【作者】 于波；

【导师】 毛萍莉；

【作者基本信息】 沈阳工业大学 ， 材料工程， 2015， 硕士

【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。更多还原

【Abstract】 Magnesium alloy is widely used in automobile,3C, aerospace and defence industriesbecause it has a series of excellent performance. However, the application of magnesiumalloys is still limited due to the restrained properties. Alloying is regarded as an important wayto improve the performance of magnesium alloy.The structural, mechanical properties, electronic structures and Debye tempertatures ofMg2Sn, MgCu2, MgZn2, Mg2Sr and Mg2Ca phases were investigated by means of first-principles calculations from CASTEP program based on density functional theory (DFT) withthe generalized gradient approximation. The calculated lattice parameters were in goodagreement with the experimental and literature values. The calculated heats of formation andcohesive energies showed that Mg2Sn had the strongest alloying ability and MgCu2had thestrongest structural stability. The elastic constants of the five kinds intermetallic compoundswere calculated and the mechanical parameters, such as bulk moduli B, shear moduli G,Young’s moduli E, Poisson’s ratio and ansiotropy A were determined by using the Voigt-Reuss-Hill (VRH) averaging scheme. The calculated results showed that Mg2Sn was brittlephase, while others were all ductile phases. Among the five phases, MgCu2had the strongeststiffness, the plasticity of MgZn2phase was the best. Melting points and hardness of the fivephases were predicted by using cohesive energy and elastic constants. Density of states (DOS),Mulliken population and charge density difference were discussed. Finally, Debyetemperatures were calculated and discussed. It could be concluded that the mechanicalproperty of Mg-Ca alloy were improved by adding Sn, Cu, Zn and Sr elements.The mechanical, electronic and thermodynamic properties of Mg2Sr and Mg2Ca withC14-type structure under pressures had been firstly studied by using the first-principlescalculations. The five independent elastic constants of Mg2Sr and Mg2Ca structures werecalculated and the mechanical parameters and Poisson’s ratio were determined by usingthe Voigt-Reuss-Hill (VRH) averaging scheme. The Cauchy pressure and elastic anisotropy ofMg2Sr and Mg2Ca were also investigated. The calculated results showed that Mg2Sr andMg2Ca were ductile phases according to the calculation results of Cauchy pressure and G/Bvalues under different pressures. In addition, the electronic densities of states (DOS) as a function of pressures were analyzed. The Debye temperatures obtained by elastic constantswere investigated. The dependences of thermodynamic properties on temperature and pressurewere also discussed by using the quasi-harmonic approximation.更多还原