近共晶成分Ni-P非晶合金的微結構特征分析

近共晶成分Ni-P非晶合金的微結構特征分析An Exact Analysis for Local Atomic Structures of Amorphous Ni-P Alloys with Near-eutectic Compositions

采用分子動力學方法模擬了液態(tài)金屬Ni100-xPx (x=19.0, 19.4, 19.6, 19.8, 20.0, 21.0)合金在冷速為5×1012K/S下的快速凝固過程，并采用Voronoi多面體指數?n_3,n_4,n_5,n_6 ?和團簇類型指數(Z n_i?(ijkl)_i …)對其局域原子結構進行了表征。結果發(fā)現：Ni原子的團簇屬性主要是高配位（Z≥12）的Frank-Kasper團簇及其變形結構，典型的化學短程序為NiZ-2P3，基本團簇間可通過IS聯結形成中程序結構；而P原子的局域結構除了Z=10的BSAP多面體外，還存在大量高配位（特別是Z=12）的Frank-Kasper結構形態(tài)，典型的化學短程序為Ni12P；并且，P芯基本團簇的殼層原子全部為Ni，其間只能通過VS、ES和FS聯結形成擴展團簇。BSAP多面體及其相關結構被證實對Ni100-xPx非晶合金的形成具有重要影響，其數量在共晶點x=19.6時最多，偏離共晶點越遠，所占比例越小，其結果與不同濃度下Ni100-xPx合金非晶形成能力的變化趨勢一致。這也許就是Ni-P合金在共晶點具有最強非晶形成能力的原因。

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 300K are characterized by Voronoi polyhedron index ?n_3,n_4,n_5,n_6 ? and cluster type index (Z n_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 BSAP polyhedrons, but lots of Frank-Kasper 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 related structures to all P-centered clusters, which is consistent with the variation tendency of glass forming abilities (GFAs) of Ni100-xPx alloys. Maybe, it should be responsible for the existence of the strongest GFAs at the eutectic composition point of Ni100-xPx alloys.

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