【摘要】：鎂合金的低密度、高比強(qiáng)度的輕量化優(yōu)點(diǎn)使其成為一直以來的研究熱點(diǎn),這些優(yōu)點(diǎn)也使其在汽車、3C、國防等方面具有廣闊的應(yīng)用前景。我國的鎂資源儲(chǔ)備豐富,開發(fā)出性能卓越的鎂合金對有效利用這一資源具有重大意義。本文采用基于密度泛函理論第一性原理計(jì)算方法研究Ag加入到Mg-Ca合金中所形成的MgAg、Mg_2Ca和AgCa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)。首先計(jì)算了二元合金相的晶格參數(shù)并與實(shí)驗(yàn)室和其他工作的結(jié)果作對比,結(jié)果一致。合金形成熱和結(jié)合能的計(jì)算結(jié)果分析,MgAg相的合金形成能力和穩(wěn)定性最強(qiáng)。計(jì)算了MgAg、Mg_2Ca和AgCa金屬間化合物的彈性常數(shù),根據(jù)其彈性常數(shù)計(jì)算出體模量B,剪切模量G、楊氏模量E、泊松比n和各向異性系數(shù)A,計(jì)算結(jié)果表明,MgAg的抗變形能力和抗剪切能力最強(qiáng),MgAg和Mg_2Ca為脆性相,AgCa為延展性相。MgAg剛度最強(qiáng),而AgCa塑性最好。根據(jù)彈性模量和結(jié)合能的計(jì)算結(jié)果近似計(jì)算了熔點(diǎn)和硬度。研究了MgAg、Mg_2Ca和AgCa的態(tài)密度(DOS)。根據(jù)各個(gè)相的性能結(jié)果得知,合金化元素Ag加入到Mg-Ca合金所形成的MgAg和AgCa相的性能要強(qiáng)于Mg_2Ca,從而推斷加入Ag元素可提高原來合金性能。材料的實(shí)際應(yīng)用都要受到壓力,本文在MgAg和MgY上施加壓力,進(jìn)一步研究其力學(xué)性能和電子結(jié)構(gòu)以揭示力學(xué)性能變化的原因。計(jì)算了MgAg和MgY在不同壓力下的彈性常數(shù)、MgAg和MgY在壓力作用下的彈性模量、泊松比以及彈性各向異性。計(jì)算結(jié)果表明,隨著壓力的增加二者的抗變形能力和抗剪切能力都有所增加,MgAg和MgY的脆性在減弱,二者態(tài)密度峰值在壓力作用下降低,此現(xiàn)象說明二者的雜化能量也在降低,對于MgAg來說主要是Mg p和Ag p軌道的雜化變?nèi)鯇?dǎo)致雜化能降低,對于MgY來說其主要Y p軌道和Mg p軌道的雜化變?nèi)鯇?dǎo)致雜化能降低。采用非簡諧近似模型計(jì)算了MgAg和MgY在各個(gè)溫度下的熵、焓、自由能和熱熔的變化情況,計(jì)算結(jié)果表明熵、焓和熱容隨溫度升高而增加,而二者的自由能隨溫度的升高而減小,對計(jì)算結(jié)果分析可知壓力對MgAg和MgY的熱力學(xué)性質(zhì)影響很小。本文還計(jì)算了Mg-Ag固溶鎂合金的電子結(jié)構(gòu),具體闡述了Ag原子置換鎂原子固溶強(qiáng)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.
【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】：2017
【分類號】：TG146.22

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