Study on fabrication of bulk metallic glassy composites by horizontal continuous casting method

Accepted Manuscript Study on Fabrication of Bulk Metallic Glassy Composites by Horizontal Continuous Casting Method B.W. Zhou, S.J. Yin, R.H. Tang, H.S. Yang, B. Ya, B.Y. Jiang, Y. Fang, X.G. Zhang PII:

S0925-8388(15)31665-0

DOI:

10.1016/j.jallcom.2015.11.108

Reference:

JALCOM 35963

To appear in:

Journal of Alloys and Compounds

Received Date: 19 October 2015 Revised Date:

10 November 2015

Accepted Date: 17 November 2015

Please cite this article as: B.W. Zhou, S.J. Yin, R.H. Tang, H.S. Yang, B. Ya, B.Y. Jiang, Y. Fang, X.G. Zhang, Study on Fabrication of Bulk Metallic Glassy Composites by Horizontal Continuous Casting Method, Journal of Alloys and Compounds (2015), doi: 10.1016/j.jallcom.2015.11.108. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Study on Fabrication of Bulk Metallic Glassy Composites by Horizontal Continuous Casting Method B.W. Zhou, S.J. Yin, R.H. Tang, H.S. Yang, B. Ya, B.Y. Jiang, Y. Fang, X.G. Zhang∗

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School of Materials Science and Engineering, Dalian University of Technology, Dalian, 116024, China, P R

Abstract:

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For developing bulk metallic glasses or glassy composites efficiently with high strength and low cost, Zr55Cu30Ni5Al10, (Cu47Zr45Al8)96Y4 and Cu40Zr50Al10 alloys rods

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and plates have been studied by horizontal continuous casting (HCC) method. Numerical simulation technique has been applied for investigating the solidification processes of the molten alloys in the water cold graphite-copper mould. The optimum

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withdrawal procedures have also been discussed for the fabrication of metallic glassy composite rod and plate in the HCC process. Experimental results indicated that Zr-Cu-based bulk metallic glassy composites without length limitation could be

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successfully fabricated by this method. The (Cu47Zr45Al8)96Y4 rod sample with 10 mm

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in diameter exhibited high fracture strength of 1.58 GPa and good superplastic deformation ability in the supercooled liquid region

Key words: Bulk metallic glass; Horizontal continuous casting; Numerical simulation of casting process; Microstructure; Mechanical property

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Corresponding author: X.G. Zhang, E-mail address: [email protected] 1 / 13

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1. Introduction Since discovered by Duwez from 1961, the bulk metallic glasses (BMGs) have acquired numerous attentions due to their high mechanical strength, large elastic

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strain limit, high hardness, good soft magnetic properties, excellent corrosion resistance and viscous flow workability in the supercooled liquid region (∆Tx=Tx - Tg, Tg: glass transition temperature; Tx: crystallization temperature) [1-3]. A variety of

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BMGs have been developed in Pd-, Pt-, Zr-, Mg-, Ln-, Ti- and Cu- based systems by

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rapid cooling processes such as water quenching, copper mold casting (suction, injection or tilt) and grooved roller casting, etc [3-9]. The critical diameter of these BMGs can be achieved for tens of centimeters size, which is defined as the glass formation ability (GFA) [10]. However, by the traditional foundry technique, once a

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single bulk glassy rod sample with limited length can be obtained by several hours or long, which is formidable to meet the strong demand of BMGs for industrial application. Therefore, for more practical applications as structural materials, such as

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electric power industry, biomedical field, micro electro-mechanical systems and

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information technology, the BMGs are desired to be produced with high efficiency and low cost [11].

It is well known that continuous casting method for massive production of steel,

aluminum, copper or other crystalline alloy ingots is a very important industrial technology due to its low energy consumption and high productivity. Previous work has shown that horizontal continuous casting (HCC) method with a specific crystallization mould, water cold graphite-copper mould, is adaptive to provide 2 / 13

ACCEPTED MANUSCRIPT enough cooling rate for continuous casting Zr48Cu36Ag8Al8 bulk metallic glassy rod [12]. This method has been emphasized for potential advantages to produce BMGs efficiently. However, in the first place, the solidification process of the alloys in

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continuous casting mould is still unclearly for the complicated condition in the high temperature and vacuum. And there is one more point, the BMG rod with Ag element costs too much for industrial applications. Recently, many low cost (Zr,Cu)-based

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multicomponent compositions associated with high GFA, high stabilization of

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supercooled liquid and high strength have been captured much attention for scientific studies as well as practical applications. The Zr55Cu30Ni5Al10 and (Cu47Zr45Al8)96Y4 glassy alloys exhibit GFA of 30 and 25 mm in diameter, compressive strength of 1860 and 1500 MPa and ∆Tx of 108 and 101 K respectively, which are suitable for

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superplastic deformation for structural productions [3, 13-14].

In the present work, the solidification process of the alloys in the water cold graphite-copper mould has been investigated by numerical simulation technology.

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The low cost Zr-Cu based alloys have been validated for fabricating bulk metallic

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glassy or composites rods and plates by horizontal continuous casting (HCC) method. Deformation behavior in the supercooled liquid region and the mechanical properties of the continuous casting samples have also been studied. A major goal of this work is to extend the utilization of HCC method for developing metallic glassy or composite alloys with good mechanical properties and low cost.

2. Experimental methods Alloy ingots with nominal compositions of Zr55Cu30Ni5Al10, (Cu47Zr45Al8)96Y4 3 / 13

ACCEPTED MANUSCRIPT and Cu40Zr50Al10were prepared by arc melting mixtures of Zr, Cu, Al, Ni and Y with a purity of 99.9, 99.99, 99.99, 99.99 and 99.9 %, respectively, in a Zr-gettered high purity argon atmosphere. The alloy ingots were remelted four times to improve

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compositional homogeneity. The schematic illustration of horizontal continuous casting system is shown in Fig. 1. The molten metal was solidified in the water cold graphite-copper mould and the intermittent withdrawal procedure was controlled by

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the withdrawing device. The Optical microstructures were obtained by optical

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microscopy (OM), the etching for OM observation specimens was made in an aqueous fluoride solution for 5 s at 298 K. The structure of the as-cast samples was examined by X-ray diffraction (XRD) with Cu-Kα source. The supercooled liquid region (∆Tx) was examined by differential scanning calorimetry (DSC) at a heating

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rate of 0.67 K/s. Mechanical properties were measured under uniaxial compression employing an Instron testing machine. In accord with ASTM standards, the gauge dimensions of 2×2×4 mm3 were cut from HCC rod and plate samples for room

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temperature uniaxial compression test at a strain rate of 5×10-4 s-1. The fracture

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morphology was examined by scanning electron microscopy (SEM). The Vickers hardness was measured by a HVS-5 Vickers microhardness tester with a 10N (1kgf) load for 15s. The characteristic deformation behavior in the supercooled liquid state was studied by vacuum induction hot pressing furnace (ZRY-55) at a constant pressure of 250 MPa. ANSYS and ProE softwares were used to simulate the solidification process and calculate the cooling rates of the molten alloy in the HCC processes. In the simulation, 4 / 13

ACCEPTED MANUSCRIPT three basic assumptions are as following: (1) during the solidification process, the thermophysical properties of the molten alloys and the casting mould are temperature dependent; (2) the solidification shrinkage and the flow of the internal molten alloy in

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the mould are neglected; (3) the products possess full glassy structure, and the latent heat of crystallization is ignored [15].

3. Results and discussion

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Fig. 2 shows the temperature-time curves of Zr55Cu30Ni5Al10 alloy solidified in

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the composite rod mould with three different drawing rates. The cooling rates associated with the drawing rates of 1 mm/s (PPI), 2 mm/s (PPII) and 3 mm/s (PPIII) can be calculated for 28 K/s, 24 K/s and 21 K/s, respectively. Fig. 3(a) shows the Zr55Cu30Ni5Al10 rod in a diameter of 10 mm and tens of centimeters in length

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fabricated by HCC method with different withdrawal rates. All these rods have peripheral bands, which generated as the withdrawing stopped during the intermittent casting procedure. For these rods samples, the withdrawal time was 5 s and the

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stopping time was 2 s. It is believed that the distance between the two adjacent bands

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corresponds to the distance the rod moved in the water-cooled mould during the withdrawal period [12]. Fig. 3(b) shows the cross-section X-ray diffraction patterns of the Zr55Cu30Ni5Al10 rods with different withdrawal rates. The patterns of the rod sample with the withdrawal rate of 2 mm/s only consists of halo peaks and no distinct crystalline peak can be found. The result may be indicative of almost amorphous structure distributed in this sample. For the rods obtained by PPI and PPIII, massive crystalline peaks can be observed in the patterns, which can be defined as CuZr2, 5 / 13

ACCEPTED MANUSCRIPT Cu10Zr7 and Zr2Al phases. In addition, the simulation results also suggest that the present three drawing rates in HCC process can provide enough cooling rate for the glass formation of

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Zr55Cu30Ni5Al10 alloy (the critical cooling rate about 10 K/s [16]). However, for the sample with PPIII, the molten alloy was not sufficiently cooled down below Tg in the period of the water-cooled mould, which resulted in heterogeneous nucleation in the

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supercooled liquid. For the sample with PPI, the long residence time of the molten

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alloy in the mould may decrease the capacity of heat transmission between the graphite and copper. Thus, the optimum withdrawal procedure should be considered for the fabrication of bulk metallic glassy alloys by HCC method. In this work, the HCC process of Zr55Cu30Ni5Al10 BMG rod are 2 mm/s for withdrawal rate, 5 s for

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drawing and 2 s for stopping periods, respectively. The DSC traces of continuous casting Zr55Cu30Ni5Al10 BMG rod is shown in Fig. 3(c). The sample exhibits a distinct endothermic heat event characteristic of the glass transition, followed by exothermic

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transformations from the supercooled liquid due to crystallization. The Tg, Tx and ∆Tx

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of the rod sample are 687 K, 772 K and 85 K, respectively. It is indicated that the Zr55Cu30Ni5Al10 rod prepared with the withdrawal rate of 2 mm/s is consisted of good glassy structure.

As for further reduction of BMGs’ production costs, the (Cu47Zr45Al8)96Y4

metallic glassy rod was prepared by the optimization process above. Fig. 4(a) shows a (Cu47Zr45Al8)96Y4 rod in a diameter of 10 mm and over 200 mm in length made by HCC method. The glassy structure distributed homogeneously throughout the whole 6 / 13

ACCEPTED MANUSCRIPT cross section except a small number of Y2O3 and CuZr particles (see Fig 4(b, c)). The rare earth element yttrium has large enthalpy of mixing (~1900 kJ/mol) with oxygen, which is believed to preferentially react with oxygen or other harmful impieties living

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in the alloy liquid and do not promote crystal nucleation but scavenge the alloy liquid [17]. In this way, the supercooled liquid can be stabilized and as a consequence, GFA of the alloy in HCC process is enhanced.

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The compressive test specimens were taken from the central and outer surface

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regions in the transverse cross section of the (Cu47Zr45Al8)96Y4 rod and the stress-strain curves are shown in Fig5 (a). The (Cu47Zr45Al8)96Y4 rod with composite structures (amorphous and crystallization) exhibits compressive strength of 1.58 GPa and Vickers hardness value of 532 Hv in room temperature. The insert SEM picture

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shows that the fracture surface consists of mainly vein pattern, suggesting that the fracture behavior is similar to other BMGs with good toughness [18, 19]. Fig5 (b) shows the superplastic deformation behavior of the HCC (Cu47Zr45Al8)96Y4 composite

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rod. The rod sample was cut for gauge dimensions of 10 mm in diameter and about 10

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mm in length before putting into the vacuum induction hot pressing furnace. It can be obviously observed that the cylindrical sample shows marked superplastic deformation about 70% at 718 K, which exceeds its Tg of 45 K. This behavior indicated that the superplastic deformation of the glassy composite rod was shown a degree of lagging after heating up to Tg. It should be ascribed to the poor thermal conductivity of the glassy structures and the dispersed crystalline particles, which will restrain the process of the superplastic deformation. Moreover, it should be noticed 7 / 13

ACCEPTED MANUSCRIPT that once the deformation occurred, the composite rod exhibited high compressive strain rapidly, i.e. excellent fluidity and mold-filling capacity for complex production molding [20, 21].

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As we all known, it is more convenient for development products by superplastic deformation with BMG plate samples rather than rod samples. Thus, we further investigated the HCC method for fabricating metallic glassy or composite plate by

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Cu40Zr50Al10 alloy, which is only consisted of conventional metal elements. The

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residence time of the molten alloy in the water cooled graphite-copper plate mould, considered as the rapid cooling time, is also determined by withdraw rate in the HCC process. High withdraw rate makes the solidification too fast to release latent heat timely, remaining the sample temperature still above Tg after throughout the mould,

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which is difficult to forming glassy structure. Conversely, low withdraw rate may result in crystallization before the metal melt filling into the mould, leading to large friction force between the casting billet and the mould. Thus, we focused on the

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different withdraw rates of Cu40Zr50Al10 alloy plate in the intermittent HCC process

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(4s for drawing and stopping periods, respectively). Fig. 6 illustrates the calculated temperature-time curves of Cu40Zr50Al10 alloy

plate in withdrawal rates of 1 mm/s, 1.5 mm/s and 2 mm/s. The cooling rates can be obtained for 27.2 K/s, 23.1 K /s and 17.2 K/s , respectively, which means the corresponding withdrawal rates of 1 mm/s and 1.5 mm/s can provide higher cooling rate than the critical cooling rate of Cu40Zr50Al10 alloy (about 20 K/s [22]) for the glass formation. Meanwhile, the numerical simulation result also shows that the 8 / 13

ACCEPTED MANUSCRIPT temperature of alloy before filling into the mould is higher than the melting point (Tm) under all three conditions. And lower casting temperature could reduce the internal chaos of the molten alloy, which enhance the stabilization of metallic liquid and the

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trend of glass formation [23]. Hence, the withdrawal rate of 1mm/s was used for solidification numerical simulation and HCC examination of Cu40Zr50Al10 alloy plate. Fig. 7(a, b) show the schematic illustrations of plate mould and its body mesh for

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ProE simulation. The temperature field during casting is calculated based on the heat

conduction equation [24]:

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conduction differential equation of Fourier three-dimensional unsteady heat

∂ ∂T  ∂  ∂T  ∂  ∂T  ∂T ∂T = ρC p (T )  k (T )  +  k (T )  +  k (T )  + q& − ρc pν ∂x  ∂x  ∂y  ∂y  ∂z  ∂z  ∂z ∂t

(1)

Where x, y and z are spatial coordinate axes; T is temperature; k(T) is the heat

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transfer coefficient variation with temperature； q& is the heat resource inside the casting；ρ is the density; Cp(T)is the specific heat capacity variation with temperature;

∂T is heat transfer cause by the movement of the casting. ∂z

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t is the time; ρc pν

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Due to the assumptions above, by selecting a micro unit and moving with the casting in the same velocity, the two-dimension cross section heat conduction equation of the casting could be simplified as: ∂  ∂T  ∂  ∂T  ∂T  k (T )  +  k (T )  = ρC p (T ) ∂x  ∂x  ∂y  ∂y  ∂t

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Fig. 7(c-e) show the temperature field in the mould at 50 s, 150 s and 250 s, respectively, with withdrawal rate of 1 mm/s for HCC Cu40Zr50Al10 alloy plate. According to the results of simulation, the part of graphite channel provided 9 / 13

ACCEPTED MANUSCRIPT calculated temperature gradient and the rapid solidification occurred as the molten metal contacting to the copper side. Furthermore, during the process, the temperature of the plate edge increased slightly due to the continuous supply of high temperature

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liquid metal, but heat conduction of graphite by water cold cooper mould can still meet the rapid solidification conditions.

Fig. 8 shows the appearance and X-ray diffraction patterns of Cu40Zr50Al10 alloy

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plate by HCC method. The Cu40Zr50Al10 alloy plate with a cross-sectional size of 6

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mm×50 mm and about 300 mm in length was fabricated by HCC method. With the intermittent continue casting procedure, uniform peripheral bands were formed on the plate each time at the pause period. Although the Cu40Zr50Al10 alloy plate was not consisted of full glassy structure, the high compressive fracture strength of 1400 MPa

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could also been obtained in room temperature (see Fig. 9). The insert picture in Fig. 9 shows the fracture surface of the Cu40Zr50Al10 alloy plate sample. The vein-like patterns and molten droplets are similar to some metallic glassy composites fracture

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morphology [13]. In conclusions, the metallic glassy composites alloys with high

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strength and low cost can be produced with high efficiency process by means of HCC, which is beneficial for further extension of their application fields.

4. Conclusions

In summary, this paper has presented a novel method for fabrication of bulk

metallic glassy composites by means of horizontal continuous casting method and the solidification process of the rod and plate samples in the water cold graphite-copper mould has also been studied. The optimum withdrawal rate should be considered for 10 / 13

ACCEPTED MANUSCRIPT the formation of bulk metallic glassy composites alloys in HCC process. With the intermittent casting procedure of 5 s withdrawal and 2 s paused, the withdrawal rate should be 2 mm/s for Zr55Cu30Ni5Al10 and (Cu47Zr45Al8)96Y4 continuous casting rods.

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The Cu40Zr50Al10 composite alloy plate can be obtained by 4 s withdrawal and 4 s stopped in withdrawal rate of 1 mm/s. The (Cu47Zr45Al8)96Y4 bulk metallic glassy composites samples exhibited high fracture strength of 1.58 GPa and good

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superplastic deformation ability in the supercooled liquid region by HCC method.

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Acknowledgments

This research is financially supported by the National Natural Science Foundation

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of China (Grant No.51301029 and 51375071).

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[8] Y. Yokoyama, K. Fukaura, A. Inoue, Intermetallics 10 (2002) 1113-1124.

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Comp. 638 (2015) 349-355.

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[12] T. Zhang, X.G. Zhang, W. Zhang, F. Jia, A. Inoue, H. Hao, Y.J. Ma, Mater Lett, 60 (2011) 2257-2260. [13] L. Deng, B.W. Zhou, H.S. Yang, X.J. Jiang, B.Y. Jiang, X.G. Zhang: J. Alloys Comp. 632 (2015) 429-434

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[14] N. Yodoshi, R. Yamada, A. Kawasaki, A. Makino, J. Alloys Comp. 612 (2014) 243-251. [15] J. G. Lee, S.S. Park, S.B. Lee, H. Chung, N.J. Kim, Scripta Mater. 53 (2005) 693-697. [16] Q.S. Zhang, D.Y. Guo, Intermetallics 10 (2002) 1197-1201.

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[17] W.H. Wang, Prog. Mater. Sci. 52 (2007) 540-596.

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[19] W. Zhang and A. Inoue, J. Mater. Res. 21 (2006) 234-241. [20] Y. Saotome, S. Miwa, T. Zhang, A. Inoue, J. Mater. Process. Tech. 113 (2001) 64-69. [21] J. Schroers, Acta Mater. 56 (2008) 471-478. [22] X. H. Lin, W. L. Johnson, J. Appl. Phys. 78 (1995) 5619-6514. [23] D. H. Xu, G. Duan, W. L. Johnson, Phys. Rew. Lett. 92 (2004) 245504-1-245504-4. [24] A.F. Mills, Heat Transfer. Prentice Hall Inc. 9th Ed. (1999) 147.

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Figures Captions Fig. 1 Schematic of the horizontal continuous fabrication equipment. Fig. 2 Temperature-time curves of Zr55Cu30Ni5Al10 alloy solidified in the composite

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rod mould with different withdrawal rates. Fig. 3 Surface appearances of Zr55Cu30Ni5Al10 rods in diameter of 10 mm with different withdrawal rates (a). The cross-section X-ray diffraction patterns of the rods

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(b). The DSC curve of rod sample by PPⅡ (c).

Fig. 4 Optical micrographs of the continuous casting (Cu47Zr45Al8)96Y4 alloy rod (a).

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The cross-sectional structure (b) and X-ray diffraction patterns (c) the taken from center of the alloy rod.

Fig. 5 Compressive stress-strain curves and the fracture feature of (Cu47Zr45Al8)96Y4 glassy composite rods (a). The temperature-strain curve and appearance of the

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superplastic deformation specimen of (Cu47Zr45Al8)96Y4 alloy rod (b). Fig. 6 The temperature-time curves of Cu40Zr50Al10 alloy plate in HCC with different withdrawal rates.

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Fig. 7 Schematic illustrations of plate mould and its body mesh for ProE simulation (a, b). The temperature field change of the Cu40Zr50Al10 alloy plate with withdrawal

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rate of 1 mm/s for HCC (c-e).

Fig. 8 The appearance (a) and X-ray diffraction patterns (b) of Cu40Zr50Al10 alloy plate.

Fig. 9 Compressive stress-strain curves and the fracture feature of Cu40Zr50Al10 alloy plate.

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ACCEPTED MANUSCRIPT Highlights

● Zr-Cu-based bulk metallic glassy composites were successfully fabricated by continuous casting method;

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● The solidification process of the molten alloys in the composite mould was studied;

was discussed;

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● Optimum withdrawal procedure for fabricating BMGs composites in HCC process

● High strength and good superplastic deformation ability could be obtained for

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(Cu47Zr45A18)96Y4 rod with HCC method.