第一性原理计算论文：第一性原理计算 AMgNi4合金 稳定性
力学性能 电子结构
【中文摘要】纯金属镁虽有丰富的含量和各种优异的性能,如低密度、高的比强度和刚度、好的减震性和电磁屏蔽性等等,但因其活泼的化学性质,在室温或高温下较差的力学性能等方面的原因,极大地限制了它在现代工业上的应用。为了提高镁的性能尤其是高温下的力学性能,和满足工业上对结构材料的大量需求,对镁合金的研究探索已经成为开发轻质结构材料的热点,引起了实验和理论上的持续关注。虽然目前对稀土镁合金进行了大量的实验研究,但是对一些合金及合金中的相缺乏深入的了解,尤其对一些内在的作用机制还不是很明确,需要理论方面的研究指导。本文采用基于密度泛函理论之上的第一性原理计算的方法,对稀土镁合金中典型的C14型Mg2Y（Yb）强化相进行了理论上的计算,得到了与实验一致的结构参数。计算所得到的结合能表明Mg2Y（Yb）相,具有较强的结构稳定性,且Mg2Y相对Mg2Yb而言更稳定。对弹性常数及力学性质的计算分析表明Mg2Yb相比Mg2Y展示了好的塑性和各向同性,而Mg2Y比Mg2Yb相具有较大的弹性常数Cij和较好的刚度。接着,采用相同的计算方法对新型三元镁合金AMgNi4（A=Y, La, Ce, Pr和Nd）进行了结构参数、力学性质、电子结构等方面的研究。计算得到的平衡晶格常数与实验很好的一致,负的形成焓ΔH和结合能Ecoh表明这些合金有很强的稳定性。其次,计算结果指出YMgNi4合金在这些合金中有最大的弹性常数
Cij、剪切模量G、体模量B和杨氏模量E,却有最小的泊松比υ和最差的韧性。再次,结果还表明三元合金AMgNi4（A=La, Ce, Pr和Nd）的弹性常数Cij、剪切模量G、体模量B、杨氏模量E以及G/B这些物理量的值,均随着元素A原子序数的增大而增大,而泊松比υ却是逐渐变小、韧性逐渐减弱,依次呈现规律性变化。为了得到稳定性以及力学性能的微观作用机制,本文还详细分析了这些合金的电子结构。本文还对MgCuSn和MgCu4Sn金属间化合物的结构、力学性能等进行了研究,结果表明此两者是结构稳定的,MgCu4Sn比MgCuSn有较大的弹性常数Cij、杨氏模量E、体模量B和剪切模量G,MgCuSn比MgCu4Sn有较好的塑性、韧性和各向同性。最后,分析了MgCuSn和MgCu4Sn化合物的电子态密度。
【英文摘要】Although pure magnesium is rich in content, and has various excellent properties, such as low density, the high specific strength and rigidity, good damping capacity and electromagnetism shielding property and so on, the poor mechanical properties at room temperature or high temperature limit its application in the modern industry greatly because of its active chemical properties. In order to improve the mechanical properties of magnesium, especially at high temperature, meanwhile, in order to meet the industry demand for a large number of lightweight structural materials, the study of magnesium alloys has become a hot spot, and received
a sustaining attention both on experiment and theory. At present, although researches have conducted massive experimental study to the rare earth magnesium alloy, the thorough understanding of Mg alloys and compounds is still very lacking, especially the intrinsic mechanism of structural stability and mechanical properties is not very explicit. Therefore, further theoretical research is needed.In this paper, we used the method of the first principle calculation based on density functional theory, performed a calculation on the property of enhanced phases Mg2Y and Mg2Yb. The calculated cohesive energies indicated that both of them were stable, and Mg2Y was more stable than Mg2Yb. The obtained equilibrium lattice constants for Mg2Y and Mg2Yb were in good agreement with the available experimental values. The calculated results also showed that Mg2Yb has better plasticity and isotropic property than Mg2Y, while Mg2Y has larger value of Cij, so is stiffer than Mg2Yb.Then the same method was used to research the structural parameters, mechanical properties, electronic structures of the new ternary magnesium alloys AMgNi4 （A= Y, La, Ce, Pr and Nd）. The optimized structural parameters were in good agreement with the available experimental datas. The calculated negative cohesive energies and formation enthalpies
第一性原理计算论文：第一性原理计算AMgNi4合金稳定性力学性能电子结构
