本文選題：第一性原理計算 + Mg-Ca系合金��； 參考：《沈陽工業(yè)大學(xué)》2015年碩士論文

【摘要】：鎂合金具有一系列優(yōu)良的性能被廣泛應(yīng)用于汽車、3C、航空航天及國防等領(lǐng)域。不過，由于受其自身性能的約束使得鎂合金在應(yīng)用過程中受到了限制。合金化被認為是改善鎂合金性能的一種重要手段。 本文以Mg-Ca系合金為基，采用基于密度泛函理論第一性原理計算方法的CASTEP軟件包，研究合金化元素Sn、Cu、Zn、Sr與Mg-Ca系合金作用生成Mg2Sn、MgCu2、MgZn2、Mg2Sr和Mg2Ca五種AB2型金屬間化合物的結(jié)構(gòu)穩(wěn)定性、力學(xué)性質(zhì)、電子結(jié)構(gòu)以及德拜溫度。晶格參數(shù)的計算結(jié)果與相關(guān)文獻報道值吻合的很好。合金形成熱的結(jié)果表明，Mg2Sn的合金形成能力最強，結(jié)合能的結(jié)果表明，MgCu2的結(jié)構(gòu)穩(wěn)定性最強。計算了五種AB2型金屬間化合物的彈性常數(shù)，推導(dǎo)了彈性模量（體模量B，剪切模量G，楊氏模量E），泊松比和各向異性系數(shù)A，計算結(jié)果表明，，Mg2Sn為脆性相，其余四種均為延性相。在五種AB2型金屬間化合物中，MgCu2剛度最大，MgZn2塑性最好。預(yù)測了五種AB2型金屬間化合物的熔點和硬度。研究了五種AB2型金屬間化合物的態(tài)密度、Mulliken電子占據(jù)數(shù)和差分電荷密度，最后計算并分析了五種AB2型金屬間化合物的德拜溫度。通過計算結(jié)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學(xué)性能。 本文進一步采用第一性原理計算方法首次研究了Mg2Sr和Mg2Ca在不同壓力下的力學(xué)、電子和熱力學(xué)性質(zhì)。計算了Mg2Sr和Mg2Ca在不同壓力下的彈性常數(shù)，研究了Mg2Sr和Mg2Ca在壓力作用下的彈性模量、泊松比、柯西壓力以及彈性各向異性。計算結(jié)果表明，Mg2Sr的彈性模量、泊松比和柯西壓力，Mg2Ca的體模量和柯西壓力均隨壓力的增加而升高，Mg2Ca的剪切模量和楊氏模量則隨壓力的增加先升高后降低，二者在各自壓力研究范圍內(nèi)均為延性相，各向異性程度隨壓力增加有減小趨勢。此外，分析了在壓力作用下Mg2Sr和Mg2Ca的電子結(jié)構(gòu)，研究了二者在壓力作用下的德拜溫度，以及在不同溫度和壓力下的熱力學(xué)性質(zhì)。
[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.
【學(xué)位授予單位】：沈陽工業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TG146.22

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