Molecular Dynamics Simulation Of Microstructure And Crystallization Behavior Of Zr-Al-Ni-Cu Amorphous Alloys

Amorphous alloys have a unique atomic stacking structure compared to traditional crystalline metals,thus exhibiting better mechanical properties and excellent physical and chemical properties.The difficulties in the preparation of bulk amorphous alloys have limited the development and application of amorphous alloys,and welding can break this restriction.However,during welding,it is easy to occur that the atomic structure changes from long-term disorder to long-term order crystallization,and the brittle and hard crystallization phase will make the amorphous lose its original excellent properties.In this paper,aiming at the crystallization phenomenon in the welding process of amorphous alloys,a three-dimensional atomic stacking model of Zr based amorphous alloys was established by molecular dynamics(MD)simulation method.The atomic stacking structure evolution process of Zr-Al-Ni-Cu and Zr-Al-Ni-Cu-Fe amorphous systems under different conditions was analyzed by radial distribution function,nearest neighbor coordination number,HA bond type index,Voronoi polyhedron cluster and other methods,The electronic structure of the cluster was analyzed,and then the crystallization phenomenon was analyzed.The specific research contents and main conclusions include the following aspects.Firstly,a brief understanding of the amorphous structure of Zr-Cu-Al was given.At the same time,the modeling method and process of Zr-Al-Ni-Cu amorphous alloy are introduced,and the potential function is optimized from the aspects of glass transition temperature,radial distribution function,elastic modulus,etc.The results indicate that the EAM combination potential has high accuracy and strong applicability in describing the Zr-Al-Ni-Cu amorphous alloy system.A four component Zr-Al-Ni-Cu amorphous alloy model was constructed based on the EAM combination potential,and the crystallization behavior of this component amorphous alloy under different conditions was studied.The results indicate that the degree of order of the amorphous increases during the cooling process,forming a glassy structure.In the Zr-Al-Ni-Cu system amorphous,the dense stacking structure dominated by CN=14 accounts for the most,with a large number of icosahedron structures and a high atomic stacking density.Moreover,the higher the content of Zr atoms,the higher the order of the atomic short range structure.Among them,Zr50Al12.5Ni12.5Cu25 amorphous alloy has the highest degree of amorphization and the strongest glass forming ability.In addition,the simulation results of the annealing process indicate that annealing treatment can cause an increase in the density of amorphous structure atoms.The annealing temperature is not sensitive to changes in bond pairs and polyhedral clusters,and the longer the annealing time,the smaller the density of amorphous alloy atoms and the more stable the structure.Secondly,a model of Zr-Al-Ni-Cu-Fe amorphous alloy was established and its atomic stacking structure under different conditions was studied.The results show that the close packed structure dominated by CN=15 accounts for the largest proportion in the Zr-Al-Ni-Cu-Fe system amorphous,and the glass transition temperature of Zr50Al10Ni10Cu20Fe10 amorphous alloy is about 1000 K.When cooled to this temperature,the atomic stacking structure of the amorphous has changed greatly.With the cooling process,the close packed structure of icosahedron becomes more and more,and the glass forming ability of the amorphous increases.The results of MSD analysis show that A1 atom is the main factor causing the change of icosahedron structure content in Zr50Al10Ni10Cu20Fe10 amorphous system at lower temperature.At the same time,the atomic stacking structure of Zr-Al-Ni-Cu-Fe amorphous alloys with different compositions shows that with the increase of Fe atom content,the denser the amorphous system is,the less likely crystallization reaction will occur.In addition,a short high temperature thermal action time will not cause changes in the short-range structure of amorphous atoms,while the pressure has a significant impact on the short-range structure of amorphous atoms.Increasing the pressure will increase the atomic stacking density and shortrange order of amorphous systems,but too high the pressure will cause distortion of icosahedron cluster atoms,and reduce the dense structure inside the amorphous.Finally,the electronic structure information of Zr50Al12.5Ni12.5Cu25 and Zr50Al10Ni10Cu20Fe10 amorphous clusters,such as XRD,density of states,atomic population and charge density,were studied.The results show that the Zr50Al12.5Ni12.5Cu25 amorphous cluster has a lower density of states at the Fermi level,a more stable structure,and strong bonding between Zr atoms and Al,Ni,and Cu atoms in the cluster,which shows that Zr atoms lose electrons and Cu,Al,and Ni atoms gain electrons.The direction of electron transfer is from Zr atoms with lower electronegativity to Cu,Al,and Ni atoms with higher electronegativity.The differential charge density distribution of Zr50Al10Ni10Cu20Fe10 amorphous cluster shows that the electrons of Zr and Al atoms are transferred to Cu,Ni and Fe atoms,and the interatomic interaction is more complex.In this paper,molecular dynamics simulation method is mainly used to study the crystallization behavior of amorphous alloys at the atomic scale,revealing the universal characteristics of the atomic distribution of amorphous alloys,studying the crystallization behavior and crystallization dynamics characteristics of amorphous alloys from the aspects of local structure and atomic stacking,and discussing the evolution law of local structure of amorphous alloys under different conditions,providing a theoretical basis for the atomic stacking mechanism in amorphous alloys.At the same time,it provides theoretical guidance for the study of crystallization behavior in amorphous welding.