Effect of boron on the corrosion properties of Al0 ...

ECS Transactions, 2 (26) 15-33 (2007) 10.1149/1.2409020, copyright The Electrochemical Society

Effect of boron on the corrosion properties of Al0.5CoCrCuFeNiBx high entropy alloys in 1N sulfuric acid C. P. Lee, Y. Y. Chen, C. H. Wu, C. Y. Hsu, J. W. Yeh, H. C. Shih Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 300, Taiwan, ROC High entropy alloys are a newly developed family of multi-component alloys composed of several major alloying elements, such as copper, nickel, aluminum, cobalt, chromium, iron, etc. Each element in the alloy system is between 5 at.-% and 35 at.-%. High entropy alloy has a lot of advantages regarding its mechanical, magnetic and electrochemical properties. This study discusses the corrosion resistance of Al0.5CoCrCuFeNiBx alloys with various amounts of boron addition. Surface morphology and EDS analysis confirmed that the addition of boron produced Cr and Fe borides. Therefore the content of Cr in the region besides borides precipitates was very scanty. The anodic polarization curves and electrochemical impedance spectra of Al0.5CoCrCuFeNiBx alloys, obtained in 1 N H2SO4 aqueous solution, clearly indicated that the general corrosion resistance decreases as the amounts of boron increases. Introduction For thousands of years the development of tradition alloy systems has mainly base on one principal element as the matrix, as in iron-based, aluminum-based, magnesium-based alloys and nickel-based superalloys (1). Since the 1970s, intermetallic compounds of Ti-Al, Ni-Al and Fe-Al binary systems have attracted much attention because of their extremely high specific strengths and thermal resistance (2). In the 1960s, Duwez et al. attained an Au-25 at% Si amorphous phase by rapid solidification (3). If the cooling rate (about 106K/s) was fast enough to inhibit the nucleation and growth of crystals. Such a high cooling rate limited the specimen shape. Only thin films could be formed, which could not be used as a structural material. Unit the 1984, Kui et al. successfully produced a bulk Pd40Ni40P20 amorphous alloy of 10 mm in diameter by using fluxing method to remove heterogeneous nucleation (4). The designs of the above mentioned alloys are still limited in that the matrix always contains one or two major element. In order to break through from the traditional alloy design habit, a novel high entropy alloy was developed. High entropy alloys are those composed of five or more principal element, each element in the alloy system is between 5 at.-% and 35 at.-%. The present study is focused on a new alloy design with multiple principal elements in equimolar or near-equimolar ratios. Solid solutions with multiprincipal elements will tend to be more stable because of their large mixing entropies. The relationship between entropies and system complicacy, the change per molar in configurational entropy during the formation of a solid solution from n elements with equimolar fractions may be calculated from the following equation.

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ECS Transactions, 2 (26) 15-33 (2007)

7

∆Sconf = −k lnω = −R∑ X i ln X i = R ln 7 ≈ 1.95R , X i = i =1

1 7

[1]

Where k is Boltzmann’s constant, ω is the number of ways of mixing, and R is the gas constant: 8.314J/K mole. For instance, ∆Sconf for equimolar alloys with 3, 5, 7and 9 elements are 1.10R, 1.61R, 1.95R and 2.20R, respectively. In fact, considering other positive contribution from vibrational, electronic and magnetic, the entropy change of mixing for equimolar high entropy alloy is higher than calculated (5). Extensive trials have led to many alloy systems with simple crystal structures and exceptional properties. From our previous studies (6) (7), AlxCoCrCuFeNi alloys with different aluminum contents (i.e., x values in molar ratio, x = 0 to 1.0) were synthesized using the casting method. These alloys possessed simple fcc/bcc structures. With aluminum contents less than 0.5 molar, the alloys were composed of a simple fcc solid-solution structure. As the aluminum content reached 0.8 molar, mixed fcc/bcc phases resulting from a eutectic reaction were observed. Spinodal decomposition further occurred when the aluminum contents were higher than 1.0 molar. The Al0.5CoCrCuFeNi alloy is ductile, well ability in work hardening and strong at high temperature up to 800℃. Boron addition in Al0.5CoCrCuFeNi alloys can increase the wear resistance and hardness by the formation of boride. However, the corrosion properties of the Al0.5CoCrCuFeNiBx alloys in most aqueous solution are not available. The purpose of this study is to investigate the electrochemical behavior of Al0.5CoCrCuFeNiBx alloys in 1N sulfuric acid. In 1821, Berthier (8) found that iron alloyed with considerable Cr was more resistant to acid than was unalloyed iron. But the accompanying high carbon content impaired corrosion resistance .Only in 1904 did Guillet (9) produce low-carbon Cr alloys overlapping the passive composition range. And recognition of the outstanding property of passivity in such alloys initiating at a minimum of 12% Cr was first described by Monnartz (10) in 1911. The 18% Cr, 8% Ni austenitic stainless steel is the most popular of all the stainless steels now produced. For example, AISI type-304 stainless steel was used by architectural and automobile trim, and various structural units for the food and chemical industries (11). The chemical compositions of 304 stainless steel and the Al0.5CoCrCuFeNi alloy can be quite similar in that both can be made of Fe, Cr and Ni, being different only in their relative proportions. There is wealthy information on the corrosion behaviors of 304 stainless steel exposed to H2SO4 solutions (12-19). Therefore, it is of interest to determine the corrosion behavior of high entropy alloys in comparison with conventional ferrous alloys (20), such as 304 stainless steel. Experimental procedures

Test materials Element Al, Co, Cr, Cu, Fe and Ni with purity higher than 99wt pct were used in granular shape as raw materials. Fe-18.2 wt pct B master alloy was used for boron addition in the alloy. The foundation characteristics of the seven compositional elements listed in Table Ⅰ.



The high entropy alloy was a seven-component alloy in the form of Al0.5CoCrCuFeNiBx, for 0.5 mole of aluminum, 1 mole of the other five alloying elements and addition boron from zero to 1 mole. The compositions of the alloys are listed in Table Ⅱ. The multiprincipal-element Al0.5CoCrCuFeNiBx alloy system with different boron contents (i.e., x values in molar ratio, from 0 to 1.0) was prepared in this study by induction furnace in air. The size of the ingots was 8×7×14 (cm). For electrochemical measurements, the high entropy alloy cylinder was obtained by cutting the bulk material using a electric arc line cutting that were 3 mm thick and 8 mm in diameter. On the other hand, a 304 stainless steel rod was machined down to 10mm thick and 12.7mm in diameter. Each test specimen was then cold mounted, using an epoxy resin to give an exposed surface area of 0.5 cm2 for high entropy alloys and 1.26 cm2 for 304 stainless steel. Before each electrochemical experiment, all specimens were mechanically polished with a series of 240-600 SiC grit paper and cleaned with distilled water. Electrochemical measurements Test solutions were conducted in 1N H2SO4 solution at 25℃ under atmospheric pressure. The solution was deaerated by bubbling purified nitrogen gas through the test solution before and throughout the electrochemical experiment, to reject the effect of dissolved oxygen. Both dc electrochemical polarization and electrochemical impedance spectroscopy were carried out in a typical 3-electrode cell consisted of a specimen as the working electrode, an Ag/AgCl in 3M KCl as the reference electrode, and a Pt sheet as the counter electrode. The Ag/AgCl scale is 194mV lower than the SHE, i.e., VAg/AgCl+0.194mV = VSHE (21). Anodic polarization measurements were conducted at a scan rate of 1 mV/s from the initial potential of -0.8V to the final potential of 1.5 V versus open current potential. The potential was controlled and the current was measured, using a potentiostat / galvanostat (AUTOLAB PGSTAT30). The electrochemical impedance spectra were recorded in a frequency range between 10 kHz and 10 mHz. The amplitude of sinusoidal signals was 10 mV around the open corrosion potential, using an AUTOLAB PGSTAT30/FRA system from ECO CHEMIE. Before either of these testing, the open-circuit potential (OCP) was recorded for about 15 min to obtain a steady-state potential. Afterward the specimen was cathodically polarized to a potential of -400mV (Ag/AgCl) for 5 min to reduce the existing surface films. Surface morphology observation and chemistry analysis After the polarization experiment, the specimen was cleaned with distilled water, and then dried in nitrogen. Immediately, the morphology of the corroded surface of the high entropy alloy was investigated in a JEOL-5410 scanning electron microscope (SEM). Results and discussion

Anodic polarization curves The electrochemical parameters of the Al0.5CoCrCuFeNiBx alloys (x=0, 0.2, 0.6 and 1.0)



and 304 stainless steel in deaerted 1N H2SO4 solution are given in Table Ⅲ. In Fig. 1, we can see that the corrosion potential (Ecorr) for the Al0.5CoCrCuFeNi high entropy alloy (-0.094 VSHE) is apparently more noble than that of 304 stainless steel (-0.165 VSHE), and the corrosion current density (icorr) of the Al0.5CoCrCuFeNi high entropy alloy (3.188×10-6 ) is also lower than that of 304 stainless steel (3.318×10-5 ) in 1N H2SO4 solution. Furthermore, 304 stainless steel has a wider region of passive potentials than Al0.5CoCrCuFeNi high entropy alloy. It is obvious that the Al0.5CoCrCuFeNi alloy is more resistant to general corrosion than 304 stainless steel (higher Ecorr, lower icorr) in 1N H2SO4 solution. But, if general corrosion occurs at higher potential, the corrosion resistant of the Al0.5CoCrCuFeNi alloy will be less than that of 304 stainless steel, because of the difference in the passivation range. Fig. 2 shows the anodic polarization curve of the Al0.5CoCrCuFeNiBx alloys with different content of boron (x=0.2, 0.6 and 1.0) in deaerated 1 N H2SO4 solution at room temperature (~25 ℃). The corrosion potential for Al0.5CoCrCuFeNiBx alloys various from -0.128 to -0.135VSHE, and corrosion current density various from 7.257×10-6 to 2.259×10-5 A/cm2. Al0.5CoCrCuFeNi alloy has higher corrosion potential and lower corrosion current density than Al0.5CoCrCuFeNiBx alloy (x=0.2, 0.6 and 1.0). Due to the Cr borides precipitates take place as the addition of the boron in the Al0.5CoCrCuFeNi alloy. According to Hsu’s study (7), as boron content increases in the alloys, the peak intensities of Cr and Fe borides increase in the XRD patterns. The anodic polarization of Al0.5CoCrCuFeNiBx alloy (x=0.2, 0.6 and 1.0) is referred to as a pseudo-passive curve because the curve does not have a distinct primary passivation potential (Epp), but there appears to be a breakdown potential (Eb) and a transpassive region (22). Cyclic potentiodynamic polarization It is clear that 304 stainless steel does not suffer from pitting corrosion in halide-free solution (21). In order to determine whether the Al0.5CoCrCuFeNiBx alloy (x=0, 0.2, 0.6 and 1.0) behave likewise in H2SO4 solution at room temperature; a cyclic polarization technique was used. Cyclic polarization curve hysteresis can provide information on pitting corrosion rate and how readily a passive film repairs itself. Cyclic polarization measurements were conducted at a scan rate of 10 mV/s. The potential scan began at -0.8VSHE and continued in the anodic direction until the potential was reached 1.7 VSHE. At this point, the potential scan direction was reversed to where the polarization started. The cyclic polarization curves of Al0.5CoCrCuFeNiBx alloys are shown in Fig. 3. The black and gray arrows next to the forward and reverse anodic branches indicate potential scan directions. The negative hysteresis in the reverse scans of cyclic polarization curves indicated that Al0.5CoCrCuFeNiBx alloys (x=0, 0.2, 0.6 and 1.0) are not susceptible to localized corrosion, such as pitting, in 1N H2SO4. Negative hysteresis occurs when reverse scan current density is less than that for the forward scan, and positive hysteresis occurs when reverse scan current density is greater than that for the forward scan. A passive film is damaged when potential is raised into the transpassive region of a anodic polarization curve, and pits can initiate when film damage is at discrete locations on the metal surface (23). In fig. 3 the repassivation potential (Erp) is more noble than the



corrosion potential (Ecorr) no matter including boron or not. It is generally believed that a passive film repairs itself when repassivation potential is greater than corrosion potential. With increasing of boron in the Al0.5CoCrCuFeNiBx alloys, the respassivation potential decreases from 0.276 to -0.108 VSHE. It is apparent that the restore ability of passive film will be reduce due to the addition of boron in Al0.5CoCrCuFeNiBx alloys SEM photographs of the corroded surfaces Figure 4(a) shows the SEM microstructure of Al0.5CoCrCuFeNi alloy after anodic polarization in deaerated 1 N H2SO4, which is composed of dendrite and interdendrite. The occurrence of corrosion on the Al0.5CoCrCuFeNi alloy was aggregated at the interdendrite. According to previous report, the interdendrite of Al0.5CoCrCuFeNi alloy is Cu-rich phase, and dendrite is Cu-depleted phase (24). When decreasing the Cu concentration, the phenomenon of Cu segregation in interdendrites will be gradually removed. Figure 4 (b) to (d) are the SEM microstructure of Al0.5CoCrCuFeNiBx alloys (x=0.2, 0.6 and 1.0). Stringer-Shaped precipitates can be seen in Figure 4(b) though (d). It is noted that volume fraction of stringer precipitates increase as the amount of boron increases in the alloy. The occurrence of corrosion on the Al0.5CoCrCuFeNiBx (x=0.2 to 1.0) alloy was concentrated at the region close to the stringer precipitates. Surface composition analysis by EDS Figure 5. (b) is the elemental mapping on Chromium for the Al0.5CoCrCuFeNiB0.6 alloy after anodic polarization in deaerated 1 N H2SO4. It was quite obvious that the stringer precipitates are rich in Cr. In order to verify the composition of the stringer phase, the EDS analysis was used. Table Ⅳ shown the EDS results corresponding to Fig. 5(a) with different selected area A and B after anodic polarization in deaerated 1 N H2SO4. Selected area A is the stringer precipitates on the Al0.5CoCrCuFeNiB0.6 alloy; selected B is the other region besides stringer precipitates. As the results of EDS analysis, the stringer precipitates of the Al0.5CoCrCuFeNiB0.6 alloy is rich in Cr, Fe and B. It is therefore concluded that the stringer precipitates are borides of Cr and Fe (7).The atomic percentage of Cr on the stringer precipitates (50.06%) is much more than the other region (2.48%) in the Al0.5CoCrCuFeNiB0.6 ally. Because of the content of Cr in the region besides stringer precipitates was very scanty. Therefore the localized attack was appeared on the side of borides precipitates. From the results of EDS analysis and polarization data, we can confirmed that the addition of boron produced Cr and Fe borides, which is decreased the corrosion resistance of the Al0.5CoCrCuFeNiBx alloy. Electrochemical impedance spectroscopy measurement As shown in Fig. 6(a), the Nyquist plot for the Al0.5CoCrCuFeNi alloy presents one depressed semicircle with a long tail at low frequency region, while only one depressed semicircle for 304 stainless steel. On the other hand, it can be observed that the diameter of semicircle for the Al0.5CoCrCuFeNi alloy is much larger than 304 stainless steel. The resistance values of 304 stainless steel were estimated by the EIS curves. The solution resistance (Rs ) was estimated from the impedance in a high frequency range, while the sum of Rs and the polarization resistance Rp was estimated from the impedance in the low



frequency range. The difference between these two impedance values results in Rp, which is inversely proportional to the corrosion rate (25) (26). The corresponding Bode impedance plots as shown in Figure 6(b) also show that the impedance value in the Al0.5CoCrCuFeNi alloy is much larger than 304 stainless steel. These mean that the corrosion rate of the Al0.5CoCrCuFeNi alloy is much smaller than 304 stainless steel. This result is consistent with the anodic polarization curves shown in Figure 1 at the open current potential. Figure 7 shows the Nyquist plot for the Al0.5CoCrCuFeNiBx (x=0, 0.2, 0.6 and 1.0) alloys in deaerated 1 N H2SO4.The impedance values of the Al0.5CoCrCuFeNiBx alloy decreases as the amounts of boron increases. Therefore, these tendencies in EIS measurement are conform to the anodic polarization curves shown in Figure 2. The entire Al0.5CoCrCuFeNiBx alloys present a long tail at low frequency region. A diffusion tail was often observed following the electrochemical reaction process due to the mass transfer difficulty of corrosion products of substrates (27) (28). Figure 8(a) and (b), respectively, depict the experimental and simulated Nyquist plot and Bode plots for the Al0.5CoCrCuFeNi alloy. It is found from the Nyquist plot that a diffusion tail appears at low frequency. The equivalent electrical circuit that better fitted the experimental results for the electrode is shown in Figure 8(c), where Rs is the solution resistance, Rf and Cf are the resistance and constant phase element associated with the passive film on surface. The constant phase element is related to the impedance (Z). ZCPE can be presented as

Z CPE = [Q( jω ) n ] −1

[2]

where, j is the imaginary root, ω the angular frequency (ω=2πf, f is the frequency)and n an exponential term. CPEs are used in the analysis of impedance spectra to account deviations produced by surface roughness (29) (30). For a smooth electrode, n approaches the unity and CPE response would be that of a capacitor. Porous surfaces yield lower n values. Rt is the change transfer resistance and Cdl is double-layer capacitance that characterizes the charge separation between metal and electrolyte interface. Zw is the Warburg impedance. Zw can be presented as (31-33) Z w = σω

−1

2

(1 − j )

[3]

where, σ is the Warburg coefficient (Ω cm2 s-1/2). When the 0.6 mole of boron was added to the Al0.5CoCrCuFeNi alloy, the Nyquist plot presented two capacitive loops and a diffusion tail at low frequency. (Figure 9(a)); the corresponding experimental and simulated Bode plots are shown in Figure 9(b). The Cr borides precipitates take place on the surface as the addition of the boron in the Al0.5CoCrCuFeNi alloy. The content of Cr on the surface besides stringer precipitates would not enough to form the passive film. Therefore a lot of localized attack was appeared on the side of borides precipitates in deaerated 1 N H2SO4. Therefore, the equivalent electrical circuit used to analyze the EIS data was the one shown in Figure 9(c). Rs is the solution resistance, Rf and Cf are the resistance and constant phase element



associated with the passive film on surface. Rpore is the electrolyte resistance through the pore (34) (35), and CB is the capacitance of boride precipitates. Rt and Cdl are the resistance and the CPE associated with the charge-transfer reaction. In both situations (Al0.5CoCrCuFeNi and Al0.5CoCrCuFeNiB0.6), good agreement between the experimental and the simulated data was noted. Table Ⅴ gives the values for the equivalent circuit elements derived from simulation. The Al0.5CoCrCuFeNi alloy presents higher Rt values than the Al0.5CoCrCuFeNiB0.6 alloy indicated that the addition of boron in the Al0.5CoCrCuFeNi alloy was decreased the corrosion resistance. Conclusions

1.

2. 3. 4. 5. 6.

Anodic polarization shows that the corrosion potential for the Al0.5CoCrCuFeNi high entropy alloy (-0.094 VSHE) is apparently more noble than that of 304 stainless steel (-0.165 VSHE), and the corrosion current density of the Al0.5CoCrCuFeNi high entropy alloy (3.188×10-6 ) is also lower than that of 304 stainless steel (3.318×10-5 ) in 1N H2SO4 solution. It is obvious that the Al0.5CoCrCuFeNi alloy is more resistant to general corrosion than 304 stainless steel in 1N H2SO4 solution. Al0.5CoCrCuFeNi alloy has higher corrosion potential and lower corrosion current density than Al0.5CoCrCuFeNiBx alloy (x=0.2, 0.6 and 1.0). The negative hysteresis in the reverse scans of cyclic polarization curves indicated that Al0.5CoCrCuFeNiBx alloys (x=0, 0.2, 0.6 and 1.0) are not susceptible to localized corrosion, such as pitting, in 1N H2SO4. As the results of EDS analysis, the stringer precipitates of the Al0.5CoCrCuFeNiB0.6 alloy is rich in Cr, Fe and B. Electrochemical impedance spectroscopy shows the impedance value in the Al0.5CoCrCuFeNi alloy is much larger than 304 stainless steel. These mean that the corrosion rate of the Al0.5CoCrCuFeNi alloy is much smaller than 304 stainless steel. The Al0.5CoCrCuFeNi alloy presents higher Rt values than the Al0.5CoCrCuFeNiB0.6 alloy indicated that the addition of boron in the Al0.5CoCrCuFeNi alloy was decreased the corrosion resistance.



TABLE Ⅰ. Elemental characteristics of the seven compositional elements. Element Atomic Atomic Melting Boiling Density weight radius point point (g / cm3) (g / mole) (Å) (℃ ) (℃ )

Crystal structure

B

10.81

1.17

2300

2550

2.45

—

Ni

58.69

1.24

1453

2732

8.90

FCC

Co

58.93

1.25

1495

2870

8.80

HCP

Fe

55.85

1.27

1538

2870

7.41

BCC

Cu

63.55

1.28

1083

2567

7.94

FCC

Cr

52.00

1.34

1875

2680

7.19

BCC

Al

26.98

1.46

660

2467

2.56

FCC

TABLE Ⅱ. Alloys used in this experiment. High Entropy Alloys Composition(Atomic Ratio) Boron (Atomic Pct.) Designation B-0

Al0.5CoCrCuFeNi

0

B-0.2

Al0.5CoCrCuFeNiB0.2

3.5

B-0.6

Al0.5CoCrCuFeNiB0.6

9.8

B-1.0

Al0.5CoCrCuFeNiB1.0

15.4

TABLE Ⅲ. Electrochemical parameters of Al0.5CoCrCuFeNiBx alloys and 304 stainless steel in deaerated 1 N H2SO4 solution. High Entropy Alloys Icorrb(A/cm2) Ecorra(VSHE) Designation Al0.5CoCrCuFeNi

-0.094

3.188×10-6

Al0.5CoCrCuFeNiB0.2

-0.128

7.257×10-6

Al0.5CoCrCuFeNiB0.6

-0.132

1.290×10-5

Al0.5CoCrCuFeNiB1.0

-0.135

2.259×10-5

304 stainless steel

-0.165

3.319×10-5

a

Ecorr: corrosion potential. icorr: corrosion current density.

b



TABLE Ⅳ. EDS results corresponding to Fig. 5(a) for the Al0.5CoCrCuFeNiB0.6 alloy with different selected area A and B after anodic polarization in deaerated 1 N H2SO4. A B Element

Weight%

Atomic%

Weight%

Atomic%

Al K Co K Cr K Cu L Fe K Ni K BK Totals

0.32 11.87 63.71 — 14.85 4.43 4.82 100.00

0.53 9.05 55.06 — 11.95 3.39 20.02

11.18 11.56 2.46 23.87 7.02 43.91 — 100

21.73 10.28 2.48 19.70 6.59 39.22 —

TABLE Ⅴ. Equivalent circuit elements values for EIS data corresponding to the Al0.5CoCrCuFeNi and Al0.5CoCrCuFeNiB0.6 alloys in deaerated 1 N H2SO4 solution.

B0

RS Rf Ωcm2 Ωcm2

Cf (F/cm2)

1.3

1000

2.5×10-5 0.48 —

—

—

350

6×10-5

1×10-3

0.93 900

B0.6 1.4

nf

Rpore CB Ωcm2 (F/cm2)

0.34 600

nB

Rt Cdl Ωcm2 (F/cm2)

2500

ndl

W

7.5×10-4 0.95 1.3×10-3 8×10-3

0.92 2.5×10-2



Al0.5CoCrCuFeNi 304S

E (Volts) vs. SHE

1.5 1.0 0.5 0.0 -0.5 -1.0 1E-8

1E-7

1E-6

1E-5

1E-4

1E-3

0.01

0.1

1

2

i (A/cm ) current density Figure 1. Comparisons of the anodic polarization curves for Al0.5CoCrCuFeNi and 304 stainless steel in deaerated 1 N H2SO4.

1.5

E (Volts) vs. SHE

1.0

Al0.5CoCrCuFeNiBx B 0.2 B 0.6 B 1.0

0.5

0.0

-0.5

-1.0 1E-8

1E-7

1E-6

1E-5

1E-4

1E-3

0.01

0.1

1

2

i (A/cm ) current density Figure 2. The anodic polarization for Al0.5CoCrCuFeNiBx in deaerated 1 N H2SO4 with different content of boron.



1.5

negative hysteresis Al0.5CoCrCuFeNi

E (Volts) vs. SHE

1.0

0.5

Erp 0.0

Ecorr -0.5

-1.0 1E-7

1E-6

1E-5

1E-4

1E-3

0.01

0.1

1

2

i (A/cm ) current density 1.5

negative hysteresis

E (Volts) vs. SHE

1.0

Al0.5CoCrCuFeNiB0.6

0.5

0.0

Erp

Ecorr -0.5

-1.0 1E-7

1E-6

1E-5

1E-4

1E-3

0.01

0.1

1

2

i (A/cm ) current density

Figure 3. The cyclic polarization curves for Al0.5CoCrCuFeNiBx in deaerated 1 N H2SO4 with different content of boron.



(a)

(b)

(c)

(d)

Figure 4. SEM micrograph for the Al0.5CoCrCuFeNiBx alloys with different content of boron (a)x=0, (b)x=0.2 mole, (c)x=0.6 mole and (d)x=1.0 mole after anodic polarization in deaerated 1 N H2SO4.



(a)

(b)

Figure 5. (a)Secondary electron image and (b)elemental mapping on Chromium for the Al0.5CoCrCuFeNiB0.6 alloy after anodic polarization in deaerated 1 N H2SO4.



(a) 3500 304 stainless steel Al0.5CoCrCuFeNi

-ZImage/Ohm*cm

2

3000 2500 2000 1500 1000 500 0

0

500

1000

1500

2000

2500

3000

3500

2

ZReal/ohm*cm

2

4.0

80

3.5

70

3.0

60 50

2.5

40 2.0 30 1.5

20

1.0

10

0.5

0

0.0 -3

-2

-1

0 1 2 log (f / Hz)

3

4

5

- phase/deg(+)

log(| z| / Ohm*cm )

(b)

-10

Figure 6. EIS spectra of Al0.5CoCrCuFeNi alloy (＋) and 304 stainless steel (□) in deaerated 1 N H2SO4. (a) Nyquist plot; (b) Bode plots.



4000 Al0.5CoCrCuFeNiBx B0 B0.2 B0.6 B1.0

3500

-ZImag/Ohm*cm

2

3000 2500 2000 1500 1000 500 0 0

500 1000 1500 2000 2500 3000 3500 4000 2

ZReal/ohm*cm

Figure 7. The EIS Nyquist plot for Al0.5CoCrCuFeNiBx (x=0, 0.2, 0.6 and 1.0) alloys in deaerated 1 N H2SO4 with different content of boron.



(a) 4000

- ZImage/Ohm*cm

2

3000

2000

1000

0 0

1000

2000

3000

4000

2

ZReal/ohm*cm

80

3.5

70

3.0

60

2.5

50

2

4.0

2.0

40

1.5

30

1.0

- phase/deg(+)

log(| z| / Ohm*cm )

(b)

20

0.5

10

0.0 -2

0

2

4

0

log (f / Hz)

(c)

Figure 8. Experimental ( ○ and ＋) and simulated (—) of Nyquist plot (a), Bode plots (b) and the equivalent electrical circuit representative of the electrode interface (c) for the Al0.5CoCrCuFeNi alloy in deaereted 1N H2SO4 solution.



(a) 1200

- ZImage/Ohm*cm

2

1000 800 600 400 200 0 0

200

400

600

800

1000

1200

2

ZReal/ohm*cm

2

4.0

80

3.5

70

3.0

60

2.5

50

2.0 40 1.5 30

1.0 0.5

20

0.0

10 -2

(c)

-1

0

1 log (f / Hz)

2

3

- phase/deg(+)

log(| z| / Ohm*cm )

(b)

4

Figure 9. Experimental ( ○ and ＋) and simulated (—) of Nyquist plot (a), Bode plots (b) and the equivalent electrical circuit representative of the electrode interface (c) for Al0.5CoCrCuFeNiB0.6 alloy in deaereted 1N H2SO4 solution.



References

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28.

J.W. Yeh, S.K. Chen, S.J. Lin, J.Y. Gan, T.S. Chin, T.T. Shun, C.H. Tsau, S.Y. Chang, Adv. Eng. Mater., 6, 299 (2004). C.J. Tong, M.R. Chen, S.K. Chen, J.W. Yeh, T.T. Shun, S.J. Lin, S.Y. Chang, Metallurgical and Materials Transaction A, 36, 1263 (2005) P. Duwez, Trans. Am. Soc. Metals, 60, 607 (1967). H.W. Kui, A.L. Greer, D. Trnbull, Appl. Phys. Lett., 45, 615 (1984). R.A. Swalin, Thermodynamics of Solids, second ed., P. 21, Wiley, NY (1991). C.J. Tong, Y.L. Chen, S.K. Chen, J.W. Yeh, T.T. Shun, C.H. Tsau, S.J. Lin, S.Y. Chang, Metallurgical and Materials Transaction A, 36, 881 (2005) C.Y. Hsu, J.W. Yeh, S.K. Chen, T.T. Shun, Metallurgical and Materials Transactions A, 35, 1465 (2004) P. Berthier, Ann. Chimie Phys., 17, 55 (1821). L. Guillet, Rev. Met., 1, 155 (1904). P. Monnartz, Metallurgie, 8, 161 (1911) H.H. Uhlig, R.W. Revie, Corrosion and Corrosion Control, Third ed., Wiley, NY (1985). C.K. Lee, H.C. Shih, Corrosion, 52, 690 (1996). S.Y. Tsai, K.P. Yen, H.C. Shih, Corros. Sci., 40, 281 (1998). L. Fu. Li, M. Daerden, P. Caenen, J.P. Celisb, J. Electrochem. Soc., 153, B145 (2006). N. D. Budiansky, J. L. Hudson, J. R. Scully, J. Electrochem. Soc., 151, B233 (2004). A. E. Thomas, Y. E. Sung, M. Gamboa-Aldeco, K. Franszczuk, A. Wieckowaki, J. Electrochem. Soc., 142, 476 (1995). R. Gasparac, C.R. Martin, J. Electrochem. Soc., 148, B138 (2001). J.H. Potgieter, H.C. Brookes, Corrosion, 51, 312 (1995) S. Maximovitch, G. Barral, F. Lecras, F. Claudet, Corros. Sci., 37, 271 (1995). Y.Y. Chen, T. Duval, U.D. Hung, J.W. Yeh, H.C. Shih, Corros. Sci., 47, 2257 (2005). D.A. Jones, Principles and Prevention of Corrosion, Second ed., Prentice Hall, NJ, (1996). S. Shah, R.N. Grugel, B.D. Lichter, Journal of Applied Electrochemistry, 21, 1013 (1991). Z. Szklarska-Smialowska, Pitting Corrosion of Metals, p. 40, NCAE, Houston TX (1986). Y.J. Hsu, W.C. Chiang, J.K. Wu, Materials Chemistry and Physics, 92, 112 (2005) . K.L. Chang, S.C. Chung, S.H. Lai, H.C. Shih, Applied Surface Science, 236, 406, (2004). K.L. Chang, S. Han, J.H. Lin, J.W. Hus, H.C. Shih, Surface and Coatings Technology, 172, 72 (2003). F. Deflorian, V.B. Miskovic-Stankovic, P.L. Bonora, L. Fedrizzi, Corrosion, 50, 438 (1994). P.L. Bonora, F. Deflorian, L. Fedrizzi, Electrochim. Acta, 41, 1073 (1996).



29. A.V. Benedetti, P.T.A. Sumodjo, K. Nobe, P.L. Cabot, W.G. Proud, Electrochim. Acta, 40, 2657 (1995). 30. M.R.F. Hurtado, P.T.A. Sumodj, A.V. Benedetti, Electrochim. Acta 48, 2791 (2003). 31. G.W. Walter, Corrosion Science, 26, 681 (1986). 32. J.M. Hu, J.T. Zhang, J.Q. Zang, C.N. Cao, Corrosion Science, 47, 2607 (2005). 33. Y. Chen, T. Hong, M. Gopal, W.P. Jepson, Corrosion Science, 42, 979 (2000). 34. R.G.. Kelly, J.R. Scully, D.W. Shoesmith, R.G.. Buchheit, Electrochemical Techniques in Corrosion Science and Engineering, Marcel Dekker, NY (2003). 35. A. Carnot, I. Frateur, S. Zanna, B. Tribollet, I.D. Brugger, P. Marcus, Corrosion Science, 45, 2513 (2003).
