Atomic Structure Of Ternary Fe-Nb-B Liquid And Amorphous Alloys Analyzed By Ab-initio Molecular Dynamics

Amorphous alloy is a new material with unique properties.The long-range disorder and short-range order atomic structure of this material is of scientific interest.Study on the atomic structure of amorphous alloys helps to understand and explain their properties.Fe-based amorphous alloys are one of the most applicable alloys in the field of industry.Compared to metal-metal-based amorphous alloys,Fe-based amorphous alloys possess more complex atomic structure due to other metalloid element composition.Ab initio molecular dynamic(AIMD)simulation was employed to study the atomic structure of binary Fe80B20 and ternary Fe90-xNb10Bx(x= 10,20,30)alloys in liquid and amorphous state and the structure evolution during cooling process.The difference in glass forming ability and crystallization process of these alloys were discussed based on these results.The basic structure of clusters have already formed in binary Fe80B20 and ternary Fe90-xNb10Bx(x=10,20,30)melts and the difference in local atomic structure of these four melts exist here,which have influence on dynamic properties of atoms,thereby resulting in different glass forming ability.From the study of atomic structure of binary Fe80B20 and ternary Fe90-xNb10Bx(x= 10,20,30)amorphous alloys,it was found that the degree of order for the structure of alloys in amorphous state is more than that in liquid state,however the difference in coordination number is small.Icosahedral-like cluster<0 1 10 2>centered by Fe atoms has the largest fraction in these four amorphous alloys while bcc-like cluster<0 3 6 4>centered by Fe atoms dominate in structure of four melts.The clusters centered by B atoms are prism-like.<0 2 8 0>clusters dominate in Fe80Nb10B10 amorphous alloy with less B content.<0 3 6 0>clusters are more likely to dominate in amorphous alloys with high B content.Meanwhile,the results of bonding preference indicate that B atoms prefer to link with Nb atoms.The different local structure around B atoms and its bonding preference may has some correlations with their different crystallization modes and glass forming ability.The short range order atomic structure can be found during cooling,whereas the atomic distance remains unchanged,which can be obtained from a series of pair correlation functions of four alloys during cooling process.The content of B atoms affects the evolutional trend of local structure around B atoms.Moreover,the content of B and the addition of Nb atoms make the structure more inhomogeneous and complexed.More kinds of clusters form in melts and compete with each other.The fierce competition between different clusters contributes to good glass forming ability of system.The density of states(DOS)of binary Fe80B20 and ternary Fe90-xNb10Bx(x=10,20,30)amorphous alloys were also calculated and reveal that the electronic structure does not change too much with different composition and the addition of Nb atoms does not have apparent influence in DOS of binary Fe-B amorphous alloy.The charge densities between Fe-Fe,Fe-Nb,Fe-B,Nb-Nb,Nb-B,B-B indicate that only Fe-B and B-B bonds exhibit covalent character.Simulation considering electrons’ spins was conducted and the results show that the structures with or without spin polarization only have small difference.