Mg-RE-TM合金强化相中的点缺陷及其对力学性能的影响

Mg alloy is praised as a new type of green engineering materials. Using density functional theory, this project would study the atomic scale microstructure of point defects in strengthening phases of Mg-RE-TM alloys and the formation energy of these point defects, so as to construct the corresponding structural models and reveal formation mechanism and microscopic process. Based on the function of formation energy of point defects, the environment dependence of formation, structure and distribution of the point defects would be further investigated. Especially the relation curves of concentration versus temperature and component concentration would be established and improved to deepen the understanding of temperature dependence of concentration and distribution of point defects, and to construct and improve phase diagrams. From the formation enthalpy of doping process in defect system, influence of defect structure and distribution on position preference of dopants and doping thermodynamics would be uncovered, important and close relationship of defect structure with doping process, micro-alloying mechanism and microstructure would be established, and micro-alloying and its performance would be optimized. By calculation of generalized stacking fault energy surface, interaction of point defect with stacking faults and dislocations would be revealed, and influence of defect structure on deformation micro-process and property of strength and toughness, along with the underlying mechanism, would be deeply understood. Furthermore, elastic property of point defect system would be studied to reveal the feature of mechanical property such as strength, stiffness, brittleness and ductility. This program would provide evidence and instruction for optimization and design of formation, structure and property of Mg-RE-TM alloys, so as to promote the application of Mg alloys.

镁合金被誉为新型绿色工程材料。本课题运用密度泛函理论研究Mg-RE-TM合金强化相中点缺陷的原子尺度微结构特征和形成能，建立结构模型，揭示形成机制和微观过程，进而运用化学势探索点缺陷形成能、结构和分布组分环境改变。完善和建立浓度-温度及浓度-组成曲线，深化理解不同温度下点缺陷的浓度和分布以及强化相的化学组成配比，从而发展和完善相图组成。通过点缺陷掺杂体系形成焓，确立点缺陷结构和分布对掺杂位置倾向选择性和热力学过程的影响，揭示点缺陷结构与掺杂过程、微合金化机制和微结构之间重要的密切关联，优化微合金化过程和性能。运用点缺陷体系中广义层错能量曲面，揭示点缺陷与层错位错的相互作用，以及点缺陷结构浓度对材料形变微观过程和强韧性的关键性影响和机制。进一步研究点缺陷体系弹性性能等揭示强度、硬度、延展性，揭示其力学性能。为优化控制Mg-RE-TM合金的形成、结构和性能并促进其应用提供依据和指导。

本项目主要运用密度泛函理论研究了Mg-RE-TM 合金强化相中点缺陷及其对力学性能的影响。确立了典型点缺陷形成能作为化学势的函数，以及点缺陷结构特征和浓度-温度曲线，并探明了缺陷附近局域几何结构和电子结构的演变，及建立了研究浓度-组成曲线，揭示了点缺陷的形成能随着组分环境改变、重要强化相的组成配比及相图演变特征。发现：点缺陷浓度与温度的倒数呈现线性关系，点缺陷的形成和结构对环境条件非常敏感，极大地依赖化学势。原子尺寸失配对缺陷结构具有明显影响，点阵振动效应也具有一定作用，并深刻揭示了点缺陷形成及结构的内在机制。进一步通过点缺陷掺杂体系形成焓，阐明了点缺陷对掺杂原子的陷阱效应和补偿效应以及对合金化元素和杂质原子位置选择性的影响，确立了点缺陷与掺杂原子相互作用能随距离变化特征，以及杂质相微合金化的原子结构，并揭示点缺陷结构与掺杂过程、微合金化机制和微结构之间的关联及其电子机制。进而研究了点缺陷体系掺杂扩散动力学和热力学特征，得到了扩散过程能量轮郭，确立了鞍点位置和迁移激活能，扩散激活能表明：点阵原子主要通过最邻空位跳跃方式扩散，三步跳循环机制和反结构桥亚点阵机制也有一定贡献。还研究了过渡元素(Ti, Y, Zr 或 Hf)掺杂对Al3Sc原子扩散过程的影响，发现：扩散激活能垒随着杂质原子与基体原子之间原子尺寸失配的增加而增加，并阐明了其电子机制。继续以三元合金为代表性模型材料，研究和确立合金化元素和杂质原子对点缺陷形成、相对稳定性和缺陷体系结构的影响及其物理机制。还研究了多元合金中关键沉淀相力学性能，确立主要强化效应和协同强化机制，进一步揭示点缺陷对材料力学行为的影响和机制。进一步研究了多元混合固溶体弹性力学，揭示了多元点缺陷对强度、硬度、延展性等力学性能的影响，深化了点缺陷对弹性力学性能的直接影响和机制理解。