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Heliyon
Heliyon
Heliyon
2405-8440
Elsevier

S2405-8440(24)13657-2
10.1016/j.heliyon.2024.e37626
e37626
Research Article
The temperature field characteristics and amorphous formation ability during the continuous casting process of Zr-based bulk metallic glass
Yang Erxu
Ding Tao
Ren Tingzhi rtz@ysu.edu.cn
⁎
National Engineering Research Center for Equipment and Technology of Cold Strip Rolling, Yanshan University, Qinhuangdao, Hebei, 066004, China
⁎ Corresponding author. rtz@ysu.edu.cn
07 9 2024
30 9 2024
07 9 2024
10 18 e376263 5 2024
5 9 2024
6 9 2024
© 2024 The Authors
2024
https://creativecommons.org/licenses/by-nc/4.0/ This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/by-nc/4.0/).
This study utilized FLUENT dynamic mesh simulation technology to simulate the temperature field distribution characteristics during the continuous casting (CC) process of 5 mm thick Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 (Vit1) bulk metallic glass (BMG), analyzed and discussed the amorphous forming ability of the Vit1 BMG plate prepared through CC. The results indicate that during the CC process, the temperature gradient and cooling rate of Vit1 BMG plate decrease with increasing distance from the cooling copper block surface and prolonged solidification time. Even at the lowest cooling rate, it still remains significantly higher than the critical cooling rate (Rc) of Vit1 bulk amorphous alloy. The temperature variations recorded by the thermocouple during the alloy melt solidification process are in basic agreement with the simulation data. The experimental test and simulation results show that 5 mm thick Vit1 BMG slab can be prepared theoretically by continuous casting technology. Finally, XRD, DSC and TEM were used to analyze the amorphous formation ability and microstructure of the Vit1 BMG slab.

Keywords

Amorphous materials
Cast
Numerical simulation
Solidification
Thermal analysis
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pmc1 Introduction

Amorphous alloy with a critical size larger than 1 mm can be called bulk metallic glass (BMG) [1]. BMGs have the special structure of long-range disorder and short-range order, which exhibit some unique mechanical behaviors such as high strength, excellent corrosion resistance, high fracture toughness, high hardness and good wear resistance. Therefore, they have great development potential and application prospect in sports, aerospace, microelectronics, military, automotive industry, medical and many other fields [2,3]. In recent years, related research on the additive manufacturing of BMG has been increasing year by year [4,5]. However, the additive manufacturing has some limitations, including the generation of residual stresses and internal defects [6], and the forming mechanism of additive manufacturing causes the formed parts to be prone to crystallization and cracks [7]. At present, the preparation methods of bulk amorphous alloys mainly include suction casting [8], die casting [9], gravity casting [10] and centrifugal casting [11], etc. However, these techniques are characterized by high costs and low efficiency, which limit the extensive application of BMG.

Continuous casting (CC) is an advanced technology characterized by high production efficiency and high metal utilization rates. CC technology has evolved over nearly 200 years and has become the primary production method for crystalline alloys such as steel, copper, aluminum, etc. Currently, the CC technology for BMG is at its early stage of development. Zhang et al. developed a novel CC device and prepared 10 mm diameter (Cu47Zr45Al8)96Y4 BMG bar and 50 mm × 6 mm × 300 mm Zr48Cu36Al8Ag8 BMG slab [[12], [13], [14], [15]].

Numerical simulation technology can visually represent the dynamic changes in temperature fields and is widely used to calculate the temperature field in physical metallurgy solidification processes. Previous studies simplified the CC technology model into a one-dimensional model and used the finite volume method to perform numerical simulations of the CC process [16]. In order to further simulate the CC technology completely, a three-dimensional model should be adopted for numerical simulation, which can more intuitively show the temperature field changes in the whole process of CC technology.

In this study, a new CC technology was designed for preparing BMG slab. FLUENT (computational fluid dynamics software) dynamic mesh technology was employed to simulate the temperature fields during solidification process and analyze cooling rates in the thickness direction of the slab. A slab with cross-section size of 160 mm × 5 mm and length of 200 mm was prepared by experiment, and its amorphous forming ability was discussed by sampling at different positions of the slab.

2 Experimental method

The CC experiment was conducted by utilizing a self-designed crawler-type CC device, as illustrated in Fig. 1(a). The device was placed in a vacuum tank. During the operation of the CC device, the molten metal was firstly injected into the tundish through the insulated bag, and then the molten metal was injected into the casting cavity (composed of moving cooling copper block and steel strip) after stabilizing the flow through tundish. The geometric model of the casting cavity section is shown in Fig. 1(b). The moving cooling copper block circulates around the frame under the drive of the drive pulley and driven pulley.Fig. 1 The crawler-type CC device (a), the section geometry of the casting cavity (b), the initial state and grid division of the simulation model (c).

Fig. 1

The experimental material was Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 (Vit1) amorphous alloy. The temperature field of the CC process from molten metal entering to leaving the casting cavity was simulated and calculated, by using FLUENT dynamic mesh simulation technology. The pouring temperature was 1123 K, the environment temperature was 300 K, and the CC speed was 21 mm/s. The casting cavity exhibits symmetry, hence numerical simulations were conducted using half of the casting cavity. The hexahedral mesh division was employed with a grid size of 1 mm, the initial state and grid division of the simulation model is shown in Fig. 1(c). The thermal physical parameters of Vit1 were selected from the parameters in Table 1 of reference [10].Table 1 Thermal physical parameters of samples from different positions on the plate.

Table 1Position	Tg/K	Tx/K	ΔTx/K	Trg	ΔH/(J/g)	σm/MPa	
A	629.0	699.9	70.9	0.670	−0.58	1951.47	
B	630.1	700.4	70.3	0.671	−0.55	1947.83	
C	629.5	700.8	71.3	0.670	−0.61	1957.37	

During the CC experiment, the pouring temperature and CC speed were consistent with the simulated parameters, and the temperature change of the molten metal in the casting cavity was recorded by a thermocouple (the signal acquisition position was about 2 mm away from the copper block). XRD was employed to identify the amorphous phase of the slab. TEM was used to analyze the microstructure of the slab. The thermal physical parameters of the plate samples were determined using DSC with a heating rate of 20 K/min under argon flow.

3 Results and discussion

Fig. 2(a)–(d) show the temperature fields of slab and its symmetric surfaces at different times from the start of CC, respectively. It can be seen that with the increase of CC time, the temperature of the slab solidification front decreases, and the temperature on the symmetrical surface in the width direction of the slab is higher than that at the steel block position. The temperature field at the same position of slab at different times is basically the same, so the heat transfer in the direction of CC can be ignored. The temperature fields of the symmetric surface at different times show that the temperature at different positions in the thickness direction increases with the increase of the distance from the cooled copper block. In order to more intuitively show the temperature variation, the temperature curves with respect to time at different positions on the symmetry surface of solidification front were plotted in Fig. 2(e). It can be seen that in the initial solidification period, the molten metal at 1 mm away from the cooling copper block is rapidly cooled to below the glass transition temperature (Tg). The cooling rate of the molten metal at 2 mm is lower than that at 1 mm, and the cooling rate of the molten metal at 3 mm decreases again compared with that at 2 mm. The cooling rate of the molten metal at 4 mm and 5 mm is basically the same and the lowest. During the later stage of solidification period, the temperature decreases slowly at different positions, and the temperature at each position is basically same when the slab leaves the casting cavity. The calculated cooling rates at different positions from the cooling copper block at Tg are as follows: 83.72 K/s (at 1 mm), 46.92 K/s (at 2 mm), 46.19 K/s (at 3 mm), 46.08 K/s (at 4 mm), and 45.31 K/s (at 5 mm). Fig. 2(f) shows the comparison between the recorded data of the thermocouple and the simulation calculation results. The experimental results are basically consistent with the simulation results. The cooling rate calculated from the measured data is 58.75 K/s at Tg. The results indicate that both the simulated and measured cooling rates are significantly higher than Rc (1–10 K/s) [[17], [18], [19]] required for the formation of Vit1 BMG.Fig. 2 The temperature field at different time (a–d), the temperature curve with time at different positions on the symmetry surface of slab solidification front (e), comparison of temperature curve with time between experimental records and simulation results (f).

Fig. 2

The results of simulation and measurement show that the temperature variation of the molten metal satisfies the dynamic conditions required for the formation of Vit1 BMG during the cooling process. The theoretical analysis suggests that the slab prepared by the CC technology is amorphous, but the microstructure of the slab needs to be further analyzed. Fig. 3(a) [16] shows the slab prepared by the CC technique and the samples at A, B and C positions on the slab were selected for microstructure analysis. Fig. 3(b)–(d) show XRD patterns, TEM images and SAED at different locations. There is no crystal structure diffraction peak in the XRD patterns. TEM images of the samples all show disordered structures, and SAEDs only show diffraction rings of amorphous phase, which further indicate that the slab samples are amorphous. Fig. 3(e) shows the DSC curves of the samples. All three DSC curves show a wide supercooled liquid phase region (i.e. ΔTx=(Tx-Tg)), followed by three crystallization exothermic peaks. The DSC curves clearly exhibit the glass transition behavior and crystallization reaction. Fig. 3(f) shows the stress-strain curves of the samples, and it can be observed that samples at different positions all exhibit higher compressive strength. The specific thermophysical properties of the samples are listed in Table 1. The glass transition temperature (Trg) values at the three positions are all around 0.67, which is basically consistent with the results reported in literature [20]. The Trg of the slab samples indicates that the CC technology can guarantee the amorphous forming ability of Vit1. As can be seen from Table 1, the relaxation enthalpy (ΔH) values of the samples at different positions basically maintain within the range −0.58 ± 0.03 J/g, indicating that the energy states at different positions of the slab are basically the same. The maximum compressive strength (σm) of the samples is basically maintained around 1952.50 ± 5 MPa, which is basically consistent with the results reported in the literature [21], indicating that the mechanical property of BMG is guaranteed while the size of BMG is increased. This CC technology can efficiently produce 5 mm thick Vit1 BMG slab, significantly reducing the production cost of BMG.Fig. 3 Slab sample (a), XRD, TEM and SAED patterns of samples (b–d), DSC curves of samples (e), Stress-strain curves of samples (f).

Fig. 3

4 Conclusions

(1) Based on the temperature field characteristics from simulation results and the measured temperatures during CC, the cooling rate at Tg for the Vit1 BMG slab produced by the crawler-type CC is calculated as 58.75 K/s. This cooling rate is significantly higher than the Rc of Vit1, which makes the slab prepared by CC form an amorphous structure.

(2) According to the simulation results, Vit1 BMG slab with a size of 160 mm × 5 mm × 200 mm was prepared by the crawler-type CC technology.

(3) The structural analysis indicates that the slab prepared by the crawler-type CC technology is amorphous, and this CC technology ensures the amorphous forming ability of Vit1.

Data availability statement

Data will be made available on request.

CRediT authorship contribution statement

Erxu Yang: Writing – original draft, Validation, Software, Investigation, Formal analysis, Data curation, Conceptualization. Tao Ding: Visualization, Validation. Tingzhi Ren: Writing – review & editing, Funding acquisition.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This research was financially supported by the National Science and Technology Support Program of China (Grant No. 2011BAF15B01 )
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