Molecular Dynamics Study On The Relationship Between Structure And Dynamic Properties Of Cu₅₀Zr₅₀ Melt

Molecular dynamics(MD)simulation has been performed to explore the correlation between dynamic characteristics and structural heterogeneity in undercooled Cu50Zr50 melt based on the embedded atom method.It is found that atoms in the undercooled liquid can be classified into three groups in terms of the probability distribution of atoms' displacement,named 'fast atoms'(FAs),'intermediate atoms'(IAs),'slow atoms'(SAs).Meanwhile,the undercooled liquid can be divided into three temperature regime:as the temperature is higher than 1120K,the distribution of FAs become network connectivity,in which the SAs region are surrounded;as the temperature is in the range from 1120K to 900K,the network of FAs region decompose into several isolated region gradually;after that the single relaxation separates into ?-and ?-relaxation at temperature lower than 900K,the FAs region become isolated islands,while the SAs have connected into networks where the FAs regions are surrounded,which cause the significant decreasing of atomic mobility and sharp increasing of the relaxation time.The FAs,located in loose packaging and isolated region,which corresponds to ?-relaxation reflected by the time-scale of intermediate plateau in mean-squared displacement(MSD)and intermediate scattering function(ISF).The SAs which develop into the backbone of the system and surround clusters formed by FAs,are responsible for the glass formation and have a connection with ?-relaxation.The compressive deformation in the CusoZrso metallic glass shows that the 'fast atoms',anticipating in ?-relaxation of undercooled liquid,mostly are located in large shear strain zones.Since metallic glass(MG)can be regarded as frozen undercooled liquid,our study is helpful for understanding the structural origins of dynamical relaxation in MGs.The atomic structures and dynamic property of Cu50Zr50 and Cu46Zr46Als metallic glass-forming liquid have been investigated by molecular dynamic simulations.The addition of A1 increase the peak value of NGP under different temperatures,indicating that the metallic liquid become more disordered.The addition of A1 also enlarges the population of full icosahedra and other Voronoi polyhedrons with high five-fold local symmetry,while Voronoi polyhedrons with low five-fold symmetry decrease.It can be concluded that Al atoms contribute to dense cluster packing.Meanwhile,through the comparison of full icosahedra in both Cu50Zr50 and Cu46Zr46Al8 metallic liquid,we find that the full icosahedra is more perfect without the addition of Al,but the interpenetrating between these full icosahedra is more complex in Cu46Zr46Al8 than in CusoZrso,which might be favor of medium-range order.We also studied the effect of pressure on dynamic relaxation and structural characteristics in CusoZrso metallic liquid.High pressure play an important role in dynamic slowing-down and lead to the divergence of relaxation at high temperature.The relaxation time of Cu50Zr50 melt is longer in high pressure than in low pressure.From the relation between relaxation time and five-fold symmetry structure parameter W,it shows that the sensitivity of relaxation time to structure change is less in high pressure.The partial pair correlation function shows that the high pressure reduces the distance of neighbor atoms and favors dense packing.