Mg-Ca系合金中相稳定性，力学及热力学性质的第一性原理计算

发布时间：2018-06-15 17:41

本文选题：第一性原理计算 + Mg-Ca系合金　；参考：《沈阳工业大学》2015年硕士论文

【摘要】：镁合金具有一系列优良的性能被广泛应用于汽车、3C、航空航天及国防等领域。不过，由于受其自身性能的约束使得镁合金在应用过程中受到了限制。合金化被认为是改善镁合金性能的一种重要手段。本文以Mg-Ca系合金为基，采用基于密度泛函理论第一性原理计算方法的CASTEP软件包，研究合金化元素Sn、Cu、Zn、Sr与Mg-Ca系合金作用生成Mg2Sn、MgCu2、MgZn2、Mg2Sr和Mg2Ca五种AB2型金属间化合物的结构稳定性、力学性质、电子结构以及德拜温度。晶格参数的计算结果与相关文献报道值吻合的很好。合金形成热的结果表明，Mg2Sn的合金形成能力最强，结合能的结果表明，MgCu2的结构稳定性最强。计算了五种AB2型金属间化合物的弹性常数，推导了弹性模量（体模量B，剪切模量G，杨氏模量E），泊松比和各向异性系数A，计算结果表明，，Mg2Sn为脆性相，其余四种均为延性相。在五种AB2型金属间化合物中，MgCu2刚度最大，MgZn2塑性最好。预测了五种AB2型金属间化合物的熔点和硬度。研究了五种AB2型金属间化合物的态密度、Mulliken电子占据数和差分电荷密度，最后计算并分析了五种AB2型金属间化合物的德拜温度。通过计算结果分析可知，合金化元素Sn、Cu、Zn、Sr加入到Mg-Ca系合金中可以提升合金的力学性能。本文进一步采用第一性原理计算方法首次研究了Mg2Sr和Mg2Ca在不同压力下的力学、电子和热力学性质。计算了Mg2Sr和Mg2Ca在不同压力下的弹性常数，研究了Mg2Sr和Mg2Ca在压力作用下的弹性模量、泊松比、柯西压力以及弹性各向异性。计算结果表明，Mg2Sr的弹性模量、泊松比和柯西压力，Mg2Ca的体模量和柯西压力均随压力的增加而升高，Mg2Ca的剪切模量和杨氏模量则随压力的增加先升高后降低，二者在各自压力研究范围内均为延性相，各向异性程度随压力增加有减小趋势。此外，分析了在压力作用下Mg2Sr和Mg2Ca的电子结构，研究了二者在压力作用下的德拜温度，以及在不同温度和压力下的热力学性质。
[Abstract]:Magnesium alloys have been widely used in automotive, aerospace, national defense and other fields with a series of excellent properties. However, magnesium alloys are restricted in application due to their properties. Alloying is regarded as an important means to improve the properties of magnesium alloys. In this paper, based on Mg-Ca alloys, the structural stability and mechanical properties of five kinds of AB _ 2-type intermetallic compounds, mg _ 2SnCu _ 2C _ 2H _ (2) mg _ (2) Zn _ (2) mg _ (2Sr) and mg _ (2CA), were studied by using CASTEP software package based on the first principle calculation method of density functional theory (DFT). Electronic structure and Debye temperature. The calculated results of lattice parameters are in good agreement with the reported values. The results of formation heat show that the formation ability of mg _ 2SN alloy is the strongest, and the binding energy shows that the structure stability of MgCu _ 2 is the strongest. The elastic constants of five AB2-type intermetallic compounds are calculated. The elastic moduli (bulk modulus B, shear modulus G, Young's modulus E ~ (1), Poisson's ratio and anisotropy coefficient A) are derived. The calculated results show that mg _ 2SN is a brittle phase, while the other four are ductile. Among the five kinds of AB _ 2 intermetallic compounds, MgCu _ 2 has the highest stiffness and the best plasticity is MgZn _ 2. The melting point and hardness of five AB 2 intermetallic compounds were predicted. The density of states and the differential charge density of five AB2-type intermetallic compounds are studied. Finally, the Debye temperature of the five AB2-type intermetallic compounds is calculated and analyzed. The results show that the mechanical properties of the alloy can be improved by adding the alloying element Sno CuCuZN Sr to the Mg-Ca alloy. In this paper, the mechanical, electronic and thermodynamic properties of mg _ 2Sr and mg _ 2Ca under different pressures have been studied for the first time by using first-principle calculation method. The elastic constants of mg _ 2Sr and mg _ 2Ca under different pressures are calculated. The elastic modulus, Poisson's ratio, Cauchy pressure and elastic anisotropy of mg _ 2Sr and mg _ 2Ca under different pressures are studied. The results show that the elastic modulus of mg _ 2Sr, Poisson's ratio and the bulk modulus and Cauchy pressure of mg _ 2Ca increase with the increase of pressure. The shear modulus and Young's modulus of mg _ 2Ca increase first and then decrease with the increase of pressure. Both of them are ductile phase in their respective pressure range, and the anisotropy tends to decrease with the increase of pressure. In addition, the electronic structures of mg _ 2Sr and mg _ 2Ca under pressure were analyzed, and the Debye temperature and thermodynamic properties of mg _ 2Sr and mg _ 2Ca at different temperatures and pressures were studied.
【学位授予单位】：沈阳工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG146.22

【参考文献】