Molecular dynamics simulation of the crystal structure evolution of titanium under different Tdamp values and heating/cooling rates

doi:10.1016/j.cplett.2020.138187

Chemical Physics Letters

Volume 763, 16 January 2021, 138187

https://doi.org/10.1016/j.cplett.2020.138187 Get rights and content

Highlights

•
The S-shaped phenomenon appears in the diagram of potential energy vs temperature.
•
An optimization method is proposed to obtain suitable Tdamp value for simulation.
•
A new method is proposed to judge the melting point of metal.
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The lower cooling rate is beneficial to the crystallization of titanium atoms.

Abstract

Molecular dynamics (MD) was used to study the evolution of crystal structure of titanium (Ti) under different temperature damping parameter (Tdamp) values and heating/cooling rates. In the heating process, when the temperature reaches the melting point, the temperature of the system with lager Tdamp value decreases with the increase of average atomic potential energy. However, an increase in heating rate will cause the melting point to rise slightly. In the cooling process, a larger Tdamp value or a lower cooling rate is more conducive to the crystallization of Ti, which corresponding to the higher crystallization temperature.

Graphical abstract

Introduction

Titanium and its alloy have been widely used in aerospace, marine and medical fields due to their high strength ratio mechanical properties, excellent corrosion resistance and chemical compatibility [1], [2], [3], [4]. However, it’s poor materials-processing and components-manufacturing abilities for traditional manufacturing processing as known to all [5], [6]. Fortunately, the emergence of new technologies, such as metal additive manufacturing (AM) technology, will overcome the problems caused by the difficulty of material processing. AM relies on its unique processing characteristics controlling laser/electron beam to melt metal powder fast then solidify quickly, which can greatly improve mechanical properties of materials [6], [7], [8]. Hence, great attention has been drawn for AM in industries in recent years. Nevertheless, the challenge of directly observing metal rapidly melting and solidification process remains, let alone characterize the evolution of crystal structure. Thereby, a workable way is required to research the evolution of crystal structure of metals during the rapidly heating/cooling process.

Molecular dynamics (MD) provides us an effective way to study the evolution of metal crystal structure from atom scale, which has been widely used to research crystallization of materials during solidification [9], [10], [11], [12]. M. Azadeh et al.[13] utilized MD to study the distribution of surface energy and potential energy when the crystal structure of Pd nanoparticles transformation. S. Şerzat et al.[14] researched the evolution of the crystal structure of Ag-Cu-Ni ternary nanoparticles during heating/ cooling process by MD method. Furthermore, S. Kurian et al.[15] studied the nucleation and growth of nano-Al particles in the molten pool during selective laser melting via MD simulation.

Based on the research ideas of predecessors, we utilized MD to research the evolution of the crystal structure of Ti under different Tdamp values and heating/ cooling rates. The results show that the crystal structures have no obvious changes in the heating process, except for the sudden rise of disordered atoms ratio at the melting point. We believe that it will be another feasible way to judge melting point, where the ratio of disordered atoms rises suddenly. However, in the cooling process, the crystal structures show the great changes under different Tdamp values, which also appears in different cooling rates.

For the real situation of MD simulation, only one Tdamp value is suitable. Other values are not appropriate. In our work, four groups of Tdamp values were used to research the relationships between average atomic potential energy vs temperature and crystal structure ratio vs temperature. It is interpreted that the phenomenon of S-shaped change at average atomic potential energy vs temperature diagram during the heating process, which provides a reference to optimize Tdamp values to suit current simulation. Then, the optimized Tdamp value was utilized to research the evolution of crystal structure under different heating/cooling rates. The results show that a higher heating rate slightly rise the melting point of Ti. However, it’s more conducive to the crystallization of disordered atoms (type of Other) at a lower cooling rate. Besides, there are some FCC (face-centered cubic) crystal structures transforming to HCP (close-packed hexagonal) structures during the solidification process.

Section snippets

Interatomic interactions

We utilized the embedded atom model (EAM) provided by G.J. Ackland [16] to simulate. This EAM describes the anisotropy of the shear constant and the deviation of the c/a lattice parameter ratio from the ideal value, while maintaining a smooth monotonic function. Moreover, G.J. Ackland (1987) and Finnis (1988) insisted that the potential energy function could be used for molecular dynamics simulation at finite temperature [16]. Compared with other EAM provided by M.I. Mendelev [17] and R.G.

Influence of Tdamp values on crystal structure evolution and the melting point

The melting point is one of the important properties of metal materials, and is related to the first-order phase transition [20], [21], [22]. Crystalline materials undergo phase transitions to disordered state at the melting point when being heated [22]. Thereby, the structure evolution of the crystal can be used to research its melting behavior in the heating process. An increase of potential energy will happen between atoms during the heating process when the crystal structures transform to

Conclusions

In this work, MD was used to study the structural evolution of Ti atoms under different Tdamp values and heating/cooling rates. A series of simulations has been performed and the following results are summarized.

(1)
It is found that the atoms in a larger Tdamp value system are heated to the melting point, due to the insufficient energy supplied from the heater which causing the kinetic energy of system decrease, and a phenomenon of S-shaped potential energy jump will appear in the potential energy

CRediT authorship contribution statement

Juze Jiang: Writing - original draft, Conceptualization, Software, Formal analysis, Visualization. Xiaoxun Zhang: Resources, Supervision, Funding acquisition. : . Fang Ma: Supervision, Funding acquisition. Sensen Dong: Project administration, Visualization. Wei Yang: Methodology. Minghui Wu: Software, Methodology.

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.

Acknowledgements

This work was financially supported by National Natural Science Foundation of China under Grant No. 51805313 and Industry-University-Research Collaboration Project between Shanghai University of Engineering Science and PMG 3D Technologies (Shanghai) Co., Ltd.

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Research paperMolecular dynamics simulation of the crystal structure evolution of titanium under different Tdamp values and heating/cooling rates

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Interatomic interactions

Influence of Tdamp values on crystal structure evolution and the melting point

Conclusions

CRediT authorship contribution statement

Declaration of Competing Interest

Acknowledgements

Appl. Surf. Sci.

Mater. Sci. Eng., A

Acta Biomater.

Comput. Mater. Sci.

J. Alloy. Compd.

Met. Powder Rep.

Mater. Lett.

Mat Sci Eng a-Struct

J. Non-Cryst. Solids

J. Non-Cryst. Solids

Comput. Mater. Sci.

Comput. Mater. Sci.

Addit. Manuf.

J. Non-Cryst. Solids

J. Alloy. Compd.

Comput. Mater. Sci.

Ceram. Int.

Research paper
Molecular dynamics simulation of the crystal structure evolution of titanium under different Tdamp values and heating/cooling rates