Processing and Properties of CuZr-Based Amorphous Microwires

Processing and Properties of CuZr-Based Amorphous Microwires

Available online at www.sciencedirect.com Procedia Engineering 36 (2012) 551 – 555 IUMRS-ICA 2011 Processing and Properties of CuZr-Based Amorphous...

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Available online at www.sciencedirect.com

Procedia Engineering 36 (2012) 551 – 555

IUMRS-ICA 2011

Processing and Properties of CuZr-Based Amorphous Microwires Yangyong Zhao, Jiming Hu, Y Zhang a* State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China

Abstract In the paper, amorphous microwires of [(Zr43Cu50Al7)99.5Si0.5]99.9Y0.1 (Zr43) and Zr50.5Cu27.45Ni13.05Al9 (Zr50.5) alloys were fabricated by the melt-extraction technique. Their mechanical properties were evaluated by carrying out tensile and bending tests which show they have nearly the same strength. The cryogenic resistivity of CuZr-based amorphous microwires was investigated by four point probe method below 300 K. With the temperature increasing, the resistivity of these microwires decreases. Temperature coefficient of resistivity of these wires is close to zero, which manifests potential application as precision resistance material for its constant resistivity in such wide range of temperature.

© 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of MRS-Taiwan Keywords: Amorphous microwire; melt-extraction; tensile strength; cryogenic resistivity

1. Introduction Amorphous microwires have received increasing interest in recent years because their advantages of properties, such as high strength, wear resistance, and giant magneto-impedance effect [1-2]. They also exhibit an electrical resistivity of about two orders of magnitude higher than their crystalline counterparts. Metallic glasses often have a relatively high electrical resistivity and a small even negative temperature coefficient of resistivity (TCR) [3]. In most cases, the electrical resistance is used as a means to study the glass transition behavior and the relaxation behavior of metallic glasses from room temperature to the supercooled liquid state [4]. However, measurement of electrical resistivity at low temperature has been reported only in a few Zr-based BMG alloys. Okai et al. measured the electrical resistivity of Zr55Cu30* Corresponding author. Tel.: Tel.: +86 10 62334927; fax: +86 10 62333447. E-mail address: [email protected]

1877-7058 © 2012 Published by Elsevier Ltd. doi:10.1016/j.proeng.2012.03.080

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xAl10Ni5Nbx (x=1, 2, 3, and 5 at %) BMG alloys at temperatures from 300 K down to about 2 K [5], and their specimens were always either bulk or ribbon. In this paper, the amorphous microwires of CuZrbased alloys were produced by the melt-extraction technique, and cryogenic electrical resistivity of amorphous microwires was investigated from 11 K to 298 K. Their mechanical properties were evaluated by carrying out tensile and bending tests.

2. Experimental procedure Ingots with nominal atomic-percent composition of the Zr43 and Zr50.5 were prepared by arc melting the mixture of Zr, Cu, Ni, Al, Si, Y metals with purity higher than 99.9% weight percent (wt. %) in a Tigetted high-purity argon atmosphere. The alloys were remelted several times in order to improve homogeneity under high vacuum (10-3 Pa). The BMGs samples were produced by suction casting into a water-cooled copper mold to form rods samples with a diameter of 8 mm, which were ready for producing amorphous wires by the melt-extraction technique [6]. Under high vacuum (10-3 Pa), the top of the alloy sample was melted by induction heater, and then extracted by the sharp edge of a rotating copper wheel. Under proper conditions, amorphous wires were produced. The amorphous structure of microwires were carried out by X-ray diffraction (XRD) using a MXP21VAHF diffractometer with Cu KĮ radiation. Thermal analysis was performed with differential scanning calorimeter (DSC) at a heating rate of 20 K/min. The tensile tests of the wire samples were performed using an Instron 5848 MicroTester at a macroscopic strain of 8.33×10-5 s-1. The wire diameter was approximately 50 μm, and the gauge length was fixed to 20 mm, approximately 400 times the wire diameter. Four-point probe method was used to measure the electrical resistance (R). Four points of the wire, with nearly equal distance from each other, was connected to copper wires by soldering. Certain current flowed through the wire and the voltage between two middle points was measured, then the resistance between these two points and resistivity of microwires was calculated. 3. Results and discussion The SEM images of the produced microwires are shown in Figure 1. Fig. 1(a) shows the lateral surface of Zr43 microwire which fractured under tensile load. No voids, contaminants, and oxide layers can be seen in the enlarged surface. Only few shear bands could be seen near the fracture plane. The surface of Zr50.5 microwire which was bent is shown in Figure 1(b). It could be bent easily, associated with lots of shear bands on the surface. (a)

20µm

(b)

10µm

Fig.1 SEM micrographs of the surface of (a) Zr43 which fractured under tensile load (b) Zr50.5 which was bent.

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Fig.2 (a) shows X-ray diffraction patterns of Zr43 and Zr50.5 micowires. They show similar diffused patterns without any sharp crystalline peaks indicating the fully amorphous structure. The DSC results of the amorphous Zr50.5 and Zr43 microwires at a heating rate of 20 K/min are shown in Fig.2 (b). The glass transition temperature (Tg) of Zr43 microwire is 488 K, which is 49 K higher than that of Zr50.5. The onset crystallization temperatures (Tx) of Zr43 and Zr50.5 microwires are 515 K and 481 K respectively. It means that the Zr50.5 microwire has a wider supercooled liquid region (¨Tx=Tx-Tg) than Zr43. The XRD and DSC results confirm the amorphous structure of the Zr43 and Zr50.5 wires. Zr 43 wi r e Zr 50. 5 wi r e

(a)

(b)

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Tg 200

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30

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50

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Fig.2. (a) The XRD patterns of Zr50.5 and Zr43 wires. (b) The DSC measurement results for the amorphous Zr50.5 and Zr43 wires at a heating rate of 20 K/min.

The tensile tests were performed at room temperature in air, and the tensile stress is evaluated under the assumption that the cross section of melt-extracted microwires have perfect circular morphology and that there is no fluctuation in diameter. Figure 3 shows the typical tensile stress-strain curves of meltextracted wires. The wires show high tensile fracture strength of 1.6 GPa and large elastic limit reaching approximately 2%. All the samples display only an elastic deformation behavior and catastrophic fracture without yielding. Zr50.5 Zr43

1800 1600 1400

stress MPa

1200 1000 800 600 400 200 0 0

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strain %

Fig.3. Tensile stress-strain curves of Zr43 and Zr50.5 wires.

Fig.4 (a) presents the temperature dependence of the electrical resistivity (ȡ) of Zr50.5 and Zr43 microwires. The minimum test temperature is about 11 K. For both amorphous microwires, their electrical resistivity (ȡ) decreases with the temperature increasing. The resistivity ȡ of Zr50.5 changes from 183.457 ȝȍ·cm at 11 K to 179.815 ȝȍ·cm at 298 K, while that of Zr43 starts at 110.96 ȝȍ·cm at 11 K and drops steadily to 109.90ȝȍ·cm at 298 K. Considering test error, there is no change for the electrical resistivity of Zr43 between 50 K and 250 K.

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1 .0 3

(b )

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Z r 4 3 w ir e Z r 5 0 .5 w ir e

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Z r5 0 .5 w ire Z r4 3 w ire

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U7U

Resistivity(P:˜cm)

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0 .9 9 0

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T e m p e ra tu re (K )

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T e mp e r a t u r e ( K )

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Fig.4 (a) Temperature dependence of the resistivity for Zr43 and Zr50.5micowires. (b) Temperature dependence of ȡT/ȡ298 for Zr50.5 and Zr43 microwires.

Temperature coefficient of resistance (TCR), defined as Į = (1/ȡ)(dȡ/dT), of the Zr50.5 is about 7.25×10-5 K-1 in the range from 11 K to 298 K ,while that of Zr43 is about -3.45×10-5 K-1. It shows that the temperature coefficient of resistance (TCR) of both Zr50.5 and Zr43 microwires are negative and close to zero, although the absolute value of Zr50.5 is larger than that of Zr43. Mooij found that there was obvious relativity between the magnitude of resistivity and positive or negative of TCR in amorphous alloys [7]. If ȡ<100 ȝȍ·cm, TCR is positive. If ȡ>150 ȝȍ·cm, TCR is negative. TCR could be either when ȡ is between 100 ȝȍ·cm and 150 ȝȍ·cm. The results indicate Zr50.5 and Zr43 microwires also follow this empirical rule. Fig.4 (b) shows temperature dependence of ȡT/ȡ298 for Zr50.5 and Zr43 microwires at low temperature. The ȡT and ȡ298 represent the resistivity at a certain temperature T and 298 K respectively. We could find clearly that the ȡT/ȡ298 of Zr50.5 decreases faster than that of Zr43 with temperature increasing, which may be resulted by the addition of magnetic element Ni. 185.0

( a)

or i gi na l f i t t ed

184.5

Resistivity(P:˜cm)

Resistivity(P:˜cm)

185.0

184.5

184.0

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183.0

( b)

o r i gi na l f i t t ed

184.0 183.5 183.0 182.5 182.0 181.5 181.0

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l nT( K)

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or i gi nal f i t t ed

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Temperture (k)

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Fig. 5 Fitted curves between resistivity and temperature of Zr50.5 amorphous microwire. (a) from 11 K to 26 KΙ(b) from 26 K to 150 KΙ (c) from 150 K to 298 K.

Yangyong Zhao et al. / Procedia Engineering 36 (2012) 551 – 555

In conventional amorphous alloys, resistivity could be fitted as different function of temperature in different temperature range. Fig.5 shows the fitted curves between the resistivity and temperature of Zr50.5 microwire. At low temperature, from 11 K to 26 K, there is a linear relationship between the resistivity and the logarithm of temperature, as presented in Fig.5 (a). Instead of resulting in T5 term in crystals, scattered electron and phonon may lead to T2 term in amorphous alloys with temperature increasing. Fig.5 (b) shows it presents a polynomial relationship between the resistivity and temperature from 26 K to 150 K, just as a formula ȡ =183.95446-0.02633T+6.36212E-5T2. Then the T2 term disappeared, presenting a linear relationship between the resistivity and temperature from 160 K to 298 K. Fitting analyses indicate cryogenic resistivity property of CuZr-based amorphous microwires is consistent with that of conventional amorphous alloys. 4. Conclusions 1. Amorphous Microwires of Zr43 and Zr50.5 alloys were fabricated by the melt-extraction technique successfully. They could be bent easily and that shows they have high toughness and high tensile fracture strength of 1.6 GPa. 2. With the temperature increasing, the resistivity of these microwires decreases. Temperature coefficient of resistivity (TCR) of these wires is close to zero from 11 K to 298 K, which manifests potential application as precision resistance material. 3. Fitting analysis between resistivity and temperature indicates that cryogenic resistivity property of CuZr-based amorphous microwires is consistent with that of conventional amorphous alloys.

Acknowledgements Authors are grateful to Dr H Wang for the technical assistance in the sample preparation. The National High Technology Research and Development program of China (No. 2009AA03Z113) is gratefully acknowledged.

References [1] M. Vázquez*. Physica B. 2001; 299: 302–313. [2] M Vázquez, A Hernando. J. Phys. D: Appl. Phys. 1996; 29: 939–949. [3] Kun Huang. Solid State Physics.Beijing; Higher Education Press. 1988; 318-319. [4] Osami Haruyama, et al. Materials Science and Engineering: A. 2001; 304-306: 740-742. [5] D. Okai, A. Nanbu, T. Fukami, et al. Materials Science and Engineering A. 2007; 449–451: 548–551. [6] Bruno Zberg, Edward R. Arata, Peter J. Uggowitzer, ea al. Acta Materialia. 2009; 57: 3223–3231. [7] J.H.Mooij. Phys Stat Sol A. 1973; 17: 521-530.

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