Journal of Alloys and Compounds xxx (2014) xxx–xxx

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Journal of Alloys and Compounds

journal homepage: www.elsevier .com/locate / ja lcom

Microstructural characterization of rapidly solidified Cu50Zr40Ni5Ti5

amorphous alloy

http://dx.doi.org/10.1016/j.jallcom.2014.10.0410925-8388/� 2014 Elsevier B.V. All rights reserved.

⇑ Corresponding author. Tel.: +90 344 280 1438; fax: +90 344 219 1042.E-mail addresses: celalkursun@ksu.edu.tr, celalkursun@hotmail.com (C. Kursun).

Please cite this article in press as: C. Kursun et al., J. Alloys Comp. (2014), http://dx.doi.org/10.1016/j.jallcom.2014.10.041

Celal Kursun a,⇑, Musa Gögebakan a, Yucel Gencer b

a Department of Physics, Faculty of Art and Sciences, Kahramanmaras Sutcu Imam University, Kahramanmaras 46100, Turkeyb Department of Materials Science and Engineering, Gebze Institute of Technology, Gebze, 41400 Kocaeli, Turkey

a r t i c l e i n f o

Article history:Available online xxxx

Keywords:Rapid solidificationMicrohardnessCopper based alloyCrystallisationKissenger plot

a b s t r a c t

The amorphous Cu50Zr40Ni5Ti5 alloy was produced by melt-spinning at wheel speeds of 35, 38 and41 m s�1. The resulting melt-spun ribbons were characterised using X-ray diffraction (XRD), scanningelectron microscopy coupled with energy dispersive spectroscopy (SEM-EDX), differential scanningcalorimetry (DSC) and Vickers microhardness (HV) tester. The XRD and SEM results revealed that therapidly solidified ribbons have a fully amorphous structure. After partial or fully crystallisation ofCu50Zr40Ni5Ti5 ribbons upon annealing, the microstructure had uneven and irregularly shaped featureswith the existence of Cu10Zr7, Cu8Zr3, CuZr and FCC-Cu phases while as quenched ribbons had featurelessmicrostructure. The SEM-EDX analysis confirmed compositional homogeneity of the Cu50Zr40Ni5Ti5 alloyribbon. According to DSC results, the amorphous ribbons exhibited distinct glass transition temperature(Tg) and wide supercooled liquid region (DTx = Tx � Tg) before crystallization. Accordingly, Tg and DTx arearound 409–414 �C and 37–54 �C, respectively. The microhardness of the as-quenched ribbons was about522 HV while it decreased with increasing annealing temperature and had a value of 463 HV for 725 �C.

� 2014 Elsevier B.V. All rights reserved.

1. Introduction

Amorphous alloys have drawn increasing attention, due to theirexcellent corrosion resistant, ultrahigh strength and soft ferromag-netic properties [1–4]. These outstanding features are attributed totheir chemically and structurally homogeneous nature [5,6]. More-over, chemical compositions of the amorphous alloys are not lim-ited by solubility limits in comparison with the crystallinematerials. Therefore, they can be produced on a wide compositionrange. Amorphous alloys exhibiting high mechanical strength,good electrical and thermal conductivity are continually neededin various applications such as electrical, defence and automobileindustries. For these applications, copper based amorphous alloysare promising materials as they also have superior corrosionresistance in various environment, high ductility and simplemanufacturing process [7]. Copper alloys are widely used as thehigh-performance switches, the condenser tubes of ships, thewelding electrodes, the rocket nozzles, the heat exchangers andthe pipeline network of desalination technology industry [7–9].

Many studies have been carried out on mechanical propertiesand microstructural characterization of Cu–Ti and Cu–Zr [10,11]

binary alloys, Cu–Mg–Ni, Cu–Zr–Al [12,13], Cu–Zr–Ti [14],Cu–Zr–Ni, Cu–Zr–Ag [15,16] ternary alloys, Cu–Ti–Zr–Ni [17], qua-ternary alloys and also Cu–Ti–Zr–Ni–Be [18,19], Cu–Ti–Zr–Ni–Si[20,21] quinary alloys which manufactured by different tech-niques. Hence, the properties of Cu-based alloys have beenimproved continuously.

The aim of this research is to systematically investigate theeffect of wheel speeds of melt spinning and different annealingprocess of melt-spun ribbons on the microstructural and mechan-ical properties of Cu50Zr40Ni5Ti5 amorphous alloy. Therefore, therapidly solidified Cu50Zr40Ni5Ti5 amorphous alloys were producedby melt spinning at different wheel speeds and by annealing.

2. Experimental

An ingot with nominal composition Cu50Zr40Ni5Ti5 (at.%) alloy was preparedfrom the pure elements, Cu (99.7%), Zr (99.9%), Ni (99.5%), and Ti (99.99%) by arcmelting in a titanium-gettered argon atmosphere. The ingot was remelted fourtimes in order to obtain chemically homogenous Cu50Zr40Ni5Ti5 alloy. The rapidlysolidified ribbons were manufactured from the ingot in a single-roller EdmundBühler melt spinner at wheel surface velocities of 35, 38 and 41 m s�1. Themelt-spun ribbons were typically 4–5 mm wide and 20–80 lm thickness. The phasecontent of the melt-spun ribbons was characterized by XRD using a Philips X’Pertpowder diffractometer with Cu Ka radiation generated at 40 kV and 30 mA. Thethermal behaviour was examined by Perkin-Elmer Sapphire DSC unit under inertgas atmosphere using continuous heating mode with the heating rate of 40 K min�1

for all melt-spun ribbons. A further DSC analysis was carried out for the melt-spun

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ribbon at wheel speed of 35 m s�1 using continuous heating mode with the heatingrates of 5–40 K min�1. The cross section of the melt-spun ribbons was examined byZeiss Evo LS10 SEM and SEM-EDX after conventional metallographic preparation.

The melt-spun ribbons were annealed under vacuum/inert gas atmosphere atthe temperatures of 200, 470, 500, 550, 600, 725 and 800 �C for 30 min. Theannealed samples were characterised by XRD from surface, SEM from cross-sectionwith the same conditions used for as-quenched ribbons. The Vickers microhardnessmeasurements of the as-quenched and subsequently annealed ribbons were per-formed using a Shimadzu HMV-2 by an applied load of 0.98 N with a dwell timeof 10 s at ten different locations.

Fig. 2. The DSC curves of the rapidly solidified Cu50Zr40Ni5Ti5 alloys at wheel speedsof 35, 38 and 41 m s�1 obtained with continuous heating at a heating rate of40 K min�1.

Table 1Thermal values obtained from DSC curves for melt-spun Cu50Zr40Ni5Ti5 ribbons atdifferent wheel speed.

Wheel (speed/m s�1) Tg (�C) Tx (�C) Tx (�C) Tp (�C)

35 409 463 54 47238 412 459 47 47241 414 451 37 467

3. Results and discussion

Fig. 1 shows typical XRD spectrum of the melt-spun Cu50Zr40-

Ni5Ti5 ribbons obtained using wheel surface velocities of 35, 38and 41 m s�1. The XRD spectrums of the melt-spun ribbons showthe broad maxima characteristic for amorphous material withoutthe evidence of any crystalline peaks within the sensitivity limitsof XRD. It is concluded from the XRD results that these 3 surfacevelocities of 35, 38 and 41 m s�1 are high enough to obtain theCu50Zr40Ni5Ti5 alloy as completely amorphous state.

Fig. 2 shows the DSC curves of the rapidly solidified Cu50Zr40Ni5-

Ti5 alloys at wheel speeds of 35, 38 and 41 m s�1 during continuousheating at a heating rate of 40 K min�1. As seen in Fig. 2, the DSCtraces exhibit distinct and similar glass transition temperature fol-lowed by a wide supercooled liquid temperature range. There is anobvious exothermic reaction for all the samples according to thecrystallization behaviour of Cu50Zr40Ni5Ti5 ribbons. Table 1 sum-marises thermal values obtained from DSC curves for melt-spunCu50Zr40Ni5Ti5 ribbons with the characteristic values of the glasstransition temperature Tg, crystallization temperature Tx, super-cooled liquid region DTx (DTx = Tx � Tg), and crystallization tem-perature Tp. Table 1 shows that Tx, DTx and Tp decrease while Tg

increases with increasing melt-spun wheel surface velocity. It isconcluded that the amorphous phase obtained at the highest wheelspeeds is the least stable for Cu50Zr40Ni5Ti5 alloy. This finding issimilar to the result which was reported by Yang et al., for amor-phous Cu52.5Ti30Zr11.5Ni6 alloy [22].

Fig. 3 shows the DSC plots of the alloy at the heating rates; 5, 10,20 and 40 K min�1. The values of the peak temperatures (Tg, Tx, Tp)and the super-cooled liquid region (DTx) of Cu50Zr40Ni5Ti5 alloy arelisted Table 2. As shown in Table 2, peak temperatures and super-cooled region are shifted to higher temperatures with increasingheating rate. It reveals that the parameters of crystallization andglass transition rely on the heating rate during continuous heating[23]. Thus, it is possible to mention the importance of the kineticaspects of the glass transition for amorphous alloys [24].

Fig. 1. Typical XRD spectrum of the melt-spun Cu50Zr40Ni5Ti5 ribbons obtainedusing wheel surface velocities of 35, 38 and 41 m s�1 as-quenched.

Fig. 3. DSC analysis results for the melt-spun ribbon obtained at wheel speed of35 m s�1 using continuous heating mode with the heating rates of 5–40 K min�1.

Table 2Thermal values obtained from DSC curves for melt-spun Cu50Zr40Ni5Ti5 amorphousribbons produced at wheel speed of 35 m s�1 at different heating rates.

/ (K/min) Tg (K) Tx (K) DTx (K) Tp (K)

5 665 714 49 72210 673 724 51 73220 678 731 53 74040 682 736 54 745

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The activation energy, E which affects the thermal stability of anamorphous alloy is often estimated by the Kissinger equation (Eq.(1)) by using data from different heating rates of the alloy [25].

://dx.doi.org/10.1016/j.jallcom.2014.10.041

C. Kursun et al. / Journal of Alloys and Compounds xxx (2014) xxx–xxx 3

ln/

T2

� �¼ � E

RTþ A ð1Þ

Fig. 5. Typical XRD spectrum of the melt-spun ribbon of Cu50Zr40Ni5Ti5 alloyprepared at a wheel speed of 35 m s�1 and annealed in the temperature range of200–800 �C for 30 min.

where T is the specific temperature, such as glass transition tem-perature Tg, onset temperature Tx, or peak temperature Tp, of crys-tallization, / is the heating rate, R is the gas constant(8.314 J/mol K), E is the activation energy, A is a constant.Approximately a straight line is obtained by plotting ln(//T2) versus1/(RT). The corresponding activation energy Eg, Ex or Ep of the totalreaction of the certain peak temperatures (Tg, Tx, Tp) obtained fromthe slope of this straight line. The Kissenger plots of amorphousCu50Zr40Ni5Ti5 alloy by manufactured at wheel speed of 35 m s�1

are shown in Fig. 4. According to the present results, the activationenergies of Eg, Ex and Ep are calculated 442.47 (±15), 393.24 (±8) and381.13 (±11) kJ/mol, respectively from the DSC results in the pre-sent study. These activation energy values are higher than theamorphous alloys of Cu45Zr45Ag7Al3 (Eg = 377, Ex = 307, Ep = 340 -kJ/mol) [26], Cu52.5Zr11.5Ti30Ni6 (Eg = 357, Ex = 297, Ep = 289 kJ/mol)[22] and Cu54Zr37Ti8In1 (Eg = 321, Ex = 392 kJ/mol) [23]. Moreover,the Ex values of Cu- or CuZr-based metallic glasses which have beenreported in previous studies are generally calculated above250 kJ/mol [23]. This indicates the mentioned metallic glasses havegood thermodynamic stability [23], therefore, it can be concludedthat the Cu50Zr40Ni5Ti5 alloy with the calculated the Eg value of393.24 kJ/mol has also good thermodynamic stability.

In order to characterise the crystallisation behaviour of themelt-spun ribbon of Cu50Zr40Ni5Ti5 alloy prepared at a wheel speedof 35 m s�1, the ribbon was annealed in the temperature range of200–800 �C for 30 min. The typical XRD spectrum of Cu50Zr40Ni5Ti5

alloy shows the crystallization stages alloy depending on theannealing temperature (Fig. 5). The XRD spectrum of Cu50Zr40Ni5-

Ti5 amorphous ribbons annealed at 200 �C, that is, before theexothermic reaction, shows fully an amorphous phase. However,several sharp diffraction peaks have been observed after heatingthe Cu50Zr40Ni5Ti5 amorphous ribbons to the annealing tem-perature of 470 �C, which is just above the crystallization peak inDSC traces. This is directly related to formation of crystalline phas-es. The determined crystalline phases in the XRD pattern weremainly indexed as orthorhombic-Cu10Zr7 and Cu8Zr3, monoclinic-CuZr and f.c.c-Cu phases. It was reported in the literature that Cu10-

Zr7, Cu8Zr3 and CuZr phases were also observed after annealing forcopper based Cu45Zr45Ag7Al3 bulk metallic glass [26], Cu54.8Zr39.7-

Ag5.5 [16] and Cu50�xCoxZr50 (x = 2, 5 at. pct) alloys [27]. Withincreasing annealing temperature (up to 800 �C), no change in

Fig. 4. Kissinger plots of the amorphous Cu50Zr40Ni5Ti5 alloy manufactured atwheel speed of 35 m s�1.

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the crystallization peaks occurred. Thus, it may be suggested thatthe thermal stability of the crystallized Cu50Zr40Ni5Ti5 alloy is high.

Fig. 6 shows typical SEM images from the cross-section of themelt-spun ribbon of Cu50Zr40Ni5Ti5 alloy prepared at a wheel speedof 35 m s�1 and annealed in the temperature range of 200–800 �Cfor 30 min. It can be seen clearly in Fig. 6 that the microstructureof Cu50Zr40Ni5Ti5 alloy changes with increasing annealing tem-perature. In Fig. 6a and b, the ribbons display featureless mor-phology. This morphology is typical characteristic of theamorphous ribbons which was reported in previous many similarstudies previously as well [28–30]. The SEM results in (Fig. 6aand b) are in accord with the XRD patterns which display fullyamorphous features for as quenched and annealed (200 �C) ribbonsof Cu50Zr40Ni5Ti5 alloy.

After partial or fully crystallisation these ribbons displaymicrostructure with uneven and irregularly shaped features whichhave already been reported in previous works [16,23,31–33]. TheSEM images (Fig. 6c–e) of annealed (470, 600 and 800 �C) Cu50Zr40-

Ni5Ti5 alloy ribbon imply that the amorphous phase transformsinto the crystallite phases similar to the findings of the reportedprevious works [16,23,31–33].

According to XRD results of the annealed (470, 600 and 800 �Cfor 30 min) ribbons, the crystallite phases that are seen inFig. 6c–e are defined Cu10Zr7, Cu8Zr3 or CuZr phases. Furthermore,in order to confirm the compositional homogeneity of the Cu50Zr40-

Ni5Ti5 alloy ribbons, the SEM-EDX analysis was performed. Fig. 7shows the EDX analysis of the Cu50Zr40Ni5Ti5 alloy ribbon (pre-pared at a wheel speed of 35 m s�1). It can be seen clearly fromSEM-EDX results that the peaks in the spectrum belong to Cu, Zr,Ni and Ti elements. As shown in Fig. 7, the nominal compositionof the amorphous alloy is also so close to the percentages of ele-ment compositions.

The rapidly solidified Cu50Zr40Ni5Ti5 alloy ribbons as-quenchedand annealed at different temperature were examined by VickersHV measurements to study the effect of annealing temperatureon the hardness. The following Vickers HV formula was employedto evaluate the microhardness of the Cu50Zr40Ni5Ti5 alloy ribbon:

HV ¼ 2P sin ðh=2Þd2 ¼ 1:8544ðPÞ

d2 ð2Þ

where P is the indentation force, d is the average diagonal lengthand 1.8544 is the geometrical factor for the diamond pyramid[34]. The change in Vickers microhardness values for Cu50Zr40Ni5Ti5

://dx.doi.org/10.1016/j.jallcom.2014.10.041

Fig. 6. Typical SEM images from the cross section of the melt-spun ribbon of Cu50Zr40Ni5Ti5 alloy prepared at a wheel speed of 35 m s�1 (a) as quenched and annealed at thetemperatures (b) 200 �C, (c) 470 �C, (d) 600 �C, and (e) 800 �C.

Cu50Zr40Ni5Ti5 (at. %)Element Element

(wt. %) Element (at. %)

Cu K 49.18 50.48Zr L 43.67 39.61Ni K 3.75 4.69Ti K 3.40 5.22Total 100.00 100.00

Fig. 7. Typical SEM-EDX analysis result of the melt-spun ribbon of Cu50Zr40Ni5Ti5 alloy prepared at a wheel speed of 35 m s�1 as quenched.

4 C. Kursun et al. / Journal of Alloys and Compounds xxx (2014) xxx–xxx

alloy produced (the wheel speed of 35 m s�1) with annealingtemperatures shown in Fig. 8.

The microhardness values decreased with the annealing tem-perature, and they were calculated as 522–473 HV in the annealing

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temperature range of 200–400 �C (Fig. 8). There are similar report-ed results associated with this decline of the microhardness valuesof Cu-based amorphous alloys with increasing annealing tem-peratures [7,35–39]. The microhardness value of the alloy which

://dx.doi.org/10.1016/j.jallcom.2014.10.041

Fig. 8. The change in Vickers microhardness values for Cu50Zr40Ni5Ti5 alloyproduced with the wheel speed of 35 m s�1 with annealing temperatures.

C. Kursun et al. / Journal of Alloys and Compounds xxx (2014) xxx–xxx 5

annealed at the temperature range of 400–725 �C, was determinedas approximately 463 HV since the crystalline phases in themicrostructure of Cu50Zr40Ni5Ti5 alloy were the same. Therefore,the highest microhardness value of 522 HV was measured for theribbons as-quenched state. This hardness value is also the highestcompared with the Cu-based alloys which have been produced bydifferent techniques [7,9,35–43]. It is very interesting that the allcompared Cu-based alloys have crystal structures. Thus, it maybe easily mentioned that the effect on the hardness of the amor-phous structure for rapidly solidified Cu50Zr40Ni5Ti5 alloy is prettygood. The decline in the microhardness of amorphous structuremay be attributed to the lack of slip system which would normallyexist in a material with crystallite structure. Therefore, amorphousmetallic materials show much greater resistance to plastic defor-mation than crystalline metals. Thus, this behaviour leads togreater Vickers microhardness, as well as yield stress and fracturestress [44].

4. Conclusions

1. The amorphous Cu50Zr40Ni5Ti5 alloys were successfully synthe-sized by melt-spinning at wheel speeds of 35, 38 and 41 m s�1.

2. DSC traces of the Cu50Zr40Ni5Ti5 ribbons exhibited similar dis-tinct glass transition followed by a wide super-cooled liquidregion. According to the results, Tg and DTx are around 409–414 �C and 37–54 �C, respectively.

3. The activation energies of Eg, Ex and Ep were calculated 442, 393and 381 kJ/mol, respectively.

4. The existence of the Cu10Zr7, Cu8Zr3, CuZr and FCC-Cu phases inthe microstructure were determined annealing temperature of470 �C and higher while the amount of Cu8Zr3 phase decreasesslightly as the annealing temperature increases.

5. After partial or fully crystallisation of Cu50Zr40Ni5Ti5 ribbons,the microstructure had uneven and irregularly shaped featureswhile as quenched ribbons had featureless microstructure.

6. SEM-EDX analysis confirmed the compositional homogeneity ofCu50Zr40Ni5Ti5 amorphous ribbons.

7. The microhardness of the Cu50Zr40Ni5Ti5 ribbons decreasedwith increasing annealing temperature. The highest value ofthe microhardness was measured about 522 HV for the ribbonsas-quenched state.

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Acknowledgments

We would like to thank Kahramanmaras Sutcu Imam Universityfor financial support of the research programme (Project No: 2013/3-41M). C. Kursun, one of the authors, would like to thank Councilof Higher Education (YÖK) for graduate research support and Tech-nische Universität Dresden, IFW, Germany for providing laboratoryfacilities and also to Fatemeh A. Javid for assistance in the produc-ing of the alloys.

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