Molecular Dynamics Study On Plastic Deformation Anisotropy Of CuZr Metallic Glasses

Metallic glass is an amorphous solid material with special mechanical properties due to its special structure,such as higher strength,hardness and good elastic deformation ability,which has great application potential in engineering field.However,the excellent properties of metallic glass are limited by brittle fracture.Macroscopically,brittle fracture appears in the form of shear band.Once the shear band is formed,it will expand rapidly until the material breaks and fails.Microscopically,the formation and propagation of shear band can be regarded as plastic deformation elements,which are interrelated in space.Although a lot of research work has been carried out on the spatial correlation of plastic deformation of metallic glass,there are still differences on the decay of plastic correlation so far,which needs to be further explored and improved.Studying the plastic correlation characteristics of metallic glass is helpful to master its deformation characteristics,which is directly related to the practical application of this kind of material in engineering.In this paper,molecular dynamics simulations are used to study Cu Zr metallic glasses.The main research works are as follows:(1)In this work,molecular dynamics simulations of the shear deformation of Cu Zr metallic glasses are performed under two different conditions: one is the athermal quasistatic shear(AQS)condition and the other is the room temperature shear(RT)condition.Here,we focus on the decay form of plastic correlation,and quantitatively characterize the plastic correlation characteristics of these two different plastic metallic glasses through spherical harmonic projection function,as well as the relationship between plastic deformation and static structure.The results show that AQS samples have higher strength and brittleness,and form shear bands under larger shear strains.The critical strain and the width of shear bands show significant finite size effect.The formation of shear band directly leads to the anisotropic decay of plastic correlation,which is exponential decay in the direction perpendicular to the shear band,but power-law decay in the direction parallel to the shear band.After the shear band is formed,the plastic correlation shows obvious polar symmetry and weak quadruplar symmetry in space.There is a relationship between static structural anisotropy induced by shear force and plastic deformation.Generally,the anisotropy of static structure is more obvious in the area with large plastic deformation.Under the influence of thermal fluctuation,the plastic deformation distribution of RT samples are more uniform,and the plastic correlation shows isotropic exponential decay as a whole.(2)The cyclic oscillatory shear of Cu Zr metallic glass with different shear amplitudes is carried out,and the spatial correlation characteristics of non-affine displacement field and stress field in the stable shear interval are analyzed.The results show that the plastic deformation of the smallscale samples is uniform,and the plastic correlation is isotropic exponential decay.Under larger shear amplitudes,the plastic deformation of largescale samples is highly concentrated in the shear band,the plastic correlation shows obvious polar symmetry and weak quadruplar symmetry,and shows power-law decay along the direction of the shear band.The correlation of the stress field is not affected by the shear band,and its decay form conforms to the long-range power-law decay and shows a quadruplar symmetrical distribution.