An Atomistic Simulation For Local Atomic Structures Of Amorphous Ni-P Alloys With Near-eutectic Compositions

Ni100-xPx alloys have relatively large glass forming ability(GFA)among numerous transition metal-metalloid binary alloys.And can obtain amorphous alloy within a wide composition range(x=16.5-21.0)under the condition of rapid quenching.Therefore,it becomes an ideal research object of amorphous alloy.Ni100-xPx alloys has the strongest GFA at the eutectic composition point x=19.6,As we all known that there is a close relationship between GFA and local atomic configurations,it is likely to have some unique characteristic structure at the eutectic composition point,so it is very important to in depth investigate the microstructures of near-eutectic Ni-P amorphous alloy from atomic level.In this thesis,a series of molecular dynamics simulations for the rapid solidification process of liquid Ni100-xPx(x=19.0,19.4,19.6,19.8,20.0,21.0)alloys are performed at a cooling rate of 5×1012K/s,and their local atomic configurations at 300 K are characterized by means of pair distribution function,H-A bond type index method,Voronoi polyhedron index method and extended cluster type index method.The following provides the main contents of this thesis.(1)A molecular dynamics simulation study on the rapid solidification process of liquid eutectic Ni80.4P19.6 alloy at a cooling rate of 5×1012K/s is carried out using EAM potential.The results indicate that an obvious binding tendency exists between heterogeneous atoms in rapidly solidified solid,namely,Ni atoms tend to form bonds with P atoms,at the same time,P-P bond types are almost non-existent.1551,1541 and 1431 H-A bond pairs are dominant in amorphous solid,the increase trend of 1551 H-A saturated bond pair is more evident in the whole solidification process,the result shows that five symmetry has good stability,which may be beneficial to the stability of liquid structure during the cooling process.and local atomic configurations at 300K are characterized by Voronoi polyhedron index<n3,n4,n5,n6>and cluster type index(Z ni/(ijkl)l...)we conclude that numerous cluster types are found in eutectic Ni80.4P19.6 alloy system,the local atomic structures of Ni atoms are mainly Frank-Kasper clusters with high coordination as well as their distorted configurations.Their chemical short-range orders are mostly NiZ-2P3,and these basic clusters can be further aggregated into medium-range orders(MROs)by intercross-sharing(IS)linkages.The local atomic structures of P atoms are dominated by Frank-Kasper clusters with relative low coordination,Their typical chemical short-range orders are NiZP.In these short range orders(SROs)centered by P,all shell atoms are found to be Ni atoms,and no MRO can be detected except for their extended clusters linked by vertex-sharing(VS),edge-sharing(ES)and face-sharing(FS).(2)The rapidly solidified solids of Ni100-xPx(x=19.0,19.4,19.6,19.8,20.0,21.0)alloys are obtained by performing molecular dynamics simulations at a cooling rate of 5×1012K/s.Combining structural characterization methods,we found that the characteristic structures of the local atomic configurations around P atoms are BSAP polyhedrons and its deformed structures,and these structures play a crucial role in the formation of amorphous Ni100-xPx alloys.Their quantity is demonstrated to have a significant impact on the glass transformation of rapidly solidified Ni100-xPx alloys.It is found that the percent of BSAP and its deformed structures at eutectic composition point x=19.6 is the largest among Ni100-xPx alloys,and the farther x deviates from the eutectic composition point,the smaller the proportion of BSAP polyhedrons and their related structures to all P-centered clusters,which is consistent with the variation tendency of glass forming ability(GFA)of Ni100-xPx alloys.Maybe,it should be responsible for the existence of the strongest GFA at the eutectic composition point of Ni100-xPx alloys.