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Article

The Correlation among the Atomic Structure, Electronic Valence Band and Properties of Zr-Cu-Al-Ag Bulk Metallic Glasses

by
Parida Hopur
1,
Wenqi Chen
2,
Yulong Zhou
1,
Jialu Zhou
1 and
Tuo Wang
1,2,*
1
Xinjiang Key Laboratory of Solid State Physics and Devices, School of Physical Science and Technology, Xinjiang University, Urumqi 830017, China
2
School of Physics Science and Technology, Xinjiang University, Urumqi 830017, China
*
Author to whom correspondence should be addressed.
Metals 2023, 13(7), 1181; https://doi.org/10.3390/met13071181
Submission received: 22 May 2023 / Revised: 18 June 2023 / Accepted: 23 June 2023 / Published: 25 June 2023
(This article belongs to the Section Metal Casting, Forming and Heat Treatment)
Browse Figures
Versions Notes

Abstract

:
Investigating the relationship between the glass-forming ability (GFA), mechanical properties, and structure of metallic glasses is crucial to understanding the nature of the metallic glass state. In this study, the correlation among the atomic structure, electronic valence band, and properties have been studied using Zr50Cu44.5−xAl5.5Agx (x = 0, 1.5, 3 at.%) bulk metallic glasses (BMGs). The results reveal that through the micro-addition of Ag, the GFA of Zr50Cu44.5Al5.5 BMG can be enhanced; meanwhile, the critical diameter of Zr50Cu44.5Al5.5 glass rods increases from approximately 2.5 mm to 5.0 mm with the addition of 3% Ag. Through the addition of Ag, the thermal stability of Zr50Cu44.5Al5.5 BMG is improved, and the proportion of icosahedral-like clusters increases. The plasticity of the Zr50Cu44.5−xAl5.5Agx (x = 0, 1.5, 3 at.%) BMGs decreased from 4.6% to 0.8% with the addition of Ag. The valence band spectrum of the Zr50Cu44.5−xAl5.5Agx (x = 0, 1.5, 3 at.%) BMGs indicates that with the addition of Ag, the p-d hybridization near the Fermi level is enhanced, and the binding energy will move to a lower value.

1. Introduction

Due to the lack of long-range ordered structures and grain boundaries, metallic glasses (MGs) have a range of excellent physical and mechanical properties [1], such as a large elastic strain limit of about 2%, a high strength, and an excellent corrosion resistance [2,3], etc. However, their poor glass-forming ability (GFA) and plasticity have limited their application in structural engineering. For materials, there is an important link between their structure and properties [4]. Therefore, specifying the relationships among structure, mechanical properties, and GFA is of great significance for investigating the essence of amorphous materials and the application of MGs.
The microstructure of MGs is mainly composed of various types of atomic clusters [5,6], whose structure, properties, and combination determine the properties of MGs [7,8]. Researchers have used experimental methods and theoretical calculations to reveal the microstructural organization of MGs [9,10]. Li et al. [11] have put forward a three-dimensional atomic structure model of Zr-Cu MGs, demonstrating a strong correlation between their medium-range structure and the icosahedral (ICO) <0, 0, 12, 0> clusters in them. Zhang et al. [12] used additive-increase multiplicative-decrease (AIMD) simulation to investigate the effect of quasi-metallic elements on the structure and properties of Fe-based bulk metallic glasses (BMGs). They found that compared with Fe-B bonds, longer Fe-Fe bonds and stronger Fe-C bonds were favorable for increasing atomic occupancy in BMGs and the complexity of the melt structure, resulting in the improvement in GFA. More recently, Yang et al. [13] proposed that there was a linear relationship among the mechanical properties of Young’s moduli, shear moduli, yield strength, and valence electron density, who suggested that the physical properties of BMGs were mainly inherited from the dominant elements in their electronic-specific heat coefficients.
The micro-addition of alloy elements is one of the most important methods to improve the GFA or plasticity of BMGs [14]. Zeng et al. [15] prepared Ni60Pd20P14Si2B4 BMG with a maximum processing diameter of 25 mm by replacing 2 at.% of P with Si and 4 at.% of P with B, more than four times the size of the original Ni60Pd20P20 BMG. Zhang et al. [16] added elements La and Co to Al-Ni-Er BMGs, enhancing their stability while improving GFA. Wang et al. [17] have found that the plasticity of Zr-Cu-Al BMGs could be enhanced from nearly 0 to 9.2% with the micro-addition of oxygen, which also enhanced their structural heterogeneity. Pan et al. [18] found that phase separation would occur when a minor of Fe was added in Cu-Zr-Al BMG, whose plasticity would be improved greatly. Although micro-alloying may be beneficial to improving the properties of some BMGs, its mechanism is a matter of debate.
In this study, a micro-addition of Ag has been performed on Zr50Cu44.5Al5.5 BMG, whose GFA has been improved; however, their plasticity will have deteriorated. The correlations among the atomic structure, electronic valence band, and properties (GFA and plasticity) of Zr50Cu44.5−xAl5.5Agx (x = 0, 1.5, 3 at.%) BMGs have been explained by studying the changes in the atomic structure and electronic valence bond. This study may provide a sight of research for the mechanism of micro-alloying effect on the properties of BMGs.

2. Methodology

2.1. Molecular Dynamic Simulations

In terms of computational simulation, the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS, 17 November 2016, Albuquerque, NM, USA) [19] software with the potential of an embedded atom method (EAM) [20] was used to perform molecular dynamic (MD) simulations for the rapid solidification process of BMGs. The selection of interatomic potential is crucial to conducting molecular dynamics (MD) simulations, and the accuracy of the potential function is the most important factor affecting the precision of results. Many researchers have proposed various forms of potential functions by different methods, such as EAM potential, modified embedded atom method (MEAM) potential [21,22], Lennard-Jones potential, etc. However, finding the most accurate and simplest potential function is still a challenge for most atoms. EAM potential is well-suited to describe the formation of metallic bonds, which is similar to embedding the properties of metal atomic nuclei into free electrons and placing the main parameters in the atomic electron density representation and related forms. Therefore, in this study, EAM potential was chosen to simulate the rapid solidification process of BMGs by MD. Although some previous reports have suggested that the results obtained by this EAM potential cannot explain the interaction between Al [23,24,25,26] and Ag [24,25] in the system very well, for the Zr-Cu-Al-Ag quaternary system of this study, there is currently no reported potential functions available, and different potential functions cannot be combined arbitrarily. Therefore, this EAM [20] potential is almost the only choice for analyzing the Zr-Cu-Al-Ag quaternary metallic glasses system.
After selecting the potential function, a cube-shaped box with three-dimensional (3D) periodic boundary conditions containing 200,000 atoms was constructed. The simulations were carried out with a constant-pressure and constant-temperature ensemble under 0 external pressure at a temperature of 2000 K for dissolution, followed by a constant cool rate of 2 × 1011 K/s from 2000 K to 300 K for melt quenching. The structure was then relaxed for 1 ns at 300 K to reach an equilibrium. The final sample size of the structural model was approximately 100(x) × 100(y) × 100(z) Å3, which was used to analyze the structural differences among different compositions. To ensure the accuracy of the simulations, each simulation process was repeated at least 3 times to ensure the reliability of the results. To obtain the geometric arrangement characteristic and the evolution of atomic clusters during their transition from liquid to an amorphous state, the number and proportion of Voronoi polyhedrons with the highest frequency in the last 10 frames of the 3 models at 300 K were extracted at uniform intervals, and the Voronoi polyhedrons contained in each metallic glass system were analyzed after summation and averaging.
A Voronoi polyhedron is defined as the smallest closed convex polyhedron surrounded by vertical bisector planes where a central atom is connected to a nearby atom. A Voronoi polyhedron is characterized by the number of faces ni of the sides, whose exponents are usually expressed as <n3, n4, n5, n6>, i.e., the number of triangles, quadrilateral, pentagon, and hexagon of the polyhedron. Icosahedral clusters (clusters with the largest number of pentagons) widely exist on metallic glasses and can be used as important parameters to describe the structural characteristics of metallic glasses [27,28].

2.2. Experiments

The raw materials of Zr, Cu, Al, and Ag, with a purity of 99.95%, were selected and weighed accurately. The alloys were prepared through arc-melting using a Ti-getter in a furnace with an argon atmosphere (Zhongke New material Technology Engineering Co., LTD, NMS-GYI, Chengdu, China). Each alloy was remelted at least five times to ensure its compositional homogeneity. The cylindrical samples with different sizes in diameter were obtained via copper mold casting, whose structure was measured using an X-ray diffractometer (XRD, Fusang Industrial Co., Ltd, Rigaku SmartLab, Cu Kα, Osaka, Japan). Differential scanning calorimetry (DSC, Netzsch 404F1, Bavaria, Germany) was used to obtain the characteristic temperature parameters of the samples at a heating rate of 30 K/min. The valence band spectra of the samples were examined using an X-ray photoelectron spectrometer (XPS, Thermo Scientific ESCALAB 250XiAl, Kα, Waltham, MA, USA). The compression performance of the samples was tested using a mechanical tester (WANCE ETM 105D, Shenzhen, China) at a length-to-diameter ratio of 2:1, and the initial strain rate was 4.0 × 10−4 s−1. The fracture surfaces were investigated through scanning electron microscopy (SEM, LEO1430VP, Zeiss, Jena, Germany) after compression.

3. Results and Discussion

3.1. The Structure and GFA of Zr50Cu44.5−xAl5.5Agx (x = 0, 1.5, 3 at.%) BMGs

The model of the Zr50Cu44.5−xAl5.5Agx (x = 0, 1.5, 3 at.%) alloys with different Ag contents is shown in Figure 1 were constructed by LAMMPS software. No significant compositional segregation or crystallization can be observed in any model, which indicates that the structure of these alloys is homogeneously amorphous.
In order to obtain the structural changes more clearly, the inter-atomic bonding information about pair correlation function (PCF) g(r) at the 300 K steady state as is shown in Figure 1. The PCF g(r) reflects the average distribution of different atomic pairs in the neighbor shells of real spaces. Figure 1a shows the g(r) curves of Zr50Cu44.5Al5.5, Zr50Cu43Al5.5Ag1.5, and Zr50Cu41.5Al5.5Ag3. The second peak of all three alloys is split, whose degree decreases with Ag addition, indicating that the amorphous structure and GFA of the three alloys may increase with Ag addition [29]. The first peak of Zr50Cu43Al5.5Ag1.5 and Zr50Cu41.5Al5.5Ag3 also seems split, which may be because the local environment of the first nearest neighbor in the atomic configuration of the alloys is changed with the addition of Ag, and two different types of short-range orders may exist. As there is a positive enthalpy of mixing between Cu and Ag [30], both atoms will repel each other. Therefore, with the addition of Ag, the environment around Cu may change, and two different types of short-range orders may be formed. Additionally, the strength of the acromion appearing at the main peak increases constantly with Ag addition, which indicates that the short-range order is enhanced. The intensity of the main g(r) peak decreases and shifts to the right slightly with the addition of Ag, indicating that the ordering of local atomic stacking decreases while the spacing of the nearest neighbor atom increases [31]. As is shown in Figure 1b, the intensity of the Cu-Al and Al-Al pairs at the first peak presents an obvious reduction with the addition of Ag; however, the other atom pairs do not change significantly. Herein, Al atoms in the alloy tend to coordinate with Ag atoms as there is a larger negative enthalpy of mixing in Ag-Al than Cu-Al [31], so the intensity of gi(r) in Cu-Al and Al-Al will decrease with the addition of Ag.
Through the PCF, only the bond trend and general structure information among atoms can be obtained, but not their specific atomic arrangement. In order to further understand the types of microscopic atomic clusters in BMGs, a Voronoi polyhedron analysis has been carried out on the 3 BMGs. Figure 2 shows the proportion of Voronoi polyhedrons with an average content of greater than 2% in Zr50Cu44.5−xAl5.5Agx (x = 0, 1.5, 3 at.%) BMGs. It can be seen that Voronoi polyhedrons with a pentagon index of 6, 8, 10, and 12 constitute the main clusters in these BMGs. Those with the highest content are the <0, 3, 6, 4> polyhedrons, which are mixed-type Voronoi polyhedrons with a distorted ICO structure and can be regarded as icosahedral-like (ICO-like) clusters. The other <0, 2, 8, x>, <0, 1, 10, x> and <0, 3, 6, x> ICO-like polyhedrons show a varying change with Ag addition. The content of <0, 3, 6, 4> ICO-like clusters in Zr50Cu43Al5.5Ag1.5 BMG is lower than that in the other two BMGs. There are varying-degree changes among <0, 2, 8, x>, <0, 1, 10, x>, <0, 3, 6, x> ICO-like and <0, 0, 12, 0> ICO clusters. As the amount of Ag replaces Cu, clusters centered on Ag atoms gradually replace some of the ICO stable clusters centered on Al atoms in the alloy. Voronoi polyhedrons with Ag atoms at their centers, such as <0, 0, 12, 0> and <0, 1, 10, 2>, have a higher stability in the system, which leads to a decrease in the number of <0, 0, 12, 0> Voronoi polyhedrons in the system and greatly changes the cluster structure of the Zr-Cu-Al alloy system. Although the content of <0, 0, 12, 0>, which is a complete icosahedron with no distortion in Zr50Cu44.5−xAl5.5Agx (x = 0, 1.5, 3 at.%) BMGs, presents a monotonically decreasing trend, this may not be a determining factor of the GFA [32], on which the total proportion of theses ICO-like and ICO clusters has an obvious impact [33]. Herein, the total proportion of these 10 types of Voronoi polyhedrons in the Zr50Cu44.5Al5.5, Zr50Cu43Al5.5Ag1.5, and Zr50Cu41.5Al5.5Ag3 BMGs is 45.19%, 45.25%, and 45.64%, respectively, which presents a slightly increasing trend with the increase in Ag content. The small difference is due to the small amount of Ag added. In order to ensure the accuracy of this tendency, two more sets of simulations were repeated. Figure S1a shows the proportions of ICO-like and ICO clusters in the first set of simulations as 45.287%, 45.292%, and 45.479%, respectively. In the second set of simulations (Figure S1b), ICO-like and ICO clusters accounted for 51.19%, 52.32%, and 53.10%, respectively. The results also showed that the total proportion of these ICO-like and ICO clusters would rise slightly with the addition of Ag. The more the addition of Ag is, the more ICO-like clusters there will be in the system. It has been found in some simulation studies [34,35] that the ICO-like structure increases sharply during glass transition; that is, it is related to the GFA of the system. More ICO-like clusters may mean a higher GFA. Therefore, the increase in Ag content stabilizes the glassy-state structure, contributing significantly to the great enhancement of GFA. Computational simulations can be used to predict that the GFA of Zr50Cu41.5Al5.5Ag3 BMG may be the highest among Zr50Cu44.5Al5.5, Zr50Cu43Al5.5Ag1.5, and Zr50Cu41.5Al5.5Ag3 BMGs.
The XRD pattern and critical size (Dmax) of the Zr50Cu44.5Al5.5, Zr50Cu43Al5.5Ag1.5, and Zr50Cu41.5Al5.5Ag3 samples are shown in Figure 3, in which it can be seen that a characteristic broad diffuse halo peak of amorphous structure is exhibited near 2θ = 38° in all samples, indicating that the as-cast state of these three alloys is amorphous at a diameter of 2.5 mm, 3 mm, and 5 mm.
Figure 4a shows the DSC curves of Zr50Cu44.5Al5.5, Zr50Cu43Al5.5Ag1.5, and Zr50Cu41.5Al5.5Ag3 BMGs with a diameter of 2 mm, which can be used to determine the glass transition temperature (Tg), initial crystallization onset temperature (Tx) and liquidus temperature (Tl) of the samples. These characteristic temperatures are marked with arrows in the figure, whose specific values are listed in Table 1.
From the DSC curves and Table 1, it can be seen that with the addition of silver, the Tl of the alloy increase, but at Zr50Cu43Al5.5Ag1.5, there will be a turning point, which may be due to the addition of Ag element, the system changed from a three-component system to a four-component system, and changed the atomic environment of Zr-Cu-Al; Tx and the width of the supercooled liquid region (ΔT) also continue to increase. The Tg remains relatively unchanged. As can be seen from Figure 4b, the solidification curve of potential energy with temperature during cooling from 1473 K to 273 K of Zr50Cu44.5−xAl5.5Agx (x = 0, 1.5, 3 at.%), BMGs were simulated at the cooling rate of 2 × 1011 K/s. There is no obvious mutation in the curve, indicating that the system does not crystallize during the solidification process; that is, the solidification process is amorphous. Through analysis, the Tg of metallic glasses are 875 K, 866 K, and 859 K. Additionally, Figure 4b also shows that the energy becomes lower at the same temperature after the addition of Ag. Due to the limitations of technology and computing resources, the spatial scale of MD simulation is very different from that of real experimental techniques. In this study, the cooling rate set in the simulation is 2 × 1011 K/s, which is eight orders of magnitude faster than the cooling rate of about 1 × 103 K/s in the experiment, and the high cooling rate leads to a significantly increasing Tg. This results in a bias between the simulation results and the experimental results, which cannot be quantitatively compared. It is difficult for MD simulation to correspond numerically with macroscopic experiments; it is still possible to compare the trends obtained by simulation with those under real macroscopic experiments. Although MD simulation does not necessarily reproduce the specific values of the experiment, it can provide predictions for real experiments. Therefore, it can be concluded that with the addition of Ag element, the Tg of metallic glasses shows a slightly decreasing trend.
The increase in Tx indicates that the thermal stability of the alloy is improved with the addition of Ag. In addition, it can be seen that the first exothermic peak appearing at about 840 K gradually disappears with the addition of Ag, which can also prove that the thermal stability of the system is increasing. ΔT increases from 56 K of the Zr50Cu44.5Al5.5 BMG to 78 K of the Zr50Cu41.5Al5.5Ag3 BMG, with the parameter γ increasing from 0.395 to 0.410. These thermodynamic parameters show a positive correlation in the critical size of the Zr50Cu44.5−xAl5.5Agx (x = 0, 1.5, 3 at.%) BMGs, indicating that their thermal stability has been improved and that the addition of Ag may be beneficial for the GFA of Zr50Cu44.5Al5.5 BMG [36].

3.2. Mechanical Properties of the Zr50Cu44.5−xAl5.5Agx (x = 0, 1.5, 3 at.%) BMGs

The room-temperature compressive stress-strain curves of Zr50Cu44.5−xAl5.5Agx (x = 0, 1.5, 3 at.%) BMGs are shown in Figure 5. The values of yield strength, fracture strength, and plasticity of these 3 BMGs are shown in Table 2. All three alloys exhibit an elastic deformation of nearly 2% before yielding. With the addition of Ag, the yield strength of Zr50Cu44.5Al5.5 BMG increases, but their compressive plastic strain shows a decreasing trend with the increase of Ag, from 4.6% to 0.8%.
Figure 6 presents the SEM images of the fracture surface and the lateral surfaces of Zr50Cu44.5−xAl5.5Agx (x = 0, 1.5, 3 at.%) BMGs after compression at room temperature. The overall fracture morphology after failure is shown in Figure 6a–c. All of these BMGs have experienced a catastrophic failure. The angle between the fracture surface and compression axis is close to 45°. There are some parallel multiple shear bands with a spacing of about ~0.1 mm in Zr50Cu44.5Al5.5 BMG, as is shown in Figure 6d. While only a few shear bands with a larger parallel spacing of about 0.2 mm can be found in the Zr50Cu43Al5.5Ag1.5 BMG, as is shown in Figure 6e. The Zr50Cu41.5Al5.5Ag3 BMG has almost no shear bands, indicating that with the addition of Ag, the plasticity of the Zr50Cu44.5Al5.5 BMG decreases. Figure 6g–i shows the fracture surface morphology of the samples, all of which exhibit a vein-like pattern. The fracture pattern of Zr50Cu44.5Al5.5 and Zr50Cu43Al5.5Ag1.5 samples is uniform, with an average diameter of about ~60 μm and a vein-like pattern. However, the fracture pattern of Zr50Cu41.5Al5.5Ag3 samples is discontinuous; meanwhile, the average diameter of the vein-like pattern is significantly smaller (~25 μm) than that of Zr50Cu44.5Al5.5 and Zr50Cu43Al5.5Ag1.5 samples. According to the plastic fracture theory [37,38], the fracture toughness KC can be estimated through Equation (1). Here, rp is the size of the plastic zone, and σy is the yield strength. For Zr50Cu44.5Al5.5 BMG, rp is about 30 μm, and σy = 1437 MPa, so their KC can be estimated to be 34 MPa·m½. The KC of Zr50Cu41.5Al5.5Ag3 BMG is estimated to be 24 MPa·m½, indicating that with the addition of Ag, the toughness of the Zr50Cu44.5Al5.5 BMG also decreases.
r p = 1 6 π K C σ y 2

3.3. Relationship between the Properties and Valence Band Positions of Zr50Cu44.5−xAl5.5Agx (x = 0, 1.5, 3 at.%) BMGs

Some studies show that an electronic structure is related to mechanical properties and the GFA of metallic glasses [39,40]. Figure 7a shows the results of the valence band spectra of Zr50Cu44.5−xAl5.5Agx (x = 0, 1.5, 3 at.%) BMGs through XPS. The position of the Fermi level, EF = 0, is marked by a dashed line. As is shown in Figure 7a, the peak near the Fermi level moves closer with the increase in Ag addition, shifting from 1.06 eV to 0.67 eV, which is marked by a dashed arrow. In addition, the Cambridge sequential total energy package (CASTEP) module of materials studio (MS, 8.0, Oxford, UK) software was used to describe the exchange-correlation potential and energy are described using the Perdew Burke Ernzerhof (PBE) in the generalized gradient approximation (GGA) [41], and the elemental electron state density diagram of Zr-Cu-Al metallic glass near the Fermi level was obtained, as shown in Figure 7b. It can be seen from the figure that the largest contribution to the electron state density at EF = 0 is the 4d orbital of the Zr atom and the 3p orbital of the Al atom, which undergo p-d hybridization at the Fermi level. Resonance of the density of states is an obvious sign of atomic bonding, and the more the density of states overlap, the stronger the bonding between atoms. The p-d hybridization is the main hybridization near the Fermi level in Zr-based metallic glasses [42], which can lead to more directional bonds, resulting in the brittleness of the materials. Therefore, p-d hybridization is localized near the Fermi level in brittle MGs, while it is far from the Fermi level in tough MGs [43]. It can be seen that the peaks have a tendency to shift to the left with Ag addition, as is shown in Figure 7a. There will be more p-d hybridization after Ag addition to the Zr50Cu44.5Al5.5 BMG, resulting in the brittleness of Zr50Cu43Al5.5Ag1.5 and Zr50Cu41.5Al5.5Ag3 BMGs. It should also be noted that the outermost electron of Ag is 4d105s1, which may introduce more s-p hybridization to the Zr-Cu-Al-Ag system, leading to a more complex hybridization and higher disorders, resulting in the increase in GFA.
The valence band position of the Zr50Cu44.5−xAl5.5Agx (x = 0, 1.5, 3 at.%) BMGs is indicated by the intersection of the dashed lines in Figure 7a. The binding energy will move from the valence bond spectrum of XPS to a lower value with the addition of Ag, which indicates that the valence band edge is moving to a lower value when Ag is added to Zr50Cu44.5Al5.5 BMG. According to Einstein’s photoemission law, binding energy decreases and shifts to the left as the kinetic energy of outgoing photoelectrons increases. This is due to the hybridization of Ag; the orbital energy level becomes deeper so that the valence band energy is reduced, resulting in more difficulty for electrons to transition. Therefore, the valence band energy of the Zr50Cu41.5Al5.5Ag3 BMG is the lowest. Compared with the Zr50Cu44.5Al5.5 and Zr50Cu43Al5.5Ag1.5 BMGs, electrons in the Zr50Cu41.5Al5.5Ag3 BMG are less likely to transit; thus, the system has lower and more stable energy. Therefore, the Zr50Cu41.5Al5.5Ag3 BMG is less prone to deformation compared with Zr50Cu44.5Al5.5 and Zr50Cu43Al5.5Ag1.5 BMGs under external loading.

4. Conclusions

(1) With a micro-addition of Ag, the GFA and thermal stability of Zr50Cu44.5Al5.5 BMG can be enhanced from 2.5 mm to 5 mm in diameter. Suggests that Ag element addition is beneficial for improving GFA. (2) With the increasing addition of Ag, the total proportion of ICO-like and ICO clusters in Zr50Cu44.5−xAl5.5Agx (x = 0, 1.5, 3 at.%) BMGs would slightly increase, which has a positive correlation with GFA. Voronoi polyhedrons with Ag atoms at their centers changed the cluster structure of the Zr-Cu-Al alloy system, and the total proportion of ICO-like clusters had a clear effect on GFA. (3) The plasticity of Zr50Cu44.5−xAl5.5Agx (x = 0, 1.5, 3 at.%) BMGs gradually decreases with the addition of Ag. (4) The p-d hybridization of Zr50Cu44.5−xAl5.5Agx (x = 0, 1.5, 3 at.%) BMGs near the Fermi level is enhanced with the addition of Ag.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/met13071181/s1, Figure S1: Two sets of simulations were repeated for the percentage of major polyhedra in the Zr50Cu44.5Al5.5, Zr50Cu43Al5.5Ag1.5 and Zr50Cu41.5Al5.5Ag3 BMGs.

Author Contributions

Data curation, software, formal analysis, investigation, and writing—original, P.H. and T.W.; Investigation, formal analysis, supervision, and validation, W.C., J.Z. and Y.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This research was sponsored by the National Natural Science Foundation of China (No. 52101153), Innovation Training Program for College Students of Xinjiang University (No. S202210755105).

Data Availability Statement

Data will be made available on request.

Conflicts of Interest

The authors declare no conflict of interest.

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Metals 13 01181 g001 550
Figure 1. (a) Pair correlation function (PCF) g(r) of Zr50Cu44.5Al5.5, Zr50Cu43Al5.5Ag1.5 and Zr50Cu41.5Al5.5Ag3 bulk metallic glasses (BMGs); (b) gi(r) of Zr-Zr, Zr-Cu, Zr-Al, Cu-Cu, Cu-Al, Al-Al, and Ag-Ag atom pairs.
Figure 1. (a) Pair correlation function (PCF) g(r) of Zr50Cu44.5Al5.5, Zr50Cu43Al5.5Ag1.5 and Zr50Cu41.5Al5.5Ag3 bulk metallic glasses (BMGs); (b) gi(r) of Zr-Zr, Zr-Cu, Zr-Al, Cu-Cu, Cu-Al, Al-Al, and Ag-Ag atom pairs.
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Figure 2. The percentage of major Voronoi polyhedrons in Zr50Cu44.5Al5.5, Zr50Cu43Al5.5Ag1.5, and Zr50Cu41.5Al5.5Ag3 BMGs.
Figure 2. The percentage of major Voronoi polyhedrons in Zr50Cu44.5Al5.5, Zr50Cu43Al5.5Ag1.5, and Zr50Cu41.5Al5.5Ag3 BMGs.
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Metals 13 01181 g003 550
Figure 3. X-ray diffractometer (XRD) patterns of as-cast Zr50Cu44.5Al5.5, Zr50Cu43Al5.5Ag1.5, and Zr50Cu41.5Al5.5Ag3 alloys.
Figure 3. X-ray diffractometer (XRD) patterns of as-cast Zr50Cu44.5Al5.5, Zr50Cu43Al5.5Ag1.5, and Zr50Cu41.5Al5.5Ag3 alloys.
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Figure 4. Zr50Cu44.5Al5.5, Zr50Cu43Al5.5Ag1.5 and Zr50Cu41.5Al5.5Ag3: (a) differential scanning calorimetry (DSC) curves of the as-cast glassy rods, (b) the solidification curve of potential energy with temperature during cooling.
Figure 4. Zr50Cu44.5Al5.5, Zr50Cu43Al5.5Ag1.5 and Zr50Cu41.5Al5.5Ag3: (a) differential scanning calorimetry (DSC) curves of the as-cast glassy rods, (b) the solidification curve of potential energy with temperature during cooling.
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Figure 5. The room-temperature compressive stress-strain curves of rod samples of Zr50Cu44.5−xAl5.5Agx (x = 0, 1.5, 3 at.%) BMGs.
Figure 5. The room-temperature compressive stress-strain curves of rod samples of Zr50Cu44.5−xAl5.5Agx (x = 0, 1.5, 3 at.%) BMGs.
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Figure 6. Scanning electron microscopy (SEM) images reveal the fracture surface and outer appearance of Zr50Cu44.5−xAl5.5Agx (x = 0, 1.5, 3 at.%) BMGs rod samples through compression testing. Fracture surfaces: (a,d) Zr50Cu44.5Al5.5, (b,e) Zr50Cu43Al5.5Ag1.5, (c,f) Zr50Cu41.5Al5.5Ag3; lateral surfaces: (g) Zr50Cu44.5Al5.5, (h) Zr50Cu43Al5.5Ag1.5, (i) Zr50Cu41.5Al5.5Ag3.
Figure 6. Scanning electron microscopy (SEM) images reveal the fracture surface and outer appearance of Zr50Cu44.5−xAl5.5Agx (x = 0, 1.5, 3 at.%) BMGs rod samples through compression testing. Fracture surfaces: (a,d) Zr50Cu44.5Al5.5, (b,e) Zr50Cu43Al5.5Ag1.5, (c,f) Zr50Cu41.5Al5.5Ag3; lateral surfaces: (g) Zr50Cu44.5Al5.5, (h) Zr50Cu43Al5.5Ag1.5, (i) Zr50Cu41.5Al5.5Ag3.
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Figure 7. (a) X-ray photoelectron spectrometer (XPS) valence band spectrum of Zr50Cu44.5−xAl5.5Agx (x = 0, 1.5, 3 at.%) BMGs, (b) the elemental electron state density diagram of Zr-Cu-Al metallic glass near the Fermi level.
Figure 7. (a) X-ray photoelectron spectrometer (XPS) valence band spectrum of Zr50Cu44.5−xAl5.5Agx (x = 0, 1.5, 3 at.%) BMGs, (b) the elemental electron state density diagram of Zr-Cu-Al metallic glass near the Fermi level.
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Table
Table 1. Characteristic temperature of Zr50Cu44.5−xAl5.5Agx (x = 0, 1.5, 3 at.%) BMGs.
Table 1. Characteristic temperature of Zr50Cu44.5−xAl5.5Agx (x = 0, 1.5, 3 at.%) BMGs.
Zr50Cu44.5Al5.5Zr50Cu43Al5.5Ag1.5Zr50Cu41.5Al5.5Ag3
Dmax (mm)2.53.05.0
Tg (K)687683680
Tx (K)743749758
Tl (K)119611781171
ΔT = Tx − Tg (K)566678
γ = Tx/(Tg + Tl)0.3950.4020.410
Table
Table 2. The value of yield strength, fracture strength, and plasticity of Zr50Cu44.5−xAl5.5Agx (x = 0, 1.5, 3 at.%) BMGs.
Table 2. The value of yield strength, fracture strength, and plasticity of Zr50Cu44.5−xAl5.5Agx (x = 0, 1.5, 3 at.%) BMGs.
x (at.%)Yield Strength (MPa)Fracture Strength (MPa)Plastic Strain (%)
0143719144.6
1.5170719523.2
3156518420.8
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Hopur, P.; Chen, W.; Zhou, Y.; Zhou, J.; Wang, T. The Correlation among the Atomic Structure, Electronic Valence Band and Properties of Zr-Cu-Al-Ag Bulk Metallic Glasses. Metals 2023, 13, 1181. https://doi.org/10.3390/met13071181

AMA Style

Hopur P, Chen W, Zhou Y, Zhou J, Wang T. The Correlation among the Atomic Structure, Electronic Valence Band and Properties of Zr-Cu-Al-Ag Bulk Metallic Glasses. Metals. 2023; 13(7):1181. https://doi.org/10.3390/met13071181

Chicago/Turabian Style

Hopur, Parida, Wenqi Chen, Yulong Zhou, Jialu Zhou, and Tuo Wang. 2023. "The Correlation among the Atomic Structure, Electronic Valence Band and Properties of Zr-Cu-Al-Ag Bulk Metallic Glasses" Metals 13, no. 7: 1181. https://doi.org/10.3390/met13071181

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