Effect Of External Defects On The Deformation Behavior Of Metallic Glasses At The Atomic Scale

As a new structural material with great potential in the 21st century,due to the excellent physical properties such as the ultra-high strength and hardness,metallic glasses（MGs）have attracted much attention in the fields of national defense,aerospace and civil engineering.However,because of their special internal structures,the plastic deformations at room temperature of metallic glasses are easily localized,while the formed shear band will rapidly expand,resulting in the catastrophic failure of the material.In order to achieve a wider application of metallic glasses,it is necessary to understand the internal mechanism of their deformation behaviors,mechanical properties and microstructures,which is also one of the hot issues in the field of amorphous materials in recent years.At the same time,as an unavoidable pain point in the preparation and use of materials,external defects also have a profound impact on the deformation behavior of metallic glasses.It is found that a large number of studies have been carried out on the influence of external defects on the deformation behavior of metallic glasses,including the experimental and numerical simulation works.Nevertheless,people have not yet formed a unified understanding of the above scientific issues.Based on this,in this paper,effects of the external structural defects,including the notch and pore on the materials,on the deformation behavior of Cu₄₅Zr₄₅Al₁₀ metallic glasses under the uniaxial tension are systematically studied by the advanced molecular dynamics（MD）simulations.The correlations among the notch radius,pore size and distribution,together with the mechanical properties,shear band behaviors and microstructures of metallic glasses were discussed,and the corresponding explanations were given at the atomic scale.First,according to the MD simulations of the nano-notched MGs under the uniaxial tension,the yield strength of material shows notch strengthening with the increase of notch radius.On the other hand,with the increase of notch radius,the deformation behavior of metallic glasses can be clearly observed from the shear deformation caused by the single dominant shear band to the necking deformation at the intersected location of multiple shear bands.By analyzing the Voronoi volume of atoms and the evolution of icosahedral clusters through the tension deformation,it is found that the introduction of notches will increase the disordered degree of atomic structures among the shear band region in the plastic deformation of metallic glasses and reduce its structural stability.Finally,we also monitored the distribution of atomic displacement field during the deformation of MGs.Results show that the existence of notches will inhibit the generation of atomic displacement flow perpendicular to the loading direction,which results in the specific deformation behavior of MGs that forming a single dominant shear band losing the prerequisite.Secondly,according to the MD simulation results of nano-porous MGs under the uniaxial tension,the yield strength of MGs shows the weakening phenomenon of pore size.That is,with the increase of the pore size,the yield strength will get lower.At the same time,we also found that within a certain range of pores,larger pores can activate and produce more shear transformation zones（STZs）,thereby reducing the degree of strain localization in the plastic deformation of MGs.On the other hand,changing the distribution of pores in metallic glasses will lead to the change of the nucleation path of the shear band,that is,the shear band has a tendency to expand along the oblique direction of the pore connection.In terms of the influence of pore distribution on mechanical properties,pores in metallic glasses should be avoided to be distributed along the 45°oblique direction.By analyzing the stress state in the deformation,it is found that the maximum shear stress required for the shear band nucleation and continuous plastic deformation of metallic glasses is relatively smaller.Finally,the deformation behaviors of MGs with different external defects are analyzed and verified by using the energy criterion of deformation behavior of MGs.The results show that most of the energy stored in the material deformation is provided to the generation of shear bands in the plastic deformation of metallic glasses.In general,through the above molecular dynamics simulation process and the analysis of these results,the work of this paper provides a certain degree of theoretical guidance for understanding the influence of external defects on the deformation behavior of MGs.