Study on the Process of the Structural Relaxation of Vacancy Clusters by the Visualizing Method with an MD Simulation

用分子动力学(MD)的计算机模拟方法研究了镍中空位的聚集态。这是为了研究辐照金属中空位聚集的原子过程。首先，通过一次辐照实验计算了pKa截面，以了解有多少个Frenkel对形成。其次，使用Dynamo VER进行了仿真。8.5通过实现嵌入式ATOM方法(EAM)的潜力来编写代码。首先，在1300K、1500K、1700K和1800K下对完美晶体进行加热，然后在(111)面上随机选择位置引入4个大小为10的三角形空位团簇。在输出的非常小的时间步长内进行了MD模拟，以观察空位运动的原子过程。结果表明，随着空位团簇的保持，空位团簇发生移动和聚集。因此，空缺不会从一个集群中蒸发出来，被一个更大的集群吸收。空位团的聚集经历了三个不同的过程。一种是空位的四面体结构中的原子移动到另一个晶格位置。另一种是空位的六面体结构中的一个原子移动到了另一个晶格位置。另一个是一个原子沿着一排移动。单空位的迁移能为1.13 eV(=E_m)，小空位簇的迁移能为0.4 eV(3V)。17V团簇和单个空位的结合能为0.8 eV=E_b，因此单个空位从团簇蒸发的能量为E_m+E_b=1.93 eV，这意味着空位不会从团簇中蒸发。

Computer simulations of molecular dynamics (MD) were used to study the clustering of vacancies in nickel. This is to investigate the atomistic processes of vacancy agglomeration in irradiated metals. First, PKA cross section was calculated to know how many Frenkel pairs form by an irradiation experiment. Next, simulations were carried out with DYNAMO ver. 8.5 code by implementing the potential of the embedded atom method (EAM). First, the perfect crystal was thermalized at 1300K, 1500K, 1700K and 1800K.Then, four triangular vacancy clusters whose sizes were 10 were introduced on (111) planes at randomly selected positions. MD simulations were performed in a very small time step of outputs to observe the atomistic processes of the movement of a vacancy. It was found that vacancy clusters moved and agglomerated with keeping the cluster. Thus a vacancy did not evaporate from a cluster to be absorbed in a larger cluster. There were three different processes in an agglomeration of vacancy clusters. One was an atom caged in a tetrahedral structure of vacancies moved to another lattice site. Another was an atom caged in a hexahedral structure of vacancies moved to another lattice site. The other was an atom moved along a <110> row. The migration energy was 1.13eV(=E_m) for a single vacancy and 0.4eV for a small vacancy cluster (3v). The binding energy of 17v cluster and a single vacancy was 0.8eV=E_b. So the energy for a single vacancy to evaporate from a cluster was E_m+E_b=1.93eV.Therefore it means that a vacancy does not evaporate from a cluster.