Mg晶体与Mg合金（Al、Zn、Mn掺杂）滑移的第一性原理研究

发布时间：2018-06-19 15:21

  本文选题：Mg合金 + 第一性原理　； 参考：《北京交通大学》2017年硕士论文

【摘要】：Mg是密度比较小的金属材料,密度仅有Al的2/3,铁的1/4左右,是比较重要的轻型材料之一。由于材料比较轻,从而使Mg及其合金在轻量化方面具有难以替代的地位。另外,Mg合金的比强度、比刚度也非常高,具有易于回收利用的优良特性,使它在航天、汽车的领域应用非常广泛。然而,Mg及Mg合金是密排六方结构(HCP),它的对称性低(c/a= 1.624),能够滑移的面少,常温下只有基面提供的两个独立滑移系,不能达到Von-Mises准则中五个独立滑移系的需求。因此导致在常温下Mg合金的可塑性差,不易变形,这就限制了它的应用。另外,Mg是比较活泼的金属,导致它的抗腐蚀能力差,虽然Mg合金的比强度较高,但仍然比Al合金强度要低,因此研究Mg合金塑性变形的本质,寻找改善变形Mg合金塑性和韧性的方法,提高Mg合金抗腐蚀能力,为最终Mg合金开发、设计以及加工提供理论指导具有重要的意义。本文主要运用基于密度泛函的第一性原理,利用VASP软件计算了 Mg单晶、Mg-Al、Mg-Zn、Mg-Mn二元合金和Mg-Al-Zn三元合金中的层错能。首先计算了基面不同尺寸超胞的本征层错能和不稳定层错能,确定采用1×2×12的超胞进行计算。计算了 Mg单晶的4个主要的滑移面(基面(0001}1120、柱面{1010}1120以及Ⅰ型锥面{1011}1120和Ⅱ型锥面{1122}1123)的广义层错能、电荷密度和态密度,分析发现基面最易滑移,Ⅱ型锥面最难滑移,柱面和Ⅰ型锥面滑移难度相差不大。并利用电荷密度图和态密度图分析了不同轨道之间电子的杂化现象。另外由于元素掺杂可以提高镁合金的塑性,因此本文计算了 Al、Zn、Mn原子分别替位掺杂Mg原子后的层错能、电荷密度和态密度,分析发现Zn元素最能降低层错能,Mn次之,Al最差,并通过电荷密度图和态密度图分析了 Mg-Al、Mg-Zn合金电子的转移和轨道的杂化现象。利用广义层错能权重模型,计算各滑移面的平均层错能。最后本文计算了 Mg-Al-Zn三元Mg合金的层错能,由于双元素替位掺杂的位置较多,因此本文首先通过确定含有32个原子的Mg-Al-Zn合金的形成焓确定元素的掺杂位置,再计算了 Mg-Al-Zn三元Mg合金的广义层错能,分析发现Mg-Al-Zn三元Mg合金的层错能低于Mg-Al、Mg-Zn合金,因此Mg-Al-Zn合金具有更好的塑性。
[Abstract]:Mg is one of the most important lightweight materials, with a density of only 2 / 3 of Al and about a quarter of that of iron. Because the material is lighter, mg and its alloy have irreplaceable position in light weight. In addition, the specific strength and specific stiffness of mg alloy are also very high, and it is easy to be recycled, which makes it widely used in the field of aerospace and automobile. However, the mg and mg alloys are hexagonal structure with low symmetry (c / a = 1.624) and few slip surfaces. At room temperature, there are only two independent slip systems provided by the base plane, which cannot meet the requirements of the five independent slip systems in the Von-Mises criterion. Therefore, the plasticity of mg alloy at room temperature is poor and the deformation is not easy, which limits its application. In addition, mg is a relatively active metal, which leads to its poor corrosion resistance. Although the specific strength of mg alloy is higher, it is still lower than that of Al alloy. Therefore, the nature of plastic deformation of mg alloy is studied. It is of great significance to find ways to improve the ductility and toughness of the deformed mg alloy and to improve the corrosion resistance of mg alloy. It is of great significance to provide theoretical guidance for the development, design and processing of the final mg alloy. In this paper, based on the first principle of density functional, the stacking fault energy of mg single crystal Mg-AlN Mg-Zn Mg-Mn alloy and Mg-Al-Zn ternary alloy are calculated by using VASP software. The intrinsic stacking fault energy and unstable stacking fault energy of the supercell with different sizes on the base plane are calculated, and the supercell of 1 脳 2 脳 12 is used to calculate the intrinsic fault energy and unstable stacking fault energy. The generalized stacking fault energy, charge density and density of states of four main slip surfaces (base plane 0001} 1120, cylindrical {1010} 1120, type 鈪，

本文编号：2040324