镍基非晶合金的结构和性质的第一性原理模拟计算

发布时间：2018-05-30 01:14

本文选题：镍基非晶态合金 + 第一性原理模拟　；参考：《新疆大学》2017年硕士论文

【摘要】：在本硕士论文中,我们运用第一性原理从头算分子动力学计算机模拟的方法对Ni_(80)(P,B,C)_(20)非晶态合金以及含Ni的Fe_(80)P_(13)C_7非晶态合金进行了研究,主要工作包括以下两个部分。(1)为了研究类金属元素(P,B,C)对Ni基非晶态合金的原子排布结构以及玻璃化形成能力的影响,我们选取三个典型的Ni基非晶态合金,即Ni_(80)P_(14)B_6,Ni_(80)B_(14)C_6和Ni_(80)P13C7,作为研究对象,对这三个合金从1800K逐步降温至300K的过程进行分子动力学计算模拟。双体分布函数分析结果表明,Ni_(80)P_(14)B_6和Ni_(80)P13C7这两个非晶态合金中的Ni-P和Ni-C键的键强比Ni_(80)B_(14)C_6中Ni-B键要大,并且P-P,P-B,P-C和C-C键相互吸引,这有利于合金的玻璃化形成能力。相反,在Ni_(80)B_(14)C_6非晶态合金中,B-B键和B-C键有相互排斥的倾向,这不利于非晶态合金的玻璃化形成能力。通过Voronoi多面体分析技术,我们发现P原子有两种占位方式,一种在反棱柱团簇的中心,另一种是在Ni原子的替换位置。相比于Ni_(80)P13C7,Ni_(80)P_(14)B_6非晶态合金中有更多以P原子为中心的类二十面体团簇,导致了更为复杂的溶体结构,这对玻璃化形成能力是有利的。通过以上分析,我们得到的结论是,这三种合金的玻璃化形成能力按照Ni_(80)P_(14)B_6,Ni_(80)P13C7和Ni_(80)B_(14)C_6的顺序依次降低。(2)我们对Fe_(80)P_(13)C_7和Fe50Ni30P13C7非晶态合金进行了第一性原理模拟计算,基此调查Ni的添加导致Fe_(80)P_(13)C_7块体非晶态合金塑性得到很大提高的原因。结果表明,Fe_(80)P_(13)C_7非晶态合金中以类二十面体团簇结构为主;而Fe50Ni30P13C7非晶态合金中阿基米德反棱柱团簇的比例明显升高,即五次对称性降低。相较于其它的原子配位方式,五次对称结构的排列使体系更致密,具有更高的构型转换障碍,因而更难发生剪切转变。因此,从短程有序中五次对称性的数量来看,模拟计算结果说明Ni的添加将导致Fe_(80)P_(13)C_7非晶态合金塑性的提高。进一步,通过电荷密度图可以看到,Fe_(80)P_(13)C_7合金中的金属-类金属元素之间电荷密度大于Fe50Ni30P13C7合金,这意味着,相比于Fe50Ni30P13C7,Fe_(80)P_(13)C_7非晶态合金中金属-类金属元素间的键合有更多的共价键特性。相比于金属键合,共价键的强度较高,这使得合金的剪切模量升高,泊松系数减小,剪切流动阻碍变大,从而导致非晶态合金的塑性变差。并且,共价键的定域性很强,当块体非晶态合金受到足够大的应力迫使原子间发生相对位移时,将破坏它们之间的共价键键合,从而使材料发生断裂。因此,从键合特性的角度考虑,模拟计算的结果同样表明Ni的添加将导致Fe_(80)P_(13)C_7中非晶态合金塑性的提高。
[Abstract]:In this master's thesis, we use the first-principle ab initio molecular dynamics computer simulation method to study the amorphous alloy and the Fe_(80)P_(13)C_7 amorphous alloy containing Ni. In order to study the effect of the metal-like element PbBCon on the atomic arrangement and glass-forming ability of Ni-based amorphous alloys, we select three typical Ni-based amorphous alloys. The main work is as follows: 1) in order to study the effect of the metal-like elements on the atomic arrangement and glass-forming ability of Ni-based amorphous alloys, we select three typical Ni-based amorphous alloys. That is, Nitiao 80 / PX / P / T / C / C / C / C / C / C / C / T / C / C / C / C / C / C / C / C / C / C / C / C / C / C / C / C / C / C / C / C / C / C / C / C / C / C / C / C / T / C / C / C / C / C / C / C / C / C The results of the analysis of the catamorphic distribution function show that the bond strength of the Ni-P and Ni-C bonds in the two amorphous alloys, NII _ S _ T _ (80) P _ (+) _ (14) S _ (6) and Ni_(80)P13C7, is larger than that of the Ni-B bond in Ni_(80)B_(14)C_6, and that the bond is attracted to each other by the P-P _ (P) -B _ (P) -P _ (P-C) and C-C bond, which is beneficial to the glass-forming ability of the alloy. On the contrary, there is a tendency of mutual repulsion between B-B bond and B-C bond in Ni_(80)B_(14)C_6 amorphous alloy, which is not conducive to the glass forming ability of amorphous alloy. By means of Voronoi polyhedron analysis, we find that there are two kinds of occupation modes of P atom, one is in the center of antiprism cluster, the other is in the substitution position of Ni atom. There are more icosahedron clusters centered on P atoms in the amorphous alloys than in Nitig / T / P _ (80) P _ (13) C _ (7) / Ni / T _ (80) P _ (14) B _ (6) amorphous alloys, which leads to a more complex solution structure, which is beneficial to the glass-forming ability. From the above analysis, it is concluded that the vitrification capacity of the three alloys is reduced by the order of Nis / T / P / P / T / P / T / P / T / P / T / P / T / T / P / T / P / T / T / P / C / C / C / C / Ni_(80)B_(14)C_6.) We have carried out first-principles simulation calculations for Fe_(80)P_(13)C_7 and Fe50Ni30P13C7 amorphous alloys. Therefore, the addition of Ni can improve the plasticity of Fe_(80)P_(13)C_7 bulk amorphous alloy. The results show that the structure of icosahedron cluster is dominant in the C7 amorphous alloy, while the ratio of the archimedean antiprism cluster in the Fe50Ni30P13C7 amorphous alloy increases obviously, that is, the fifth symmetry decreases. Compared with other atomic coordination modes, the arrangement of quintic symmetry structure makes the system denser and has higher barrier of configuration transition, so it is more difficult to take place shear transition. Therefore, according to the number of five-order symmetry in short-range order, the simulation results show that the addition of Ni will lead to the improvement of the plasticity of Fe_(80)P_(13)C_7 amorphous alloy. Furthermore, it can be seen from the charge-density diagram that the charge density between metal-like elements is greater than that of Fe50Ni30P13C7 alloys in the Festav / PSC-13C7 alloy, which means that there are more covalent bonding properties between metal-like elements than Fe50Ni30P13C7FeS-1 P13C7 amorphous alloys. Compared with metal bonding, the strength of covalent bond is higher, which leads to the increase of shear modulus, the decrease of Poisson coefficient and the increase of shear flow hindrance, which leads to the plasticity of amorphous alloy becoming worse. Moreover, the covalent bond is very local. When the bulk amorphous alloy is subjected to enough stress to force the relative displacement between atoms, the covalent bond between them will be destroyed and the material will be broken. Therefore, from the point of view of bonding properties, the simulation results also show that the addition of Ni will lead to the improvement of the plasticity of Fe_(80)P_(13)C_7 amorphous alloys.
【学位授予单位】：新疆大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG139.8

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