Correlation Between The Atomic Structure And Mechanical Properties Of Phase-separated Cu₅₀Ag₅₀Glass

Although the phase-separated metallic glass has been reported in literature,its relationship of atomic structure and mechanical properties is still open to date.In this thesis,molecular dynamics(MD)simulation based on embedded atom method(EAM)potentials are performed to explore the plastic deformation mechanism of phase-separated glass Cu50Ag50 metallic glass during the compression and tension deformation,and its dynamic mechanical properties.Our finding indicates that the homogeneous atom pairs show stronger interaction than that of heterogeneous atom pairs in Cu50A50glass,which also shows higher plastic deformation ability and same deformation mechanism under compression and tension deformation.The degree of phase separation increases with increasing compression and tension deformation.Ag atom undergo flow deformation preferentially,which shows higher Voronoi volume and potential energies and larger local shear strain than Cu atom,then shear bands extend along the Ag-rich region,and form a network of interpenetrating shear bands.eventually start to propagate through the Cu-rich region.It is can be speculated that pentagon-rich clusters,which connect back-bone,can resist shear transformation.Voronoi volume and potential energy of Ag atom in the entire region keep unchanged during plastic deformation period because of the release of elastic energy and atom arrangement;while it increases for Cu atom due to its resistance to the shear transformation in this case.And in our case,the resistance to shear deformation of Cu atoms under tension strain is stronger than that under compression strain.The dynamic mechanical analysis of Cu50A50 amorphous alloy was analyzed.It is found that the inelastic deformation occurs in the liquid-like region with loose inner arrangement under the action of strain,and the flow in the liquid-like region consumes energy and leads to mechanical hysteresis,w-hich increases with the increase of temperature.The beta relaxation of Cu50Ag50 glass is shown excess tails in the loss modulus curve.When the temperature is low,the storage modulus increases with the increase of frequency;when the temperature is high,the change with frequency is opposite to that at low temperature,which may be caused by the crystallization behavior in the sample at high temperature and low frequency.The effects of mechanical strain and temperature on relaxation dynamics of samples are similar.Amorphous alloys are thermodynamically metastable and tend to crystallize under the influence of external temperature and strain.We studied the crystallization behavior of samples under different temperatures and amplitude and found that the crystal content increased with the increase of amplitude.When the temperature is lower than 500K,the crystal content increases with the increase of temperature,but when the temperature is higher than 500K,the crystal content decreases instead,which is because the atoms move violently under high temperature,the crystal nucleus is unstable,and the crystallization rate is limited.By studying the crystallization behavior of samples with a loading period of 200ps at 500K and an amplitude of 5%,we found that the crystallization origin was stress-induced,and the crystal nucleus was first generated in the Ag rich region,and then grew continuously,followed by the crystal structure in the Cu rich region.During the crystallization process,the fraction of crystalloid Voronoi polyhedra(0.3,6,3)(0,4,4,4)increases continuously,and the average atomic potential energy decreases continuously.Moreover,the change of Ag-centered polyhedron and the decrease of average potential energy of Ag atom are earlier than that of Cu atom,which is because the Ag rich region first forms the crystal structure in the crystallization process.