Quantitative analysis of structure evolution of Zr-Cu amorphous alloys caused by cooling rates based on atomic bond proportion
Graphical abstract
The changes in the atomic structure of Zr–Cu amorphous alloys caused by different cooling rates were studied by X-ray diffraction synchrotron radiation and molecular dynamic calculation. Results show that the content of high-strength Zr–Cu bonds increases, whereas those of Zr–Zr and Cu–Cu bonds decrease as the cooling rate decreases. The increase of high-strength atomic bonds leads to the increase of Young's modulus of Zr-Cu amorphous alloys. The lower cooling rate facilitates the formation of a more efficient atomic packing model, suggesting that more atomic bonds form in the system without increasing the number of atoms. The effect of cooling rate on the atomic structure and Young's modulus of Zr–Cu amorphous alloys with different components is proportional to the content of Zr–Cu bonds in the system as a whole.
Introduction
Amorphous alloys are a new type of material, in which atoms are arranged in a disorderly state. They were first produced in the 1960s by rapidly cooling molten metallic liquids [1]. Since then, a great deal of scientific research has been devoted to studying their various properties and applications [2], [3], [4]. The cooling rate is an important technical parameter in the preparation of amorphous alloys as it will directly affect the atomic structure and properties of metallic materials after solidification. Previously, the cooling rate was mainly used to judge the glass-forming ability of amorphous alloys, but its effect on the structure of amorphous alloys was rarely reported. Amorphous alloys have no periodic and directional long-range order, only a certain degree of short- and medium-range order; therefore, their atomic structure is difficult to characterize [5], [6], [7]. Previous research has provided a wide range of structural models. Among them, considering clusters as the basic building blocks or short-range order in the amorphous alloys is the most widely accepted. The center of the cluster is the solute atom surrounded by solvent atoms, and familiar cluster packing schemes contain efficient cluster packing on a cubic lattice [5], icosahedral packing in a quasicrystal [7], and self-similar packing of atomic clusters [8]. However, none of these models propose a specific parameter to characterize the amorphous structure. In our previous work, a simplified structural parameter, atomic bond proportion, that can establish a direct relationship with performance was proposed [9]. In the current work, the structures of Zr–Cu binary amorphous alloys made with different cooling rates are studied based on the new structural parameter.
Section snippets
Simulation calculation and practical experiment
The preparation process simulation of Zr40Cu60 amorphous alloy models with cooling rate values of 1e12, 5e12, 1e13, 5e13, 1e14, 5e14, and 1e15 K/s was carried out using the embedded atom method potential [10] supplied in LAMMPS [11]. The dimension of the model structures used in the calculations was 17.1 nm × 25.6 nm × 4.3 nm the in x, y, and z direction, respectively. The model was heated from 300 K to 2000 K at a constant rate of 10 K/ps. To keep the system in a natural state, the liquid
Results and discussion
The PDFs of the Zr40Cu60 amorphous alloy models obtained at different constant cooling rates are calculated, as shown in Fig. 2(a). The first peak of the PDF produces remarkable cleavage when the cooling rate is 1e15 K/s. The PDFs of the Zr–Cu system consist of three partial PDFs that are related to the Zr–Zr, Zr–Cu, and Cu–Cu pairs by superposition. The values of the first peak position r correspond to the average spacing between two adjacent atoms. A previous study [6] reported a radius of
Conclusion
The cooling rate has a remarkable effect on the atomic structure of Zr–Cu amorphous alloys. As the cooling rate decreases, the adjacent atomic clusters of single elements integrate with one another more closely, forming more high-strength Zr–Cu bonds. The increase of Zr-Cu bonds is the main reason for the increase of Young's modulus of Zr-Cu amorphous alloys. The effect of cooling rate on the atomic structure and Young's modulus of Zr–Cu amorphous alloys with different components is
CRediT authorship contribution statement
W. Zhao: Conceptualization, Methodology, Software, Writing - original draft. J.L. Cheng: Data curation, Visualization, Investigation. G. Li: Supervision, Writing - review & editing.
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 work was supported by Excellent Youth Foundation of Jiangsu Scientific Committee (BK20180106), Scientific Foundation of Nanjing Institute of Technology (CKJA201703 and JCYJ201809), and Opening Project of State Key Laboratory of Metastable Materials Science and Technology (201910).
Data availability statement
The data that support the findings of this study are available from the corresponding author upon reasonable request.
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