Surface & Coatings Technology 240 (2014) 286–292

Contents lists available at ScienceDirect

Surface & Coatings Technology

j ourna l homepage: www.e lsev ie r .com/ locate /sur fcoat

Laser processing of Fe based bulk amorphous alloy coating on zirconium

Himanshu Sahasrabudhe, Amit Bandyopadhyay ⁎W.M. Keck Biomedical Materials Research Center, School of Mechanical & Materials Engineering, Washington State University, Pullman, 99164 WA, USA

⁎ Corresponding author.E-mail address: amitband@wsu.edu (A. Bandyopadhy

0257-8972/$ – see front matter © 2013 Elsevier B.V. All rihttp://dx.doi.org/10.1016/j.surfcoat.2013.12.043

a b s t r a c t

a r t i c l e i n f o

Article history:Received 27 August 2013Accepted in revised form 18 December 2013Available online 29 December 2013

Keywords:Bulk amorphous alloyZr substrateLaser processingCoatingWear

Laser Engineered Net Shaping (LENS™), a commercially available laser-based additive manufacturing technique,was employed for the processing of Fe-bulk amorphous alloy (Fe-BAA) coating on zirconium. SEM analysis re-vealed an amorphous–crystalline mixed phase composite microstructure of the coating. Crystalline phase wasdispersed in an amorphous matrix. Moreover, considerable mixing of the Fe BAA in the zirconium substratewas noticed. The Fe BAA coatings showed 800% increase in hardness and decrease in normalized wear volumewas ~30 times compared to the control Zr substrate. During the wear testing in 3.5% NaCl solution, Fe BAA coat-ings showed evidence of fretting corrosion. Overall, our results demonstrate that laser processing can be used todeposit amorphous coatings on Zr substrate.

© 2013 Elsevier B.V. All rights reserved.

1. Introduction

Bulk amorphous alloys (BAA) or bulk metallic glasses (BMG) showextraordinary mechanical and electrochemical properties that resultfrom theabsence of grain boundaries in the amorphous structures [1–7].Processing of bulk amorphous alloys is challenging due to the need for ahigh cooling rates to retain the amorphous phases. Therefore, interest isgrowing in harnessing properties of this class of materials in the form ofcoatings on important engineering materials [8–10]. Even then, chal-lenges remain in the areas of retaining the amorphous nature of thecoating and creating a strong interfacial bond between the substrateand the coating particularly for high melting point substrates. Apartfrom those two, some other factors include improving mechanicalproperties of the coating without compromising the substrate quality,avoiding oxidation of the substrate and BAA during processing, abilityto coat large area complex shaped components, and reliability as wellas reproducibility of the coatings. The viability of many different pro-cessing methods has been investigated in the past. These methodsinclude sputtering [10], copper mold casting [11–14], aluminothermicreaction [15], compression shearing technique [16], rapid quenchingfrom the melt [17,18], plasma processing [19], spraying processing[20,21], spin casting/melt spinning [22–24], microwave processing[25] as well as high power laser processing [26–32]. The simultaneousdeposition and melting method can also create amorphous coatings ina single step preventing crystallization of the amorphous precursorpowders to the maximum extent with small morphological variations[33]. For coatings of various thicknesses and relatively complex shapeson different metallic substrates, laser-based freeform fabrication tech-nique can be ideally suited for different applications. In the present

ay).

ghts reserved.

study, Laser Engineered Net Shaping (LENSTM), an example of such atechnique, is used for processing of Fe-based bulk amorphous alloycoating on Zr-substrate.

Fe-based bulk amorphous alloys (BAA) have shown excellentmechanical and electrochemical performance [34–44]. In this study, Febased BAA coatings are deposited on zirconium, a high temperaturemetal of significant engineering importance due to their different appli-cations in structures demanding corrosion resistance at elevated tem-peratures. These amorphous coatings on zirconium were processedand characterized for their microstructure, hardness and corrosion be-havior under load using a ball-on-disc setup in salt water. Further, acomposite zone model is used to show the microstructural evolutionof the Fe-BAA coating on Zr during laser processing.

2. Experimental procedure

2.1. Laser processing

Gas atomized NanoSteel NSSHS9172 Super Hard Alloy Steel Powder(from TheNanoSteel Company Inc, Idaho Falls, ID)with a nominal com-position (atomic %) of Crb25Mob6Wb15Cb4Mnb2 Sib2 Bb5 Nb b12 Febalancehaving particle size distribution between 15 μm and 53 μm was used.The substrate used was a 2 mm thick plate of commercially pure zirco-nium (Purity level N99%). We have used LENS™ 750 (Optomec Inc.,Albuquerque, NM) available in our laboratory to fabricate rectangularshaped samples (6 cm × 1.5 cm) with 0.865 ± 0.080 mm thick BAAcoating deposited layer-wise from the feedstock powder. The LENSTM

750 uses a 500 W continuous wave Nd:YAG laser. The Fe BAA powderwas fed into the melt zone via delivery nozzles through Argon carriergas. Laser power for deposition of the Fe BAA powder was set at450 W, which was needed to melt the Zr-substrate, and the laser scan-ning speed was 48 in/min (122 cm/min). LENSTM offers consistent and

Table1

Establishing

LENS™

processpa

rametersforprocessing

ofFe

BAAcoatings

onZr.

Srno

Processing

parameters

Result

Commen

t

Laserpo

wer

Powde

rfeed

rate

Scan

spee

d

137

5W

1.2

48in/m

inInsufficien

tlaserpo

wer

Unm

eltedsu

bstratean

dfeed

stockpo

wde

r2

400W

1.2

48in/m

inInsufficien

tlaserpo

wer

Unm

eltedfeed

stoc

kpo

wde

r3

400W

1.2

24in/m

inIncreasedga

spo

rosity

andun

meltedpa

rticles

Laserpo

wer

sufficien

ttojust

meltthesu

bstratean

dpo

wde

rbu

tslow

ersp

eedgive

sincrea

sedpo

rosity

445

0W

1.2

48in/m

inSu

fficien

tlaserpo

wer

Powde

rmelting

achiev

ed,g

oodbo

ndingto

substrate,toplaye

rslightly

unmelted

545

0W

1.4

48in/m

inUnm

eltedpo

wde

rdu

eto

high

erfeed

rate,g

aspo

rosity

Laserpo

wer

sufficien

tbut

feed

rate

istoohigh

togive

completepo

wde

rmelting

287H. Sahasrabudhe, A. Bandyopadhyay / Surface & Coatings Technology 240 (2014) 286–292

reliable processing conditions for all samples. The entire assembly isenclosed in a glove box and the oxygen level is constantly monitoredby a highly sensitive oxygen sensor, maintaining the environmentalO2 level at than 10 ppm. This limits any possible oxidation and relatedcontamination of the amorphous alloy during the melt cast operationof LENSTM processing.

2.2. Microstructural characterization

The LENS™ processed samples were carefully polished using siliconcarbide paper. Final polishing was done using 0.03 μm alumina suspen-sions on rotating velvet cloth wheel. LENS™ processed Fe BAA coatingson Zrwere characterized using optical microscopy and SEM (FEI Quanta200 and Hitachi S570). XRD analysis was done using a Siemens D 500Kristalloflex diffractometer with Cu Kα radiation at 20 kV betweenthe 2θ range of 20˚ and 80˚ and a Ni filter keeping the step size at 0.1 s.

2.2.1. Samples for corrosion-wear testingThe surface of the coatings was carefully polished to mirror finish

prior to wear testing. The BAA coated samples were in 6 cm × 1.5 cmin shape. The coated top surface was wet grinded on 120 grit SiCpaper and then subsequently fine grinded till 1200 grit. Final polishingwas done using 1, 0.5 and 0.03 micron alumina suspensions in deion-ized water. Care was taken to keep the coating surface extremely flatthroughout the sample preparation process. Before performing weartests, the samples were ultrasonically cleaned in 50% ethanol solutionfor 30 min.

2.3. Corrosion-wear and hardness testing

Corrosion-wear testing was done in saline medium (3.5% NaCl)at room temperature on coatings using linear reciprocating weartest with a Nanovea series tribometer. Silicon nitride ball of diameter(Hardness ~1550 HV0.1) was used in the tests. Load was kept constantat 7 N, and speed was 1200 mm/min. The amplitude of wear trackwas 10 mm and tests were performed for a distance of 1 km for allthe samples.

Vickers microhardness (Shimadzu, HMV-2 T) tests were performedon the Fe BAA coated Zr and the Zr substrate with a standard diamondVickers indenter. The load was 100 g (0.98 N) and dwell time was15 s for all samples. Each reported hardness value is an average of atleast 5 similar tests performed on the sample. Variation of hardnesswith the depth of the coating was recorded by testing the samples incross section andmaintaining equal spacing in between the consecutivetests. General hardness of the Fe BAA coatings was recorded approxi-mately at the center of the cross section.

3. Results

The LENS™ processed Fe BAA coatings on Zr were analyzed usingSEM. Wear and wear induced corrosion phenomena were also studiedalong with hardness measurements.

3.1. Establishing process parameters for processing Fe BAA coatings on Zr

Numerous trials had to be carried out in order to establish the pro-cessing parameters of the LENS™ setup for Fe BAA. The most importantones were the laser power; powder feed rate and the scan speed.The various trials are tabulated in Table 1. The effect of every trial wasstudied using simple optical microscopy and visual examination of thecoatings. To adequately melt the Zr substrate and the fine Fe BAA pow-der, laser power of at least 400 W was necessary. Anything below400 W could not melt the powder and the substrate; and producedcoatings of poor morphology. The powder could not be adequatelymelted and bonding to the Zr substrate was weak. This causeddelaminating or ‘peeling off’ of the BAA coating during grinding and

Fig. 1. Scanning electron micrograph of Fe BAA feedstock powder.

288 H. Sahasrabudhe, A. Bandyopadhyay / Surface & Coatings Technology 240 (2014) 286–292

polishing of the samples. However, at 400 W power setting and scanspeed of 24 in/min, there was increased gas porosity and unmeltedparticles. Hence the laser power was increased to 450 W and the scanspeed was increased to 48 in/min. This gave coatings of good morphol-ogy. However, there was still a small layer of unmelted particlestowards the uppermost surface of the coatings. The majority of thebulk of the BAA layer remained free of gas porosity and unmelted parti-cles. Increasing the feed rate to 1.4 (from the previous setting of 1.2) atthe same laser power (450 W) and scan speed (48 in/min) increasedgas porosity and unmelted particles in the bulk of the coating. Thusthe process parameters were set at laser power of 450 W, feed rate of1.2 and scan speed of 48 in/min.

500 µm

~40 µm

~612±55 µm

Fe BAA

Zr

Fig. 2. One layer of Fe BAA on Zr at 200×.

3.2. Morphology and microstructure of Fe BAA coating on Zr

The SEM image of the feedstock powder is shown in Fig. 1. The pow-der was spherical with particle size distribution between 15 and 53 μm.One layer of Fe BAAwas deposited on the Zr substrate. After LENS™ pro-cessing, the layer thickness of the coating was 612 ± 55 μm. Porositywas also visible in the Fe BAA coatings and the average diameter ofthe pores was measured to be 80 ± 20 μm. Fig. 2 shows the SEMimage of one layer Fe BAA on Zr.

SEM on the coating revealed the amorphous–crystalline nature ofthese coatings and shown in Fig. 3. Crystalline phase or ‘crystallites’can be seen dispersed in the amorphous matrix. The shape of the parti-cles in these samples was not entirely rectangular. Some crystallites ap-peared spherical and some appear somewhat oblong. Hence tomeasurethe size of these crystallites, a mix of different methods had to be ap-plied. For the spherical crystallites the diameter was measured. Theirregular shaped crystallites were approximated to the closet sphericalshape. For the rectangular shaped, the diagonals were measured andfor the oblong shaped, only the length was measured. The variation inthe size of the crystallites was less. The crystallite size was measuredto be 0.60 ± 0.10 μm. SEM images of Fig. 4 show this amorphous–crystalline microstructure in detail.

Fig. 5 describes the ‘Composite Zone Model’ proposed to elaboratethe amorphous crystalline microstructure and the different zones inthe Fe-BAA coating on Zr. This model is based on the SEM findings ofFig. 4a, b and c. Zone 1 is the region in which the BAA has dissolvedinto the Zr substrate or the dilution zone. This zone, based on SEMimage of Fig. 1, was approximately between 30 and 40 μm thick. TheZone 2 is the interface between the zirconium substrate and the FeBAA coating. The thickness of this zone was approximately 5 and 10 μmand hence it was small compared to the BAA coating. The Zone 3 in theFig. 4 is ‘only Fe BAA’ region of the coating. The thickness of this regionwas approximately 600 μm for one layer of Fe BAA. This zone has anamorphous matrix with multi shaped crystallites dispersed in it.

Thus, from the figure it is seen that, although the interface betweenthe Fe BAA coating and Zr appeared to be the zone 2, it was not the realinterface. It was the starting point of the dilution of Fe BAA feedstockpowder into the Zr substrate. This dilution then continued as zone 1

Fig. 3. SEM acquired microstructures of Fe BAA coatings on zirconium at 1500×.

Fig. 4. (a): Fe BAA coating on Zr, Zone 3 of coating, at 10,000×. (b): Fe BAA coating on Zr,Zone 3 of the coating and Zone 2 of the interface, at 20,000×. (c): Fe BAA coating on Zr,Zone 1 of the Zr substrate and Zone 2 of the interface, at 10,000×.

Fig. 5. Composite zone model for Fe BAA coating on Zr.

289H. Sahasrabudhe, A. Bandyopadhyay / Surface & Coatings Technology 240 (2014) 286–292

for another ~30 and 40 μm into the zone 1 until there was only the Zrsubstrate. Hence the real interface between the coating and the sub-strate was at the lowermost region of the zone 1. This was visible tosome extent in Fig. 4c as the dilution region.

To further verify the partial amorphous character of the coating, XRDscanwas performed on the feedstock powder and on the Fe BAA coatingprocessed from LENSTM. The Fe BAA coating was then heat treated at650˚C for two hours. Fig. 6 shows the XRD results of the feedstock pow-der, processed coating and the heat treated coatings. By simply notingthe strength of the peaks, the amorphous nature of the coating isclear. It should be noted that the feedstock Fe BAA powder was notfully amorphous.

3.3. Microhardness measurement

The average top surface hardness values for sampleswith the Fe BAAcoating were measured to be 1450 ± 40 HV0.1. The Zr substrate had ahardness of 160 ± 8 HV0.1. One layer of Fe BAA coating thus increasedthe hardness of the substrate by more than 800%. Hardness depth pro-file measurement of the Fe BAA coatings on Zr showed less variationin hardness with the depth of the coating. Hardness was found to be1450 ± 40 HV0.1 at the top surface and gradually dropped down to1390 ± 20 HV0.1 near the BAA–Zr interface. Fig. 7 shows the hardnessdepth profile of Fe BAA coatings on Zr.

3.4. Wear behavior in 3.5% NaCl solution

Wear test were performed via linear reciprocation more under con-stant load and silicon nitride ball (φ = 3 mm). The load was 7 N andthe speed was 1200 mm/min for amplitude of 10 mm. The total weardistance recorded was 1000 m and the samples were fully immersedin 3.5% NaCl solution throughout the test duration at 20 °C. The totalnormalized wear volumes reported are average values for each sample,where at three tests were conducted on every sample.

The normalized wear volume of the Zr substrate under exactly sameconditions was measured to be 31.70 × 10−5 mm3/Nm. This heavywear can also be seen in the SEM image of thewear track on Zr substratein Fig. 8. The normalized wear volume of one layer of Fe BAA coatingwas measured to 0.77 × 10−5 mm3/Nm. Figs. 9 and 10 show the SEMimage of the wear track on the Fe BAA coating. Thus one layer of FeBAA on Zr reduced the surface wear by up to ~30 times.

The Fe BAA coatings wear extremely hard. Hence, the silicon nitrideball used in these tribological tests wore out when the wear test dis-tance or the load was increased. Hence the testing parameters had tobe optimized to get results with a visible wear track on the BAA coatingand at the same time have as less wear on the ball as possible. Thevolumetric wear occurring on the silicon nitride intender was alsomea-sured. For the BAA coating in this study, the wear on the ball was ~5.5%of the original ball volume. One of such worn silicon nitride balls isshown in SEM image in Fig. 11.

Higher magnification SEM image of the Fe BAA coating in Fig. 10showed that considerable amount of wear has taken place in the upper-most region of the coating where the BAA feedstock powder did notmelt completely. There were also some signs of fretting corrosion

Fig. 6. XRD 2θ scan on the Fe BAA feedstock powder, LENS™ process coating and the BAA coating annealed for 2 h.

290 H. Sahasrabudhe, A. Bandyopadhyay / Surface & Coatings Technology 240 (2014) 286–292

observed in the dense region of the coating with complete melting. Be-cause of a considerable amount of wear taking place in the unmelted re-gion, the data of the coefficient of friction of the coating was considerednot reliable.

4. Discussions

Bulk amorphous alloy coatings can be processed using LaserEngineered Net Shaping without losing the amorphous character ofthe feedstock powder. This was demonstrated before by Balla et al. [8].However, in comparison to that, the coating in this studywas processedusing a much finer BAA powder. The composition in our study was alsoslightly different due the addition of 12% niobium.

LENS™ processing of finer BAA powder on Zr evolved the coatings asan amorphous–crystalline composite. Fine crystallites were formed firsthaving a variety of shapes. The crystallites also appeared to grow along

Fig. 7. Hardness profile of Fe BAA on Zr from surface to inside.

lines. This observation was a clear distinction from other earlierattempts at processing of BAAs, where the crystallization of theBAAs was predominant [9]. In some reported studies crystallizationwas completely avoided [21,37,45]. Crystallites or crystalline phasescoexisting with amorphous phase were also reported in different stud-ies before [8,29,31,34,42] but the size of thesewas considerably smaller.Amorphous–crystalline microstructure observed in the current studyvaried less in its morphology as compared to other similar studies[30]. The size of the crystallites here is however considerable if notsmaller than those observed by other researchers [13,27,28]. The

Fig. 8.Wear track on zirconium substrate in 3.5% NaCl medium.

Fig. 9.Wear track on Fe BAA coating on Zr in 3.5% NaCl medium at 100×.

Fig. 11. SEM image of silicon nitride ball, used in wear test of Fe BAA coatings, shownbetween 5 and 6 volume % wear at 85×.

291H. Sahasrabudhe, A. Bandyopadhyay / Surface & Coatings Technology 240 (2014) 286–292

composition and processing techniques used in the above cited studieswere different.

The composite zone model described in Fig. 5 also remains distinctfrom the BAA coating processed using the same LENS™ technique in[8]. In comparison, no distinct amorphous band or region was observedin the current study. The dilution of the Fe BAA processed from coarserpowder on SS 316 substrate however is more readily and clearly visiblethan in the current study on Zr substrate. This difference can be attrib-uted to the fact that Fe BAA coatings will be more readily miscible inthe SS 316 substrate due to the presence of a major fraction of Fe inboth the substrate and the feedstock powder. From the SEM imagesand the variation of the hardness depth profile, it is observed that theFe BAA coating on Zr has lesser microstructural variation that the FeBAA coating on SS 316. The composite zone model described here isalso distinctly different from other earlier attempts related to BAA coat-ings on different metallic substrates [30]. Relative retention of theamorphous character of the coatings was verified in this study via anXRD scan of feedstock powder, LENSTM processed coating and heattreated LENS™ processed coating. From reference [8], amorphous–crystalline character of the feedstock powder is visible and the XRDresults in this study show the retention of this amorphous characterupon LENS™ processing.

The hardness of the Fe BAA coatings on Zr is higher than the similarFe BAA coating on SS316 [8]. This is mainly due to the finer size of the

Localized fretting corrosion

Wear on the unmelted regionof the Fe BAA coating

Fig. 10.Wear track of Fe BAA coating on Zr in 3.5% NaCl medium at 400×.

feedstock powder thatwas used to process the coatings on Zr. The hard-ness value in the current study is considerably higher than thoseobserved in other Fe BAA systems investigated [9,12,28] and nearly sim-ilar to those reported by Singh et al. [19]. The hardness depth profile, inthe study as shown in reference 9[9], shows an irregular pattern in theupper regions of the coating, whereas it gradually drops to muchlower values in other studies [28,32]. The hardness depth profile ofthe BAA coating in this current study shows a uniform gradual dropwith the depth of the coating to not very low values. This again pointstowards an amorphous–crystalline coating that is more uniform interms of microstructural features.

The Fe BAA coating processed using LENSTM reduced the surface nor-malizedwear volume of the Zr substrate by ~30 times in saline solution.A major portion of the wear occurred in the uppermost region of thecoating where some of the feedstock powder remained unmelted. Thewear track after 1000 m of wear distance appeared smaller than thosereported earlier [9,10,21,26,32,37,39]. The method of representation ofthe wear loss in most of these studies was different such as mass ofthe material lost, depth of wear track, etc. Also most of these studiesutilized differing testing conditions like ultra-high vacuum, dry air,shorter or longer wear distances, etc. Due to these reason, a commoncomparison of the wear performance of coating was rather difficult. Inthe regions of the wear track where the powder had completely meltedand solidified, evidence of some fretting corrosion can be observed. Thiscorrosion was similar to the corrosion observed by Zhou et al. [21]where nano crystalline phases were formed in the Fe BAA system.

The LENS™ processed coatings in this study were hard and hadsmall microstructural variations. Some processing problems howeverstill existed. Porosity was visible in the coatings. Also there was a thinlayer at the uppermost region of the coating where some of the feed-stock powder did not melt completely. Changing the processingparameters of the LENS™ machine such as laser power and feed ratecan counter these anomalies in the coatings. During LENS™ processing,the feedstock powder is fed in argon carrier gas. The powder is meltedand deposited by a high power laser almost instantly. The process canthus sometimes amalgamate some of the carrier argon gas in the finalstructure as gas porosity. Reducing the powder feed rate tends to in-crease the porosity (as there is more carries gas than powder) whereasincreasing the feed rate will decrease the porosity. However, increasingthe powder feed ratemeans addingmore feedstock particles in themeltpool. The laser power may sometimes be insufficient to melt all theparticle and this can lead to the inclusion of unmelted particles in thestructure. This happened in trial no. 5 of Table 1. To melt the powder

292 H. Sahasrabudhe, A. Bandyopadhyay / Surface & Coatings Technology 240 (2014) 286–292

completely the laser power can be increased. But, this in turnmay delaysolidification and may form coarse grains or in this case higher amountof crystalline phase. More careful optimization of the processing parame-ters can hence yield near perfect Fe BAA coatings. The LENSTM techniquethus, overall proves to be a useful and promising technique in processingof temperature sensitive bulk amorphous alloys.

5. Conclusions

This study demonstrates that Laser Engineered Net Shaping(LENS™) technique can be successfully employed to process Fe BAAcoatings on various metallic substrates to improve their surfacemechanical properties such as wear behavior and hardness. The LENS™technique offers the advantages of fast cooling rates of 103 K/s to 105 K/s, layer wise deposition and prevention of oxidation due to processingin an atmosphere of 10 ppm or less oxygen concentration. In additionto this, LENS™ is capable of processing large components of complexshapes. BAA coatings were processed in this study from fine Fe basedBAA powder on Zr substrate. These coatings had an amorphous–crystal-line composite microstructure with fine crystallites that appeared togrow along lines. The variation in the microstructural features of thesecoatings was small. The Fe BAA coating of ~600 μm thickness improvedthe hardness of the Zr substrate from 160 ± 8 HV0.1 to 1450 ± 40HV0.1, thus by over 800%. The Fe BAA coating also decreased the normal-ized wear volume on the Zr substrate by nearly 30 times.

Acknowledgements

Authors acknowledge theW.M. Keck Foundation's financial supportto establish the Biomedical Materials Research Lab atWSU. Authors alsoacknowledge experimental help from Mr. Stanley Dittrick related toLENS™ processing of samples. Authors also like to acknowledge finan-cial support from the Joint Center for Aerospace Technology Innovation(Seattle, WA).

References

[1] W. Klement, R.H. Willens, P. Duwez, Nature 187 (1960) 869.[2] R.W. Cahn, Nature 260 (1976) 285.[3] John R. Scully, A. Gebert, Joe H. Payer, J. Mater. Res. 22 (2007) 302313.[4] W.L. Johnson, Mater. Sci. Forum 225–227 (1996) 35–50.[5] A. Inoue, T. Zhang, et al., Mater. Sci. Forum 269–272 (1998) 855–864.[6] K.B. Kim, H. Koshiba, et al., Mater. Sci. Forum 343–346 (2000) 81–90.

[7] C. Schuh, T. Hufnagel, et al., Acta Mater. 55 (12) (2007) 4067–4109.[8] V.K. Balla, A. Bandyopadhyay, Surf. Coat. Technol. 205 (7) (2010) 2661–2667.[9] A. Basu, A.N. Samant, et al., Surf. Coat. Technol. 202 (12) (2008) 2623–2631.

[10] X.-Y. Li, E. Akiyama, H. Habazaki, A. Kawashima, K. Asami, K. Hashimoto, Corros. Sci.41 (1999) 1849–1869.

[11] A. Inoue, A. Takeuchi, T. Zhang, A. Murakami, IEEE Trans. Magn. 32 (5) (September1996).

[12] V. Ponnambalam, S.J. Poon, et al., J. Mater. Res. 19 (10) (2011) 3046–3052.[13] R. Li, M. Stoica, et al., Metall. Mater. Trans. A 41 (7) (2009) 1640–1645.[14] B.-L. Sheng, H. Koshiba, T. Mizushima, A. Inoue, Mater. Trans. JIM 41 (7) (2000)

873–876.[15] P. La, Y. Wei, et al., Mater. Sci. Eng. A 528 (24) (2011) 7140–7148.[16] T. Saitoa, H. Takeishi, N. Nakayama, J. Mater. Res. 20 (3) (Mar 2005).[17] N. Nishiyama, K. Takenaka, et al., Intermetallics 30 (2012) 19–24.[18] L.A. Davis, Y.T. Yeow, P.M. Anderson, J. Appl. Phys. 53 (1982) 4834.[19] A. Singh, S. Paital, A. Andapally, N. Dahotre, S. Harimkar, Adv. Eng. Mater. 14 (6)

(2012).[20] C. Zhang, R.Q. Guo, Y. Yang, Y. Wu, L. Liu, Electrochim. Acta 56 (2011) 6380.[21] X. Zhou, L. Hu, Q. Chen, X. Hua, Adv. Mater. Res. 189–193 (2011) 428–432.[22] H. Ma, W. Wang, J. Zhang, G. Li, C. Cao, H. Zhang, J. Mater. Sci. Technol. 27 (12) (2011)

1169.[23] A. Inoue, A. Katsuya, K. Amiya, T. Masumoto, Mater. Trans. JIM 36 (7) (1995)

802–809.[24] Y. Zhang, N. Wanderka, U. Czubayko, F. Zhu, W. Wollenberger, Mater. Sci. Forum

343–346 (2000) 371–376.[25] S. Li, G. Xie, et al., J. Alloys Compd. 536 (2012) S315–S318.[26] X.L. Wu, Y.S. Hong, Surf. Coat. Technol. 132 (2000) 194.[27] P. Zhang, H. Yan, P. Xu, Q. Lu, C. Li, Z. Yu, Surf. Coat. Technol. 206 (2012) 4981–4987.[28] R. Li, Z. Li, J. Huanga, Y. Zhua, Appl. Surf. Sci. 258 (2012) 7956–7961.[29] B. Chen, Y. Li, Y. Cai, R. Li, S. Pang, T. Zhang, J. Alloys Compd. 511 (2012) 215–220.[30] S. Katakam, J.Y. Hwang, S. Paital, R. Banerjee, H. Vora, N.B. Dahotre, Metall. Mater.

Trans. A. 43a (December 2012)(4959).[31] S. Katakam, S. Santhanakrishnan, H. Vora, J.Y. Hwang, R. Banerjee, N.B. Dahotre,

Philos. Mag. Lett. 92 (2011) 617–624.[32] I. Manna, J. Dutta Majumdar, B.R. Chandra, S. Nayak, N.B. Dahotre, Surf. Coat.

Technol. 201 (2006) 434–440.[33] A. Bandyopadhyay, B.V. Krishna,W. Xue, S. Bose, J. Mater. Sci. Mater. Med. 20 (2009)

S29.[34] S. Katakam, S. Santhanakrishnan, N.B. Dahotre, JOM 64 (6) (2012).[35] K. Amiya, A. Urata1, N. Nishiyama, A. Inoue, Mater. Trans. 45 (4) (2004) 1214–1218.[36] S. Pang, T. Zhang, K. Asami, A. Inoue, J. Mater. Res. 17 (3) (Mar 2002).[37] D. Huang, R. Li, L. Huang, V. Ji, T. Zhang, Intermetallics 19 (2011) 1385.[38] X.J. Gu, S.J. Poon, G. Shiflet, J. Mater. Res. 22 (2) (Feb. 2007).[39] Z. Zheng, W. Lu, H. Dingyong, L. Yanbo, Z. Guangzhen, Rare Metal Mater. Eng. 40

(S3) (2011) 160–165.[40] S. Katakam, J.Y. Hwang, H. Vora, S. Hamirkar, R. Banerjee, N.B. Dahotre, Scr. Mater. 66

(2012) 538–541.[41] Q.J. Chen, J. Shen, D.L. Zhang, H.B. Fan, J.F. Sun, J. Mater. Res. 22 (2) (Feb 2007).[42] H. Sahasrabudhe, S.A. Dittrick, A. Bandyopadhyay, Metall. Mater. Trans. A (2013),

http://dx.doi.org/10.1007/s11661-013-1846-0.[43] G.C. Lavorato, G. Fiore, A. Castellero, M. Baricco, J.A. Moya, Physica B 407 (2012)

3192–3195.[44] C. Jiang, J. Pei, J. Hao, Adv. Mater. Res. 150–151 (2011) 881–884.[45] Giovanni Mastrogiacomo, Jürg Kradolfer, Jörg F. Löffler, J. Appl. Phys. 99 (2006)

023908.