Atomistic Simulation for Local Atomic Structures of Amorphous Ni-P Alloys with Near-Eutectic Compositions
C Peng and Y Li and YH Deng and P Peng, ACTA METALLURGICA SINICA, 53, 1659-1668 (2017).
Ni100-xPx alloys with near-eutectic compositions have a strong glass forming ability (GFA), but the microstructure prototypes and their evolution in various solidification processes are still unclear now. To reveal their unique structures, 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 were performed at a cooling rate of 5x10(12) K/s, and their local atomic configurations at 300 K were characterized by Voronoi polyhedron index < n(3), n(4), n(5), n(6)> and cluster type index (Zn-i/(ijkl)(i)...). The results show that the local atomic structures of Ni atoms are mainly Frank-Kasper clusters with high coordination (Z >= 12) 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 majority of P-centered clusters are bi-capped square Archimedean anti-prism (BSAP) polyhedrons, but lots of FrankKasper clusters with higher coordination exist in the amorphous Ni100-xPx alloys. Their typical chemical short- range orders are Ni12P. 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). The BSAP polyhedrons and their correlative structures play a crucial role in the formation of amorphous Ni100-xPx alloy. Their quantity is demonstrated to have a significant impact on the glass transformation of rapidly solidified Ni100-xPx alloys. It is found that the number of BSAP polyhedrons and their 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 structures more related to all P-centered clusters, which are consistent with the variation tendency of GFAs of Ni100-xPx alloys. Maybe, it could be responsible for the existence of the strongest GFAs at the eutectic composition point of Ni100-xPx alloys.
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