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Intermetallics 19 (2011) 1913e1918

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Intermetallics

journal homepage: www.elsevier .com/locate/ intermet

Study on corrosion behavior of continuous bulk metallic glass-coated steel wirecomposite

Xiaohua Chen a,b,*, Baoyu Zhang a, Guoliang Chen a,*, Xidong Hui a,*, Xianran Xing a,b

a State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, PR ChinabDepartment of Physical Chemistry, University of Science and Technology Beijing, Beijing 100083, PR China

a r t i c l e i n f o

Article history:Received 11 February 2011Received in revised form18 April 2011Accepted 30 April 2011Available online 23 September 2011

Keywords:A. CompositesB. GlassesC. CoatingD. MicrostructureF. corrosion behaviour

* Corresponding authors. State Key Laboratory forrials, University of Science and Technology Beijing, Bfax: þ86 010 62332350.

E-mail addresses: chenxh@skl.ustb.edu.cn (X.(X. Hui).

0966-9795/$ e see front matter � 2011 Published bydoi:10.1016/j.intermet.2011.04.016

a b s t r a c t

Zr41.2Ti13.8Cu12.5Ni10Be22.5 (atomic percent) (Vit1) Bulk metallic glass (BMG)-coated steel wire compositewas produced by using continuous process. The existence of amorphous structure in the BMG coatingwas proved by differential scanning calorimeter (DSC) measurement and transmission electron micro-scope (TEM). The corrosion behaviors of the bare steel wire and the wire composite in 3.5 wt% NaClsolution corrosive media were investigated by immersion tests and electrochemical polarizationmeasurements at room temperature. Scanning electron microscopy (SEM) was utilized to examinemorphology of the corroded surface. By comparing the corrosion behaviors of the wire composite andthe bare steel wire as well as the Vit1 BMGs reported in the literatures, the results of the presentinvestigation reveal (1) it is important to choose sound technical parameters such as processingtemperature to avoid the crystallization for the BMG coating of steel wire (2) the Vit1 BMG-coated steelwire composite has better corrosion resistance than the bare steel wire from perspective of either massloss or polarization behavior (3) strong protective layers grow on the surface of the coated steel wire byanodization, of which the barrier effect to initiate pitting is slightly lower than that of the monolithic Vit1BMG, but the general polarization behavior is quite similar to that of the monolithic Vit1 BMG.

� 2011 Published by Elsevier Ltd.

1. Introduction

To improve the anticorrosion property of steel wires, galvani-zation process is usually conducted [1]. The corrosion resistance ofthe coating of galvanized wire is originated from the protection ofsacrificing anode. Bulk metallic glasses (BMG) have potential asengineering materials because of their excellent mechanical prop-erties [2e6]. Recently, the applications of BMG alloys for specialcoating have attracted more and more attention considering thatthey exhibit excellent wear or corrosion resistance [7e9].Undoubtedly, it is of significance not only in metallurgy but also ineconomical value if the BMG alloy can be coated on steel wire. Forthis purpose, the authors developed a continuously manufacturingtechnology of BMG-coated metallic wire composite, and Vit1 alloycoated tungsten wire has been prepared [10e12]. The progress incoating technology of BMG opens new opportunities for practicalapplications of wear and corrosion resistance of BMG coating.

Advanced Metals and Mate-eijing 100083, PR China. Tel./

Chen), xdhui@ustb.edu.cn

Elsevier Ltd.

Unfortunately, the corrosion behavior of this kind of composite hasseldom been explored although some corrosion data of pure BMGin aqueous solutions have been obtained [13]. In this work, Vit1BMG-coated steel wire composites were prepared and theirmicrostructure was characterized. By using immersion tests andthe electrochemical polarization measurements, the corrosionresistance properties of BMG-coated steel wire composites in 3.5%NaCl solution at room temperature are investigated. These resultsare believed to provide a technological basis for the application ofBMG alloys as a coating material.

2. Experimental methods

2.1. Preparation of the Vit1 BMG-coated steel wire composite

The bare steel wire with 200 mm in nominal diameter wasmanufactured by China Anping Ya-li-jia Steel Production Coopera-tion Ltd. The chemical composition and mechanical property of thesteel wire are listed in Table 1. The steel wire was ground along thelongitudinal direction by an 800 grit SiC, and cleaned with acetoneand rapidly dried by compressed air. Vit1 BMG alloys were preparedby arc melting and suction cast in a Ti-gettered argon atmosphere.Thepurity rangeof the constituent elements is from99.5% to99.99%.

Table 1Constituent elements of as-received bare steel wire.

Material Diameter/mm

Fe% C% Si% Mn% P% S% Fracturestrength/MPa

steel wire 0.2 99.492 0.08 0.09 0.30 0.018 0.020 150

X. Chen et al. / Intermetallics 19 (2011) 1913e19181914

The schematic of continuous production unit is shown in Fig. 1[12], which consists of a vacuum system (8), temperature controller,motor-drive system and a cooling system. A crucible (3) for a moltenmetalwith a heater (4) is equipped. The crucible has an exit orifice (5)at the bottom in order to pass wire through the crucible. An argoncooling system (6) is closely equipped with the exit orifice. The pre-treated steel wire which was fed continuously from a bobbin (1) firstpassed through preheating system (2), and then, into molten metalfor infiltration. After infiltration the wire passed through the argoncooling system that offers an enough cooling rate for the formation ofmetallic glass coating. The speed of the wire movement and infil-tration time can be adjusted by controlling the movement of motor-drive wheel (7). By using the continuous production unit, Vit1 BMG-coated steel wire composites were prepared with the followingtechnical parameters: (1) the vacuum pressure 1 x 10-4 Pa; (2) thetemperature of the Vilt1 alloy melt 780 �C; (3) the preheatedtemperature 300 �C; (4) the speed of wire movement 8 mm/s.

DSC was performed to Vit1 BMG-coated steel wire compositewith a NETZSCH DSC 404C differential scanning calorimeter underargon atmosphere to examine the thermal stability and amorphousfraction of the sample. A constant heating rate of 20 K/min wasemployed. The BMG-coated steel wire was then sectioned viafocused ion beam (FIB). Transmission electron microscope (TEM)specimen was prepared with an FEI Helios Nanolab workstation,operating at 30 Kev, using the “lift-out” technique. Prior tosectioning, a platinummetal line was ion beam deposited using FIB,which prevents the outer surface of the sample from beingdamaged during subsequent ion milling operations. The finelyfocused Gaþ ion beam was used to cut out electron transparentmembranes from the sample. Then the electron transparentmembrane was lift out and positioned on a copper mesh grid. Themicrostructure of the BMG-coated steel wire was characterized bya Zeiss Supra 55 field emission scanning electronmicroscope (SEM)and a Philip F200 field emission TEM.

low

(a.u

.)

BMG-coated steel wireZone A

2.2. Corrosion resistance experiments

Corrosion resistance of the steel wire and the coated steel wirecomposite was evaluated by immersion tests. The mass loss at room

8 vacuum system

7 motor-drive wheel

6 cooling system

4 heater

3 crucible

2 preheating system

Ar

1 bobbin

5 exit orifice

Fig. 1. Schematic of continuous wire coating unit.

temperature in the solution of 3.5 wt% NaCl, which is similar toseawater, was measured for the immersion periods of up to 72 h.Prior to immersion tests, the area and the weight of samples weremeasured in an accuracy of 10�4 mm2 and 10�4 g, respectively. Asimmersion tests were finished, the samples were cleaned withalcohol, and dried with compressed air. At last the samples wereweighted again. The immersion tests were repeated at least threetimes to ensure the accuracy of measurements. In this way, the massloss per unit surface for different immersion time was calculated.

To compare the electrochemical polarization resistance of thesteel wire and the coated steel wire composite, we performedelectrochemical polarization measurements by using PS-268APotentiostat and a three-electrode cell. The counter electrodeused here is graphite and the reference electrode is saturatedcalomel electrode (SCE). All potentials cited in this study willhenceforth be in reference to the SCE. The electrolyte used was3.5 wt% NaCl solution, which was prepared from reagent gradechemical and distilled water. The samples were immersed in 3.5 wt% NaCl solution for at least 20 min to attain stable open circuit.Polarization curves were then measured with the cell open to air atroom temperature with a 20 mv min�1 potential sweep rate.

3. Results and discussion

3.1. Microstructure characterization

The DSC curve of the coated steel wire composite is shown inFig. 2, together with that of Vit1 BMG. The glass transitiontemperature (Tg) and onset crystallization temperature (Tx) aremarked with arrows in Fig. 2. The thermogram of the monolithicVit1 BMG exhibits a glass transition endotherm (Tg ¼ 622K) andcrystallization exotherms (Tx1 ¼ 678K, Tx2 ¼ 748K). The thermo-gram of the coated steel wire composite exhibits no obvious glasstransition but a crystallization exotherm, as marked by the rect-angle (zone A), which is due to the very little weight percent of theBMG coating in the whole composite sample.

Fig. 3(a) is a higher magnification backscattering electron imageof a selected interface region of the coated steel wire. Most of thecoating is amorphous (white contrast), but there are crystals (graycontrast) available in the coating near the steel/coating interface. Inorder to confirm the dual-phase structure in the coating, TEM is

200 250 300 350 400 450 500 550 600

Exo

ther

mic

f

Temperature (Deg.)

Vit1 BMG

Tx1

TgTx2

Fig. 2. DSC traces of the Vit1 BMG-coated steel wire composite, showing no obviousglass transition followed by crystallization (zone A) because of the very little weightpercent of the BMG coating in the DSC sample. The data of the Vit1 BMG sampleprepared by suction casting is shown for comparison, which shows obvious glasstransition temperature Tg and crystallization temperature Tx1 and Tx2.

Fig. 3. (a) Backscattering electron image near steel/coating interface of Vit1 BMG-coated steel wire composite. Steel appears dark, and coating appears light with dual phases. SAEDpatterns corresponding to the white contrast at the outer side of the coating are shown in the inset. (b) SAED patterns corresponding to the dual phases in the coating. Small greyregions of the dual phase are verified to be Fe-rich crystals by (c) energy-dispersive X-ray spectrum. (d) HRTEM image at the interface of the dual phases, with A and C indicatingamorphous and crystalline phases, respectively. (e) Backscattering electron image of Vit1 BMG-coated tungsten wire composite is presented for comparison [12]. Tungsten appearslight, and coating appears dark. Almost no crystallized region of coating is visible near tungsten/coating interface. (f) EDS Line scan analysis of weight percent variation of elementsof Vit1 BMG-coated steel wire along the steel wire core, interface and coating, corresponding to line BE indicated in (a).

X. Chen et al. / Intermetallics 19 (2011) 1913e1918 1915

10 20 30 40 50 60 70 80-1

0

1

2

3

4

5

6

Time (h)

Mas

s L

oss

(mg.

cm-2

)

BMG-coated steel wire

bare steel wire

Fig. 4. Mass losses of the bare steel wire and Vit1 BMG-coated steel wire as function ofimmersion time in the 3.5 wt% NaCl solutions at room temperature, respectively.

X. Chen et al. / Intermetallics 19 (2011) 1913e19181916

employed to obtain the selected-area-electron-diffraction (SAED)patterns. A diffuse diffraction pattern, corresponding to an amor-phous structure of the white contrast in the coating is shown in theinset in Fig. 3(a). From Fig. 3(b), obviously, a diffuse diffractionpattern, corresponding to an amorphous structure, and a set ofdiffractionpattern, associatedwith the crystalline structure, prevail.TheSAEDpatterns shown inFig. 3(b) are in agreementwith thedual-phase structure in the coating region. A body-centered cubic (bcc)structure for the crystals corresponding to the gray contrast regionsin the coating is revealed. Small gray regions of the dual phase areverified to be Fe-rich crystals by energy-dispersive X-ray spectrum,which is shown in Fig. 3(c). Fig. 3(d) displays the high-resolutiontransmission electron microscopy (HRTEM) image of the interfaceof the dual phase in the coating. It can be seen that the dual phaseinterface is atomically sharp, indicated by a dash line (“C”and “A”denoting the crystalline and amorphous phases, respectively).

The backscattering electron image of the Vit1 BMG-coated tung-sten wire is shown in Fig. 3(e) for comparison. The amorphousstructure of the coating layer of Vit1 BMG-coated tungsten wirecomposite has been verified by X-ray diffraction, DSC, and backscat-teringelectron image inRef. [12]. It canbe seen thatno crystalswithinthe coating region is detected which is in agreement with Ref. [12].Contrarily, forBMG-coatedsteelwire, theFe-richphase is foundalongthe interface. To study the diffusion mechanism of atom near theinterface, Line scan analysis of the element constituents along theinterface forVit1BMG-coated steelwire compositewas conductedbyusing EDS. As shown in Fig. 3(a), the line scandirection is frompoint Btopoint E,wherepoint B andpoint E are corresponding to the seventhand the thirteenth scanpoint, respectively.Within the coating region,the grey contrast region is from point B to point D, and the whitecontrast region is from point D to point E. A survey of variation ofelements (Fe, Zr, Ti, Cu, Ni) along the line BE shown in Fig. 3(f), indi-cates that weight percent of iron continuously decreases near theinterface from the steel wire hand to the coating layer hand. Weightpercent of iron in the steelwire and amorphous part of the coating faraway from the interface keeps relatively stable. Thus the interface isthe formation site of Fe-rich phase during the processing, and theatom diffusion prevails. The diffusion coefficient D is an Arrhenius-type temperature dependence:

D ¼ D0 exp ð � H=KBTÞ (1)

where D0, H, KB, and T are the preexponential factor, the activationenthalpy for diffusion, Boltzmann’s constant, and the temperatureof diffusion, respectively. Generally, D0 can be expressed as follows:

D0 ¼ A exp ðH=BÞ (2)

where A and B are constants. D0 in amorphous alloys show a muchlarger variation (from 10�15 to 1015 m2 s�1) than those reported forcrystalline alloys (about10�6 to102m2 s�1), butHdiffers very little inboth amorphous and crystalline alloys [14]. Combining the Eq. (1)with Eq. (2), during the processing, the diffusion for the amor-phous melt dominates. It is seen that whether the crystallizationoccurs within the coating region depends on the wire material.Actually, the melting points of the steel and tungsten are largelydifferent, about 1400 and 3400�, respectively. The processingtemperature is over than the melting temperature of Vit1 alloy of720� [15]. With the increase of the processing temperature, espe-cially close to the melting temperature of steel wire, the diffusionmore easily happens. Currently, the processing temperature is closeto the melting point of wire compared to tungstenwire, which mayleads obvious interdiffusion between the amorphous melts and thesteelwire core. As a consequence, Fe-rich crystals are easily detectedwithin the coating region in this study. The above analysis givesa reasonable explanation to the crystallization within the coating

region, and suggests the importance to choose a sound processingtemperature to avoid the crystallization for the BMG coating.

Besides, it is noted that the crystallization is mainly due to theatom diffusion of high-temperature melts. The finding givesevidence that the crystallization for the Vit1 melt itself is difficult,in accordance with its high glass-forming ability [15].

3.2. Corrosion behavior

Fig. 4 shows the mass loss variations of the bare steel wire andthe coated steel wire as immersion time increases in 3.5 wt% NaClsolutions at room temperature. It can be seen that mass lossamount of bare steel wire in the solutions, in general, increases asimmersion time during the periods of 72 h, while for coated steelwire, the average value of mass loss is almost zero compared to thatof the bare steel wire. According to this, we can conclude that themass loss variation for the bare steel wire is significantly larger thanthat for the coated steel wire. So the coated steel wire has moreexcellent corrosion resistance, which can be indicated from thecorroded samples. Fig. 5(a) and Fig. 5(b) show the SEMmorphologyof the corroded bare steel wire and the corrodedwire composite forimmersion time of 72 h in 3.5% NaCl solution at room temperature,respectively. For comparison, the SEM images of coated steel wirecomposite and pretreated steel wire are show in Fig. 5(c) andFig. 5(d), respectively. For the pretreated steel wire shown inFig. 5(a), the rough surface can be seen clearly and the grindingtrace along the longitudinal direction is apparent. The corrodedsteel wire (Fig. 5(c)) shows the significantly decreased diameter, i.e.170 mm, after immersion time of 72 h in NaCl electrolyte, incomparison to the diameter value 196 mm of the pretreated baresteel wire shown in Fig. 5(a). Depending on the nature of a defect onthe surface of the bare steel wire, corrosion products dissolve or fallout of the material. As shown from themagnified image in the insetof Fig. 5(c), corrosion products precipitated from the over-saturatedsolution close to the corroded surface accumulate in the corrodedsurface. On the other hand, shown in Fig. 5(b), the surface of thecoated steel wire appears to be smoother than that of the originalbare steel wire because of the melt infiltration casting on thesurface during coating. From the magnified images in the inset ofFig. 5(d), it is seen that the coated wire composite still has a rela-tively stable protective surface layer to resist electrolyte corrosionafter 72 h immersion time, with no apparent corrosion productfalling out of the surface. The diameter variations between thecoated steel wire composite and the corroded steel wire composite

Fig. 5. SEM images of surface morphology: (a) pretreated steel; (b) BMG-coated steel wire; (c) and (d) are the corroded bare steel wire and the corroded coated steel wire,respectively, after immersed in 3.5% NaCl solution for 72 h at room temperature. The insets give closer views of area at the corroded surfaces, respectively.

X. Chen et al. / Intermetallics 19 (2011) 1913e1918 1917

after immersion time of 72 h in NaCl electrolyte are very small.From above analysis, it can be concluded that the coated wirecomposite has better corrosion resistance than the bare steel wire,which is in good agreement with the above mass loss result.

Fig. 6 showsanodicpolarizationcurves for thebare steelwire,Vit1BMG-coatedsteelwire composite, respectively.Opencircuitpotential(OCP) (Ecorr), corrosion current density (Icorr), and difference betweenpitting potential (Epit) and Ecorr, derived from the polarization testsand other reports in the literature, are presented in Table 2 forcomparison. For these two materials, the potential scan is startedbelow the Ecorr. Tafel behavior governed the obtained cathodicportions of the curve. For the coated steel wire composite, the opencircuit potential value is�298mV.At Ecorr, the current density goes tozero, and then increases to a low anodic value. There is an unobviouspassive range on the potential up scan. From OCP to all this range,a barrier-type film protects the material from high corrosion rates.

-8 -7 -6 -5 -4 -3 -2 -1 0

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

Pote

ntia

l E

(V)

Current Density logi (A/cm2)

1-bare steel wire 2- Vit1 BMG-coated steel wire

1

2

Epit

Fig. 6. Comparison of potentiodynamic polarization for the bare steel wire (1, solidline) and the Vit1 BMG-coated steel wire (2, dash line) in NaCl 3.5% solution open to airat room temperature.

With the potential up scanning, a steep current increase is observeddue to local surface layer breakdown, indicating that thinfilm formeduponanodicpolarization isunable to fullyprotect the sample [16]andthe coated wire composite is shown to undergo a pitting corrosion.Apparently, depending on above analyses, Vit1 BMG-coated steelwire composite shows an activeepassive transition by anodic polar-ization in 3.5%NaCl solution. Contrarily, shown from the polarizationcurves, with the potential up scan, the steel wire does not forma passive film and only a small polarization is needed to dramaticallyincrease its dissolution rate. Clearly, under free corrosion conditions,the diffusion controlled oxygen reduction reaction is what limits itscorrosion rate to a relatively low for bare steel wire. This is consistentwith the results in above immersion tests. The open circuit potentialvalue of bare steel wire sample is �532 mV which is more negativethan that of the coated wire composite, �298 mV. The corrosioncurrent density value of the bare steel wire is 122.12 mAcm�2, about100 times higher than that of coated wire composite, 1.06 mAcm�2,under nature corrosioncondition. Theopencircuitpotential is shiftedtoward more positive potential and the corrosion current densitydecreases that indicates an improvement in corrosion resistance forBMG-coated steel wire composite compared to that of the bare steelwire. Relatively poor corrosion resistance of bare steel wire is mainlyattributed to its constituent elements and partially to metallurgicaldefects suchasgrainboundarieswhichcanenhancepreferential localcorrosion tendency leading to the decrease in overall corrosionresistance. The improvement of the corrosion resistance of coatedwire composite can be partially explained by the following reasons.That is, the BMG coatingmaterial played amajor role in its resistanceto corrosion [17,18]. For BMG coating, a very high corrosion resis-tance can be expected due to the high fraction of strong passi-vating components, in particular zirconium. Furthermore, excellentcorrosion resistance is attributed to its chemically and structurallyhomogeneous nature resulting in a lack of local electrochemicallyactive sites [19].

Seen from the anodic polarization curve, the corrosion currentdensity value is 1.06 mAcm�2. This corrosion current density isextremely low and reflective of the passive state [7]. So, for the

Table 2Result of potentiodynamic polarization measurements in current study compared to that of Vit1 BMG in references.

Material Electrolyte Ecorr (mV) Icorr (mAcm�2) Epit�Ecorr (mV) Reference

steel wire 3.5 wt% NaCl �532 122.12 Current studyVit1 BMG-coated steel wire 3.5 wt% NaCl �298 1.06 50 Current studyVit1 BMG 0.6 M NaCl �250 � 40 0.31 � 0.25 97 � 54 Morrison [13]Vit1 BMG 0.5 M NaCl �205 � 30 1 207 Schroeder [21]

X. Chen et al. / Intermetallics 19 (2011) 1913e19181918

undisturbed condition, the wire composite was in the passive stateat the natural corrosion potential, Ecorr. Then, the concern for thiswire composite is its resistance to the onset of pitting corrosion.(Epit � Ecorr) is an important parameter in evaluating the pittingcorrosion behavior [7], which reflects pit initiation. The smaller thevalue, the easier the pit initiation [20]. Morrison et al. [13] reporteda difference of 95 � 54 mV for the Vit1 BMG in a 0.6 M NaCl elec-trolyte and discovered that Vit1 BMG showed susceptibility topitting corrosion in the 0.6 M NaCl electrolyte at room temperaturein polarization test. The value of (Epit � Ecorr) for wire composite isabout 50 mV in this study. Compared to that reported by Morrisonet al, the value indicates that Vit1 BMG-coated steel wire compositeis susceptibility to pitting corrosion in a 0.6 M NaCl electrolyte atroom temperature. On the other hand, Schroeder et al. [21] alsoreported a difference of 207 mV for the same Vit1 BMG in a 0.5 MNaCl electrolyte. Though the (Epit � Ecorr) value reported here issmaller than that reported by Schroeder et al, the reason is alsoapparent. That is, chloride-induced pitting corrosion occurs on bulkamorphous Vit1 alloy samples. An increase in chloride concentra-tion results in a drastic increase of pitting processes as observed bythe significant shift of the pitting potential to more negatives.When chloride concentration increased from 0.5 M to 0.6 M forNaCl electrolytes, a decrease of Epit value can be seen, thus toa decreased value of (Epit � Ecorr).

Here something must be concerned, that is, when BMGmaterialwas used to produce BMG coating, what is the difference ofcorrosion resistance behavior between the Vit1 BMG coating andthe pure Vit1 BMG? For this, comparison is conducted. As shown inTable 2, the corrosion current is 1.06 mAcm�2 (current study),0.31 � 0.25 mAcm�2 [13], 1 mAcm�2 [21], respectively. The Ecorris �298 mV (current study), �250 � 40 mV [13], �205 � 30 Mv[21], respectively. The (Epit � Ecorr) has been compared above. Fromthese data, we can conclude that Vit1 BMG-coated steel wirealmost have the similar OCP, the similar corrosion current and thesimilar pitting initiation susceptibility as pure Vit1 BMG in thereference mentioned above.

Nevertheless, it should be noted that comparisons betweenthese results and others are also dependent upon differing surfaceconditions and potential scan rates as well as other test parameters.For example, Asam et al. [22] have reported in their study of thepitting corrosion of amorphous NieZr alloys that the main reasonfor the low pitting potential is the irregular surface morphology. Sorelatively limited difference among these data is sure to exist and isacceptable.

4. Conclusions

Vit1 BMG-coated steel wire can be continuously produced.Based on the reason of crystallization within the coating region, it

was shown that it is important to choose a sound processingtemperature to avoid the crystallization for the BMG coating, whichshould be further investigated with respect to different kinds ofsteel wire materials and different BMG coating materials. Mass lossin immersion tests and potentiodynamic measurement showedthat Vit1 BMG-coated steel wire composites exhibit better corro-sion resistance than bare steel wire in NaCl solutions at roomtemperature. The corrosion resistance of commercial steel can beoptimized for extensive practical applications through controllingthe coating technique parameters as well as different kinds of steelwire and BMG coating materials.

Acknowledgments

The authors are greatly indebted to Dr. Hongxiang Li andDr. Junwei Qiao for valuable discussions. This work was supportedby the Specialized Research Fund for the Doctoral Program ofHigher Education of China (No. 20100006120020), the China Post-doctoral Science Foundation (No. 20090460207) and the NationalScience Foundation of China (No. 51071018).

References

[1] Xue WH, Zhao XD. Steel Wire Products 2003;29:21 (in Chinese).[2] Conner RD, Dandilker RB, Scruggs V, Johnson WL. Int J Imp Eng 2000;24:435.[3] Chou-Yim H, Schroers J, Johnson WL. Appl Phys Lett 2002;80:1906.[4] Yokoyama Y, Yamono K, Fukaura K, Sunada H, Inoue A. Mater Trans 1999;40:

1018.[5] Chen XH, Zhang Y, Zhang XC, Zhang Y, Chen GL. J Non-Cryst Solids 2008;354:

3308.[6] Zhang XC, Zhang Y, Chen XH, Chen GL. Int J Miner Metall Mater 2009;16(1):77.[7] Peter WH, Buchanan RA, Liu CT, Liaw PK, Morrison ML, Horton JA, et al.

Intermetallics 2002;10:1157.[8] Huang L, Qiao DC, Green BA, Liaw PK, Wang JF, Pang SJ, et al. Intermetallics

2009;17:195.[9] Yu P, Chan KC, Xia L, Yu BH, Bai HY. Mater Trans JIM 2009;50:2451.

[10] Chen XH, Zhang Y, Zhang XC, Hui XD, Wei BC, Chen GL. Electrochem Solid-State Lett 2007;10:E21.

[11] Zhang Y, Chen XH, Chen GL, Zhang XC, Wang ZD. China patent numberZL200710120355.4 2009.

[12] Chen XH, Zhang BY, Chen GL, Zhang Y, Hui XD, Lu ZP, et al. Intermetallics2010;18:2034.

[13] Morrison ML, Buchanan RA, Peker A, Peter WH, Horton JA, Liaw PK. Inter-metallics 2004;12:1177.

[14] Faupel F, Frank W, Macht MP, Mehrer H, Naundorf V, Ratzke K, et al. Rev ModPhys 2003;75:237.

[15] Lu J, Ravichandran G, Johnson WL. Acta Mater 2003;51:3429.[16] Qin FX, Zhang HF, Deng YF, Ding BZ, Hu ZQ. J Alloys Compd 2004;375:318.[17] Li HX, Yi S. Mater Chem Phys 2008;112:305.[18] Pardo A, Otero E, Merino MC, Lopez MD, Vazquez M, Agudo P. Corros Sci 2002;

44:1193.[19] Gebert A, Buchholz K, Leonhard A, Mummert K, Eckert J, Schultz L. Mater Sci

Eng A 1999;267:294.[20] Jiang WH, Jiang F, Green BA, Liu FX, Liaw PK. Appl Phys Lett 2007;91:041904.[21] Schroeder V, Gibert CJ, Ritchie RO. Scripta Mater 1998;38(10):1481.[22] Asam K, Habazaki H, Kawashima K, Hashimoto K. Corros Sci 1993;34:445.