Thermoplastic micro-formability of TiZrHfNiCuBe high entropy metallic glass

Accepted Manuscript Title: Thermoplastic micro-formability of TiZrHfNiCuBe high entropy metallic glass Authors: Xinyun Wang, Wenlei Dai, Mao Zhang, Pan Gong, Ning Li PII: DOI: Reference:

S1005-0302(18)30095-1 https://doi.org/10.1016/j.jmst.2018.04.006 JMST 1236

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31-1-2018 1-3-2018 30-3-2018

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Thermoplastic micro-formability of TiZrHfNiCuBe high entropy metallic glass

Xinyun Wang 1,* , Wenlei Dai1, Mao Zhang1, Pan Gong1, Ning Li1,2,*

State Key Laboratory for Materials Processing and Die & Mould Technology,

Huazhong University of Science and Technology, Wuhan 430074,

China

State Key Laboratory of Solidification Processing, Northwestern Polytechnical

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University, Xi’an 710072, China

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* Corresponding author.

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E-mail addresses: [email protected] (X.Y. Wang);

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[email protected] (N. Li).

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Graphical Abstract:

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[Received 31 January 2018, revised 1 March 2018, accepted 30 March 2018]

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Highlights: 

Newtonian flow is beneficial to the thermoplastic formability of high entropy MG.

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The low fragility hinders the micro-forming of high entropy MG.

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The micro-formability of high entropy MG could be improved by vibration loading.

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Abstract High entropy metallic glasses (MGs) have attracted tremendous attentions owing to high

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entropy that benefits the probing of new MG-forming systems. However, the micro-formability of high entropy MGs is lack of investigation in comparison with these

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conventional MG counterparts, which is crucial to the development of this kind of metallic

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alloys. In this work, the thermoplastic mciro-formability of TiZrHfNiCuBe high entropy MG

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was systemically investigated. Time-Temperature-Transformation (TTT) curve was first

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constructed based on isothermal crystallization experiments, which provides thermoplastic

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processing time of the supercooled high entropy MGs. By comparison with the deformation map, Newtonian flow was found beneficial to the thermoplastic formability. While the

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thermoplastic forming becomes arduous with reducing mould size to tens micrometer,

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because of the strong supercooled TiZrHfNiCuBe high entropy MG (fragility=27). Fortunately, the micro-formability of TiZrHfNiCuBe high entropy MG could be improved by vibration loading, as demonstrated by finite-element-method simulation. Our findings not

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only systemically evaluate the thermoplastic micro-formability of high entropy MG, but also provide fundamental understanding of the phenomenon.

Keywords: Metallic glass; High entropy; Thermoplastic forming; Supercooled liquid region

1.

Introduction 2

Metallic glasses (MGs) are a fascinating class of metallic alloys with an isotropic amorphous structure that is rapidly quenched from liquid melts. The absence of a crystalline micro-structure endows them with a combination of excellent mechanical properties such as ultrahigh (near theoretical) strength, wear resistance, and hardness, and physical properties

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such as soft magnetic properties [1–8]. It is worth noting that most MGs usually with three or more components based on a single principal element such as Zr, Cu, Ti, and Fe, which limits

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the glass-forming ability (GFA) of MGs [9–11]. Recently, the concept of high entropy alloys

(HEAs) introduces a novel way for developing advanced metallic materials with unique

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physical and mechanical properties that cannot be achieved by the conventional approach

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based on only a single base element [12,13]. Especially, the high entropy alloys are

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solid-solution alloys containing five or more than five principal elements in equal or

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near-equal atomic percent, which has provided a fresh approach in searching new MG

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systems with significances in scientific studies and potential applications [14]. The recent discovery revealed that the Ti16.7Zr16.7Hf16.7Cu16.7Ni16.7Be16.7 (at.%) high

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entropy MG possesses large GFA with a critical diameter larger than 15 mm, which provided

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a suitable alloy for investigating fundamental issues of high entropy MGs [15]. Also, the high entropy MGs exhibit superior mechanical properties. For example, the TiZrHfCuNiBe high entropy MG exhibits ultrahigh strength of about 2539 MPa at ambient temperature [16], and

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the CoCrBFeNiSi high entropy MG presents excellent wear resistance under high temperature, displaying potential applications especially as coatings of components [17]. The high entropy MGs also display special physical features, such as the NbSiTaTiZe, GexNbTaTiZr (x=0.5, 1) and ZrTiCuNiBe high entropy MGs possess unusual thermal stability owing to their high 3

entropy [18–20]. The Fe25Co25Ni25(B, Si)25 and Fe25Co25Ni25(P, C, B)25 high entropy MGs exhibit superior soft magnetic property and favorable mechanical feature, which could be applied in transformers to replace silicon steel [21]. Furthermore, the Ca20Mg20Zn20Sr20Yb20 high entropy MG could stimulate the proliferation and differentiation of cultured osteoblasts,

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showing the potential application in biomedicine [22]. The crystallization behavior of the TiZrHfCuNiBe high entropy MG has been investigated, and a multi-stage crystallization

entropy MGs show the main relaxation (α relaxation) [24].

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characteristic was found [23]. The study of dynamic mechanical properties found that the high

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It is worth noting that supercooled liquid region (SCLR) is one of the most intriguing

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properties of the MGs, wherein the viscosity drops down quickly with the increase in

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temperature, thus exhibiting superplasticity under external loading, namely the thermoplastic

[25–35]. However, the micro-formability of high entropy

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applications in modern industries

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forming (TPF) of MGs. The property of the TPF in MGs makes itself exhibit wide

MGs is still unclear, and no systemic research has been carried out yet. The evaluation of

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micro-formability of high entropy MGs is very important because high entropy MGs are

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exhibiting potential applications in the miniaturization of modern industry. In the present study, Ti16.7Zr16.7Hf16.7Cu16.7Ni16.7Be16.7 (at.%) alloy system was selected and investigated systemically. By constructing TTT curve and the deformation map, the Newtonian flow was

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found facilitate the thermoplastic micro-formability. While the thermoplastic forming becomes difficult with reducing mould size to tens micrometer, owing to the strong supercooled liquid with high viscosity. The finite-element-method simulation will reveal that the micro-formability of TiZrHfNiCuBe high entropy MG could be improved by vibration 4

loading.

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Experimental procedures The Ti16.7Zr16.7Hf16.7Cu16.7Ni16.7Be16.7 (at.%) high entropy MG system was chosen for this

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study, because of its excellent GFA and high thermal stability. The MG plates (dimension of 100 mm × 10 mm × 2 mm) and rods (Ø 3 mm) were fabricated by arc-melting a mixture of

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pure Ti, Zr, Hf, Cu, Ni and Be metals (purity > 99.99%) under a Ti-gettered argon atmosphere, followed by jet casting into a copper mould. The glassy structure of the as-cast alloy was

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verified by X-ray diffraction (XRD, PHILIPS χ’ Pert PRO) and transmission electron

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microscopy (TEM, JEOL-2010). The thermal response was determined by differential

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scanning calorimetry (DSC, TA Q2000) at a heating rate of 20 ℃ /min, showing a glass

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transition temperature ( Tg ) of 415℃ with a supercooled liquid region of 55 ℃. The isothermal

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crystallization experiments were carried out by DSC at various temperatures (420 ℃ to 470 ℃) in SCLR.

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The uniaxial compression specimens with normal aspect ratio of 1.0 were cut from the

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corresponding cylindrical rods (Ø 3 mm) using a diamond blade under water cooling. Two ends of the specimens were polished carefully to ensure that they were parallel to each other and were perpendicular to the longitudinal axis of the sample. Uniaxial compression tests

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were conducted at different ambient temperatures ranging from 420 ℃ to 460 ℃ in the SCLR and a variety of strain rates ranging from 5×10-4 s-1 to 1×10-1 s-1, using a Zwick machine (Zwick/Roell 020) equipped with an air furnace. In order to shorten the time for heating the sample, the load train was preheated to the test temperature and held for 30 min to stabilize 5

the temperature, the high entropy MG specimen rapidly placed into the load train with a preload of about 0.5 MPa and held for another 1 min. The fluctuation of the temperature in the furnace during testing was about ±1 ℃. The high entropy MG samples with a cuboid size of 4.5 mm × 4.5 mm × 2 mm for hot-embossing experiments were obtained by wire-cutting

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from the as-cast amorphous plates. The hot-embossing experiments were conducted at different temperatures ranging from 420 ℃ to 450 ℃ s-1 at strain rate of 1×10-3 s-1 and a

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variety of strain rates ranging from 1×10-3 s-1 to 1×10-2 s-1 at 450 ℃. The whole durations of

hot compression and embossing process at various temperatures and strain rates were

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carefully controlled within the incubation time of the MG to avoid any possible crystallization.

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The embossed part was separated from silicon mold by etching away the silicon in a KOH

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bath. Micrographs of the hot-embossing metallic glass were observed by scanning electron

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microscopy (SEM; Quanta400), and the filling depths were measured by laser scanning

Results

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3.

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confocal microscopy (Keyence VK-X260).

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3.1 Physical features of the high entropy MG Fig. 1(a) presents the XRD pattern of the Ti16.7Zr16.7Hf16.7Cu16.7Ni16.7Be16.7 alloy. A broad

diffraction hump without any trace of crystalline peaks in the XRD pattern indicates that the

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as-cast sample is fully amorphous. The thermal response of the alloy was investigated with DSC, as illustrated in Fig. 1(b), which reveals the glass transition temperature Tg = 415 ℃ and initial crystallization temperature Tx = 470 ℃. In order to evaluate the thermoplastic processing time of the supercooled liquid MGs, the isothermal crystallization experiments are 6

usually carried out by DSC, and then the Time-Temperature-Transformation (TTT) diagram can be established on the basis of the measured incubation time. Fig. 1(c) describes the isothermal crystallization curves, in which the incubation time,   toc  Tiso / vscan  of Ti16.7Zr16.7Hf16.7Cu16.7Ni16.7Be16.7 high entropy MG under different isothermal temperatures,

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wherein the onset time ( toc ) for crystallization was determined as the intersection of the slopes of the baseline and the crystallization peak, Tiso is the isothermal temperatures

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selectively above T g (~415 °C), which revealed that the incubation time is around 0.3 min at 470 ℃, 1.8 min at 460 ℃, 11min at 450 ℃, 22 min at 440 ℃, 54 min at 430 ℃ and more than

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100 min at 420 ℃. According to the incubation time (  ) under various isothermal

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temperatures, the corresponding TTT diagram is constructed, as illustrated in Fig. 1(d). From

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processing of the high entropy MG.

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the TTT curve, we can readily distinguish the time-temperature window for thermoplastic

3.2 Deformation map and thermoplastic micro-formability

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Fig.2 presents the stress-strain curves of the high entropy MG at different temperatures

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ranging from 420 ℃ to 460 ℃ and at various strain rates ranging from 5×10-4 s-1 to 1×10-1 s-1. It is clear that the macroscopic deformation behaviors of the high entropy MG show significant temperature and strain rate dependence. With increasing the temperature and

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decreasing the strain rate, the deformation modes remarkably change from elastic-brittle fracture to plastic flow, during which the nominal flow stress decreases correspondingly. The relationship between the nominal flow stresses and the strain rates at different temperatures was given in Fig. 3, which actually constructs a deformation map similar to 7

what was developed by Li et al. [27]. Each group of data can be fitted by straight lines with different slopes, and this slope actually reflects the strain rate sensitivity ( m ) that is defined by ref. [3,36,37]

m   log  flow /  log 

(1)

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where σflow is the flow stress and  is the strain rate. It can be seen clearly that the value of

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m is very close to unity for the specimens tested at a temperature above 450 ℃ at low strain

rate regime (  ≤ 5 × 10-3 s-1 at 450 ℃ and 460 ℃), indicating that the deformation of the high entropy MG behaves nearly in a Newtonian flow. The value of m , however, decreases down

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to below 1.0 in the high strain rate and low-temperature regime, indicating a transition from

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Newtonian to non-Newtonian flow.

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In order to probe the micro-formability of the Ti16.7Zr16.7Hf16.7Cu16.7Ni16.7Be16.7 high entropy MG, the alloy was hot-embossed in SCLR with various temperatures and strain rates,

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and the filling depth (h) at various temperatures and strain rates are summarized in Fig.4. The

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largest h value, 200 m, is observed at high temperature of about 450 ℃ under strain rate of 1×10-3 s-1. The corresponding cross section of the moulded topography is described in the

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insert in Fig. 4 (a), wherein the master mould has been fully filled during the hot-embossing. The value of h, however, decreases as temperature drops at certain stain rate (such as 1×10-3

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s-1). At 430 ℃, for example, the high entropy MG was hardly hot-embossed into the master mould and forming height is just about 71 m, as illustrated in the insert of Fig. 4 (a), indicate a temperature dependence. On the other hand, the value of h also decreases with increasing strain rate at a certain temperature. Such as when the strain rate increases up to 1×10-2 s-1, the master mould was no longer be filled fully at 450 ℃, as observed in Fig. 4 (b). According to 8

the description from Figs. 3 and 4, it is a little bit surprising that the high entropy MG can only be fully filled in a Newtonian viscous flow mode, indicating that the Newtonian flow facilitating the formability of metallic glasses, while thermoplastic forming in non-Newtonian flow regime tends to become difficult.

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To further demonstrate the micro-formality of the TiZrHfCuNiBe high entropy MG, micro-bats with the minimum geometric size of 10 m was hot-embossed at high

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temperatures of 450 ℃ under strain rate of 1×10-3 s-1, as illustrated in Fig. 5 (a), from which

the outline of the micro-bat could be clearly observed. Fig. 5 (b) depicts the corresponding

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three-dimensional morphology, which reveals that the maximum and minimum filling depth

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is about 120 m and 15 m, respectively, indicating that the master mould was partially filled,

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and the filling height is dependent on the mould size.

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3.3 Vibration facilitates micro-forming

To improve the thermoplastic micro-formability of TiZrHfCuNiBe high entropy MG,

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vibrational loading was introduced according to previous work [25,38]. Here, a cavity with 50

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m diameter and 400 m height was selected, and the simulation was carried out by the commercial software ABAQUS. Wherein 8-node linear brick, reduced integration, hourglass control type (C3D8R) cell was selected to mesh the sample, 20 thousand cells and a friction

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coefficient of 0.25 between the high entropy MG and mold were selected [39]. A modified Anand’s constitutive model [25,39] is defined using the data from our uniaxial compressive test at various temperatures and strain rates. For comparison, simulations under frequencies of 0 Hz, 2 kHz, and 20 kHz were carried out. 9

Fig. 6 illustrates the distribution of effective strain of the high entropy MG thermoplastic formed at static loading, vibration loading with frequencies of 2 kHz and 20 kHz, with a strain rate of 1×10-3 s-1 under the temperature of 450 ℃. As expected, the high entropy MG was hardly hot-embossed into the micro-mould under static loading (Fig. 6a), the filling depth

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(h) is only 38 m even the mould diameter reaches to 50 m. While The filling depth increases with the increasing loading frequencies, such as h increase to 225 m under

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vibration loading with a frequency of 2 kHz (Fig. 6b), and the master mould was fully filled under ultrasonic loading wherein the frequency reaches up to 20 kHz, as illustrated in Fig.

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6(c). Correspondingly, the plastic strain also shows loading frequency dependence, indicating

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that the micro-formability of high entropy MG could be conspicuously enhanced through

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Discussion

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4.

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ultrasonic loading.

4.1 Micro-mechanism of poor micro-formability

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The above results revealed a poor micro-formability of super-cooled high entropy MG,

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especially under the reduced mould size to tens micrometers. The extremely high viscosity indicates the Reynolds number value for the hot-embossing process is within the creeping flow regime, and the metallic glass exhibits laminar flow that can be described by the

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Hagen-Poiseuille law for the micro-scale structure. The filling depth (L) could be evaluated as [29,33],

L  Pd 4 max

(2)

wherein d is the mould diameter, η is the viscosity of super-cooled liquid,  max is the 10

maximum shear strain rate and which is located at the liquid-mould interface when assuming a parabolic velocity distribution. As for the creep flow of MGs in their SCLRs, max ~ 1 s−1 [33]. Furthermore, under static loading in this work, P and d are certain in hot-embossing super-cooled TiZrHfCuNiBe high entropy MG. Therefore, in this work, the temperature

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dependent viscosity is the crucial parameter for improving the thermoplastic formability of MGs in the supercooled liquid state.

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To obtain the viscosity of super-cooled TiZrHfCuNiBe high entropy MG, the temperature dependence of relative displacement was firstly obtained by thermo-mechanical

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analyzer (TMA) at a heating rate of 10℃/min and a force of 0.8 N in the protection of argon

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atmosphere, and the corresponding viscosity (η) is calculated by Stephan equation [40], as

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indicated in the inset of Fig. 7. Though the viscosity of TiZrHfCuNiBe high entropy MG

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decreases with increasing temperature, the minimum value of η is 2.9×108 Pa·s, and η =

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7.2×108 Pa·s at 450 ℃, which is one order larger than that of supercooled Zr35Ti30Be26.75Cu8.25 MG [29]. The high viscosity seriously affects the materials flow and weakens the

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micro-formability of the TiZrHfCuNiBe high entropy MG. According to the experimental

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data and Eq. (2), the calculated filling depth of the high entropy MG is about 43 m, almost identical to the simulated value (38 m, Fig. 6(a)). To in-depth understand the poor micro-formability of the super-cooled TiZrHfCuNiBe

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high entropy MG, the temperature dependence of the viscosity that reflected in a fragility ( mf ) of the supercooled liquid is considered. Fig. 7(b) shows a “fragility plot” in the form proposed by Angell [41], in which the viscosities of various glass-forming liquids are compared in an Arrhenius plot for which the inverse temperature axis is normalized with respect to Tg 11

(corresponding to the viscosity of 1012 Pa·s). The fragility is then defined as [42],

mf   log /  Tg / T 

(3)

T Tg

By comparing the value of mf , the strong and fragile liquids are classified. From Fig. 7(b), the temperature dependent viscosity among MGs shows various steepness index ( mf ). A

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large steepness index corresponds to fragile liquid behavior, while a small index corresponds to strong, nearly Arrhenius behavior. The Pt57.5Cu14.7Ni5.3P22.5 MG displays the largest value

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of mf =81.9 [43], exhibiting fragile liquids with best micro-formability, as demonstrated by

Schroers [44]. While compared with other MGs such as Au49Ag5.5Pd2.3Cu26.9Si16.3 ( mf =52.8),

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Pd43Ni10Cu27P20 ( mf =65.2) and Mg65Cu25Y10 ( mf =42.7), the fragility of TiZrHfCuNiBe high

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entropy MG reduces dramatically to about 27.

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In general, stronger liquids with small mf are believed to be thermodynamically more

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stable than that of fragile ones, the atomic diffusion coefficient (Dc) is affect by fragility [45], (4)

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MDC-1=f0exp( D*T0 / (T-T0 ))

in which M is a multiplier that takes into account the Einstein relation between the diffusivity

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and mobility, D* and T0 are the Vogel–Fulcher–Tammann (VFT) fragility parameter and VFT

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temperature, f0 is VFT pre-exponential factor. The relationship between D* and mf can be expressed as [42] :

mf =16+590 / D*

(5)

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Accordingly, the stronger liquids with small m f perform low atomic diffusion coefficient, thus the atoms diffusion in strong liquids is difficult than the fragile ones. Furthermore, the viscosity is essentially correlated to the atomic diffusion, as expressed [46]:

DC  KT  2 / 6  a 

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For the strong liquids, the viscosity are larger at high temperatures. In this case, the jump distance  is short, which would retard the material flow and thus degrade the micro-formability, as what we observed in the results.

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4.2 Illustration for vibration-enhanced micro-formability The FEM simulation revealed that the micro-formability of TiZrHfCuNiBe high entropy

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MG could be improved by vibration loading, as illustrated in Fig. 6. Previous studies [47–50]

have reported that the microstructure of metallic glasses is intrinsically heterogeneous from a

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dynamic point of view, being composed of nano-scale liquid-like regions acting as flow units

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embedded in elastic matrix MGs. These unstable and high mobility flow units persist in MGs

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can be activated by applied stress or elevated temperature, inducing the global plasticity or

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relaxations of MGs. Especially, these liquid-like zones nonlinearly increase with temperature,

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and the proportion of flow units ( Fliquid ) reaches a critical percolation value at the glass transition temperature ( Tg ), inducing a mechanical brittle-to-ductile transition [51,52].

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The plastic deformation of MGs with a random distribution of “flow units”, can be

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fundamentally understood by a cooperative shear model (CSM) [53]. According to the CSM model, the volume (  ) of flow units has been calculated in our previous work [25], and we found that the  raises rapidly with increasing temperature in the SCLR, and the change of

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 with the temperature differs each other in various loading frequencies. Namely, the value

of  decreases with the increase of loading frequency, indicating that the distribution of flow units tends to be more homogeneous spatio-temporally. To further prove the possible difference of microstructure evaluation under static and 13

vibration loading, the molecular dynamics (MD) simulation was employed to detect the possible atoms movement information under the two processing conditions. Owing to the limitation of available potential functions, the binary Zr50Cu50 MG system was employed for analysis. Since elements during forming process in the form of atoms, the embedded atom

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method (EAM) potential function was used. The simulation box had an initial dimension of 4.28 nm × 4.28 nm × 12.85 nm, with 6000 Zr atoms and 6000 Cu atoms inside. The Zr50Cu50

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MG was generated by cooling Zr50Cu50 melt at a cooling rate of 2 ℃/ps. Periodic boundary

conditions were applied in all three directions, and NPT ensemble was set. Hence, the MD

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model can be considered as an infinite Zr50Cu50 MG cuboid. The simulation temperature was

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set as 450℃, which located in the supercooled liquid region of Zr 50Cu50 MG. The Large-scale

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Atomic/Molecular Massively Parallel Simulation (LAMMPS) was adopted for simulation.

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Vibration was realized by first tension for 3.00× 106 steps, then compression for 2.00 × 106.

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Thus, each cycle had a net strain of 0.01, with a strain rate of 1.00 × 10-6 ps-1. The timestep was set as 0.01 ps. The corresponding static process was also simulated for comparison.

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The MD simulated results are depicted in Fig. 8, which reveals the atoms displacement

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under static and vibration loading conditions. It is clear that under static loading (see Fig. 8a), the large atoms displacement can be observed in local regions, exhibiting the heterogeneous flow of the material. Though atoms flow in these areas are relatively fast, it will be restrained

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by the around atoms that with relatively small displacement. The discordant flow behavior will weaken the whole flow of atoms and degrade the micro-formability. While under vibration loading (see Fig. 8(b)), the atoms displacement is almost identical in the whole area, exhibiting cooperative movements of atoms, which will promote material flow. 14

In addition, the local atomic arrangement in the flow units is also affected by the relaxation time, high loading frequency corresponds to large strain rate at a certain temperature, indicating that the increase of loading frequency will shorten the relaxation time and slow down the structural relaxation process (i.e. annihilation of free volume), inducing a

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higher value of free volume [25]. Both high free volume concentration and homogeneous spatio-temporally distribution of flow units (i.e. cooperative movements of atoms) under high

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loading frequencies, enhance the material flow and facilitate the thermoplastic formability of

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MGs.

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5. Conclusions

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In summary, the micro-formability of Ti16.7Zr16.7Hf16.7Cu16.7Ni16.7Be16.7 high entropy MG

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has been systemically investigated. Based on results in both experimental and theoretical

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aspects, the following conclusions can be drawn. (1) Time-Temperature-Transformation (TTT) curve and deformation map were

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constructed, and Newtonian flow was found beneficial to the thermoplastic

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formability.

(2) The thermoplastic forming becomes arduous with reducing mould size to tens

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micrometer, attributed to the low fragility ( mf =27) that induces the strong supercooled TiZrHfNiCuBe high entropy MG.

(3) The micro-formability of TiZrHfNiCuBe high entropy MG could be improved by vibration loading, owing to both high free volume concentration and homogeneous spatio-temporally distribution of flow units under high loading frequencies, which 15

enhance the material flow and facilitate the thermoplastic formability of MGs.

Acknowledgements This work was supported by the National Natural Science Foundation of China [Grant Nos.

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51671090, 51725504, 51435007] and the funds of the State Key Laboratory of Solidification Processing in NWPU [Grant No. SKLSP201611]. The authors are grateful to the Analytical

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and Testing Center of Huazhong University of Science and Technology for technical

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assistance.

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[3]

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ED

[33] [34] [35] [36]

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Fig. 1 XRD pattern (a) and DSC curve (b) of the Ti 16.7Zr16.7Hf16.7Cu16.7Ni16.7Be16.7 high entropy MG, (c) the incubation time under different isothermal temperatures and (d) the corresponding

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Time-Temperature-Transformation (TTT) diagram.

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strain rates.

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Fig. 2 True compressive stress-strain curves of the high entropy MG at various temperatures and

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Fig.3 Deformation map of Ti16.7Zr16.7Hf16.7Cu16.7Ni16.7Be16.7 high entropy MG.

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Fig. 4 Summarized filling depth of the high entropy MG under various temperatures (a) and strain

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rates (b).

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Fig.5 (a) SEM micrograph of the hot-embossed micro-bat, (b) corresponding three-dimensional

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profile.

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Fig. 6 Disributions of effective strain of hot-embossing high entropy MG under static loading (a),

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2 kHz (b) and 20 kHz (c).

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Fig. 7 (a) Displacement-temperature curve obtained by TMA (the insert shows the corresponding viscosity-temperature curve), (b) Angell plots of the high entropy MG, compared with

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conventional MGs.

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Fig. 8 Molecular dynamics simulation of forming process under (a) static, (b) vibration loading

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conditions.

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