, R. Sabot, Role of a chromium ion implantation on the corrosion behaviour of nickel in artificial sea water. Appl. Surf. Sci. 151, 49–62 (1999)
O. Lavigne, T. Shoji, Y. Takeda, EIS pitting temperature determination of A182 nickel based alloy in simulated BWR environment containing dilute seawater. Nucl. Eng. Des. 273, 435–439 (2014)
A. Al-Hashem, J. Carew, The use of electrochemical impedance spectroscopy to study the effect of chlorine and ammonia residuals on the corrosion of copper-based and nickel-based alloys in seawater. Desalination 150, 255–262 (2002)
L. Machuca, S. Bailey, R. Gubner, Systematic study of the corrosion properties of selected high-resistance alloys in natural seawater. Corros. Sci. 64, 8–16 (2012)
H.M.A. El-Lateef, E.-S. Abdel-Rahman, H.S. Mohran, Role of Ni content in improvement of corrosion resistance of Zn–Ni alloy in 3.5% NaCl solution Part I: Polarization and impedance studies. Trans Nonferrous Met Soc China 25, 2807–2816 (2015)
K.M. Emran, H. Al-Refai, Resistivity and passivity characterization of Ni-base glassy alloys in NaOH media. Metals 8, 64 (2018)
K.M. Emran, A.-R. Hanaa, Electrochemical and surface investigation of Ni-Cr glassy alloys in nitric acid solution. Int. J. Electrochem. Sci. 12, 6404–6416 (2017)
Y. Zeng, C. Qin, N. Nishiyama, A. Inoue, New nickel-based bulk metallic glasses with extremely high nickel content. J. Alloys Compd. 489, 80–83 (2010)
Z.-D. Zhu, P. Jia, J. Xu, Optimization for toughness in metalloid-free Ni-based bulk metallic glasses. Scr. Mater. 64, 785–788 (2011)
A. Inoue, W. Zhang, T. Zhang, Thermal stability and mechanical strength of bulk glassy Ni–Nb–Ti–Zr alloys. Mater. Trans. 43, 1952–1956 (2002)
F.J. Millero, R. Feistel, D.G. Wright, T.J. McDougall, The composition of Standard Seawater and the definition of the Reference-Composition Salinity Scale. Deep Sea Res. Part I 55, 50–72 (2008)
O. Lavigne, C. Alemany-Dumont, B. Normand, M.-H. Berger, C. Duhamel, P. Delichére, The effect of nitrogen on the passivation mechanisms and electronic properties of chromium oxide layers. Corros. Sci. 53, 2087–2096 (2011)
B. Ter-Ovanessian, C. Alemany-Dumont, B. Normand, Electronic and transport properties of passive films grown on different Ni–Cr binary alloys in relation to the pitting susceptibility. Electrochim. Acta 133, 373–381 (2014)
J. Jayaraj, D.N.G. Krishna, C. Mallika, U.K. Mudali, Passive film properties and corrosion behavior of Ni–Nb and Ni–Nb–Ta amorphous ribbons in nitric acid and fluorinated nitric acid environments. Mater. Chem. Phys. 151, 318–329 (2015)
S.T. Arab, K.M. Emran, H.A. Al-Turaif, The electrochemical behavior of Ni-base metallic glasses containing Cr in H2SO4 solutions. J. Korean Chem. Soc. 56, 448–458 (2012)
H. Li, H. Yu, T. Zhou, B. Yin, S. Yin, Y. Zhang, Effect of tin on the corrosion behavior of sea-water corrosion-resisting steel. Mater. Des. 84, 1–9 (2015)
F.E.-T. Heakal, A. Fekry, M. Fatayerji, Influence of halides on the dissolution and passivation behavior of AZ91D magnesium alloy in aqueous solutions. Electrochim. Acta 54, 1545–1557 (2009)
A. Pardo, M. Merino, M. Carboneras, A. Coy, R. Arrabal, Pitting corrosion behaviour of austenitic stainless steels with Cu and Sn additions. Corros. Sci. 49, 510–525 (2007)
P. Jakupi, D. Zagidulin, J. Noël, D. Shoesmith, The impedance properties of the oxide film on the Ni–Cr–Mo Alloy-22 in neutral concentrated sodium chloride solution. Electrochim. Acta 56, 6251–6259 (2011)
M. Rao, Pitting corrosion of sheets of a nickel-base superalloy. Mater. Corros. 60, 49–52 (2009)
N. Al-Mobarak, K. Khaled, M.N. Hamed, K. Abdel-Azim, Employing electrochemical frequency modulation for studying corrosion and corrosion inhibition of copper in sodium chloride solutions. Arab. J. Chem. 4, 185–193 (2011)
E. Kuş, F. Mansfeld, An evaluation of the electrochemical frequency modulation (EFM) technique. Corros. Sci. 48, 965–979 (2006)
P. Singh, V. Srivastava, M. Quraishi, Novel quinoline derivatives as green corrosion inhibitors for mild steel in acidic medium: electrochemical, SEM, AFM, and XPS studies. J. Mol. Liq. 216, 164–173 (2016)
A.K. Al-Harbi, K.M. Emran, Effect of immersion time on electrochemical and morphology of new Fe–Co metal–metal glassy alloys in acid rain. Arab J Chem 12, 134–141 (2018)
The authors would like to thank Dr. Hartmann Thomas from Vacuumschmelze company for providing the specimens. Also, the authors would like to thank Mr. Abdallah Jaber of physical department for conducting surface measurements of the study samples.
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AL-Refai, H., Abdalsamad, K.M.E. Passivation Characterization of Nickel-Based Glassy Alloys in Artificial Sea Water. Met. Mater. Int. 26, 1688–1696 (2020). https://doi.org/10.1007/s12540-019-00487-w
- Ni-based glassy alloys
- Artificial seawater
- Cyclic polarization