The Study Of The Structure And Property Of The Co-based Amorphous Alloys By First-principle Simulation

In this paper,Co-based amorphous alloys were studied by computer simulation.The main work includes two parts.In the first part,the atomic structures of Co-based(Co80P14B6,Co80P13C7 and Co80B14C6)amorphous alloys are studied by ab initio molecular dynamics(AIMD)simulations,so that the effects of metalloid elements on the glass forming ability(GFA)and magnetic properties of cobalt-based amorphous alloys can be investigated.We have analyzed the local atomic structures in the liquid(at 1600 K)and glass state(at 300 K)by pair distribution functions(PDFs),Voronoi Polyhedra(VPs)and bond pair(BPs)analyses.The VPs and PDFs analyses suggest that the GFA of the three Co-based alloys increases in the order of Co80B14C6,Co80P13C7 and Co80P14B6.At the same time,the most dominated cluster for P atoms is icosahedral-like in the three Co-based alloys,suggesting that P atom has the similar environment with Co atoms or locate at the substitute position of Co atoms.And the BPs analysis uncovers that the three Co-based amorphous structures are mainly composed of perfect and distorted icosahedral BPs such as 1541,1551 and 1431.Based on the density of state(DOS)analysis,we also have calculated the contribution of Co atoms and metalloid elements(B,P,C)to the average magnetic moment of the three Co-based amorphous alloys.The analysis of DOS reveals that all the three Co-based amorphous alloys present the same weak ferromagnetism,and the major magnetization is dominated by Co 3d states.The metalloid elements of B,C and P present the similar average magnetic moments in the three Co-based amorphous alloys.The second part work can be divided further into two small parts.(1)The effects of the metalloid element B content on the local structure and mechanical properties of cobalt-based amorphous alloys(CoTaB and CoNbB)are studied by AIMD simulation.According to the simulation results,the addition of B makes the number of <0 3 6 0> increasing significantly,and also increases the number of covalent bonds between Co-B and B-B,which may result in larger strength of the amorphous alloy.(2)The effects of the transition elements M(M=Ta,Nb and Mo)on properties and strength of CoMB amorphous alloys are investigated by AIMD simulation.Based on the simulation results,the addition of Ta and Nb leads to the increase of the atomic probability on the first shell of Co atoms,and meanwhile makes the short-range order of CoTaB and CoNbB amorphous alloys stronger compared with CoMoB amorphous alloy.Secondly,we also found a certain medium-range order in the three Co-based amorphous alloys,and such the medium-order order is closely related to <0 3 6 0> cluster,which are prevalent in the three Co-based amorphous alloys and is very likely to have a significant impact on the strength of the three alloys.