| The dynamic properties and structures of miscible Cu-Zr and immiscible Cu-Ag alloys were investigated by means of molecular dynamics simulation using MEAM potential,and the dynamic mechanical properties of Cu-Zr and Cu-Ag amorphous alloys were also investigated.The above research is of great significance for the understanding of the nature of metallic glass,glass transition mechanism and deformation mechanism.The MSD is used to study on the dynamic characteristics.For the Cu-Zr system,when the temperature is below 1200K,the MSD curve appears on a plateau,the plateau becomes pronounced when the temperature is lower than 1200 K,but it is tiny for Cu-Ag system no matter how low the temperature is.And the Fs(q,t)function is the same trend as MSD.Meanwhile,the diffusion coefficient calculated by MSD of Cu-Zr is much less than that of Cu-Ag system.The process of platform is defined as beta relaxation,which shows that the Cu-Zr system has a more obvious beta relaxation than the Cu-Ag system.At the same time,the diffusion coefficient and relaxation time were fitted according to the MCT theory respectively,and the obtained Tc value are little difference,which shows the correlation between diffusion coefficient and relaxation time.In the Cu-Zr system,the number of the icosahedra clusters<0 0 12 0>and clusters with high local five-fold symmetry,such as<0281>and<0 2 8 0>,is much higher than that of the Cu-Ag system.In the Cu-Ag system,the polyhedron is mainly non-icosahedra clusters and crystal clusters,such as<0 3 6 3>,<0 3 6 4>and<0 2 8 2>.The icosahedra clusters and the icosahedra-like clusters can form the framework to block the atomic motion,and causing the atomic motion slowed down,the atomic diffusion coefficient decreased and the relaxation time increased.Therefore,the diffusion ability of Cu-Zr system is much lower than that of Cu-Ag system,and the amorphous forming ability is much larger than that of Cu-Ag system.The Relaxation time and local five-fold symmetry are comtirmed r?= ?0 exp(M/(1-W)? and the diffusion coefficient and local five-fold symmetry are also comfirmed D=A*(T*W)B,which reveals the intrinsic relation between the microstructure and the dynamics.The beta relaxation of Cu-Zr and Cu-Ag systems is shown excess tails in the loss modulus curve by studying on dynamic mechanical properties.However,the left part of the alpha relaxation peak of Cu-Ag system is higher than that of the Cu-Zr system,which indicates that the beta relaxation of Cu-Ag system is more likely to be activated than that of the Cu-Zr system.Structure reveals that the number of icosahedra clusters in Cu-Zr amorphous is much more than that of in Cu-Ag amorphous.We show that mechanical strain not only accelerates the relaxation dynamics of a model MG,but also modifies it in unique ways.Structurally,dynamical heterogeneity at the glass transition is gradually suppressed with increasing strain amplitude for the two systems.These findings emphasize the similar roles of strain compared with temperature on the relaxation dynamics.At the same time,the relationship between alpha relaxation and atomic motion and structure is studied,and we find that the primary(a)relaxation always takes place when the most probable atomic displacement reaches a critical fraction(?23%)for Cu-Zr and(?21%)for Cu-Ag of the average interatomic distance,irrespective of whether the relaxation is induced by temperature(linear response)or by mechanical strain(nonlinear),which is consistent with the results of the previous results.The relationship between the internal friction and the fast atom is found to satisfy a linear relationship,and the fast atom and the icosahedral clusters are mutually exclusive.The number of icosahedra clusters in the Cu-Zr system is much more than that of the Cu-Ag system,so the internal friction of the Cu-Zr system is far less than that of the Cu-Ag system. |
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