| With the continuous development of science and technology,the modern industry has increasingly higher requirements for material performance.Therefore,the research on improving the material properties based on the application environment is of great scientific significance.Alloy strengthening and grain boundary strengthening are two of the most common and effective methods to improve material properties.The interaction between alloying atoms and the microstructures of the material(such as grain boundaries,twin boundaries,dislocations,and point defects)will have an impact on the strengthening effect.Some alloying atoms interact with defects in the bulk to improve the performance of the material,while some lead to a decline in the performance.Therefore,exploring the influence of alloying atoms on defects in the bulk is helpful to realize the design of new alloys.In this paper,the effects of alloying elements on the mechanism induced by a grain boundary are investigated by first principles method,and the influencing factors are analyzed and discussed.The main work and results are as follows:(1)First,the occupancy tendency of Zr,Al,Zn,Mn and Si atoms near the }2110{coherent twin boundary in magnesium is calculated and analyzed.The results show that the occupancy tendency is related to the atomic radius: Zr with a larger radius tends to be close to the twin boundary;Al and Zn with a slightly smaller radius tend to be distributed far away from the twin boundary;Mn and Si with a smaller radius show no obvious tendency of occupying position.Secondly,the effects of the five alloying elements at different substitution positions on the twin boundary migration energy are calculated,and the difficulty of migration is determined by the migration energy.When Zr,Al,and Zn are located at the preferential sites respectively,they will increase the migration energy,thereby hindering the twin boundary migration;When Mn and Si substitute the Mg atoms near the twin boundary,they will greatly increase the migration energy,which has a relatively obvious hindrance to the twin boundary migration.Combined with the analysis of the local charge density near the twin boundary,it is found that the effect of alloying elements on the migration energy is related to the redistribution of the charge density near the twin boundary.In the region with strong charge accumulation,the interaction between atoms is relatively strong,and the effect on twin boundary migration is greater,which affects the plasticity of Mg-based alloy to a certain extent.(2)By calculating the effect of the interstitial atoms V,Ti,and Cr and the vacancies at different positions on the energy of the(29)(27)(50){111}1103 symmetrical tilt grain boundary in vanadium,the mechanism of point defects on the stability of the grain boundary is analyzed.The calculation results show that the effect of vacancies and interstitial atoms on the energy of the grain boundary system is almost not changed by the location of the vacancies,only by the interstitial atoms.The larger radius of interstitial atoms is,the greater distortion of the structural unit on the grain boundaries will be,which is not conducive to the stability of the grain boundary.Secondly,the activation energy required by the interstitial emission(IE)induced by the grain boundary to annihilate vacancies is calculated.Compared with interstitial atom V,Ti as interstitial atom significantly increases the activation energy of IE,while Cr slightly does.This may be because the atomic radius and electronegativity of Ti and matrix V differ greatly,and the valence electron configuration of Ti is not as stable as that of Cr.In the region dominated by the IE mechanism,the activation energy required for the interstitial atom emission annihilating a vacancy increases linearly with the distance between the vacancy to the grain boundary. |
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