Probing the Microstructure in Pure Al & Cu Melts: Theory Meets Experiment.

Lin Song,Jingyu Qin,Yanmei Yang,Hui Li,Xiaohang Lin,Xuelei Tian

doi:10.3389/fchem.2020.00607

Lin Song, Jingyu Qin + Show 4 more

Open Access

https://doi.org/10.3389/fchem.2020.00607

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Abstract

In the present work, a new model of the atomic cluster structure, which is determined by metal Wulff construction with the crystal structure inside, is proposed to describe the structures of metallic melts. The shapes of the structures are determined by surface energies of different crystal plane groups, calculated from density functional theory (DFT), while the size is given by the pair distribution function (PDF) of the experimental high-temperature X-ray diffraction (HTXRD). Taking Aluminum (Al) and Copper (Cu) as the representative examples, we demonstrate that the simulated XRD curves from present models match the experimental results quite well, not only regarding the position and width of the peaks but also the relative intensity of the first and second peaks. These results indicate a successful model to describe the properties of metallic melts. The model also explains a main peak deviation phenomenon between the XRD of metallic melt and the solid ones in pure metal Al. Finally, a physical picture of metallic melt is given, which is mainly composed of atomic cluster structures and free atoms around them.

Highlights

Around the world, higher requirements have been put forward for metallic material use in areas such as energy conservation, environment protection, etc. (Zhang et al, 2014a,b)
The metallic melts are in the condition of thermodynamic equilibrium and the structural distribution is kept constant
Wulff construction can determine the shape of the atomic cluster, but what about the structures inside? Comparing the XRD results of solid and metallic melt, though the positions of peaks does not directly match, especially for Al, it is still obvious that the XRD curves of metallic melt are more or less related to the solid ones

Summary

Introduction

Higher requirements have been put forward for metallic material use in areas such as energy conservation, environment protection, etc. (Zhang et al, 2014a,b). Hardness, lighter weight, and other superior physical and chemical properties (like electrochemistry, catalysis) are commonly required (Alayoglu et al, 2008; Ahmad and Singh, 2015; Zheng et al, 2017). A deeper understanding of the structures of metal melts are essential for the design and production of many metallic materials. Both the solidification processes of casting metals and the glass transition processes of amorphous alloys begin with the metallic melts (Kita et al, 1994; Debenedetti Pablo and Stillinger, 2001; Ganesh and Widom, 2008; Pan et al, 2015). The microstructure and physical/chemical properties of metallic materials are determined by the compositions and structures of their melts. It is necessary to understand metallic melts clearly

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