Ag合金化镁合金的第一性原理计算
发布时间：2018-09-03 06:13
【摘要】：镁合金的低密度、高比强度的轻量化优点使其成为一直以来的研究热点,这些优点也使其在汽车、3C、国防等方面具有广阔的应用前景。我国的镁资源储备丰富,开发出性能卓越的镁合金对有效利用这一资源具有重大意义。本文采用基于密度泛函理论第一性原理计算方法研究Ag加入到Mg-Ca合金中所形成的MgAg、Mg_2Ca和AgCa金属间化合物的结构稳定性、力学性质、电子结构。首先计算了二元合金相的晶格参数并与实验室和其他工作的结果作对比,结果一致。合金形成热和结合能的计算结果分析,MgAg相的合金形成能力和稳定性最强。计算了MgAg、Mg_2Ca和AgCa金属间化合物的弹性常数,根据其弹性常数计算出体模量B,剪切模量G、杨氏模量E、泊松比n和各向异性系数A,计算结果表明,MgAg的抗变形能力和抗剪切能力最强,MgAg和Mg_2Ca为脆性相,AgCa为延展性相。MgAg刚度最强,而AgCa塑性最好。根据弹性模量和结合能的计算结果近似计算了熔点和硬度。研究了MgAg、Mg_2Ca和AgCa的态密度(DOS)。根据各个相的性能结果得知,合金化元素Ag加入到Mg-Ca合金所形成的MgAg和AgCa相的性能要强于Mg_2Ca,从而推断加入Ag元素可提高原来合金性能。材料的实际应用都要受到压力,本文在MgAg和MgY上施加压力,进一步研究其力学性能和电子结构以揭示力学性能变化的原因。计算了MgAg和MgY在不同压力下的弹性常数、MgAg和MgY在压力作用下的弹性模量、泊松比以及弹性各向异性。计算结果表明,随着压力的增加二者的抗变形能力和抗剪切能力都有所增加,MgAg和MgY的脆性在减弱,二者态密度峰值在压力作用下降低,此现象说明二者的杂化能量也在降低,对于MgAg来说主要是Mg p和Ag p轨道的杂化变弱导致杂化能降低,对于MgY来说其主要Y p轨道和Mg p轨道的杂化变弱导致杂化能降低。采用非简谐近似模型计算了MgAg和MgY在各个温度下的熵、焓、自由能和热熔的变化情况,计算结果表明熵、焓和热容随温度升高而增加,而二者的自由能随温度的升高而减小,对计算结果分析可知压力对MgAg和MgY的热力学性质影响很小。本文还计算了Mg-Ag固溶镁合金的电子结构,具体阐述了Ag原子置换镁原子固溶强化的原因。
[Abstract]:Magnesium alloys with low density and high specific strength have become a research hotspot all the time. These advantages also make them have broad application prospects in automotive, 3C, national defense and other fields. The structure stability, mechanical properties and electronic structure of MgAg, Mg_2Ca and Ag Ca intermetallic compounds formed by adding Ag into Mg-Ca alloys are studied by the first-principles calculation method of density functional theory. The elastic constants of MgAg, Mg_2Ca and A gCa intermetallics are calculated. The bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio n and anisotropy coefficient A are calculated according to their elastic constants. The results show that MgAg has the best deformation resistance and shear resistance. MgAg and Mg_2Ca are the most brittle phase, AgCa is the ductile phase. MgAg has the strongest stiffness, while AgCa has the best plasticity. The melting point and hardness are approximately calculated according to the calculation results of elastic modulus and binding energy. The density of state (DOS) of MgAg, Mg_2Ca and AgCa are studied. The properties of Ag and AgCa phases are stronger than those of Mg_2Ca, so it is inferred that the properties of the original alloy can be improved by adding Ag element. The practical application of the material is subject to pressure. In this paper, the mechanical properties and electronic structure of MgAg and MgY are studied further to reveal the reasons for the mechanical properties changes. The elastic constants of MgAg and MgY under different pressures are calculated. The results show that the deformation resistance and shear resistance of MgAg and MgY increase with the increase of pressure, the brittleness of MgAg and MgY decrease, and the peak state density of MgAg and MgY decrease with the increase of pressure, which indicates that the hybridization energy of MgAg and MgY also increases. For MgAg, the decrease of hybridization energy is mainly due to the weakening of hybridization of Mg P and Ag P orbits, and for MgY, the weakening of hybridization of main Y P orbits and Mg P orbits leads to the decrease of hybridization energy. The enthalpy and heat capacity of Mg-Ag alloy increase with the increase of temperature, while the free energy decreases with the increase of temperature. The calculation results show that the pressure has little effect on the thermodynamic properties of MgAg and MgY. The electronic structure of Mg-Ag solid solution magnesium alloy is also calculated, and the reason for the solid solution strengthening of Mg atoms by replacing Ag atoms is explained in detail.
【学位授予单位】：沈阳工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.22
本文编号：2219120
[Abstract]:Magnesium alloys with low density and high specific strength have become a research hotspot all the time. These advantages also make them have broad application prospects in automotive, 3C, national defense and other fields. The structure stability, mechanical properties and electronic structure of MgAg, Mg_2Ca and Ag Ca intermetallic compounds formed by adding Ag into Mg-Ca alloys are studied by the first-principles calculation method of density functional theory. The elastic constants of MgAg, Mg_2Ca and A gCa intermetallics are calculated. The bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio n and anisotropy coefficient A are calculated according to their elastic constants. The results show that MgAg has the best deformation resistance and shear resistance. MgAg and Mg_2Ca are the most brittle phase, AgCa is the ductile phase. MgAg has the strongest stiffness, while AgCa has the best plasticity. The melting point and hardness are approximately calculated according to the calculation results of elastic modulus and binding energy. The density of state (DOS) of MgAg, Mg_2Ca and AgCa are studied. The properties of Ag and AgCa phases are stronger than those of Mg_2Ca, so it is inferred that the properties of the original alloy can be improved by adding Ag element. The practical application of the material is subject to pressure. In this paper, the mechanical properties and electronic structure of MgAg and MgY are studied further to reveal the reasons for the mechanical properties changes. The elastic constants of MgAg and MgY under different pressures are calculated. The results show that the deformation resistance and shear resistance of MgAg and MgY increase with the increase of pressure, the brittleness of MgAg and MgY decrease, and the peak state density of MgAg and MgY decrease with the increase of pressure, which indicates that the hybridization energy of MgAg and MgY also increases. For MgAg, the decrease of hybridization energy is mainly due to the weakening of hybridization of Mg P and Ag P orbits, and for MgY, the weakening of hybridization of main Y P orbits and Mg P orbits leads to the decrease of hybridization energy. The enthalpy and heat capacity of Mg-Ag alloy increase with the increase of temperature, while the free energy decreases with the increase of temperature. The calculation results show that the pressure has little effect on the thermodynamic properties of MgAg and MgY. The electronic structure of Mg-Ag solid solution magnesium alloy is also calculated, and the reason for the solid solution strengthening of Mg atoms by replacing Ag atoms is explained in detail.
【学位授予单位】：沈阳工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.22
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