Fe-Al体系扩散相关性质的研究

发布时间：2018-10-25 11:46

【摘要】：扩散过程与原子随机的热运动有关,这些热运动能产生宏观的浓度分布变化。研究扩散过程可以提供许多有关材料的原子结构以及缺陷演变过程相关的有用信息。扩散与材料的制备、热处理、以及蠕变过程都有密切关系。铁和铝都是工业生产中的重要原材料,在建筑、汽车、航天航空等领域都有广泛的应用。研究铁、铝的扩散性质,有助于了解这两种不同晶体结构金属的扩散微观机制,且对改善材料性能、改进材料锻造工艺等有重要指导意义。本文通过分子动力学方法,采用嵌入原子相互作用势(EAM)对Fe和Al扩散过程进行了模拟。得到的结果与已有的理论的结果以及实验值符合得较好,计算结果也表明铁和铝的自扩散主要通过空位机制进行。论文的主要结果如下：用静力学方法比较Fe、Al中不同结构的空位和自间隙原子点缺陷形成时所需的能量,得到Fe、Al中最稳定的空位和自间隙原子结构。并用NEB方法计算了这些结构经不同路径跃迁所需克服的势垒大小,结果显示空位跃迁到第一近邻位置的激活能最低,是自扩散中最可能发生的跃迁机制。再在Fe、Al块体中引入空位缺陷对其自扩散进行分子动力学模拟,得到的扩散系数与实验值符合得很好。除了空位和间隙原子这两种最简单的缺陷,杂质原子是实际材料中一种不可避免的缺陷。考虑到硼元素可以提高钢的表面硬度和改善铝的导电性能,同时硼也是改善铁铝金属间化合物脆性的重要元素。本文对单个硼原子在Fe、Al中的稳定存在的位置及扩散进行了计算。硼原子倾向于替代晶格中Fe、Al原子的位置,并通过跃迁到第一近邻空位进行扩散。由于硼原子的存在,还会对其附近空位的形成能产生影响。Fe中B原子周围第一近邻空位的形成能比纯Fe中的空位形成能高,而B原子第二近邻空位形成能比纯Fe空位形成能低。Al中B第一近邻和第二近邻空位形成能都比纯A1中空位形成能高。最后本文还用分子动力学模拟了Fe-Al界面的扩散过程,发现主要为Fe原子扩散进入Al中,且温度越高,扩散到A1中的Fe原子越多、越远。相同温度下,Al原子的运动速度比Fe原子快,但由于Al扩散的迁移能比Fe高,只有少量Al原子能够进入Fe中。
[Abstract]:The diffusion process is related to the random thermal movement of atoms, which can produce macroscopic concentration distribution changes. The study of diffusion process can provide a lot of useful information about the atomic structure of materials and the evolution of defects. Diffusion is closely related to material preparation, heat treatment, and creep process. Iron and aluminum are important raw materials in industrial production. They are widely used in construction, automobile, aerospace and other fields. The study of the diffusion properties of iron and aluminum is helpful to understand the diffusion mechanism of these two kinds of metals with different crystal structure, and it is of great significance to improve the properties of materials and the forging process of materials. In this paper, the diffusion processes of Fe and Al are simulated by using the embedded atomic interaction potential (EAM) by molecular dynamics method. The results are in good agreement with the theoretical and experimental results. The calculated results also show that the self-diffusion of iron and aluminum is mainly carried out through the vacancy mechanism. The main results of this paper are as follows: the energy required for the formation of defects in vacancies and self-interstitial atomic dots in Fe,Al is compared by statics method, and the most stable vacancy and self-gap atomic structures in Fe,Al are obtained. The NEB method is used to calculate the potential barrier size of these structures which need to be overcome by different paths. The results show that the activation energy of the vacancy transition to the first nearest neighbor is the lowest, which is the most likely transition mechanism in self-diffusion. Then the vacancy defects are introduced into the Fe,Al block to simulate the self-diffusion. The diffusion coefficient is in good agreement with the experimental data. In addition to the two simplest defects, vacancy and interstitial atoms, impurity atoms are an inevitable defect in practical materials. Considering that boron can improve the surface hardness of steel and improve the conductivity of aluminum, boron is also an important element to improve the brittleness of iron-aluminum intermetallics. In this paper, the stable existence and diffusion of single boron atom in Fe,Al are calculated. Boron atoms tend to replace the positions of Fe,Al atoms in the lattice and diffuse by transition to the first nearest neighbor vacancy. The formation energy of the first nearest neighbor vacancy around B atom in Fe is higher than that in pure Fe. The second nearest neighbor vacancy formation energy of B atom is lower than that of pure Fe vacancy formation energy, and the energy of B first nearest neighbor and second nearest neighbor vacancy formation in Al is higher than that in pure A1. Finally, the diffusion process of Fe-Al interface is simulated by molecular dynamics. It is found that the diffusion of Fe atoms into Al is the main one, and the higher the temperature, the more and farther Fe atoms diffuse to A1. At the same temperature, Al atoms move faster than Fe atoms, but only a few Al atoms can enter Fe because the transfer energy of Al diffusion is higher than that of Fe.
【学位授予单位】：广西大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG111.6

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