极端载荷条件下晶体镁材料中无定形区域的力学响应规律研究

The disorder region in crystalline magnesium (Mg) materials subjected to extreme loading conditions, in which the atoms distribute irregularly, has attracted more and more attention and shown significant effect on the mechanical properties of Mg materials. However, no enough knowledge has been revealed for this microstructure about its atom-scale features and micro mechanisms of its effect on the mechanical behaviors of Mg materials, which limits wider applications of Mg materials in military, aerospace and other fields. This project is to systematically study mechanical responses of the disorder region in crystalline Mg materials with molecular dynamics simulations and experiments, so as to reveal physical and mechanical characteristics of the disorder regions for better understanding of micro deformation mechanisms of crystalline Mg materials. The research work in this project includes: 1) structure, potential and temperature features of the disorder region, 2) deformation and evolution rules of the region under different loads and the atom-scale mechanisms of the rules, 3) interactions between evolution of the disorder region and dislocation motion as well as twinning deformation, and the mechanisms for the interaction. The project will reveal physical features, deformation rules of the disorder region and its effect on the mechanical behaviors of Mg materials, which could be valuable for further revealing of micro deformation mechanisms of Mg materials as well as developing and applications of these materials.

晶体镁材料在极端载荷下产生的原子排布不规则的无定形区域近来受到了人们越来越多的关注，并显示出了对力学性能重要的影响。但是，目前人们对这种无定形区域的原子尺度特征以及它对力学行为的微观影响机制的认识还不够深入，这不利于镁这种轻质金属材料在军事、航空航天等领域更广泛的应用。本项目拟结合数值模拟和实验方法系统地研究无定形区域在晶体镁材料变形中的变形演化规律，旨在通过揭示无定形区域的物理、力学特征促进人们对晶体镁材料微观变形机理更全面、更深入的认识。本项目主要研究：1）无定形区域的结构、势能、温度等物理特征；2）无定形区域在不同加载条件下的变形演化规律及其原子尺度机制；3）无定形区域变形、演化和位错运动、孪晶变形之间的相互作用规律及其内在物理机制。本项目将揭示无定形区域的物理特征及其对镁材料力学行为的微观影响机制，对进一步揭示镁材料的微观变形机理、促进镁材料的发展和应用具有积极的意义。

镁、钛等是典型的密排六方（HCP）晶格结构的金属材料，在民用车辆、航空航天飞行器、军事装备等民用、国防领域有着广泛的应用。受密排六方晶格对称性差等因素影响，HCP金属的塑性变形机制及规律相对复杂，相关认识不够充分深入，限制了这些金属材料更广泛的应用。传统观点认为位错滑移和孪晶变形是HCP金属材料的两种主要塑性变形机制，但最近的研究表明这两种机制不能很好解释镁单晶材料受c轴压缩塑性形变规律。.为了更深入认识HCP金属材料c轴压缩塑性变形机制规律，本课采用微观模拟结合理论分析研究了不同加载条件下镁单晶c轴压缩的塑性变形机制和规律。研究发现镁单晶材料在受c轴压缩载荷时会发生无定形化变形过程，产生一种非熔化的、高势能的、原子无序排布的、不稳定的无定形结构，这种结构在高速率变形过程中能够被激发并得以维持，能够参与甚至主导镁单晶c轴压缩的塑性变形过程。除此之外，位错滑移在镁单晶c轴压缩塑性变形中也起着重要的作用。受位错滑移和无定形结构塑性流动的共同影响，镁单晶c轴压缩变形在不同的载荷条件下体现出不同的规律：在低速率、低温条件小，变形以位错滑移为主导机制，但由于独立滑移系少、位错密度低，变形体现出阶段性的整体塑性-局部弹性的变形规律；在较高速率和较高温度下，无定形结构大量增殖，变形以无定形结构的塑性流动为主导，变形过程均匀且应力水平较低。进一步，由于变形机制规律的变化，镁单晶c轴压缩变形的塑性流动应力随应变率的增大体现出先增大后减小的特征，这和主导机制从位错滑移转变为无定形结构塑性流动直接相关。.本课题的研究为认识镁材料的塑性变形机制规律提供了一种新的视角，较合理的解释了镁单晶材料的c轴压缩塑性变形“位错不足且无孪晶变形”实验观测认识。研究结果有助于加深对HCP金属材料塑性变形规律的认识，促进对HCP材料力学响应规律过程更好的把握。

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