Molecular Dynamics Simulation Of Fast Surface Dynamics In Metallic Glass

Metallic glass,also known as amorphous alloy,has excellent physical,chemical and mechanical properties due to its long-range disordered atomic arrangement.As a nonequilibrium material,relaxation is an inherent characteristic of metallic glass.The study of relaxation dynamics of metallic glass is helpful to analyze its structure and explore its application.In recent years,it has been found that the surface of metallic glass has liquidlike behavior,showing fast dynamics.However,due to the difficulty in characterizing the microstructure of metallic glass,so far,the surface properties of metallic glass are not well understood.In this paper,molecular dynamics simulation is used to systematically analyze the dynamic behavior of Cu-Zr metallic glass during annealing.Combined with its microstructure,we obtained the unique dynamic behavior of the surface of Cu-Zr metallic glass.The main work of this paper is as follows:Firstly,the ?-relaxation time of each region of Cu-Zr metallic glass during annealing is analyzed quantitatively.It is found that the ?-relaxation time of the surface is much faster than that of the inner region.Through the further analysis of the motion forms of atoms,we find that the motion of atoms located on the surface is more intense and most of them show irregular diffusion,while the motion of atoms located in the body is obviously slowed down and shows string-like cooperative motion.In addition,by analyzing the displacement distribution of atoms in the surface and body at different temperatures,we find that the atoms in the surface region at lower temperatures and the atoms in the body region at higher temperatures have the same dynamic characteristics.These results show that the surface of metallic glass has fast dynamic behavior.At the same time,we found that when annealing below the glass transition temperature,the metallic glass appeared obvious crystallization at some temperatures.By analyzing the microstructure of Cu-Zr metallic glass,it is found that the crystallization of Cu-Zr metallic glass extends rapidly along the surface,and the surface growth rate is obviously faster than the bulk growth rate.Our results show that the surface crystallization of metallic glass is caused by its fast surface dynamics.Our work reveals some phenomena and basic laws of fast dynamic behavior of metallic glass surface,which provides a theoretical basis for further understanding of the surface,interface and low dimensional scientific problems of amorphous materials,and promotes the research and development of amorphous materials.