本文選題：Mg合金 + 第一性原理�。� 參考：《北京交通大學》2017年碩士論文

【摘要】：Mg是密度比較小的金屬材料,密度僅有Al的2/3,鐵的1/4左右,是比較重要的輕型材料之一。由于材料比較輕,從而使Mg及其合金在輕量化方面具有難以替代的地位。另外,Mg合金的比強度、比剛度也非常高,具有易于回收利用的優(yōu)良特性,使它在航天、汽車的領(lǐng)域應用非常廣泛。然而,Mg及Mg合金是密排六方結(jié)構(gòu)(HCP),它的對稱性低(c/a= 1.624),能夠滑移的面少,常溫下只有基面提供的兩個獨立滑移系,不能達到Von-Mises準則中五個獨立滑移系的需求。因此導致在常溫下Mg合金的可塑性差,不易變形,這就限制了它的應用。另外,Mg是比較活潑的金屬,導致它的抗腐蝕能力差,雖然Mg合金的比強度較高,但仍然比Al合金強度要低,因此研究Mg合金塑性變形的本質(zhì),尋找改善變形Mg合金塑性和韌性的方法,提高Mg合金抗腐蝕能力,為最終Mg合金開發(fā)、設計以及加工提供理論指導具有重要的意義。本文主要運用基于密度泛函的第一性原理,利用VASP軟件計算了 Mg單晶、Mg-Al、Mg-Zn、Mg-Mn二元合金和Mg-Al-Zn三元合金中的層錯能。首先計算了基面不同尺寸超胞的本征層錯能和不穩(wěn)定層錯能,確定采用1×2×12的超胞進行計算。計算了 Mg單晶的4個主要的滑移面(基面(0001}1120、柱面{1010}1120以及Ⅰ型錐面{1011}1120和Ⅱ型錐面{1122}1123)的廣義層錯能、電荷密度和態(tài)密度,分析發(fā)現(xiàn)基面最易滑移,Ⅱ型錐面最難滑移,柱面和Ⅰ型錐面滑移難度相差不大。并利用電荷密度圖和態(tài)密度圖分析了不同軌道之間電子的雜化現(xiàn)象。另外由于元素摻雜可以提高鎂合金的塑性,因此本文計算了 Al、Zn、Mn原子分別替位摻雜Mg原子后的層錯能、電荷密度和態(tài)密度,分析發(fā)現(xiàn)Zn元素最能降低層錯能,Mn次之,Al最差,并通過電荷密度圖和態(tài)密度圖分析了 Mg-Al、Mg-Zn合金電子的轉(zhuǎn)移和軌道的雜化現(xiàn)象。利用廣義層錯能權(quán)重模型,計算各滑移面的平均層錯能。最后本文計算了 Mg-Al-Zn三元Mg合金的層錯能,由于雙元素替位摻雜的位置較多,因此本文首先通過確定含有32個原子的Mg-Al-Zn合金的形成焓確定元素的摻雜位置,再計算了 Mg-Al-Zn三元Mg合金的廣義層錯能,分析發(fā)現(xiàn)Mg-Al-Zn三元Mg合金的層錯能低于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，

本文編號：2040324