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Study of Point Defect of Mg3Ce and Dislocation of Mg2Si Alloys

Author: LuoLiGuo
Tutor: TangBiYu
School: Xiangtan University
Course: Materials Science and Engineering
Keywords: Mg solid solution alloys Point defect Magnetic moment Dislocation First principle calculation
CLC: O77
Type: Master's thesis
Year: 2013
Downloads: 18
Quote: 0
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Abstract


As structural materials, magnesium alloys have attracted significant attention inthe automobile and aerospace industries due to its excellent properties, such as lowdensity, good casting, and high strength properties etc. However, the applications ofmagnesium alloys are still limited. The main reasons are the poor mechanicalproperties, such aspoor corrosion and creep resistances etc. Thus, many efforts aredevoted to developing new magnesium alloys with superior performance.The mechanical properties of magnesium alloys can be improved by the additionof some elements, because of the formation of intermetallic compound. Mg3Ce canimprove the mechanical properties of Mg alloys, it is also a hydrogen storage materialwith high performance. Another intermetallic compound Mg2Si, as a function material,it is a thermoelectric material and a kind of battery material. Moreover it is used asstructural material because of its high strength properties. The two kinds ofmultifunction materials have aroused the interest of researcher.In this study, we have carried out first principles calculations that based on thedensity function theoretic to investigate the ground state and point defect properties ofMg3Ce. The dislocation properties of Mg2Si calculated by the P-N model areinvestigated too. The obtained main conclusions are listed as follow.(1) The ground state structure and magnetic moment under GGA calculation donot accord with the experimental results. However, when the Ueff=7.0eV, the GGA+Ucalculated lattice constant, ground state structre and magnetic moment are in accordwith the experimental results, so the Ueff=7.0eV is reasonable for the GGA+Ucalculation. From the electronic structure, the f state of Ce has important contributionto the total DOS, so the f state of Ce is necessary in the calculation.(2) For the Ce-rich point defect, the Mg2-ASD has the lowest formationg energy,followed by the Mg1-ASD and Mg2vacancy. However, for the Mg-rich point defect,the Ce vacancy is easiest to be formed, followed by the Ce-ASD. The interstitialshave the highest formation energies for both Mg-rich and Ce-rich defects.(3) The Mg3.6Ce has the structure of1×1×3supercell with two the second nextneighour Ce vacancy. The Mg3.7Ce has the structure of1×1×3supercell with thefirst next neighour Ce vacancy and Ce-ASD.(4) For all the slip systems of Mg2Si, the [001](110) is the easiest slip system, following by the [100](001) and1/2[112](110).(5) Most of the peierls energies of possible slip systems for Mg2Si at the GPalevel, so these are hard to slip at the room temperture, then Mg2Si show the brittlenessat the room temperture.

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